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S2R-OC-IPX-03-2018Grant agreement n. 826238Deliverable D 2.1Converters topologies for MVDC transformersDocument detailsAuthorsIzsák Ferdinánd Ferencz, Dorin Petreu?Due date30-06-2020Actual delivery date22-06-2020Lead contractorTechnical University of Cluj-NapocaVersion1.0Prepared byTechnical University of Cluj-NapocaInput from-Reviewed byUniversity of BirminghamDissemination levelPublicProject contractual detailsProject titleFlexible medium voltage DC electric railway systemsProject acronymMVDC-ERSGrant agreement no.828638Project start date01.12.2018Project end date30.04.2022Duration41 months Supplementary notesThe document type is publicDisclaimer:* Please note that this deliverable is undergoing S2R JU review and acceptance processes. At this stage this deliverable reflects only the author’s view and the S2R JU is not responsible for any use that may be made of the information it contains.Table of Contents TOC \o "1-3" \u 1Introduction PAGEREF _Toc43738031 \h 32Abbreviations and acronyms PAGEREF _Toc43738032 \h 43History of electrical railway traction PAGEREF _Toc43738033 \h 53.1General considerations on railway electrification and traction PAGEREF _Toc43738034 \h 53.2DC traction systems PAGEREF _Toc43738035 \h 63.2.1Interoperable traction PAGEREF _Toc43738036 \h 73.3MVDC-ERS concept comparison with existing ERSs PAGEREF _Toc43738037 \h 73.4PETT – original concept and evolution PAGEREF _Toc43738038 \h 104Brief overview of state of the art PETTs and definition of suitable topologies for MVDC-ERS PAGEREF _Toc43738039 \h 174.1The last 25 years of PETT concepts (1993-today) PAGEREF _Toc43738040 \h 174.2Possible MVDC converter configurations PAGEREF _Toc43738041 \h 234.3Dual Active Bridge Converters PAGEREF _Toc43738042 \h 244.3.1DAB full bridge converter PAGEREF _Toc43738043 \h 244.3.2DAB half bridge converter PAGEREF _Toc43738044 \h 254.3.3Example of a DAB configuration for MVDC traction PAGEREF _Toc43738045 \h 254.4Voltage balancing stages (VBS) PAGEREF _Toc43738046 \h 275Specifications and requirements for traction PAGEREF _Toc43738047 \h 295.1Inductive power factor of train PAGEREF _Toc43738048 \h 295.2Capacitive power factor of train PAGEREF _Toc43738049 \h 295.3Power levels of trains PAGEREF _Toc43738050 \h 305.4Current limitation PAGEREF _Toc43738051 \h 306Regenerative braking and on-board storage PAGEREF _Toc43738052 \h 317Control and protection of traction converters PAGEREF _Toc43738053 \h 318Potential benefits of using wide band-gap semiconductors in MVDC converters PAGEREF _Toc43738054 \h 339Conclusion PAGEREF _Toc43738055 \h 3610References PAGEREF _Toc43738056 \h 37IntroductionThe present report constitutes deliverable D2.1, a document produced in the framework of WP2 “MVDC transformers for railway traction”, Task 2.1 “Definition of optimal converter topologies for MVDC transformers”.One of the main objectives of WP2 is to undertake a comparative evaluation of topologies for the medium voltage DC transformers and to define the optimal topology for railway traction applications including evaluation of the performance of the converter.Hence, D2.1 compares the conventional railway traction systems with new traction systems proposed and developed in the last decade that are also suitable for the MVDC railway electrification concept presented in this project. Differences and requirements of the MVDC traction system will be considered while investigating converter topologies for MVDC transformers and the impact of new wide band-gap (WBG) semiconductor technologies on their design. Then, D2.1 focuses on presenting the most suitable DC-DC converters for this application, defining an example of optimal configuration and requirements of control. The deliverable has the following sections:?Section 2 defines abbreviations and acronyms used in this report?Section 3 describes the history of railway power electronic traction transformers (PETTs)?Section 4 introduces the state of the art and classification of railway traction systems?Section 5 presents the specifications of high-power converters suitable for MVDC-ERS traction?Section 6 introduces the regenerative braking and on-board storage of the traction systems?Section 7 describes protection and control issues of on-board traction systems?Section 8 clarifies potential benefits of using wide band-gap semiconductors for PETTs?Section 9 draws the conclusions?Section 10 includes the referencesAbbreviations and acronyms ABBASEA Brown Boveri ACAlternating CurrentADCAnalog-Digital ConverterCANController Area NetworkCFB/CHBCascaded F-Bridge/ H-BridgeCO2Carbon-dioxideCSCCurrent Source ConverterDABDual-Active Bridge DAFB/DAHBDual-Active Full/Half BridgeDCDirect CurrentDMUDiesel Multiple UnitsDSPDigital Signal ProcessorEMCElectromagnetic CompatibilityEMIElectromagnetic InterferenceEMUElectric Multiple UnitsERSElectric Railway SystemFPGAField Programmable Gate ArrayGaNGallium NitrideHV/MV/LVHigh Voltage / Medium Voltage / Low voltageHVDCHigh-Voltage DCICIntegrated CircuitIFE/IBEIsolated Front-End / Isolated Back-EndIGBTInsulated Gate Bipolar TransistorIOInput - Output (interface)ISOPInput Series Output ParallelLCCLine Commutated ConverterLFTLine/Low Frequency TransformerMFTMedium Frequency Transformer MMCModular Multilevel ConverterMOSFETMetal Oxide Semiconductor Field Effect Transistors MVDCMedium-Voltage DCNPCNeutral-Point Clamped PCBPrinted Circuit BoardPETTPower Electronic Traction TransformerPWMPulse Width Modulation RMSRoot Mean SquareSiSiliconSiCSilicon CarbideSSTSolid State TransformerSTATCOMStatic CompensatorTHDTotal Harmonic Distortion VSC/VSIVoltage Source Converter/Voltage Source InverterWBGWide Band-GapZCS/ZVSZero Current Switching / Zero Voltage SwitchingHistory of electrical railway tractionGeneral considerations on railway electrification and traction The reason behind railway electrification was the reduction of operating costs, CO2 emissions and an improvement in energy efficiency. The newly developed electric locomotives achieved more power than diesel engines, a better reliability and quieter operations. High power electric locomotives can also pull heavier freight at higher speed over slopes, thus increasing capacity in mixed traffic conditions, when time between trains is important. Having no local emissions, electric propulsion has a great advantage over diesel in urban areas and tunnels. Electric traction offers possibility for regenerative braking (turning kinetic energy into electricity) also, which can further increase efficiency by supplying other trains or the utility grid – especially useful in mountainous areas, where heavily loaded trains must descend for long distances ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"Kalla-Bishop","given":"P. M.","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issued":{"date-parts":[["1972"]]},"publisher":"IPC Transport Press Ltd","title":"Future Railways and Guided Transport","type":"book"},"uris":[""]}],"mendeley":{"formattedCitation":"[1]","plainTextFormattedCitation":"[1]","previouslyFormattedCitation":"[1]"},"properties":{"noteIndex":0},"schema":""}[1].The costs of line maintenance is increased by electrification, but many operators such as Network Rail in the UK claim that, as electric multiple units (EMU) are lighter than diesel ones (DMU), the wear-and-tear costs are lower ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"Network Rail","given":"","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issued":{"date-parts":[["2010"]]},"number-of-pages":"31","title":"UK Network Rail electrification strategy report","type":"report"},"uris":[""]}],"mendeley":{"formattedCitation":"[2]","plainTextFormattedCitation":"[2]","previouslyFormattedCitation":"[2]"},"properties":{"noteIndex":0},"schema":""}[2]. Although electrical equipment near the tracks such as substations and catenary wires imply some additional maintenance costs, if there is enough traffic the reduced track and engine maintenance costs compensate these additional ones resulting in a significant advantage. The reason why electric railways have a higher efficiency is that central stations or power plants generate electricity with higher efficiency than mobile engines or generators. In nominal regime the energy efficiency of a diesel locomotive and a power plant would be almost the same ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"Дробинский В.А.","given":"Егунов П.М.","non-dropping-particle":"","parse-names":false,"suffix":""}],"edition":"3rd","id":"ITEM-1","issued":{"date-parts":[["1980"]]},"number-of-pages":"65","publisher":"Транспорт","publisher-place":"Moscow","title":"\"Как устроен и работает тенловоз\" (How the diesel locomotive works)","type":"book"},"uris":[""]},{"id":"ITEM-2","itemData":{"author":[{"dropping-particle":"","family":"В.Н.","given":"Иванова","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-2","issued":{"date-parts":[["1968"]]},"number-of-pages":"20","publisher":"Транспорт","publisher-place":"Москва","title":"\"Конструкция и динамика тепловозов\" (Construction and dynamics of the diesel locomotive)","type":"book"},"uris":[""]}],"mendeley":{"formattedCitation":"[3], [4]","plainTextFormattedCitation":"[3], [4]","previouslyFormattedCitation":"[3], [4]"},"properties":{"noteIndex":0},"schema":""}[3], [4], but diesel motors decrease in efficiency at lower powers (non-nominal regime) ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"Хомич А.Э. Тупицын О.И.","given":"Симсон А.Э.","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issued":{"date-parts":[["1975"]]},"number-of-pages":"264","publisher":"Транспорт","publisher-place":"Москва","title":"\"Экономия топлива и теплотехническая модернизация тепловозов\" (Fuel economy and the thermodynamic modernization of diesel locomotives)","type":"book"},"uris":[""]}],"mendeley":{"formattedCitation":"[5]","plainTextFormattedCitation":"[5]","previouslyFormattedCitation":"[5]"},"properties":{"noteIndex":0},"schema":""}[5] in comparison with a power plant that can shut down some generators or deliver elsewhere any power excess. Electric locomotives can also recuperate energy by regenerative braking and do not consume energy while being idle, except that needed for cooling systems. Additionally many fossil fuel power plants generate heat at high temperature ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"Wang","given":"Ucilia","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issued":{"date-parts":[["0"]]},"title":"Gigaom GE to Crank Up Gas Power Plants Like Jet Engines","type":"report"},"uris":[""]}],"mendeley":{"formattedCitation":"[6]","plainTextFormattedCitation":"[6]","previouslyFormattedCitation":"[6]"},"properties":{"noteIndex":0},"schema":""}[6] that can be used for heating or cooling districts. Hence such power plants are cleaner than mobile sources such as locomotive engines. Furthermore, power can also be generated by clean renewable energy sources like hydroelectric, geothermal, solar and wind ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"ISBN":"978-0-471-36400-9","author":[{"dropping-particle":"","family":"Hay","given":"William W","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issued":{"date-parts":[["1982"]]},"number-of-pages":"p.137","publisher":"Wiley","publisher-place":"New York","title":"The economics of electrification","type":"book"},"uris":[""]}],"mendeley":{"formattedCitation":"[7]","plainTextFormattedCitation":"[7]","previouslyFormattedCitation":"[7]"},"properties":{"noteIndex":0},"schema":""}[7].As in the last decade the renewable energy market has increased rapidly, new opportunities are opening also for the power supply of electric railways. In the past decade railway electrification constantly increased and electrified tracks almost reached one third of the total tracks globally in 2012 ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"International Energy Agency","given":"","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issued":{"date-parts":[["0"]]},"page":"18","title":"Railway Handbook 2015","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[8]","plainTextFormattedCitation":"[8]","previouslyFormattedCitation":"[8]"},"properties":{"noteIndex":0},"schema":""}[8]. According to a report of the International Energy Agency, between 1990 and 2015 due to the increase of railway electrification both the energy consumption per transport unit decreased and the CO2 emissions per transport unit decreased by 35.8% and 31.6%, respectively. Moreover, half of these reductions were achieved in the decade of 2005 to 2015: rail energy consumption per passenger-km decreased by 27.8% and energy consumption per freight tonne-km decreased by 18.1%. Between 2005 and 2015, rail CO2 emissions per passenger-km decreased by 21.7% and CO2 emissions per freight tonne-km decreased by 19.0%. In this time (2005-2015) the share of oil products (diesel) decreased from 62.2% to 56% in the global railway fuel mix, while the share of electricity increased, whereof electricity generated by renewables has shown an increase of 65% ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"International Energy Agency","given":"","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issued":{"date-parts":[["0"]]},"number-of-pages":"18","title":"Railway Handbook 2017","type":"report"},"uris":[""]}],"mendeley":{"formattedCitation":"[9]","plainTextFormattedCitation":"[9]","previouslyFormattedCitation":"[9]"},"properties":{"noteIndex":0},"schema":""}[9]. The data presented in these reports points to the future tendency of integration of renewables in the railway system and to the necessity of innovation. The railway electrification system must become more compatible with renewable energy sources to keep up with the increase of the proportion of power generated by renewable sources. The most promising concept is a smart interoperable electric railway grid including green energy plants. The MVDC-ERS project studies and will lay foundation for such a smart grid.At the moment, modern railway electrification systems use AC power to produce higher voltages using transformers connected to the public grid. For the same amount of power, the higher the voltage the lower the current. With lower currents, line losses are reduced and higher power can be delivered to the trains. The AC voltage is stepped down inside the locomotive with an on-board transformer and converted to a DC voltage to supply the traction motors and auxiliary loads as required. Some motors may directly use DC, but most of them are 3 or more phase AC motors which need further conversion from DC to three-phase AC using power electronics. The initial idea and advantage of AC motors was that power-wasting resistors were no longer necessary for speed control as in DC locomotives. When high-power semiconductors were developed, the classic AC and DC motors were replaced by three-phase induction motors fed by inverters that can vary frequency and voltage to control their speed. These new systems, called variable frequency drives, could operate on DC and AC of any frequency as well, therefore modern electric locomotives were designed to operate flexible under different frequencies and supply voltages simplifying cross-border operation ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"URL":"","author":[{"dropping-particle":"","family":"Wikipedia","given":"","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issued":{"date-parts":[["0"]]},"title":"Railway Electrification System","type":"webpage"},"uris":[""]}],"mendeley":{"formattedCitation":"[10]","plainTextFormattedCitation":"[10]","previouslyFormattedCitation":"[10]"},"properties":{"noteIndex":0},"schema":""}[10].DC traction systemsThe earliest systems choose DC because of the limitations connected to regulate the speed of AC motors without power converters. The first applications of DC electric energy for traction date back to the 1860s, after in Davenport and Scotland experiments were made on battery drive in the years 1837 and 1838. After the successful demonstration of an electric tramway in 1860, it did not take long to develop the first electric DC locomotive in Berlin for demonstration in 1879 by Siemens. Then in 1880 more electric traction and railway systems appeared like streetcar lines, railway and were put into operation in the following decade. Starting from 1890, tramway and metro networks started to be adopted in some large cities due to the advantage of not releasing smoke like diesel engines. As these systems were adopted more widely, the voltage values had to be increased to meet the greater power requirements as well as longer distances. By 1916 it was reached 3,000 V, which is considered the current technological limit, with some systems above 3,000 V in the 1920s. The technological limitation consists in the difficulty to design reliable circuit breakers above 3,000V.The relatively low voltage of DC systems requires very high currents from the power supply to obtain enough power for the locomotives. These high currents lead to large transmission losses. In areas like Eastern Europe, Italy, Belgium and Spain, where catenaries operate at 3?kV DC, basically two 1,500?V DC motors in series were used. However, even at 3kV power losses are very large for heavy trains and highspeed trains. Higher voltages could not be used with DC systems due to the difficulty of voltage transformation in way as efficient as AC transformers ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"URL":"","author":[{"dropping-particle":"","family":"Wikipedia","given":"","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issued":{"date-parts":[["0"]]},"title":"Electric locomotive article","type":"webpage"},"uris":[""]}],"mendeley":{"formattedCitation":"[11]","plainTextFormattedCitation":"[11]","previouslyFormattedCitation":"[11]"},"properties":{"noteIndex":0},"schema":""}[11]. Nowadays better semiconductor devices are available, DC lines are still used and under development ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"ISBN":"9781119386803","author":[{"dropping-particle":"","family":"Brenna","given":"M.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Foiadelli","given":"F.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zaninelli","given":"D.","non-dropping-particle":"","parse-names":false,"suffix":""}],"editor":[{"dropping-particle":"","family":"Hossain","given":"Ekram","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issued":{"date-parts":[["2018"]]},"publisher":"Wiley","title":"Electrical railway transportation systems","type":"book"},"uris":[""]},{"id":"ITEM-2","itemData":{"author":[{"dropping-particle":"","family":"Electric","given":"Background","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"Power Eng.","id":"ITEM-2","issue":"February","issued":{"date-parts":[["1994"]]},"page":"47-56","title":"Electric railway traction Part 1 Electric traction and DC traction motor drives","type":"article-journal","volume":"8"},"uris":[""]}],"mendeley":{"formattedCitation":"[12], [13]","plainTextFormattedCitation":"[12], [13]","previouslyFormattedCitation":"[12], [13]"},"properties":{"noteIndex":0},"schema":""}[12], [13]. Both systems (AC and DC) converts and transports high-voltage AC from the grid to lower voltage DC in the locomotive, the difference between the two electrification systems is the location where the conversion from AC to DC is done: at the feeding substation (in case of DC) or on the locomotive (AC). The choice of which one to be used, often depends on the already existing electrification system in the respective country or area and the costs of a new infrastructure. The conversion and transmission of electric energy cannot be done without magnetic field losses in transformers and inductors and ohmic losses in power electronics and wires. ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"ISBN":"5-88998-425-X","author":[{"dropping-particle":"","family":"Винокуров В.А.","given":"Попов Д.А.","non-dropping-particle":"","parse-names":false,"suffix":""}],"chapter-number":"Ch. 4: Пот","id":"ITEM-1","issued":{"date-parts":[["1986"]]},"page":"95-99","publisher":"Транспорт","publisher-place":"Москва","title":"\"Электрические машины железно-доровного транспорта\" (Electrical machinery of railroad transportation)","type":"chapter"},"uris":[""]}],"mendeley":{"formattedCitation":"[14]","plainTextFormattedCitation":"[14]","previouslyFormattedCitation":"[14]"},"properties":{"noteIndex":0},"schema":""}[14] In the case of a DC system the conversion takes place in a railway substation where can be used massive and efficient hardware systems that cannot be used on-board on a train where space is limited, and losses can be significantly higher. ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"ISBN":"978-5-458-48205-9","author":[{"dropping-particle":"","family":"Сидоров Н.И.","given":"Сидорожа Н.Н.","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issued":{"date-parts":[["1988"]]},"number-of-pages":"103-104 (5th ed.), 122-123 (4th ed.)","publisher":"Транспорт","publisher-place":"Москва","title":"\"Как устроен и работает эелктровоз\" (How the electric locomotive works)","type":"book"},"uris":[""]}],"mendeley":{"formattedCitation":"[15]","plainTextFormattedCitation":"[15]","previouslyFormattedCitation":"[15]"},"properties":{"noteIndex":0},"schema":""}[15] Cooling systems and other conversion hardware and the energy used for their operation should be considered as well.Interoperable tractionThe versatility of power electronics converters introduced the possibility of using multisystem rolling stock, which ensure interoperability between different railway power supply systems. Different countries have different economic and environmental situations; thus, the electric railway systems may differ. Therefore, interoperable traction vehicles must adapt to different frequencies and voltages of the supply network while at the same time maintain performance as high as possible for each system. Modern railway applications have a dedicated on-board DC link to supply traction converters and auxiliary services. This DC link voltage is constant, independent of the power supply technology allowing an unchanged on-board configuration. To implement this, separate input stages are responsible for conversion and transformation. However, there are space and weight limitations on-board, especially in high-speed trains preventing the installation of dedicated input stages for the different power supply systems, thus reconfigurable circuits are necessary for transition between systems in a way that takes advantage of the same components with variable functions.As the electromechanical components in multisystem vehicles consume considerable space and weight, they should be used only when they are necessary. Considering the relation of the available volume and weight distribution on wheels of bogies they must be carefully installed. Hence it is preferred, if possible, installation under the bogies in a centred position ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"ISBN":"9781119386803","author":[{"dropping-particle":"","family":"Brenna","given":"M.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Foiadelli","given":"F.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zaninelli","given":"D.","non-dropping-particle":"","parse-names":false,"suffix":""}],"editor":[{"dropping-particle":"","family":"Hossain","given":"Ekram","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issued":{"date-parts":[["2018"]]},"publisher":"Wiley","title":"Electrical railway transportation systems","type":"book"},"uris":[""]}],"mendeley":{"formattedCitation":"[12]","plainTextFormattedCitation":"[12]","previouslyFormattedCitation":"[12]"},"properties":{"noteIndex":0},"schema":""}[12].In the first years or decades of application of a new MVDC-ERS interoperable vehicles will be necessary as the transition to a new electrification system will not happen instantly. This will imply multi-voltage and multi-frequency transformer operation, the usage of four-quadrant converters and different multilevel solid-state converter or power electronic traction transformers. There are already 25kV AC - 3kV DC reconfigurable traction devices, hybrid locomotives, but a new MVDC railway electrification system will have to be investigated on this matter too, to offer smooth transition without losses in efficiency. Fortunately, new research on power electronic traction transformers with Silicon Carbide (SiC) semiconductor devices offers promising solutions ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/TPWRD.2013.2268692","ISBN":"0885-8977 VO - 29","ISSN":"08858977","abstract":"This paper proposes a new railway electrification system in which the voltage-source converter (VSC) becomes the basic building block. This will allow existing railways, comprising several ac and dc subsystems, to be transformed into simpler medium-voltage dc (MVDC) multiterminal power systems feeding mobile loads. Moreover, the VSC-based unified scheme will substantially facilitate the connectivity among otherwise heterogeneous railway systems, while the integration of distributed generation and storage is achieved in a straightforward fashion. In addition to the general MVDC architecture, details are provided about the dc catenary layout, dual-voltage locomotive configurations, and dc-dc links between urban and long-distance railways. The need for a supervisory control system, and its role in coordinating local VSC controllers, so that the resulting power flows are optimized while the catenary voltage is kept within limits, are discussed. The proposed railway electrification paradigm is compared with the standard 25-kV, ac electrification system by means of a real case study.","author":[{"dropping-particle":"","family":"Gomez-Exposito","given":"Antonio","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Mauricio","given":"Juan Manuel","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Maza-Ortega","given":"Jose Mariaa","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Power Delivery","id":"ITEM-1","issue":"1","issued":{"date-parts":[["2014"]]},"page":"422-431","title":"VSC-Based MVDC railway electrification system","type":"article-journal","volume":"29"},"uris":[""]}],"mendeley":{"formattedCitation":"[16]","plainTextFormattedCitation":"[16]","previouslyFormattedCitation":"[16]"},"properties":{"noteIndex":0},"schema":""}[16].MVDC-ERS concept comparison with existing ERSsCurrent AC rolling stocks use a traditional line frequency transformer (LFT) at the input stage tuned to meet electromagnetic compatibility standards. Since these transformers works at low frequency, they are heavy and bulky. To reduce the weight of LFTs, new medium frequency transformers (MFT) were developed and different prototypes are still under research and testing. Power Electronic Traction Transformers (PETTS), also known as Solid-State Transformers (SSTs) are new types of converters with MFTs using power electronic semiconductor devices. They achieve power efficiency and power quality comparable with LFTs, as well as providing galvanic isolation and voltage transformation ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.4316/aece.2010.02001","author":[{"dropping-particle":"","family":"Steimel","given":"A","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"The 10 th International Conference on Development and Application Systems DAS 2010","id":"ITEM-1","issue":"May 2010","issued":{"date-parts":[["0"]]},"title":"Power-Electronics Issues of Modern Electric Railway Systems","type":"article-journal","volume":"Advances i"},"uris":[""]}],"mendeley":{"formattedCitation":"[17]","plainTextFormattedCitation":"[17]","previouslyFormattedCitation":"[17]"},"properties":{"noteIndex":0},"schema":""}[17].With reference to the MVDC electrification system, the main problem for the on-board traction system is the necessity to find suitable alternatives to transformers to step-down the high voltage to levels compatible with traction inverters and motors. Whilst some work has been undertaken on PETTs in the past (most notably in the ABB project ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"Zhao","given":"Chuanhong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Lewdeni-schmid","given":"Silvia","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Steinke","given":"Juergen 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Conditions","type":"article-journal","volume":"29"},"uris":[""]},{"id":"ITEM-4","itemData":{"DOI":"10.1109/IPEMC.2012.6258820","ISBN":"9781457720888","author":[{"dropping-particle":"","family":"Dujic","given":"Drazen","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Kieferndorf","given":"Frederick","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Canales","given":"Francisco","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Drofenik","given":"Uwe","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"Proceedings of The 7th International Power Electronics and Motion Control Conference","id":"ITEM-4","issued":{"date-parts":[["2012"]]},"page":"636-642","publisher":"IEEE","title":"Power Electronic Traction Transformer Technology","type":"article-journal","volume":"1"},"uris":[""]},{"id":"ITEM-5","itemData":{"DOI":"10.1109/TPEL.2013.2248756","author":[{"dropping-particle":"","family":"Dujic","given":"Drazen","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Member","given":"Senior","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhao","given":"Chuanhong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Mester","given":"Akos","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Steinke","given":"Juergen 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Prototype","type":"article-journal","volume":"28"},"uris":[""]},{"id":"ITEM-6","itemData":{"DOI":"10.1109/TIE.2013.2278960","ISBN":"0885-8993","ISSN":"02780046","abstract":"Recently, a world's first ever power electronic traction transformer (PETT) for 15 kV, 16 2/3Hz railway grid, has been newly developed, commissioned, and installed on the locomotive, where it is presently in use. This marks an important milestone in the traction world. The design and development of the PETT are described in this paper, where a low-voltage (LV) PETT prototype is presented. It has been designed for the purposes of control hardware and software commissioning, thus serving a role of an analogue simulator. In this paper, emphasis is placed on the overall system requirements, from where control system has been developed, implemented, and successfully commissioned. The development of a 1.2MVA medium-voltage PETT prototype will be reported separately in accompanying paper.","author":[{"dropping-particle":"","family":"Zhao","given":"Chuanhong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Dujic","given":"Drazen","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Mester","given":"Akos","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Steinke","given":"Juergen K.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Weiss","given":"Michael","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Lewdeni-Schmid","given":"Silvia","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Chaudhuri","given":"Toufann","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Stefanutti","given":"Philippe","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Industrial Electronics","id":"ITEM-6","issue":"7","issued":{"date-parts":[["2014"]]},"page":"3257-3268","publisher":"IEEE","title":"Power electronic traction transformer-medium voltage prototype","type":"article-journal","volume":"61"},"uris":[""]},{"id":"ITEM-7","itemData":{"DOI":"10.1109/SPEEDAM.2012.6264496","ISBN":"9781467312998","author":[{"dropping-particle":"","family":"Zhao","given":"Chuanhong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Weiss","given":"Michael","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Mester","given":"Akos","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Lewdeni-Schmid","given":"Silvia","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Dujic","given":"Drazen","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Steinke","given":"Juergen K.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Chaudhuri","given":"Toufann","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"SPEEDAM 2012 - 21st International Symposium on Power Electronics, Electrical Drives, Automation and Motion","id":"ITEM-7","issued":{"date-parts":[["2012"]]},"page":"855-860","publisher":"IEEE","title":"Power electronic transformer (PET) converter: Design of a 1.2MW demonstrator for traction applications","type":"article-journal"},"uris":[""]},{"id":"ITEM-8","itemData":{"ISSN":"10133119","author":[{"dropping-particle":"","family":"Claesens","given":"Max","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Dujic","given":"Drazen","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Canales","given":"Francisco","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Steinke","given":"Juergen K.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Stefanutti","given":"Philipe","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Veterli","given":"Christian","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"ABB Review","id":"ITEM-8","issue":"1","issued":{"date-parts":[["2012"]]},"page":"11-17","title":"Traction transformation: A power-electronic traction transformer (PETT)","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[18]–[25]","plainTextFormattedCitation":"[18]–[25]","previouslyFormattedCitation":"[18]–[25]"},"properties":{"noteIndex":0},"schema":""}[18]–[25]), these have largely been based around AC transformers with Power Electronics, whereas the focus for this research is on DC-based power transformers. To this aim, different topologies will be explored and compared in the next two sections.In the following, the most widely used AC railway electrification systems – 25?kV, 50/60Hz (ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"id":"ITEM-1","issued":{"date-parts":[["2007"]]},"title":"EN 50163: Railway applications. Supply voltages of traction systems","type":"book"},"uris":[""]},{"id":"ITEM-2","itemData":{"edition":"3rd","id":"ITEM-2","issued":{"date-parts":[["2007"]]},"title":"IEC 60850: Railway applications – Supply voltages of traction systems","type":"book"},"uris":[""]}],"mendeley":{"formattedCitation":"[26], [27]","plainTextFormattedCitation":"[26], [27]","previouslyFormattedCitation":"[26], [27]"},"properties":{"noteIndex":0},"schema":""}[26], [27]) – will be analysed in comparison with traditional DC railway electrification systems – 1,500/3,000V, in terms of electrical railway power supply system technology, number of connections to utility grid, substation, substation interaction, possibility of feeding current back to the grid, overhead lines, current transportation and collection systems, rolling stock, power fed back to the overhead line through regenerative braking, corrosion and leaks. The advantages and drawbacks are listed for each system in Table 1. As it can be observed, most of the drawbacks of DC systems are caused by the low voltage supply, thus higher number of substations, heavier overhead lines and higher traction losses. Due to the higher current, corrosion should also be considered. For these reasons, current DC systems are not economical regarding overhead lines – implying higher investments and operational costs (tear and wear) – and regarding substations – higher number meaning more expensive connections to the grid and higher maintenance costs.Table 1 – Comparative analysis of AC and DC-ERSs. Based on ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"P. 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Moreover, the VSC-based unified scheme will substantially facilitate the connectivity among otherwise heterogeneous railway systems, while the integration of distributed generation and storage is achieved in a straightforward fashion. In addition to the general MVDC architecture, details are provided about the dc catenary layout, dual-voltage locomotive configurations, and dc-dc links between urban and long-distance railways. The need for a supervisory control system, and its role in coordinating local VSC controllers, so that the resulting power flows are optimized while the catenary voltage is kept within limits, are discussed. The proposed railway electrification paradigm is compared with the standard 25-kV, ac electrification system by means of a real case study.","author":[{"dropping-particle":"","family":"Gomez-Exposito","given":"Antonio","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Mauricio","given":"Juan Manuel","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Maza-Ortega","given":"Jose Mariaa","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Power Delivery","id":"ITEM-1","issue":"1","issued":{"date-parts":[["2014"]]},"page":"422-431","title":"VSC-Based MVDC railway electrification system","type":"article-journal","volume":"29"},"uris":[""]}],"mendeley":{"formattedCitation":"[16]","plainTextFormattedCitation":"[16]","previouslyFormattedCitation":"[16]"},"properties":{"noteIndex":0},"schema":""}[16], ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/TTE.2018.2826780","ISSN":"23327782","author":[{"dropping-particle":"","family":"Verdicchio","given":"Andrea","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Ladoux","given":"Philippe","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Caron","given":"Herve","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Courtois","given":"Christian","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Transportation Electrification","id":"ITEM-1","issue":"2","issued":{"date-parts":[["2018"]]},"page":"591-604","publisher":"IEEE","title":"New Medium-Voltage DC Railway Electrification System","type":"article-journal","volume":"4"},"uris":[""]}],"mendeley":{"formattedCitation":"[29]","plainTextFormattedCitation":"[29]","previouslyFormattedCitation":"[29]"},"properties":{"noteIndex":0},"schema":""}[29], ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"Laousse","given":"Dominique","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Brogard","given":"Cedric","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Caron","given":"Hervé","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Courtois","given":"Christian","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Denis","given":"Saint","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issue":"August 2017","issued":{"date-parts":[["2016"]]},"page":"114. 260-275","title":"Direct current - A future under which conditions?","type":"article-journal"},"uris":[""]},{"id":"ITEM-2","itemData":{"DOI":"10.1016/j.ijepes.2017.05.008","author":[{"dropping-particle":"","family":"Unibertsitatea","given":"Mondragon","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Abrahamsson","given":"Lars","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Sanz","given":"Javier","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"International Journal of Electrical Power & Energy Systems","id":"ITEM-2","issue":"November","issued":{"date-parts":[["2017"]]},"title":"Electrical railway power supply systems : current situation and future trends","type":"article-journal"},"uris":[""]},{"id":"ITEM-3","itemData":{"DOI":"10.23919/IPEC.2018.8507567","author":[{"dropping-particle":"","family":"Shigeeda","given":"Hidenori","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Morimoto","given":"Hiroaki","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Ito","given":"Kazuhiko","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Fujii","given":"Toshiyuki","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Morishima","given":"Naoki","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2018 International Power Electronics Conference (IPEC-Niigata 2018 -ECCE Asia)","id":"ITEM-3","issued":{"date-parts":[["2018"]]},"page":"2540-2546","publisher":"IEEJ Industry Application Society","title":"Feeding-loss Reduction by Higher-voltage DC Railway Feeding System with DC-to-DC Converter","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[30]–[32]","plainTextFormattedCitation":"[30]–[32]","previouslyFormattedCitation":"[30]–[32]"},"properties":{"noteIndex":0},"schema":""}[30]–[32] and [33].25?kV 50/60Hz AC1,500V/3,000V DCMVDC-ERSUtility/main grid (power supply)? possible unbalance on the utility grid? strong electric connections needed+ medium to low number of connections (depending on substation technology if it is transformer or converter based)+ no unbalances on the grid+ possible connection to weaker parts of the utility grid+ low impact on the power distribution network? high number of connections to the grid+ low impact and no unbalances on the grid+ low number of connections to the grid+ possible connection to weaker parts of the utility grid+ possibility to develop smart gridsSubstation+ low number of substations, meaning lower investments and maintenance costs+ simple circuit breakers and switching devices+ simple fault detection? in case of using converters, two conversion stages AC/DC/AC to solve unbalanced loading, larger substation (need of land)? high number of substations, meaning higher investments and maintenance costs? need of rectifiers (affects investments, maintenance and reliability)? complex circuit breakers? complex fault detection+ small substation+ fewer substations (no inductive voltage drop, allows more distance between substations) meaning lower investments and maintenance costs+ bilateral supply, substations can be paralleled to share the load+ Possibility of controlling DC short circuit currents by substation converters and using low-load or no-load DC circuit breakers+ only one conversion stage, thus improved efficiency and smaller substationInteractions in substations? complex power supply diagram due to phase separation? less flexibility in case of substation incident+ simple power supply diagram since there is no phase separation, beneficial in dense areas of traffic+ substations in parallel flexible in case of incident+ simple power supply diagram since there is no phase separation, beneficial in dense areas of traffic+ substations in parallel flexible in case of incidentCurrent fed back to the utility grid+ basic transformers needed to feed back currents to overhead line, or the two stage AC-DC-AC converters could also be used? due to low voltage, the effectiveness of regenerative braking is rather low, but may be enhanced by technological upgrades of vehicles and/or substations. These upgrades implies relatively high investment costs, since voltage inverters are needed with harmonics generated (however power factor and harmonics injected can be controlled)+/? inverters needed with harmonics generated, but power factor of AC-DC converter and harmonics injected to the grid can be controlled to meet standardsOverhead line and current transportation? high insulation distances, thus difficult implementation in urban areas and tunnels? complex impedance jωL, therefore presence of inductive voltage drops+ low losses due to high voltage in traction circuit+ light overhead line due to lower current: lower costs+ low tear & wear of contact wire+ one contact wire? neutral zones+ lower isolation distances, thus easier implementation in urban areas and tunnels+ absence of jωL complex part of impedance, thus no inductive voltage drops? high losses due to high currents/low voltage in traction circuit ? heavy overhead line due to high current: higher costs? heavy wear of the contact wire implying maintenance? two contact wires+ no neutral zones+ no skin effect? high insulation distances, thus difficult implementation in urban areas and tunnels+ absence of jωL part, thus no inductive voltage drops and reactive power consumption+ low losses (high voltage)+ no skin effect, thus smaller cross-sections; light overhead line due to lower current: lower investments+ low tear & wear of contact wire, low maintenance costs+ no neutral sections, avoiding power transfer interruptions and speed loss as well as mechanical and electrical stresses in locomotive circuit breakersCurrent collection from the overhead line+ better current fetch in case of ice on the overhead line+ light catenary line enabling high speeds+ low wear of pantograph contact strips (low current)? heavy wear of pantograph contact strips (high current)? limited speed because of heavy catenary lines? risk of contact wire fusion at standstill (high current)+ light catenary lines (since currents are lower) enabling higher performance and speeds (easier tensioning and maintenance of tension) + low wear of pantograph contact strips (low current)Rolling stock? large and heavy transformers on-board, thus heavy rolling stock? need of rectifiers on-board+ simple circuit breakers? converter complexity and reliability+ no transformer on-board, thus lighter rolling stock+ no rectifier on-board, thus light and more reliable rolling stock? converter complexity and reliability, complex circuit breakers+ smaller PETTs on-board, thus lighter rolling stock+ no rectifier on-board, thus lighter and more reliable rolling stock? converter complexity and reliability, complex circuit breakers, current has to be controlled and limited in faults in on-board PETTs? need of rolling stock developmentCurrent fed back to the overhead line (regenerative braking)? necessity to adjust the phase of the current with overhead line current+ no adjustments of the phase of the feedback current is needed + no adjustments of the phase of the feedback current is needed Current return+ low levels of current returning to substations due to high voltage? high levels of current returning to the substations due to low voltage+ lower levels of current returning to substations due to high voltage, but the new system must be able to mitigate stray currentsCorrosion and leaks+ low risk of corrosion due to low current leaks? high risk of corrosion due to high current leaks+ limited corrosion due to lower return currentsInterferences? ground currents may interfere /w communication devices near the railway installations and when power electronics are used? large filters and compensators needed to improve power quality+ no interference with signaling systems, except when power electronics are used+/- possible interference with signaling systems, no induced voltages in adjacent lines? high power converters may produce high order harmonics? EMI, EMC noise emissions have to be investigated ConclusionsAllows more powerful traffic if well dimensionedNo phase-separation, of interest in dense areas of traffic.Will combine advantages of current AC and DC systems, (most drawbacks are due to low voltage) however new operation procedures and regulations are needed.As Table 1 summarises a new MVDC-ERS is a promising solution, as it combines the advantages of AC and DC ERSs and at the same time opens new opportunities for the design of future smart grids. This implies that some aspects presented in Table 1 need more research and investigations. Some examples are the faults detection in real time, new circuit breakers for HVDC in substations as well as in PETTs on-board in rolling stocks, insulating materials, overhead line design, flexible power-supply diagrams, necessary modifications of rolling stocks design for compatibility, the impact of high DC voltage on current collection. Several studies like ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"ISBN":"1424412986","abstract":"A clearinghouse of NASA information on the Ozone.","author":[{"dropping-particle":"","family":"K. Meah and S. Ula","given":"","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"Proc. IEEE Power Eng. Soc. General Meeting","id":"ITEM-1","issued":{"date-parts":[["2007"]]},"page":"1-5","title":"Comparative evaluation of HVDC and HVAC","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[33]","plainTextFormattedCitation":"[33]","previouslyFormattedCitation":"[33]"},"properties":{"noteIndex":0},"schema":""}[33] have shown environmental, and system stability benefits of High Voltage DC (HDVC) transmission lines. In the case of DC train systems potential cost savings, complexity of infrastructure and more friendly integration into the grid are highlighted as further advantages in ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/TPWRD.2013.2268692","ISBN":"0885-8977 VO - 29","ISSN":"08858977","abstract":"This paper proposes a new railway electrification system in which the voltage-source converter (VSC) becomes the basic building block. This will allow existing railways, comprising several ac and dc subsystems, to be transformed into simpler medium-voltage dc (MVDC) multiterminal power systems feeding mobile loads. Moreover, the VSC-based unified scheme will substantially facilitate the connectivity among otherwise heterogeneous railway systems, while the integration of distributed generation and storage is achieved in a straightforward fashion. In addition to the general MVDC architecture, details are provided about the dc catenary layout, dual-voltage locomotive configurations, and dc-dc links between urban and long-distance railways. The need for a supervisory control system, and its role in coordinating local VSC controllers, so that the resulting power flows are optimized while the catenary voltage is kept within limits, are discussed. The proposed railway electrification paradigm is compared with the standard 25-kV, ac electrification system by means of a real case study.","author":[{"dropping-particle":"","family":"Gomez-Exposito","given":"Antonio","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Mauricio","given":"Juan Manuel","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Maza-Ortega","given":"Jose Mariaa","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Power Delivery","id":"ITEM-1","issue":"1","issued":{"date-parts":[["2014"]]},"page":"422-431","title":"VSC-Based MVDC railway electrification system","type":"article-journal","volume":"29"},"uris":[""]}],"mendeley":{"formattedCitation":"[16]","plainTextFormattedCitation":"[16]","previouslyFormattedCitation":"[16]"},"properties":{"noteIndex":0},"schema":""}[16], ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/TTE.2018.2826780","ISSN":"23327782","author":[{"dropping-particle":"","family":"Verdicchio","given":"Andrea","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Ladoux","given":"Philippe","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Caron","given":"Herve","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Courtois","given":"Christian","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Transportation Electrification","id":"ITEM-1","issue":"2","issued":{"date-parts":[["2018"]]},"page":"591-604","publisher":"IEEE","title":"New Medium-Voltage DC Railway Electrification System","type":"article-journal","volume":"4"},"uris":[""]}],"mendeley":{"formattedCitation":"[29]","plainTextFormattedCitation":"[29]","previouslyFormattedCitation":"[29]"},"properties":{"noteIndex":0},"schema":""}[29], ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/esars-itec.2018.8607304","ISBN":"9781538641927","author":[{"dropping-particle":"","family":"Verdicchio","given":"Andrea","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Ladoux","given":"Philippe","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Caron","given":"Herve","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Sanchez","given":"Sebastien","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2018 IEEE International Conference on Electrical Systems for Aircraft, Railway, Ship Propulsion and Road Vehicles & International Transportation Electrification Conference (ESARS-ITEC)","id":"ITEM-1","issued":{"date-parts":[["2019"]]},"page":"1-5","publisher":"IEEE","title":"Future DC Railway Electrification System - Go for 9 kV","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[34]","plainTextFormattedCitation":"[34]","previouslyFormattedCitation":"[34]"},"properties":{"noteIndex":0},"schema":""}[34],ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.23919/IPEC.2018.8507567","author":[{"dropping-particle":"","family":"Shigeeda","given":"Hidenori","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Morimoto","given":"Hiroaki","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Ito","given":"Kazuhiko","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Fujii","given":"Toshiyuki","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Morishima","given":"Naoki","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2018 International Power Electronics Conference (IPEC-Niigata 2018 -ECCE Asia)","id":"ITEM-1","issued":{"date-parts":[["2018"]]},"page":"2540-2546","publisher":"IEEJ Industry Application Society","title":"Feeding-loss Reduction by Higher-voltage DC Railway Feeding System with DC-to-DC Converter","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[32]","plainTextFormattedCitation":"[32]","previouslyFormattedCitation":"[32]"},"properties":{"noteIndex":0},"schema":""}[32].PETT – original concept and evolutionLooking at the history of PETTs, it can be observed that their origins date back as early as the 1960s. Figure 1 illustrates the concept of a PETT, as the LFT is replaced by an MFT as part of the chosen topology. With a higher operating frequency, MFTs achieve a reduced volume and weight at the same winding current density, and maximum magnetic field strength, as the induced voltage is proportional to frequency. The main difference between the MVDC-ERS concept and existing PETTs for AC-ERSs is in the first stage, having a MVDC supply instead of the MVAC one. PETTs are mostly used in applications where power density and high efficiency are targeted, therefore it is highly researched for traction applications in electric railways and ships. To illustrate this, let’s take the example of 15kV/16.7Hz ERS: according to ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/EPE.2007.4417570","ISBN":"9075815115","abstract":"The proposed Medium Frequency Topology is replacing the bulky main line transformer on board of railway vehicles. Especially in countries with 15kV railway power supply, the low frequency of 16.7 Hz is leading to huge and heavy transformers. Today's Transformers are often minimized in weight and volume, which leads to significantly high transformer losses compared with distribution transformers. The Medium Frequency Topology is the power electronic solution that considerably reduces weight and losses of the traction system.","author":[{"dropping-particle":"","family":"Steiner","given":"Michael","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Reinold","given":"Harry","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2007 European Conference on Power Electronics and Applications, EPE","id":"ITEM-1","issued":{"date-parts":[["2007"]]},"title":"Medium frequency topology in railway applications","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[35]","plainTextFormattedCitation":"[35]","previouslyFormattedCitation":"[35]"},"properties":{"noteIndex":0},"schema":""}[35], the LFT is approximately 15% of the weight of the locomotive. Also ABB reported a system weight and volume reduction of 50% and 20% respectively applying only a 400Hz PETT instead of the LFT system ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"Hugo","given":"Nicolas","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Stefanutti","given":"Philippe","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Pellerin","given":"Marc","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Sablières","given":"Rue","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"Proc. Eur. Conf. Power Electron. Appl. (EPE)","id":"ITEM-1","issued":{"date-parts":[["2007"]]},"page":"1-10","title":"Power Electronics Traction Transformer","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[36]","plainTextFormattedCitation":"[36]","previouslyFormattedCitation":"[36]"},"properties":{"noteIndex":0},"schema":""}[36]. With the appearance of low-floor vehicles or roof mounted traction equipment as well as higher power demand in the case of high-speed trains, the features offered by PETT technology are highly attractive. Additional features of PETTs include control of input and output voltages and currents, the flow of power and load protection in case of disturbances or line unbalances.Figure 1 – SST replacing traditional line frequency transformers.The article ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/MIE.2016.2588878","author":[{"dropping-particle":"","family":"Huber","given":"Jonas E","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Kolar","given":"Johann W","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Industrial Electronics Magazine","id":"ITEM-1","issue":"September","issued":{"date-parts":[["2016"]]},"page":"19-28","title":"Solid-State Transformers","type":"article-journal","volume":"10"},"uris":[""]}],"mendeley":{"formattedCitation":"[37]","plainTextFormattedCitation":"[37]","previouslyFormattedCitation":"[37]"},"properties":{"noteIndex":0},"schema":""}[37] demonstrates that all state of the art PETT topologies are derived from key concepts patented during the years 1968-1970. The article defines three basic key concepts being the common characteristic with modern PETTs: 1. medium frequency isolation stage, 2. medium input voltage and 3. controllability. All these three characteristics are desired for traction equipment. Figure 2 shows an MFT, with its resonant and non-resonant variants patented in 1968 by McMurray. One popular modern topology, the Dual Active Bridge converter is based on this concept, as well as other PETT topologies (see Fig. 5).Fig. 2 – AC-AC converter with medium-frequency link patented by McMurray in 1968, including key waveforms, illustrating output stage regulation by phase-shift between primary and secondary bridges (from this DAB converters can be derived). b) resonant AC-AC configuration variant. ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/MIE.2016.2588878","author":[{"dropping-particle":"","family":"Huber","given":"Jonas E","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Kolar","given":"Johann W","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Industrial Electronics Magazine","id":"ITEM-1","issue":"September","issued":{"date-parts":[["2016"]]},"page":"19-28","title":"Solid-State Transformers","type":"article-journal","volume":"10"},"uris":[""]}],"mendeley":{"formattedCitation":"[37]","plainTextFormattedCitation":"[37]","previouslyFormattedCitation":"[37]"},"properties":{"noteIndex":0},"schema":""}[37]As in 1968 high power fully controllable semiconductors were not available, McMurray used thyristors, which needed zero-crossing of current to turn off, therefore the transformer current was shaped into sinusoidal pulses. However, McMurray’s solution features power and load independent input-output voltage ratio and soft switching, that was necessary to reduce switching losses and it is still considered a strong advantage for many modern PETT topologies. Nonetheless, it was not possible to connect this topology directly to medium voltage power supplies for the limited blocking voltage of thyristors.Fig. 3 – Fast response stepped-wave switching power converter by McMurray, 1971. ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/MIE.2016.2588878","author":[{"dropping-particle":"","family":"Huber","given":"Jonas E","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Kolar","given":"Johann W","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Industrial Electronics Magazine","id":"ITEM-1","issue":"September","issued":{"date-parts":[["2016"]]},"page":"19-28","title":"Solid-State Transformers","type":"article-journal","volume":"10"},"uris":[""]}],"mendeley":{"formattedCitation":"[37]","plainTextFormattedCitation":"[37]","previouslyFormattedCitation":"[37]"},"properties":{"noteIndex":0},"schema":""}[37]This was achieved with a multilevel topology as presented in 1969 also by McMurray in one of his patents, as shown in Fig. 3. He described a “fast transient response stepped wave switching power converter” really similar to Cascaded H-bridge (CHB) topologies. The converter cells have an isolation stage and are connected input series, output parallel (ISOP). PETT cells today uses bidirectional bus instead of the unidirectional diode rectifier on Fig. 3, however McMurray mentioned the usage of MFT for cell supply. ISOP structures also have self-balancing features of floating capacitor voltages ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/MIE.2016.2588878","author":[{"dropping-particle":"","family":"Huber","given":"Jonas E","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Kolar","given":"Johann W","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Industrial Electronics Magazine","id":"ITEM-1","issue":"September","issued":{"date-parts":[["2016"]]},"page":"19-28","title":"Solid-State Transformers","type":"article-journal","volume":"10"},"uris":[""]}],"mendeley":{"formattedCitation":"[37]","plainTextFormattedCitation":"[37]","previouslyFormattedCitation":"[37]"},"properties":{"noteIndex":0},"schema":""}[37]. Fig. 3 – Fast response stepped-wave switching power converter by McMurray, 1971. ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/MIE.2016.2588878","author":[{"dropping-particle":"","family":"Huber","given":"Jonas E","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Kolar","given":"Johann W","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Industrial Electronics Magazine","id":"ITEM-1","issue":"September","issued":{"date-parts":[["2016"]]},"page":"19-28","title":"Solid-State Transformers","type":"article-journal","volume":"10"},"uris":[""]}],"mendeley":{"formattedCitation":"[37]","plainTextFormattedCitation":"[37]","previouslyFormattedCitation":"[37]"},"properties":{"noteIndex":0},"schema":""}[37]The third key concept is the controlling stage. Weiss proposed in 1985 a configuration for traction applications as shown in Fig. 4, with MFT isolation like in McMurray’s approach. Weiss however interfaced the low voltage side DC bus with an additional control stage, a boost converter.Fig. 3 – Fast response stepped-wave switching power converter by McMurray, 1971. ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/MIE.2016.2588878","author":[{"dropping-particle":"","family":"Huber","given":"Jonas E","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Kolar","given":"Johann W","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Industrial Electronics Magazine","id":"ITEM-1","issue":"September","issued":{"date-parts":[["2016"]]},"page":"19-28","title":"Solid-State Transformers","type":"article-journal","volume":"10"},"uris":[""]}],"mendeley":{"formattedCitation":"[37]","plainTextFormattedCitation":"[37]","previouslyFormattedCitation":"[37]"},"properties":{"noteIndex":0},"schema":""}[37]The boost converter realised by Weiss is controlled to draw a current proportional to the rectified output voltage that is in turn proportional to the primary side voltage. In this way, the power factor on the railway grid side is unity for all the load condition. As the control stage is placed on the low voltage side of the isolation stage, the converter can be referred as isolated front-end converter (IFE). This idea combined with the concept of cascaded modules has led to many PETTs developed for traction as well as other applications. Fig. 4 – Topology with main frequency transformer eliminated, proposed by Weiss in 1985. ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/MIE.2016.2588878","author":[{"dropping-particle":"","family":"Huber","given":"Jonas E","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Kolar","given":"Johann W","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Industrial Electronics Magazine","id":"ITEM-1","issue":"September","issued":{"date-parts":[["2016"]]},"page":"19-28","title":"Solid-State Transformers","type":"article-journal","volume":"10"},"uris":[""]}],"mendeley":{"formattedCitation":"[37]","plainTextFormattedCitation":"[37]","previouslyFormattedCitation":"[37]"},"properties":{"noteIndex":0},"schema":""}[37] Figure 5 from ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/MIE.2016.2588878","author":[{"dropping-particle":"","family":"Huber","given":"Jonas E","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Kolar","given":"Johann W","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Industrial Electronics Magazine","id":"ITEM-1","issue":"September","issued":{"date-parts":[["2016"]]},"page":"19-28","title":"Solid-State Transformers","type":"article-journal","volume":"10"},"uris":[""]}],"mendeley":{"formattedCitation":"[37]","plainTextFormattedCitation":"[37]","previouslyFormattedCitation":"[37]"},"properties":{"noteIndex":0},"schema":""}[37] sums up the main modern PETT topologies derived from the presented key concepts. In 1979 a concept was patented, where instead of the direct matrix converter applied in McMurray’s original patent, an additional rectifier stage has been added ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"Brewster","given":"R. F.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Barrett","given":"A. H.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"U.S. Patent 4143,414","id":"ITEM-1","issued":{"date-parts":[["1979"]]},"title":"Three phase ac to dc voltage converter with power line harmonic current reduction","type":"patent"},"uris":[""]}],"mendeley":{"formattedCitation":"[38]","plainTextFormattedCitation":"[38]","previouslyFormattedCitation":"[38]"},"properties":{"noteIndex":0},"schema":""}[38]. The obtained processed AC voltage then applied to a higher frequency transformer in the isolation stage results in the presented modern PETT topology family of indirect matrix type converters in Fig. 5a). This has been patented recently, in 2008, by General Electric, who developed a 1?MW single-phase prototype with ISOP multi-module configuration using SiC devices of 10?kV and 20 kHz switching frequency. The declared efficiency was around 97%, with a weight reduction of 75% and size reduction of 50% in comparison with traditional LFT solutions ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/ECCE.2011.6064129","ISBN":"9781457705427","abstract":"The majority carrier domain of power semiconductor devices has been extended to 10 kV with the advent of SiC MOSFETs and Schottky diodes. The devices exhibit excellent static and dynamic properties with encouraging preliminary reliability. Twenty-four MOSFETs and twelve Schottky diodes have been assembled in a 10 kV half H-bridge power module to increase the current handling capability to 120 A per switch without compromising the die-level characteristics. For the first time, a custom designed system (13.8 kV to 465/√3 V solid state power substation) has been successfully demonstrated with these state of the art SiC modules up to 855 kVA operation and 97% efficiency. Soft-switching at 20 kHz, the SiC enabled SSPS represents a 70% reduction in weight and 50% reduction in size when compared to a 60 Hz conventional, analog transformer. ? 2011 IEEE.","author":[{"dropping-particle":"","family":"Das","given":"Mrinal K.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Capell","given":"Craig","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Grider","given":"David E.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Leslie","given":"Scott","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Ostop","given":"John","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Raju","given":"Ravi","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Schutten","given":"Michael","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Nasadoski","given":"Jeffrey","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Hefner","given":"Allen","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Energy Conversion Congress and Exposition: Energy Conversion Innovation for a Clean Energy Future, ECCE 2011, Proceedings","id":"ITEM-1","issued":{"date-parts":[["2011"]]},"page":"2689-2692","publisher":"IEEE","title":"10 kV, 120 a SiC half H-bridge power MOSFET modules suitable for high frequency, medium voltage applications","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[39]","plainTextFormattedCitation":"[39]","previouslyFormattedCitation":"[39]"},"properties":{"noteIndex":0},"schema":""}[39].The combination of McMurray’s converter in Fig.?3 and the DC-DC isolation stage supplying the cascaded modules in Fig. 2b has resulted in a topology with DC output and good controllability, as shown in Fig. 5b ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"Steiner","given":"M.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Reinold","given":"H.","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issued":{"date-parts":[["1996"]]},"number":"German Patent DE 196 30 284 A 1","publisher-place":"Germany","title":"Antriebssystem für ein Schienenfahrzeug und Ansteuerverfahren hierzu","type":"patent"},"uris":[""]}],"mendeley":{"formattedCitation":"[40]","plainTextFormattedCitation":"[40]","previouslyFormattedCitation":"[40]"},"properties":{"noteIndex":0},"schema":""}[40]. This configuration is maybe the most popular among modern SSTs, patented back in 1996 in Germany.Fig. 5 – Modern SST topologies derived as a combination of the early concepts. a) modern matrix SST with ISOP configuration, similar as McMurray’s concept in Fig. 2. b) a modern isolation back-end converter with CHBs and multilevel output voltage (like concept in Fig. 3) c) modern isolation front-end topology using cascaded converter cells and resonant isolation (similar to a combination of concepts in Fig. 4 and Fig. 2b). ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/MIE.2016.2588878","author":[{"dropping-particle":"","family":"Huber","given":"Jonas E","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Kolar","given":"Johann W","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Industrial Electronics Magazine","id":"ITEM-1","issue":"September","issued":{"date-parts":[["2016"]]},"page":"19-28","title":"Solid-State Transformers","type":"article-journal","volume":"10"},"uris":[""]}],"mendeley":{"formattedCitation":"[37]","plainTextFormattedCitation":"[37]","previouslyFormattedCitation":"[37]"},"properties":{"noteIndex":0},"schema":""}[37]The controlled stage located in the MV side ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/MIE.2016.2588878","author":[{"dropping-particle":"","family":"Huber","given":"Jonas E","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Kolar","given":"Johann W","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Industrial Electronics Magazine","id":"ITEM-1","issue":"September","issued":{"date-parts":[["2016"]]},"page":"19-28","title":"Solid-State Transformers","type":"article-journal","volume":"10"},"uris":[""]}],"mendeley":{"formattedCitation":"[37]","plainTextFormattedCitation":"[37]","previouslyFormattedCitation":"[37]"},"properties":{"noteIndex":0},"schema":""}[37] refers to as isolated back-end converter (IBE). The most significant application of this topology was the first fully functional PETT tested on a real locomotive in Switzerland, implemented by ABB in 2011. It was mounted on a shunt locomotive, interfaced with the 15?kV, 16.7?Hz AC railway electrification system. However, it did not use SiC devices, but 6.5kV silicon IGBTs with an operating fundamental frequency of 1.8 kHz. ABB obtained a peak efficiency of 96%, with a power density of 0.75kVA/kg that was double in comparison to LFT, 0.35kVA/kg ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"Zhao","given":"Chuanhong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Lewdeni-schmid","given":"Silvia","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Steinke","given":"Juergen 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Topology","type":"article-journal","volume":"i"},"uris":[""]},{"id":"ITEM-3","itemData":{"DOI":"10.1109/TPEL.2013.2293402","author":[{"dropping-particle":"","family":"Besselmann","given":"Thomas","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Mester","given":"Akos","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Dujic","given":"Drazen","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Member","given":"Senior","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Power Electronics","id":"ITEM-3","issue":"8","issued":{"date-parts":[["2014"]]},"page":"3971-3981","publisher":"IEEE","title":"Power Electronic Traction Transformer : Efficiency Improvements Under Light-Load Conditions","type":"article-journal","volume":"29"},"uris":[""]},{"id":"ITEM-4","itemData":{"DOI":"10.1109/IPEMC.2012.6258820","ISBN":"9781457720888","author":[{"dropping-particle":"","family":"Dujic","given":"Drazen","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Kieferndorf","given":"Frederick","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Canales","given":"Francisco","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Drofenik","given":"Uwe","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"Proceedings of The 7th International Power Electronics and Motion Control Conference","id":"ITEM-4","issued":{"date-parts":[["2012"]]},"page":"636-642","publisher":"IEEE","title":"Power Electronic Traction Transformer Technology","type":"article-journal","volume":"1"},"uris":[""]},{"id":"ITEM-5","itemData":{"DOI":"10.1109/TPEL.2013.2248756","author":[{"dropping-particle":"","family":"Dujic","given":"Drazen","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Member","given":"Senior","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhao","given":"Chuanhong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Mester","given":"Akos","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Steinke","given":"Juergen K","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Member","given":"Senior","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Weiss","given":"Michael","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Lewdeni-schmid","given":"Silvia","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Chaudhuri","given":"Toufann","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Stefanutti","given":"Philippe","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Power Electronics","id":"ITEM-5","issue":"12","issued":{"date-parts":[["2013"]]},"page":"5522-5534","publisher":"IEEE","title":"Power Electronic Traction Transformer-Low Voltage Prototype","type":"article-journal","volume":"28"},"uris":[""]},{"id":"ITEM-6","itemData":{"DOI":"10.1109/TIE.2013.2278960","ISBN":"0885-8993","ISSN":"02780046","abstract":"Recently, a world's first ever power electronic traction transformer (PETT) for 15 kV, 16 2/3Hz railway grid, has been newly developed, commissioned, and installed on the locomotive, where it is presently in use. This marks an important milestone in the traction world. The design and development of the PETT are described in this paper, where a low-voltage (LV) PETT prototype is presented. It has been designed for the purposes of control hardware and software commissioning, thus serving a role of an analogue simulator. In this paper, emphasis is placed on the overall system requirements, from where control system has been developed, implemented, and successfully commissioned. The development of a 1.2MVA medium-voltage PETT prototype will be reported separately in accompanying paper.","author":[{"dropping-particle":"","family":"Zhao","given":"Chuanhong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Dujic","given":"Drazen","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Mester","given":"Akos","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Steinke","given":"Juergen K.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Weiss","given":"Michael","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Lewdeni-Schmid","given":"Silvia","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Chaudhuri","given":"Toufann","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Stefanutti","given":"Philippe","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Industrial Electronics","id":"ITEM-6","issue":"7","issued":{"date-parts":[["2014"]]},"page":"3257-3268","publisher":"IEEE","title":"Power electronic traction transformer-medium voltage prototype","type":"article-journal","volume":"61"},"uris":[""]},{"id":"ITEM-7","itemData":{"DOI":"10.1109/SPEEDAM.2012.6264496","ISBN":"9781467312998","author":[{"dropping-particle":"","family":"Zhao","given":"Chuanhong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Weiss","given":"Michael","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Mester","given":"Akos","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Lewdeni-Schmid","given":"Silvia","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Dujic","given":"Drazen","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Steinke","given":"Juergen K.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Chaudhuri","given":"Toufann","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"SPEEDAM 2012 - 21st International Symposium on Power Electronics, Electrical Drives, Automation and Motion","id":"ITEM-7","issued":{"date-parts":[["2012"]]},"page":"855-860","publisher":"IEEE","title":"Power electronic transformer (PET) converter: Design of a 1.2MW demonstrator for traction applications","type":"article-journal"},"uris":[""]},{"id":"ITEM-8","itemData":{"ISSN":"10133119","author":[{"dropping-particle":"","family":"Claesens","given":"Max","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Dujic","given":"Drazen","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Canales","given":"Francisco","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Steinke","given":"Juergen K.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Stefanutti","given":"Philipe","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Veterli","given":"Christian","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"ABB Review","id":"ITEM-8","issue":"1","issued":{"date-parts":[["2012"]]},"page":"11-17","title":"Traction transformation: A power-electronic traction transformer (PETT)","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[18]–[25]","plainTextFormattedCitation":"[18]–[25]","previouslyFormattedCitation":"[18]–[25]"},"properties":{"noteIndex":0},"schema":""}[18]–[25]. The concept of Weiss from 1985 has been later improved by employing the resonant high-frequency link isolation stage of McMurray (Fig. 2b) realising an isolated front-end converter topology as in Fig. 5c). In contrast to the previously mentioned isolated back-end converter, here the capacitors of the isolation stage are small resonant or commutation capacitors, since there is no energy storage required in the isolation stage. The flow of power is controlled by the boost converter in the LV side and translated to the MV side providing unity power factor. In this way the measurements can be done in the LV side, with savings on the sensing equipment. Other modern topologies based on the original concepts are the isolated modular multilevel converters and single cell configurations. The idea behind the modular multilevel converter is the simplification of modules by eliminating the necessity of DC supply for each, while keeping the cascaded structure as in Fig. 3 ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"ISBN":"9075815077","abstract":"This paper introduces a new modular multilevel converter (M2LC) topology suitable for very high voltage applications, especially network interties in power transmission. The fundamental concept, the applied control scheme and simulation results of a 36MW–network intertie are presented. With reference to the expenditure of components, a comparison between the new modular multilevel converter and a conventional converter topology is given. A suitable structure of the converter control is proposed.","author":[{"dropping-particle":"","family":"Lesnicar","given":"A","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Marquardt","given":"R","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"10th European Power Electronics Conference (EPE)","id":"ITEM-1","issued":{"date-parts":[["2003"]]},"publisher-place":"Toulouse","title":"A new modular voltage source inverter topology","type":"paper-conference"},"uris":[""]}],"mendeley":{"formattedCitation":"[41]","plainTextFormattedCitation":"[41]","previouslyFormattedCitation":"[41]"},"properties":{"noteIndex":0},"schema":""}[41]. In 2004 it was already proposed for a traction application ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1080/09398368.2004.11463567","author":[{"dropping-particle":"","family":"Glinka","given":"M.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Marquardt","given":"Rainer","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"EPE Journal","id":"ITEM-1","issue":"14","issued":{"date-parts":[["2004"]]},"page":"7-12","title":"A New Single Phase AC/AC-Multilevel Converter for Traction Vehicles Operating On Ac Line Voltage","type":"article-journal","volume":"3"},"uris":[""]}],"mendeley":{"formattedCitation":"[42]","plainTextFormattedCitation":"[42]","previouslyFormattedCitation":"[42]"},"properties":{"noteIndex":0},"schema":""}[42], however only for the MV side with a single MFT. The authors extended their work and defined this structure as a new multilevel converter family for traction in ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"Glinka","given":"M","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Marquardt","given":"R","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Trans. Ind. Electron.","id":"ITEM-1","issue":"3","issued":{"date-parts":[["2005"]]},"page":"662-669","title":"A new AC/AC multilevel converter family","type":"article-journal","volume":"52"},"uris":[""]}],"mendeley":{"formattedCitation":"[43]","plainTextFormattedCitation":"[43]","previouslyFormattedCitation":"[43]"},"properties":{"noteIndex":0},"schema":""}[43], as shown in Fig. 6. The single cell structure is available due to the technological advance of WBG semiconductors, which have higher blocking voltages. Such structures include Neutral-Point Clamped (NPC) converters or two-level converters. This approach eliminates the necessity of cascaded modules while keeping the MFT isolation stage, which can be realised as in McMurray’s concept with a half-cycle discontinuous conduction mode resonant converter. Such a single cell structure was proposed in 2018 by Verdicchio in ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/TTE.2018.2826780","ISSN":"23327782","author":[{"dropping-particle":"","family":"Verdicchio","given":"Andrea","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Ladoux","given":"Philippe","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Caron","given":"Herve","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Courtois","given":"Christian","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Transportation Electrification","id":"ITEM-1","issue":"2","issued":{"date-parts":[["2018"]]},"page":"591-604","publisher":"IEEE","title":"New Medium-Voltage DC Railway Electrification System","type":"article-journal","volume":"4"},"uris":[""]}],"mendeley":{"formattedCitation":"[29]","plainTextFormattedCitation":"[29]","previouslyFormattedCitation":"[29]"},"properties":{"noteIndex":0},"schema":""}[29] and was also pursued by the project Future Renewable Electric Energy Delivery and Management (FREEDM) ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/JPROC.2010.2081330","ISSN":"00189219","abstract":"This paper presents an architecture for a future electric power distribution system that is suitable for plug-andplay of distributed renewable energy and distributed energy storage devices. Motivated by the success of the (information) Internet, the architecture described in this paper was proposed by the NSF FREEDM Systems Center, Raleigh, NC, as a roadmap for a future automated and flexible electric power distribution system. In the envisioned BEnergy Internet, [ a system that enables flexible energy sharing is proposed for consumers in a residential distribution system. The key technologies required to achieve such a vision are presented in this paper as a result of the research partnership of the FREEDM Systems Center.","author":[{"dropping-particle":"","family":"Huang","given":"Alex Q.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Crow","given":"Mariesa L.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Heydt","given":"Gerald Thomas","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zheng","given":"Jim P.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Dale","given":"Steiner J.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"Proceedings of the IEEE","id":"ITEM-1","issue":"1","issued":{"date-parts":[["2011"]]},"page":"133-148","publisher":"IEEE","title":"The future renewable electric energy delivery and management (FREEDM) system: The energy internet","type":"article-journal","volume":"99"},"uris":[""]}],"mendeley":{"formattedCitation":"[44]","plainTextFormattedCitation":"[44]","previouslyFormattedCitation":"[44]"},"properties":{"noteIndex":0},"schema":""}[44]. Both used NPC configurations with SiC devices. Another good option for MF isolation are DAB converters (patented in 1989 by DeDoncker ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"DeDoncker","given":"R.W.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Kheraluwala","given":"M.H.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Divan","given":"D.M.","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issued":{"date-parts":[["1991"]]},"publisher":"US Patent 5027264","title":"Power conversion apparatus for dc/dc conversion using dual active bridges","type":"patent"},"uris":[""]}],"mendeley":{"formattedCitation":"[45]","plainTextFormattedCitation":"[45]","previouslyFormattedCitation":"[45]"},"properties":{"noteIndex":0},"schema":""}[45]), which are highly controllable, but more complex as well. However, in a single cell structure the complexity will not be considered a drawback as in the case of modular structures, since there is only one module. Also, employing HV SiC devices, the system complexity will be very low and efforts can be focusses on improving the reliability.As a conclusion, the original key concepts led to the definition of five main topologies for PETTs. In most traction converters developed recently, the modular structure is favoured due to its scalability to higher voltage levels and reliability (possibility of adding redundant cells), which are important requirements in traction applications. Therefore, even with the appearance of HV WBG semiconductors, cascaded modular and multicell topologies will remain integral part of PETTs. However, as mentioned earlier, some challenges must be still addressed before this technology reaches maturity. These include mainly protection issues against overvoltages, short circuit induced currents, good isolation and thermal management. IBE family is suitable and used for traction and IFE for auxiliary power supply, where high power density is needed, since IFE is less complex but also less flexible as IBE. Multilevel converters should be further researched for validation of its benefits in terms of isolation design compared to separated multi-winding transformer-based configurations. Finally, regarding single cell structure, it shows reliability issues (redundant design is challenging) at the expense of less complexity.As an addition to the conclusions of this chapter, Table 2 summarises the differences between MFT and LFT technologies. Table 2 – MFT and LFT technology comparison.LFTMFTPower densitylowhighEfficiencylimited and lowerhighTransformer design complexitylowhigh, moreover different applications need different and specific designOperating/switching frequencyline frequency (low)hundreds of Hz to tens of kHzPower qualityfairgood, due to more control optionsTechnical maturityreached its maturitynot yet mature, some topologies and configurations are reaching their potential faster than othersFault current limitationlowgoodFault isolation capabilitypoorgood, also redundant configuration is availableControl complexitylowhigh and in some applications can be difficult, but rewardingSwitch and drives countlowhigh number of devices, due to modular/multi-level structure, however WBG high-voltage devices can lower itFlexibilitylowhigh, offers additional functionalities like fault limitation and isolation, voltage flicker compensationControllabilitylow, no control over transmitted powerhigh, good control over power flowAvailabilityhighfair, difficult to design and manufactureReliabilityhighlower; under research and development, different configurations, like redundancy can bring improvementsCostslow cost compared to state of the art technologies, much better kW/cost value due to multilevel/multi-stage and/or multi-modular structure they have a higher cost (still low kW/cost value)Losseshigher losseslower lossesBrief overview of state of the art PETTs and definition of suitable topologies for MVDC-ERSBased on the early concepts presented in the previous chapter, several PETT topologies have been studied, developed, prototyped and tested for railway systems by various university research groups and train manufacturers. The new wide band-gap semiconductor materials like silicon carbide encourages PETT development, especially when the 6.5kV and 10kV and later 15kV SiC components will be ready for commercialisation. SiC semiconductors allow switching frequencies as high as tens of kilohertz, leading to higher fundamental frequency of MFTs; when SiC devices will be available for higher voltages, it will also be possible to use fewer converter modules and/or stages. The operating frequency of new PETT structures is practically the switching frequency of power semiconductor modules, therefore is independent on line frequency. The most timely application of PETTs would be for 15kV AC ERS connected traction vehicles, since the 16.7Hz supply frequency obliges locomotives to have on-board transformers heavier those for 25kV, 50 Hz or 60 Hz AC systems. In this case the new PETT technology achieves an increase of efficiency by 7% and a global weight reduction of 50% ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"ISBN":"9781119386803","author":[{"dropping-particle":"","family":"Brenna","given":"M.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Foiadelli","given":"F.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zaninelli","given":"D.","non-dropping-particle":"","parse-names":false,"suffix":""}],"editor":[{"dropping-particle":"","family":"Hossain","given":"Ekram","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issued":{"date-parts":[["2018"]]},"publisher":"Wiley","title":"Electrical railway transportation systems","type":"book"},"uris":[""]}],"mendeley":{"formattedCitation":"[12]","plainTextFormattedCitation":"[12]","previouslyFormattedCitation":"[12]"},"properties":{"noteIndex":0},"schema":""}[12]. A new ERS, such as a flexible MVDC-ERS, would require also high-performance novel PETT structures to handle new challenges such as fault handling, protection circuits and smart-grid compatibility. In the MVDC-ERS concept the setup looks different in comparison to the main topological families defined in 3.4, as the line voltage is a DC voltage; thus, the rectifier stage is not needed in MVDC-ERS traction topologies. However, to improve the new MVDC line-based traction devices voltage balancing stages could be used instead of the rectifier stages. The concept of voltage balancing will be presented in a later chapter. The last 25 years of PETT concepts (1993-today)This section presents a review of PETTs for MV ERSs at 15kV and 25kV AC. Based on 3.4, in the following PETT topology families will be presented, that could be used in MVDC-ERS (same topologies as defined in 3.4, but without the rectifier stage in the primary) ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/tvt.2019.2895500","ISSN":"0018-9545","author":[{"dropping-particle":"","family":"Winter","given":"Joachim","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Schirmer","given":"Toni","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Iraklis","given":"Athanasios","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Lusiewicz","given":"Anna","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Dittus","given":"Holger","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Vehicular Technology","id":"ITEM-1","issue":"c","issued":{"date-parts":[["2019"]]},"page":"1-1","publisher":"IEEE","title":"Overview of Three-Stage Power Converter Topologies for Medium Frequency-based Railway Vehicle Traction Systems","type":"article-journal","volume":"PP"},"uris":[""]}],"mendeley":{"formattedCitation":"[46]","plainTextFormattedCitation":"[46]","previouslyFormattedCitation":"[46]"},"properties":{"noteIndex":0},"schema":""}[46]. Let the first configuration type be the single cell structure in Fig. 6 on the next page, since the first PETT developed in ‘85 by Weiss and already presented in the previous chapter had such a structure. As seen in Fig. 4 it consisted of a matrix converter with a 400Hz MFT placed between an input and output rectifier and a boost converter at the output with the role of current shaping and voltage regulation. At that time thyristors were used, which were replaced by IGBTs in later topologies.Fig. 6 – Single cell matrix/NPC based converter. (APU means Auxiliary Power Unit and M is Motor)Later in ’93 another thyristor-based system was developed in Sweden also with matrix converter in the front-end and a four-quadrant converter at the output. The developers also suggested a cascaded configuration in the front-end with semi separated multi-winding isolation to avoid high line-current harmonics ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/JESTPE.2017.2685464","ISSN":"21686785","abstract":"In this paper, power electronic transformer (PET) based railway traction systems are comprehensively reviewed according to the unique application features and requirements. By comparing PET and conventional line frequency transformer (LFT) based systems, their pros and cons are summarized. By further reviewing all kinds of PET based designs from the early concepts to the latest ones in the order of their publication dates, the developing trends are highlighted. By synthetically considering the requirements and the state-of-the-art, the key challenges and opportunities are identified and discussed. It shows that although PET based systems are still developing and far from mature, they are already superior to LFT based systems in terms of system weight, efficiency and functionalities especially for 15kV/16.7Hz applications. With the advancements on wide bandgap power devices, medium frequency transformers and converters, PET systems will be even more promising and available for all types of railway tractions in the near future.","author":[{"dropping-particle":"","family":"Feng","given":"Jianghua","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Chu","given":"W. Q.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhang","given":"Zhixue","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhu","given":"Z. Q.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Journal of Emerging and Selected Topics in Power Electronics","id":"ITEM-1","issue":"3","issued":{"date-parts":[["2017"]]},"page":"1237-1253","publisher":"IEEE","title":"Power Electronic Transformer-Based Railway Traction Systems: Challenges and Opportunities","type":"article-journal","volume":"5"},"uris":[""]}],"mendeley":{"formattedCitation":"[47]","plainTextFormattedCitation":"[47]","previouslyFormattedCitation":"[47]"},"properties":{"noteIndex":0},"schema":""}[47]. This concept was further studied and in 2001 the thyristors were replaced by highvoltage IGBTs. In this way the switching frequency was increased, since naturally commuted thyristors switched at line frequency. In the system developed in 2001 by S Norrga, a three-phase configuration was proposed to reduce high line-current harmonics. The switching frequency was 1 kHz with ZVS and the results on a 30?kW laboratory prototype showed a 40-50% weight reduction in comparison with an equivalent LFT. In the primary side, RC snubbers were added to reduce overvoltages caused by leakage inductance ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"Kj?r","given":"Philip C","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Norrga","given":"Staffan","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"?stlund","given":"Stefan","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issue":"6","issued":{"date-parts":[["2001"]]},"page":"1824-1831","title":"A Primary-Switched Line-Side Converter Using Zero-Voltage Switching","type":"article-journal","volume":"37"},"uris":[""]}],"mendeley":{"formattedCitation":"[48]","plainTextFormattedCitation":"[48]","previouslyFormattedCitation":"[48]"},"properties":{"noteIndex":0},"schema":""}[48].Previous research has shown that the single cell structure is not the best option for PETTS, as even with 6.5kV IGBTs (those with the current highest available blocking voltage), a series connection of semiconductor devices would be unavoidable. Therefore, the application of series connected front-end converters became more popular. In the future, when higher voltage SiC devices will be available, the single cell structure may be considered again. A single cell NPC converter based on 10?kV SiC MOSFETs was proposed as a concept for future MVDC-ERS in ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/TTE.2018.2826780","ISSN":"23327782","author":[{"dropping-particle":"","family":"Verdicchio","given":"Andrea","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Ladoux","given":"Philippe","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Caron","given":"Herve","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Courtois","given":"Christian","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Transportation Electrification","id":"ITEM-1","issue":"2","issued":{"date-parts":[["2018"]]},"page":"591-604","publisher":"IEEE","title":"New Medium-Voltage DC Railway Electrification System","type":"article-journal","volume":"4"},"uris":[""]}],"mendeley":{"formattedCitation":"[29]","plainTextFormattedCitation":"[29]","previouslyFormattedCitation":"[29]"},"properties":{"noteIndex":0},"schema":""}[29] in 2018. Single cell systems have low complexity and reliability but also low availability, since it is easier to have a more redundant design with multiple modules.The next topology to be analysed is the multi-cell structure, which is modular and multi-level, as shown in Fig. 7. Several PETT systems with this configuration were developed in 2002-2008. Fig. 7 – Modular multi-level structure (multicell).After researches demonstrated the necessity of series connection of converters in the front end, in 2002, right after the concept presented in 2001, a multicell structure was proposed in ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1049/cp:20020156","ISSN":"05379989","abstract":"A novel isolated ac/dc converter topology incorporates a voltage source converter (VSC) with capacitive snubbers and a cycloconverter, connected by a medium frequency transformer. The concept offers the possibility of bilateral power flow as well as three-level pulse width modulation on the ac side. It is shown that by alternately commutating the VSC and the cycloconverter it is possible to achieve either zero-voltage or zero-current switching conditions for all of the semiconductor elements. At low load the ac load current becomes insufficient for recharging the snubber capacitors of the VSC and the commutations may therefore become too slow. However, a quasi-resonant commutation mode for the voltage source converter is proposed that allows for sufficiently fast commutations down to zero load.","author":[{"dropping-particle":"","family":"Norrga","given":"S.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEE Conference Publication","id":"ITEM-1","issue":"487","issued":{"date-parts":[["2002"]]},"page":"433-438","title":"A soft-switched bi-directional isolated AC/DC converter for AC-fed railway propulsion applications","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[49]","plainTextFormattedCitation":"[49]","previouslyFormattedCitation":"[49]"},"properties":{"noteIndex":0},"schema":""}[49] by the same author. He proposed a two-level modular structure using so called “cycloconverter sub-valve” cells with capacitive snubbers, which were included to avoid uneven voltage distribution among the “valves”. In the secondary circuit, a VSC was applied and with alternate switching of the VSC with the cycloconverter ZVS or ZCS was achieved. Norrga reported shortly after in a different paper also the design of the high-power MFT.During 2003-2005 Siemens worked on a 2?MVA modular multi-cell converter for the 15?kV catenary. They developed an 8 module 17-level converter using 1.2?kV IGBTs and a 10?kHz MFT. Siemens made a full-scale prototype of the whole system too, with a predicted peak efficiency of 98%, based on simulations ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/JESTPE.2017.2685464","ISSN":"21686785","abstract":"In this paper, power electronic transformer (PET) based railway traction systems are comprehensively reviewed according to the unique application features and requirements. By comparing PET and conventional line frequency transformer (LFT) based systems, their pros and cons are summarized. By further reviewing all kinds of PET based designs from the early concepts to the latest ones in the order of their publication dates, the developing trends are highlighted. By synthetically considering the requirements and the state-of-the-art, the key challenges and opportunities are identified and discussed. It shows that although PET based systems are still developing and far from mature, they are already superior to LFT based systems in terms of system weight, efficiency and functionalities especially for 15kV/16.7Hz applications. With the advancements on wide bandgap power devices, medium frequency transformers and converters, PET systems will be even more promising and available for all types of railway tractions in the near future.","author":[{"dropping-particle":"","family":"Feng","given":"Jianghua","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Chu","given":"W. Q.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhang","given":"Zhixue","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhu","given":"Z. Q.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Journal of Emerging and Selected Topics in Power Electronics","id":"ITEM-1","issue":"3","issued":{"date-parts":[["2017"]]},"page":"1237-1253","publisher":"IEEE","title":"Power Electronic Transformer-Based Railway Traction Systems: Challenges and Opportunities","type":"article-journal","volume":"5"},"uris":[""]}],"mendeley":{"formattedCitation":"[47]","plainTextFormattedCitation":"[47]","previouslyFormattedCitation":"[47]"},"properties":{"noteIndex":0},"schema":""}[47]. At the moment, the most commonly used topologies of PETT for MVDC applications are input-series output-parallel (ISOP) DC–DC converters, shown in Fig. 9 ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/JESTPE.2017.2685464","ISSN":"21686785","abstract":"In this paper, power electronic transformer (PET) based railway traction systems are comprehensively reviewed according to the unique application features and requirements. By comparing PET and conventional line frequency transformer (LFT) based systems, their pros and cons are summarized. By further reviewing all kinds of PET based designs from the early concepts to the latest ones in the order of their publication dates, the developing trends are highlighted. By synthetically considering the requirements and the state-of-the-art, the key challenges and opportunities are identified and discussed. It shows that although PET based systems are still developing and far from mature, they are already superior to LFT based systems in terms of system weight, efficiency and functionalities especially for 15kV/16.7Hz applications. With the advancements on wide bandgap power devices, medium frequency transformers and converters, PET systems will be even more promising and available for all types of railway tractions in the near future.","author":[{"dropping-particle":"","family":"Feng","given":"Jianghua","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Chu","given":"W. Q.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhang","given":"Zhixue","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhu","given":"Z. Q.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Journal of Emerging and Selected Topics in Power Electronics","id":"ITEM-1","issue":"3","issued":{"date-parts":[["2017"]]},"page":"1237-1253","publisher":"IEEE","title":"Power Electronic Transformer-Based Railway Traction Systems: Challenges and Opportunities","type":"article-journal","volume":"5"},"uris":[""]}],"mendeley":{"formattedCitation":"[47]","plainTextFormattedCitation":"[47]","previouslyFormattedCitation":"[47]"},"properties":{"noteIndex":0},"schema":""}[47]. However, ISOPs have a large number of dc-dc modules, meaning many medium-frequency transformers and semiconductors, which can be a limitation Therefore, other multilevel structures have been proposed that use only one transformer, as shown in Fig. 8. The main disadvantage is the lack of good bypass features in case of module break downs. Different solutions were proposed for this problem in literature, but the low power density is still a limiting factor. ISOP PETT structures can also have power balance problems, which implies more complex control systems. SiC semiconductors will make possible the development of two-level converter topologies with fewer modules, simplifying the control system. The following two topology families will be ISOP structures. b)Fig. 8 – a) Cascaded ISOP setup with semi separated multi-winding isolation (SSMW). b) Multi port multi-winding PETT configuration.In 2003 Alstom developed an 8 module CHB PETT with ISOP structure using a semi separated multi-winding (SSMW) MFT of 5 kHz as isolation. The achieved power was 1.5?MVA and 6.5?kV and 3.3?kV IGBTs were used. Another two SSMW configurations were presented by University of West Bohemia, Czech Republic in 2008 for 25?kV AC ERS. For the first, they used a 400?Hz MFT and two cascaded H-bridges in the primary for a 12?kW 400?V laboratory prototype. The second was a 4?kVA matrix converter based PETT system also with only two modules, for which they proposed the separated multi-winding isolation as an option. In both their work the robustness of control and feasibility was validated at steady-state and for different load changes. Another relevant SSMW configuration PETT concept was developed in China by Tsinghua University in 2014. They presented two options too: a SSMW with independent output DC links in the secondary for an EMU setup and a SMW for locomotive with paralleled DC link capacitors. The concept was validated on a 6?kV laboratory experimental setup with an MFT having 6 primary and secondary windings. The main novelty of their work was the multi-port configuration in the output stage, shown in Fig. 8b. The simulations were based on the 25kV AC ERS with 23 cascaded modules and 1 kHz MFT. The work also highlighted the control algorithms used: soft switching achieved with phase-shift control, voltage balancing control and power decoupling calculation ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/JESTPE.2017.2685464","ISSN":"21686785","abstract":"In this paper, power electronic transformer (PET) based railway traction systems are comprehensively reviewed according to the unique application features and requirements. By comparing PET and conventional line frequency transformer (LFT) based systems, their pros and cons are summarized. By further reviewing all kinds of PET based designs from the early concepts to the latest ones in the order of their publication dates, the developing trends are highlighted. By synthetically considering the requirements and the state-of-the-art, the key challenges and opportunities are identified and discussed. It shows that although PET based systems are still developing and far from mature, they are already superior to LFT based systems in terms of system weight, efficiency and functionalities especially for 15kV/16.7Hz applications. With the advancements on wide bandgap power devices, medium frequency transformers and converters, PET systems will be even more promising and available for all types of railway tractions in the near future.","author":[{"dropping-particle":"","family":"Feng","given":"Jianghua","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Chu","given":"W. Q.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhang","given":"Zhixue","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhu","given":"Z. Q.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Journal of Emerging and Selected Topics in Power Electronics","id":"ITEM-1","issue":"3","issued":{"date-parts":[["2017"]]},"page":"1237-1253","publisher":"IEEE","title":"Power Electronic Transformer-Based Railway Traction Systems: Challenges and Opportunities","type":"article-journal","volume":"5"},"uris":[""]}],"mendeley":{"formattedCitation":"[47]","plainTextFormattedCitation":"[47]","previouslyFormattedCitation":"[47]"},"properties":{"noteIndex":0},"schema":""}[47].The most studied PETTs topology is the cascaded ISOP with separated multi-winding MFT, and hence it is analysed here in more depth.Fig. 9 – Cascaded ISOP setup with separated multi-winding (SMW) isolation.One of the first structures was Rufer’s direct coupled multi-level based four-quadrant converter in ’96 and used the novel high-voltage IGBTs instead of thyristors. This was crucial in the evolution of PETTs, since IGBTs in comparison to thyristors are fully controllable. The DC-DC converters were bidirectional resonant converters with galvanic isolation using MFTs. Also is noteworthy to remark the ISOP structure of the whole system, since most of the later developed PETTs have used the same topology. From this configuration, four variants have been developed ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/tvt.2019.2895500","ISSN":"0018-9545","author":[{"dropping-particle":"","family":"Winter","given":"Joachim","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Schirmer","given":"Toni","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Iraklis","given":"Athanasios","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Lusiewicz","given":"Anna","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Dittus","given":"Holger","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Vehicular Technology","id":"ITEM-1","issue":"c","issued":{"date-parts":[["2019"]]},"page":"1-1","publisher":"IEEE","title":"Overview of Three-Stage Power Converter Topologies for Medium Frequency-based Railway Vehicle Traction Systems","type":"article-journal","volume":"PP"},"uris":[""]}],"mendeley":{"formattedCitation":"[46]","plainTextFormattedCitation":"[46]","previouslyFormattedCitation":"[46]"},"properties":{"noteIndex":0},"schema":""}[46], see Figures 10-13.Fig. 10 – Active Full-Bridge converter topology with ISOP setup.Fig. 11 – Cascaded Active Half-Bridge ISOP converter.Fig. 12 – Asymmetrical Active Bridge converter topology, ISOP. Fig. 13 – Diode-clamped ISOP converter topology with Half-Bridge.In ’98 Siemens developed a similar structure as Rufer’s ’96 concept (MFT, high-voltage IGBTs, CHB and ISOP configuration) having the configuration as in Fig. 10. Among these early concepts (the ones from ‘85 to 2002 presented on the previous pages) the most promising would be the one developed in ’96, having modular feature and being fault tolerant. Most of later developed topologies that will be shown in the following are based on this one, using ISOP configuration and soft switching. However, it should be noted that joint multi-winding technology is a compromise for fault tolerance. Looking at the evolution of PETTs it can be also noticed, that the number of publications per year is increasing. The new traction systems are developed by both the universities or other institutes and the leading railway traction system suppliers. The traction system suppliers have more experience and a better understanding of requirements, having also better opportunity to implement full-scale PET systems, thus offering a more practical concept approach. However, universities and institutes can develop sometimes really good ideas and theoretically well-defined concepts, which can be later used and implemented by the leading suppliers.In 2002 ABB developed a 4.2?MVA, 12 module CHB PETT concept with 10 kHz MFT using full bridges for the DC-DC conversion stage as in Fig. 10. The chosen topology was an LLC resonant DC-DC converter, however they prototyped only the MFT. The conclusions of this paper indicated that each application will require specially designed transformer to match its configuration and requirements, therefore transformer design will be a major hurdle in contrast to the other parts of the converter. ABB paid special attention on its insulation problem ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/apec.2002.989270","ISBN":"0780374045","abstract":"An actively cooled high power, high frequency transformer with high insulation capability for use in a high power multilevel converter is discussed. The transformer is designed for a power level of 350 kW and is realized with amorphous core material and coaxial windings. Special attention is paid on the insulation problem, since the dielectric losses and the influence of the voltage waveform with very steep edges have to be investigated more in detail to guarantee a long lifetime of the device.","author":[{"dropping-particle":"","family":"Heinemann","given":"Lothar","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC","id":"ITEM-1","issue":"c","issued":{"date-parts":[["2002"]]},"page":"352-357","title":"An actively cooled high power, high frequency transformer with high insulation capability","type":"article-journal","volume":"1"},"uris":[""]}],"mendeley":{"formattedCitation":"[50]","plainTextFormattedCitation":"[50]","previouslyFormattedCitation":"[50]"},"properties":{"noteIndex":0},"schema":""}[50].In 2007 Bombardier presented a PETT system of 3?MVA with 8 CHB modules and 8 kHz MFTs capable of 500?kW maximum power transfer (per module), with a reported transformer weight of 18?kg. A 750?kW laboratory testing system was also developed. Similar to ABB, Bombardier used an outer voltage control loop and inner line-current control loop with PI and proportional-resonant (PR) respectively, to control the power flow Also, an active damping mode was suggested to reduce harmonic disturbances. The controller thus improved line current quality obtaining a THD of 1.92% ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/EPE.2007.4417570","ISBN":"9075815115","abstract":"The proposed Medium Frequency Topology is replacing the bulky main line transformer on board of railway vehicles. Especially in countries with 15kV railway power supply, the low frequency of 16.7 Hz is leading to huge and heavy transformers. Today's Transformers are often minimized in weight and volume, which leads to significantly high transformer losses compared with distribution transformers. The Medium Frequency Topology is the power electronic solution that considerably reduces weight and losses of the traction system.","author":[{"dropping-particle":"","family":"Steiner","given":"Michael","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Reinold","given":"Harry","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2007 European Conference on Power Electronics and Applications, EPE","id":"ITEM-1","issued":{"date-parts":[["2007"]]},"title":"Medium frequency topology in railway applications","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[35]","plainTextFormattedCitation":"[35]","previouslyFormattedCitation":"[35]"},"properties":{"noteIndex":0},"schema":""}[35].In 2007 ABB also developed a PETT for EMU application, but this time used matrix converters with 16 cascaded modules. They achieved 1.2?MVA using 3.3?kV/400?A IGBT semiconductors with a 1.8?kV DC-link voltage, and a 400?Hz multi-winding MFT ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/JESTPE.2017.2685464","ISSN":"21686785","abstract":"In this paper, power electronic transformer (PET) based railway traction systems are comprehensively reviewed according to the unique application features and requirements. By comparing PET and conventional line frequency transformer (LFT) based systems, their pros and cons are summarized. By further reviewing all kinds of PET based designs from the early concepts to the latest ones in the order of their publication dates, the developing trends are highlighted. By synthetically considering the requirements and the state-of-the-art, the key challenges and opportunities are identified and discussed. It shows that although PET based systems are still developing and far from mature, they are already superior to LFT based systems in terms of system weight, efficiency and functionalities especially for 15kV/16.7Hz applications. With the advancements on wide bandgap power devices, medium frequency transformers and converters, PET systems will be even more promising and available for all types of railway tractions in the near future.","author":[{"dropping-particle":"","family":"Feng","given":"Jianghua","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Chu","given":"W. Q.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhang","given":"Zhixue","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhu","given":"Z. Q.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Journal of Emerging and Selected Topics in Power Electronics","id":"ITEM-1","issue":"3","issued":{"date-parts":[["2017"]]},"page":"1237-1253","publisher":"IEEE","title":"Power Electronic Transformer-Based Railway Traction Systems: Challenges and Opportunities","type":"article-journal","volume":"5"},"uris":[""]}],"mendeley":{"formattedCitation":"[47]","plainTextFormattedCitation":"[47]","previouslyFormattedCitation":"[47]"},"properties":{"noteIndex":0},"schema":""}[47]. While back in 2002 ABB prototyped only the MFT, now they managed to prototype the whole system, that lead them to develop the first ever PETT implemented into an actual locomotive, that was tested in 2011 on the Swiss Federal Railways achieving a 95% efficiency and almost unity power factor. However, in 2011 they used the half-bridge configuration for the DC-DC converter, like the one in Fig. 11. For better fault handling, they implemented a redundant design including one extra module. For the control of the power flow within the modules, a slower outer DC-link voltage control loop with PI controller was used and a faster inner line-current control loop with PR control ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"Zhao","given":"Chuanhong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Lewdeni-schmid","given":"Silvia","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Steinke","given":"Juergen K","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Weiss","given":"Michael","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Chaudhuri","given":"Toufann","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Pellerin","given":"Marc","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Duron","given":"Joseph","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Stefanutti","given":"Philippe","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Sablières","given":"Rue","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"Proceedings of the 2011 14th European Conference on Power Electronics and Applications","id":"ITEM-1","issued":{"date-parts":[["0"]]},"page":"1-10","publisher":"IEEE","title":"Design , Implementation and Performance of a Modular Power Electronic Transformer ( PET ) for Railway Application Keywords Configuration of the PET demonstrator","type":"article-journal"},"uris":[""]},{"id":"ITEM-2","itemData":{"author":[{"dropping-particle":"","family":"Dujic","given":"Drazen","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Mester","given":"Akos","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Chaudhuri","given":"Toufann","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Coccia","given":"Antonio","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Canales","given":"Francisco","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Steinke","given":"Juergen K","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"A","given":"A B B Sécheron S","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Sablieres","given":"Rue","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"Proceedings of the 2011 14th European Conference on Power Electronics and Applications","id":"ITEM-2","issued":{"date-parts":[["0"]]},"page":"1-10","publisher":"IEEE","title":"Laboratory Scale Prototype of a Power Electronic Transformer for Traction Applications Former ABB colleague Keywords Power Electronic Transformer Topology","type":"article-journal","volume":"i"},"uris":[""]},{"id":"ITEM-3","itemData":{"DOI":"10.1109/TPEL.2013.2293402","author":[{"dropping-particle":"","family":"Besselmann","given":"Thomas","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Mester","given":"Akos","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Dujic","given":"Drazen","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Member","given":"Senior","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Power Electronics","id":"ITEM-3","issue":"8","issued":{"date-parts":[["2014"]]},"page":"3971-3981","publisher":"IEEE","title":"Power Electronic Traction Transformer : Efficiency Improvements Under Light-Load Conditions","type":"article-journal","volume":"29"},"uris":[""]},{"id":"ITEM-4","itemData":{"DOI":"10.1109/IPEMC.2012.6258820","ISBN":"9781457720888","author":[{"dropping-particle":"","family":"Dujic","given":"Drazen","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Kieferndorf","given":"Frederick","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Canales","given":"Francisco","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Drofenik","given":"Uwe","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"Proceedings of The 7th International Power Electronics and Motion Control Conference","id":"ITEM-4","issued":{"date-parts":[["2012"]]},"page":"636-642","publisher":"IEEE","title":"Power Electronic Traction Transformer Technology","type":"article-journal","volume":"1"},"uris":[""]},{"id":"ITEM-5","itemData":{"DOI":"10.1109/TPEL.2013.2248756","author":[{"dropping-particle":"","family":"Dujic","given":"Drazen","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Member","given":"Senior","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhao","given":"Chuanhong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Mester","given":"Akos","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Steinke","given":"Juergen K","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Member","given":"Senior","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Weiss","given":"Michael","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Lewdeni-schmid","given":"Silvia","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Chaudhuri","given":"Toufann","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Stefanutti","given":"Philippe","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Power Electronics","id":"ITEM-5","issue":"12","issued":{"date-parts":[["2013"]]},"page":"5522-5534","publisher":"IEEE","title":"Power Electronic Traction Transformer-Low Voltage Prototype","type":"article-journal","volume":"28"},"uris":[""]},{"id":"ITEM-6","itemData":{"DOI":"10.1109/TIE.2013.2278960","ISBN":"0885-8993","ISSN":"02780046","abstract":"Recently, a world's first ever power electronic traction transformer (PETT) for 15 kV, 16 2/3Hz railway grid, has been newly developed, commissioned, and installed on the locomotive, where it is presently in use. This marks an important milestone in the traction world. The design and development of the PETT are described in this paper, where a low-voltage (LV) PETT prototype is presented. It has been designed for the purposes of control hardware and software commissioning, thus serving a role of an analogue simulator. In this paper, emphasis is placed on the overall system requirements, from where control system has been developed, implemented, and successfully commissioned. The development of a 1.2MVA medium-voltage PETT prototype will be reported separately in accompanying paper.","author":[{"dropping-particle":"","family":"Zhao","given":"Chuanhong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Dujic","given":"Drazen","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Mester","given":"Akos","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Steinke","given":"Juergen K.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Weiss","given":"Michael","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Lewdeni-Schmid","given":"Silvia","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Chaudhuri","given":"Toufann","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Stefanutti","given":"Philippe","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Industrial Electronics","id":"ITEM-6","issue":"7","issued":{"date-parts":[["2014"]]},"page":"3257-3268","publisher":"IEEE","title":"Power electronic traction transformer-medium voltage prototype","type":"article-journal","volume":"61"},"uris":[""]},{"id":"ITEM-7","itemData":{"DOI":"10.1109/SPEEDAM.2012.6264496","ISBN":"9781467312998","author":[{"dropping-particle":"","family":"Zhao","given":"Chuanhong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Weiss","given":"Michael","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Mester","given":"Akos","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Lewdeni-Schmid","given":"Silvia","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Dujic","given":"Drazen","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Steinke","given":"Juergen K.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Chaudhuri","given":"Toufann","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"SPEEDAM 2012 - 21st International Symposium on Power Electronics, Electrical Drives, Automation and Motion","id":"ITEM-7","issued":{"date-parts":[["2012"]]},"page":"855-860","publisher":"IEEE","title":"Power electronic transformer (PET) converter: Design of a 1.2MW demonstrator for traction applications","type":"article-journal"},"uris":[""]},{"id":"ITEM-8","itemData":{"ISSN":"10133119","author":[{"dropping-particle":"","family":"Claesens","given":"Max","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Dujic","given":"Drazen","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Canales","given":"Francisco","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Steinke","given":"Juergen K.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Stefanutti","given":"Philipe","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Veterli","given":"Christian","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"ABB Review","id":"ITEM-8","issue":"1","issued":{"date-parts":[["2012"]]},"page":"11-17","title":"Traction transformation: A power-electronic traction transformer (PETT)","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[18]–[25]","plainTextFormattedCitation":"[18]–[25]","previouslyFormattedCitation":"[18]–[25]"},"properties":{"noteIndex":0},"schema":""}[18]–[25]. This project was presented in more detail in section 3.4. Rufer worked on PETTs later too, he proposed another CHB based PETT in 2003 while working with EPFL. Its novelty was the reconfigurable connection between 15kV AC and 3kV DC lines. He even discussed an alternative front-end converter topology, having an asymmetrical configuration, like in Fig. 12. The concept was verified on a small scale test rig ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/JESTPE.2017.2685464","ISSN":"21686785","abstract":"In this paper, power electronic transformer (PET) based railway traction systems are comprehensively reviewed according to the unique application features and requirements. By comparing PET and conventional line frequency transformer (LFT) based systems, their pros and cons are summarized. By further reviewing all kinds of PET based designs from the early concepts to the latest ones in the order of their publication dates, the developing trends are highlighted. By synthetically considering the requirements and the state-of-the-art, the key challenges and opportunities are identified and discussed. It shows that although PET based systems are still developing and far from mature, they are already superior to LFT based systems in terms of system weight, efficiency and functionalities especially for 15kV/16.7Hz applications. With the advancements on wide bandgap power devices, medium frequency transformers and converters, PET systems will be even more promising and available for all types of railway tractions in the near future.","author":[{"dropping-particle":"","family":"Feng","given":"Jianghua","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Chu","given":"W. Q.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhang","given":"Zhixue","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhu","given":"Z. Q.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Journal of Emerging and Selected Topics in Power Electronics","id":"ITEM-1","issue":"3","issued":{"date-parts":[["2017"]]},"page":"1237-1253","publisher":"IEEE","title":"Power Electronic Transformer-Based Railway Traction Systems: Challenges and Opportunities","type":"article-journal","volume":"5"},"uris":[""]}],"mendeley":{"formattedCitation":"[47]","plainTextFormattedCitation":"[47]","previouslyFormattedCitation":"[47]"},"properties":{"noteIndex":0},"schema":""}[47]. Later, he worked with IK4 IKERLAN (a private not-for-profit Technological Research Centre in northern Spain) focusing especially on MFT design. They developed in 2011-2012 a test rig and presented a 400?kW nanocrystalline-based MFT used in an LLC converter with 5 kHz switching frequency. The converter had a weight of 58.8?kg versus a 1 kHz switching frequency silicon-steel-based 500?kW MFT DAB converter with 462.7?kg weight ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/JESTPE.2017.2685464","ISSN":"21686785","abstract":"In this paper, power electronic transformer (PET) based railway traction systems are comprehensively reviewed according to the unique application features and requirements. By comparing PET and conventional line frequency transformer (LFT) based systems, their pros and cons are summarized. By further reviewing all kinds of PET based designs from the early concepts to the latest ones in the order of their publication dates, the developing trends are highlighted. By synthetically considering the requirements and the state-of-the-art, the key challenges and opportunities are identified and discussed. It shows that although PET based systems are still developing and far from mature, they are already superior to LFT based systems in terms of system weight, efficiency and functionalities especially for 15kV/16.7Hz applications. With the advancements on wide bandgap power devices, medium frequency transformers and converters, PET systems will be even more promising and available for all types of railway tractions in the near future.","author":[{"dropping-particle":"","family":"Feng","given":"Jianghua","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Chu","given":"W. Q.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhang","given":"Zhixue","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhu","given":"Z. Q.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Journal of Emerging and Selected Topics in Power Electronics","id":"ITEM-1","issue":"3","issued":{"date-parts":[["2017"]]},"page":"1237-1253","publisher":"IEEE","title":"Power Electronic Transformer-Based Railway Traction Systems: Challenges and Opportunities","type":"article-journal","volume":"5"},"uris":[""]}],"mendeley":{"formattedCitation":"[47]","plainTextFormattedCitation":"[47]","previouslyFormattedCitation":"[47]"},"properties":{"noteIndex":0},"schema":""}[47]. This study has shown how power density of MFTs can be improved using new materials for the transformer’s core.In 2014 the Federal University of Ceará, Brazil, combined the DAB topology with three-state cells and developed a PETT system, however without experimental validation. Also they used a centre-tapped transformer setup, which is disadvantageous due to increased weight, volume and complexity ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/JESTPE.2017.2685464","ISSN":"21686785","abstract":"In this paper, power electronic transformer (PET) based railway traction systems are comprehensively reviewed according to the unique application features and requirements. By comparing PET and conventional line frequency transformer (LFT) based systems, their pros and cons are summarized. By further reviewing all kinds of PET based designs from the early concepts to the latest ones in the order of their publication dates, the developing trends are highlighted. By synthetically considering the requirements and the state-of-the-art, the key challenges and opportunities are identified and discussed. It shows that although PET based systems are still developing and far from mature, they are already superior to LFT based systems in terms of system weight, efficiency and functionalities especially for 15kV/16.7Hz applications. With the advancements on wide bandgap power devices, medium frequency transformers and converters, PET systems will be even more promising and available for all types of railway tractions in the near future.","author":[{"dropping-particle":"","family":"Feng","given":"Jianghua","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Chu","given":"W. Q.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhang","given":"Zhixue","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhu","given":"Z. Q.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Journal of Emerging and Selected Topics in Power Electronics","id":"ITEM-1","issue":"3","issued":{"date-parts":[["2017"]]},"page":"1237-1253","publisher":"IEEE","title":"Power Electronic Transformer-Based Railway Traction Systems: Challenges and Opportunities","type":"article-journal","volume":"5"},"uris":[""]}],"mendeley":{"formattedCitation":"[47]","plainTextFormattedCitation":"[47]","previouslyFormattedCitation":"[47]"},"properties":{"noteIndex":0},"schema":""}[47].FREEDM published in 2014 another PETT with ISOP structure, where the isolation was realised by flyback inductors operated at high frequency. The topology used was full bridge with diodes connected in series with the transistors, a configuration as in Fig. 13. The study validated experimentally some voltage balancing methods on a small-scale rig supplied by a single-phase 120?V 60?Hz AC voltage. The difference to other works is that FREEDM used CSC instead of VSC, which can be a disadvantage in terms of input voltage quality.In 2015 the Laboratory of Magnetic Suspension Technology and Maglev vehicle together with Southwest Jiatong University, China, analysed a three-level, multi-module diode-clamped PETT for railway applications. The DC-DC converter was a bidirectional half-bridge as in Fig. 13 and the rectifier had an H-Bridge configuration, both diode-clamped. The experimental validation was done only for 100?V input, 70?V output at the DC buses. In ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/TIE.2010.2049719","ISSN":"02780046","abstract":"Multilevel converters have been under research and development for more than three decades and have found successful industrial application. However, this is still a technology under development, and many new contributions and new commercial topologies have been reported in the last few years. The aim of this paper is to group and review these recent contributions, in order to establish the current state of the art and trends of the technology, to provide readers with a comprehensive and insightful review of where multilevel converter technology stands and is heading. This paper first presents a brief overview of well-established multilevel converters strongly oriented to their current state in industrial applications to then center the discussion on the new converters that have made their way into the industry. In addition, new promising topologies are discussed. Recent advances made in modulation and control of multilevel converters are also addressed. A great part of this paper is devoted to show nontraditional applications powered by multilevel converters and how multilevel converters are becoming an enabling technology in many industrial sectors. Finally, some future trends and challenges in the further development of this technology are discussed to motivate future contributions that address open problems and explore new possibilities. ? 2006 IEEE.","author":[{"dropping-particle":"","family":"Kouro","given":"Samir","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Malinowski","given":"Mariusz","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Gopakumar","given":"K.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Pou","given":"Josep","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Franquelo","given":"Leopoldo G.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Wu","given":"Bin","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Rodriguez","given":"Jose","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Perez","given":"Marcelo A.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Leon","given":"Jose I.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Industrial Electronics","id":"ITEM-1","issue":"8","issued":{"date-parts":[["2010"]]},"page":"2553-2580","title":"Recent advances and industrial applications of multilevel converters","type":"article-journal","volume":"57"},"uris":[""]}],"mendeley":{"formattedCitation":"[51]","plainTextFormattedCitation":"[51]","previouslyFormattedCitation":"[51]"},"properties":{"noteIndex":0},"schema":""}[51] it is highlighted that CHB configurations are more mature and can reach higher voltages than other multilevel topologies, including diode-clamped configurations. Furthermore, diode-clamped converters have higher switching losses and unbalanced voltage, which could be solved with a voltage balancing stage. However cost would increase and many high-power high-voltage diodes would be necessary. As a conclusion of this brief analyses of MV PETTs, it can be observed that most of them are designed for 15?kV AC ERS and only a few concepts are presented for 25kV ERS. Most of the projects are from Europe and the most preferred topological family is the one in Fig. 9, using CHB. Since 25kV is a higher voltage by 66% than 15kV, it implies more cascaded modules and higher costs. Therefore, as mentioned earlier, PETTs are mainly viable for 15kV ERS. However, for a MVDC-ERS, the cost for a PETT is lower since there is no rectifier stageADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/JESTPE.2017.2685464","ISSN":"21686785","abstract":"In this paper, power electronic transformer (PET) based railway traction systems are comprehensively reviewed according to the unique application features and requirements. By comparing PET and conventional line frequency transformer (LFT) based systems, their pros and cons are summarized. By further reviewing all kinds of PET based designs from the early concepts to the latest ones in the order of their publication dates, the developing trends are highlighted. By synthetically considering the requirements and the state-of-the-art, the key challenges and opportunities are identified and discussed. It shows that although PET based systems are still developing and far from mature, they are already superior to LFT based systems in terms of system weight, efficiency and functionalities especially for 15kV/16.7Hz applications. With the advancements on wide bandgap power devices, medium frequency transformers and converters, PET systems will be even more promising and available for all types of railway tractions in the near future.","author":[{"dropping-particle":"","family":"Feng","given":"Jianghua","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Chu","given":"W. Q.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhang","given":"Zhixue","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhu","given":"Z. Q.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Journal of Emerging and Selected Topics in Power Electronics","id":"ITEM-1","issue":"3","issued":{"date-parts":[["2017"]]},"page":"1237-1253","publisher":"IEEE","title":"Power Electronic Transformer-Based Railway Traction Systems: Challenges and Opportunities","type":"article-journal","volume":"5"},"uris":[""]}],"mendeley":{"formattedCitation":"[47]","plainTextFormattedCitation":"[47]","previouslyFormattedCitation":"[47]"},"properties":{"noteIndex":0},"schema":""}[47]. The cascaded H-bridge and the matrix converters are the two preferred candidates for front-end converters, with CHB systems more mature and popular. In terms of the transformer, the multi-separated MFTs configuration is better than joint multi-winding MFT configuration, because it is easier to manufacture and has better fault handling performance. In terms of the system configuration, cascaded front-end converters with fully controllable power electronic devices must be used, in order to withstand the input voltage from the catenary. Usually input-series-output-parallel configuration is the most popular, as it uses a modular design that is good for redundancy. However, they have the disadvantages of high cost and low-power density necessity, thus topologies with reduced number of cascaded front-end converters would ultimately be preferred when new semiconductors with higher blocking voltage will become availableFig. 14 – Summary of PETT classification. Possible MVDC converter configurationsOn the basis of the previous analysis, the three most promising topologies for MVDC-ERS traction converters are:a topology of cascaded buck converters with LLC resonant converters or a voltage balancing stage, as shown in Fig. 15a. In this way, the high input voltage is regulated, and the converters can use high-frequency transformers achieving galvanic isolation and soft switching [32]. Fig. 15 – a) Cascaded Buck-LLCb) Cascaded ISOP DAB c) Multi-Active-Bridges ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/ESARS-ITEC.2016.7841351","ISBN":"9781509008148","author":[{"dropping-particle":"","family":"Wang","given":"Shien","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zheng","given":"Zedong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Li","given":"Yongdong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Peng","given":"Ling","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2016 International Conference on Electrical Systems for Aircraft, Railway, Ship Propulsion and Road Vehicles and International Transportation Electrification Conference, ESARS-ITEC 2016","id":"ITEM-1","issue":"3161001","issued":{"date-parts":[["2017"]]},"page":"1-6","publisher":"IEEE","title":"A modular DC solid state transformer for future onboard DC grid","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[52]","plainTextFormattedCitation":"[52]","previouslyFormattedCitation":"[52]"},"properties":{"noteIndex":0},"schema":""}[52]Dual Active Bridge converters used in ISOP configuration, as shown in Fig. 15b. The DAB topology has the advantage of good control over power flow, having the capability of regulating both input and output voltages ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/ESARS-ITEC.2016.7841351","ISBN":"9781509008148","author":[{"dropping-particle":"","family":"Wang","given":"Shien","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zheng","given":"Zedong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Li","given":"Yongdong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Peng","given":"Ling","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2016 International Conference on Electrical Systems for Aircraft, Railway, Ship Propulsion and Road Vehicles and International Transportation Electrification Conference, ESARS-ITEC 2016","id":"ITEM-1","issue":"3161001","issued":{"date-parts":[["2017"]]},"page":"1-6","publisher":"IEEE","title":"A modular DC solid state transformer for future onboard DC grid","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[52]","plainTextFormattedCitation":"[52]","previouslyFormattedCitation":"[52]"},"properties":{"noteIndex":0},"schema":""}[52]. Multiple active bridges on the primary side with a single low voltage side cell, relying on high voltage SiC MOSFET devices, as shown in Fig. 15c. For lower conduction loss synchronous rectification can be implemented ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/ESARS-ITEC.2016.7841351","ISBN":"9781509008148","author":[{"dropping-particle":"","family":"Wang","given":"Shien","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zheng","given":"Zedong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Li","given":"Yongdong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Peng","given":"Ling","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2016 International Conference on Electrical Systems for Aircraft, Railway, Ship Propulsion and Road Vehicles and International Transportation Electrification Conference, ESARS-ITEC 2016","id":"ITEM-1","issue":"3161001","issued":{"date-parts":[["2017"]]},"page":"1-6","publisher":"IEEE","title":"A modular DC solid state transformer for future onboard DC grid","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[52]","plainTextFormattedCitation":"[52]","previouslyFormattedCitation":"[52]"},"properties":{"noteIndex":0},"schema":""}[52].For all cases, the core of a PETT is the isolated DC-DC converter, which can have different topologies too. The following figure show the power flow in DAB cells that are suitable candidate for DC-DC modules. The voltage on the capacitors are directly related to the power transferred, thus when the capacitor voltages are balanced in the primary side, the power also will be balanced. The secondary side capacitor voltages will be in the same way determined by the transferred power ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/ESARS-ITEC.2016.7841351","ISBN":"9781509008148","author":[{"dropping-particle":"","family":"Wang","given":"Shien","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zheng","given":"Zedong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Li","given":"Yongdong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Peng","given":"Ling","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2016 International Conference on Electrical Systems for Aircraft, Railway, Ship Propulsion and Road Vehicles and International Transportation Electrification Conference, ESARS-ITEC 2016","id":"ITEM-1","issue":"3161001","issued":{"date-parts":[["2017"]]},"page":"1-6","publisher":"IEEE","title":"A modular DC solid state transformer for future onboard DC grid","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[52]","plainTextFormattedCitation":"[52]","previouslyFormattedCitation":"[52]"},"properties":{"noteIndex":0},"schema":""}[52].Fig. 16 – Power flow in DAB cells.Article ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/esars-itec.2018.8607334","ISBN":"9781538641927","author":[{"dropping-particle":"","family":"Peng","given":"Ling","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Wang","given":"Shien","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Xu","given":"Lie","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zheng","given":"Zedong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"LI","given":"Yongdong","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2018 IEEE International Conference on Electrical Systems for Aircraft, Railway, Ship Propulsion and Road Vehicles & International Transportation Electrification Conference (ESARS-ITEC)","id":"ITEM-1","issued":{"date-parts":[["2019"]]},"page":"1-6","publisher":"IEEE","title":"Onboard DC Solid State Transformer Based on Series Resonant Dual Active Bridge Converter","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[53]","plainTextFormattedCitation":"[53]","previouslyFormattedCitation":"[53]"},"properties":{"noteIndex":0},"schema":""}[53] from 2018 presents the benefits of MVDC grid over MVAC grid for on-board integrated power systems. The authors proposed a DC/DC SST using ISOP series resonant DAB topology in modular structure, including steady-state modelling and a control algorithm to achieve DC bus equalization (for a stable voltage on the LV side) and fast response. Simulation results were presented for a 1.2MW system. Dual Active Bridge ConvertersThe DAB converter is a DC-DC converter implemented by a rectifier, a high-frequency transformer and an inverter. In Fig. 17, the first VSC converts the input DC voltage to a high-frequency AC, which is scaled by the high-frequency transformer, and rectified by the second two-level VSC.DAB full bridge converterDAB converter is a topology with the advantages of decreased number of devices, soft-switching commutations, low cost, and high efficiency. This topology is suitable for applications where the power density, cost, weight, and reliability are critical factors.Some advantages of DAB converters:It can be bidirectionalCompatible with MFTsConfigured with small duty cycle values (more linear output current)Can be controlled by phase-shift, duty cycle and both (single-phase-shift, dual-phase-shift, extended-phase-shift, triple-phase-shift)Fig. 17 - Dual-active bridge converterDAB half bridge converterThe benefits of the DAB half bridge converter are bidirectional power flow capability, high efficiency, low switching loss, and simple circuit structure. Other advantages:Switching regions can be improved using phase-shift and duty cycle control together, which is advantageous against large BUS voltage variationsLow number of switchesSmooth low-voltage side currentNatural soft switchingPerfect candidate for small size, high efficiencyCan be modularDrawback: Unbalanced voltage between two capacitors in DC link side.Example of a DAB configuration for MVDC tractionTo show the typical waveforms of this topology, a simulation was implemented in PSIM software, based on its mathematical model designed in Mathcad. The simulated converter has 8 modules of 150?kW and 1,500?V output. The control algorithm was a voltage control loop with PI regulator. The topology of the converter and its control are shown in Fig.?18.Fig. 18 – DAB module for MVDC PETT.The waveforms for a single module can be seen on Fig. 19. On the primary side, the voltage is kept below 5?kV thus 6.5kV IGBTs can be used (two IGBT modules are operating at the same time, transistor pairs being switched, therefore the voltage between 5 and 6 kV is supported by two IGBTs in series). The secondary side current is almost double than that in the primary, rising close to 400?A. Another simulation was made for an 8-module configuration with 25kV input voltage, using an ISOP structure, see Fig. 20.Fig. 19 – Simulation results for a 150?kW power DAB module. With red - the output voltage, brown - the voltage on the primary inductance, blue - the current on primary inductance, green - the current in the secondary and purple – the output power.Fig. 20 - ISOP of 8 modules with 3,125?V DC input voltage each (total of 25,000?V?DC) and 1,500?V DC output voltage. Simulation result for a 219?kW per module, 1.75?MW total output power configuration.Voltage balancing stages (VBS)As discussed in the previous chapter, at the moment, the most commonly used topologies of DCPET for MVDC applications are input-series output-parallel (ISOP) dc–dc converters, which has been deeply studied already. However ISOPs have an increased number of dc-dc modules, meaning many medium-frequency transformers and semiconductors. This brings up limitations and no possibility for further improvements. Therefore other multilevel structures are proposed, which uses only one transformer, but the structure has technical bottlenecks, like lack of good bypass features in case of module break downs. Different solutions were proposed for this problem in literature, but the power density is still limited. ISOP PETT structures can also have power balance problems, which implies more complex control systems. Paper ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/TPEL.2018.2842728","ISSN":"08858993","abstract":"This paper proposes a novel DC power electronic transformer (DCPET) topology for locomotive, AC/DC hybrid grid, DC distribution grid and other isolated medium-voltage and high-power applications. Compared with conventional PET topology, the proposed DCPET has fewer power semiconductor devices and high-frequency isolation transformers, which can improve the power density and reliability. Fault handling or redundancy design can be achieved to further improve the reliability when some DC-DC modules break down. In addition, input voltage sharing (IVS) control can be omitted to simplify the control system and improve the stability. Meanwhile, soft switching is guaranteed for all the switches, which is beneficial to increase switching frequency and improve power density. In this paper, the principle, evolution, and control of the proposed DCPET are respectively presented and studied in detail. Finally, a prototype of the proposed DCPET is built and the experimental results verify the validity and superiority of the proposed topology. IEEE","author":[{"dropping-particle":"","family":"Zhang","given":"Jiepin","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Liu","given":"Jianqiang","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Yang","given":"Jingxi","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhao","given":"Nan","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Wang","given":"Yang","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zheng","given":"Trillion Q.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Power Electronics","id":"ITEM-1","issue":"3","issued":{"date-parts":[["2018"]]},"page":"2119-2133","publisher":"IEEE","title":"A Modified DC Power Electronic Transformer Based on Series Connection of Full-Bridge Converters","type":"article-journal","volume":"34"},"uris":[""]}],"mendeley":{"formattedCitation":"[54]","plainTextFormattedCitation":"[54]"},"properties":{"noteIndex":0},"schema":""}[54] proposes a novel DCPET topology that can be a possible candidate to improve the aforementioned limitations. The proposed configuration has the features of ISOP structures except showing increased power density by reducing the number of switches and transformers required and eliminating the necessity of other by-pass devices. The VBS is also explained in detail, how it can achieve voltage balance in case of imbalances. For ZCS the resonant period has to be equal to the switching period and the time of conduction of the switches to be 0.5Ts. The paper presents the equations for power losses as well as design considerations for the VBS. The topology can vary according to requirements of a given application. If the number of VBSs is n, then the number of isolated bidirectional DC converter stages (IBDC) k, can be between 1 and n. These characteristics may eliminate the restrictions of the PETT, such as switching frequency, weight, volume, and costs, which makes the proposed PETT configuration superior and potential for the on-board traction applications.As seen on Fig. 21, this topology has two parts: the isolated conversion stage (blue) and a voltage-balance stage VBS (orange). The VBS is 2+1 voltage-balancing converter (VBC) with 2 series half-bridges and capacitors with output voltages 0, Vin/2 and Vin. The conversion stage is isolated input-series output-parallel converter consisting of 2 bidirectional dual active bridge DC-DC converters, having the 2 input capacitors in series between Pp and Pn – the medium voltage bus and output capacitors in parallel between Qp and Qn – the low-voltage bus.Fig. 21 - The derived topology of VBS PETT, when k=1. ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/TPEL.2018.2842728","ISSN":"08858993","abstract":"This paper proposes a novel DC power electronic transformer (DCPET) topology for locomotive, AC/DC hybrid grid, DC distribution grid and other isolated medium-voltage and high-power applications. Compared with conventional PET topology, the proposed DCPET has fewer power semiconductor devices and high-frequency isolation transformers, which can improve the power density and reliability. Fault handling or redundancy design can be achieved to further improve the reliability when some DC-DC modules break down. In addition, input voltage sharing (IVS) control can be omitted to simplify the control system and improve the stability. Meanwhile, soft switching is guaranteed for all the switches, which is beneficial to increase switching frequency and improve power density. In this paper, the principle, evolution, and control of the proposed DCPET are respectively presented and studied in detail. Finally, a prototype of the proposed DCPET is built and the experimental results verify the validity and superiority of the proposed topology. IEEE","author":[{"dropping-particle":"","family":"Zhang","given":"Jiepin","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Liu","given":"Jianqiang","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Yang","given":"Jingxi","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhao","given":"Nan","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Wang","given":"Yang","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zheng","given":"Trillion Q.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Power Electronics","id":"ITEM-1","issue":"3","issued":{"date-parts":[["2018"]]},"page":"2119-2133","publisher":"IEEE","title":"A Modified DC Power Electronic Transformer Based on Series Connection of Full-Bridge Converters","type":"article-journal","volume":"34"},"uris":[""]}],"mendeley":{"formattedCitation":"[54]","plainTextFormattedCitation":"[54]"},"properties":{"noteIndex":0},"schema":""}[54]The VBS consists of 2 switching pairs Sp1a, Sp1b and Sp2a, Sp2b between the resonant branch Lp1, Cp1. This structure can achieve self-balancing voltage in different working conditions. The isolated conversion stage can be different topology, any other bidirectional isolated converter than the chosen DAB in this application. The number of stages can be adjusted according the requirements of applications, also the number of VBSs. The improvement of this novel topology is that when some isolated bidirectional DC converter stages (IBDCs) are eliminated - thus their number is smaller than the input capacitors - the VBC will still ensure voltage balance and the rest of IBDCs will still operate at the rated voltage ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/TPEL.2018.2842728","ISSN":"08858993","abstract":"This paper proposes a novel DC power electronic transformer (DCPET) topology for locomotive, AC/DC hybrid grid, DC distribution grid and other isolated medium-voltage and high-power applications. Compared with conventional PET topology, the proposed DCPET has fewer power semiconductor devices and high-frequency isolation transformers, which can improve the power density and reliability. Fault handling or redundancy design can be achieved to further improve the reliability when some DC-DC modules break down. In addition, input voltage sharing (IVS) control can be omitted to simplify the control system and improve the stability. Meanwhile, soft switching is guaranteed for all the switches, which is beneficial to increase switching frequency and improve power density. In this paper, the principle, evolution, and control of the proposed DCPET are respectively presented and studied in detail. Finally, a prototype of the proposed DCPET is built and the experimental results verify the validity and superiority of the proposed topology. IEEE","author":[{"dropping-particle":"","family":"Zhang","given":"Jiepin","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Liu","given":"Jianqiang","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Yang","given":"Jingxi","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhao","given":"Nan","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Wang","given":"Yang","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zheng","given":"Trillion Q.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Power Electronics","id":"ITEM-1","issue":"3","issued":{"date-parts":[["2018"]]},"page":"2119-2133","publisher":"IEEE","title":"A Modified DC Power Electronic Transformer Based on Series Connection of Full-Bridge Converters","type":"article-journal","volume":"34"},"uris":[""]}],"mendeley":{"formattedCitation":"[54]","plainTextFormattedCitation":"[54]"},"properties":{"noteIndex":0},"schema":""}[54].As a conclusion, these topologies have 4 major advantages: the high-voltage IGBTs can be replaced by low voltage IGBTs, which can help increase switching frequency and reduce costs; the number of the high-frequency transformers will not increase, which can further reduce costs, improve power density, and simplify isolation design; ZCS or ZVS can be guaranteed for all the switches in the dc/dc stage, which can ensure high efficiency of the PETT and the control strategy of the dc/dc module is simple because of the voltage self-balancing capability of the proposed VSBR converter. Furthermore, the paper contains a performance comparison between three different configurations of 3000V input, 600V output, 150kW power, demonstrating improved efficiency, greater power density, reduced number of switches and reduced IGBT losses. ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/TPEL.2018.2842728","ISSN":"08858993","abstract":"This paper proposes a novel DC power electronic transformer (DCPET) topology for locomotive, AC/DC hybrid grid, DC distribution grid and other isolated medium-voltage and high-power applications. Compared with conventional PET topology, the proposed DCPET has fewer power semiconductor devices and high-frequency isolation transformers, which can improve the power density and reliability. Fault handling or redundancy design can be achieved to further improve the reliability when some DC-DC modules break down. In addition, input voltage sharing (IVS) control can be omitted to simplify the control system and improve the stability. Meanwhile, soft switching is guaranteed for all the switches, which is beneficial to increase switching frequency and improve power density. In this paper, the principle, evolution, and control of the proposed DCPET are respectively presented and studied in detail. Finally, a prototype of the proposed DCPET is built and the experimental results verify the validity and superiority of the proposed topology. IEEE","author":[{"dropping-particle":"","family":"Zhang","given":"Jiepin","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Liu","given":"Jianqiang","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Yang","given":"Jingxi","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhao","given":"Nan","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Wang","given":"Yang","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zheng","given":"Trillion Q.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Power Electronics","id":"ITEM-1","issue":"3","issued":{"date-parts":[["2018"]]},"page":"2119-2133","publisher":"IEEE","title":"A Modified DC Power Electronic Transformer Based on Series Connection of Full-Bridge Converters","type":"article-journal","volume":"34"},"uris":[""]}],"mendeley":{"formattedCitation":"[54]","plainTextFormattedCitation":"[54]"},"properties":{"noteIndex":0},"schema":""}[54]. Specifications and requirements for tractionInductive power factor of trainTable 3 – MVDC-ERS parameters from work package 1 (WP1) of this project.ParameterSymbolValue (kV)Lowest non-permanent voltageUmin217.5Lowest permanent voltageUmin119Nominal voltageVDC,nom25Highest permanent voltageUmax127.5Highest non-permanent voltageUmax229On the range of Umin1 to Umax1 (19-27.5kV) the total power factor λ (active power/apparent power) must be:λ≥0.95, if Ppant>2MWλ>0.85, if Ppant<2MW #1where Ppant is the instantaneous power at the pantograph. In the cases when this power is below 2?MW, the overall (traction and auxiliaries) average power factor must be greater than 0.85 over a complete timetabled journey ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"European Committee for Electrotechnical Standardization","given":"","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issue":"August 2012","issued":{"date-parts":[["2013"]]},"title":"Railway Applications - Power supply and rolling stock - Technical criteria for the coordination between power supply (substation) and rolling stock to achieve interoperability","type":"report"},"uris":[""]}],"mendeley":{"formattedCitation":"[55]","plainTextFormattedCitation":"[55]","previouslyFormattedCitation":"[54]"},"properties":{"noteIndex":0},"schema":""}[55].Inside yards and depots, when traction power is switched off but all auxiliaries are still running and the power drawn is greater than 200?kW, the power factor should be ≥ 0.8.λ=11+WQWP2#2Equation 2 presents the calculation of the overall average λ for a train journey, including stops as a function of active (WP in MWh) and reactive energy (WQ in MAh) ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"European Committee for Electrotechnical Standardization","given":"","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issue":"August 2012","issued":{"date-parts":[["2013"]]},"title":"Railway Applications - Power supply and rolling stock - Technical criteria for the coordination between power supply (substation) and rolling stock to achieve interoperability","type":"report"},"uris":[""]}],"mendeley":{"formattedCitation":"[55]","plainTextFormattedCitation":"[55]","previouslyFormattedCitation":"[54]"},"properties":{"noteIndex":0},"schema":""}[55].During regenerative braking, the power factor can decrease freely to keep the voltage within limits.Capacitive power factor of trainThe capacitive power factor of a train is not limited, since a train should not behave as a capacitor. However, during regenerative mode if there is capacitive power, it shall be limited to 150?kvar on the range Umin1 to Umax1 ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"European Committee for Electrotechnical Standardization","given":"","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issue":"August 2012","issued":{"date-parts":[["2013"]]},"title":"Railway Applications - Power supply and rolling stock - Technical criteria for the coordination between power supply (substation) and rolling stock to achieve interoperability","type":"report"},"uris":[""]}],"mendeley":{"formattedCitation":"[55]","plainTextFormattedCitation":"[55]","previouslyFormattedCitation":"[54]"},"properties":{"noteIndex":0},"schema":""}[55].Power levels of trainsFig. 22 – Railway power levels. ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/TTE.2017.2703583","ISSN":"23327782","abstract":"This paper reviews the modern electric propulsion architectures and configurations for railway traction, which are currently in practice. The development and advancement of power electronics and digital controllers led to the standardization of the insulated gate bipolar transistor (IGBT)-based converter fed induction motor drives. This paper summarizes the state-of-the-art technology of IGBT-based rolling stock in terms of both power and control. Control hierarchy of traction system and drive control techniques are explored. Special emphasis has been put on the technologies, which can improve energy efficiency as well as reliability to develop high-speed rails and metro trains in the near future in both urban and suburban areas. Specific attention is given to power electronic transformer technology-based traction drives and on-board energy storage systems. In addition, advances in traction drive technology and wide-bandgap power devices are addressed. Finally, major issues faced in rolling stock including the challenges for further improvement are highlighted.","author":[{"dropping-particle":"","family":"Ronanki","given":"Deepak","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Singh","given":"Siddhartha A.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Williamson","given":"Sheldon S.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Transportation Electrification","id":"ITEM-1","issue":"3","issued":{"date-parts":[["2017"]]},"page":"724-738","title":"Comprehensive Topological Overview of Rolling Stock Architectures and Recent Trends in Electric Railway Traction Systems","type":"article-journal","volume":"3"},"uris":[""]}],"mendeley":{"formattedCitation":"[56]","plainTextFormattedCitation":"[56]","previouslyFormattedCitation":"[55]"},"properties":{"noteIndex":0},"schema":""}[56]As seen in Fig. 22, locomotives and electric multiple units usually operate at powers of hundreds of kWs up to even over 10?MW depending on their load, speed and type. Current limitationEach train should have an automatic regulation device that, in case of weaker network or abnormal operation, adapts the maximum current drawn from the contact line as a function of the contact line voltage. Therefore, a current limiter has to be present in the control of the traction converter. According to standard EN 50388 from 2012, the maximum allowable current on classic lines is 800?A and 500 to 1,500?A on HS TSI (High-Speed Technical Specifications for Interoperability) lines (depending on their category), in the case of the 25kV AC power supply system ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"European Committee for Electrotechnical Standardization","given":"","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issue":"August 2012","issued":{"date-parts":[["2013"]]},"title":"Railway Applications - Power supply and rolling stock - Technical criteria for the coordination between power supply (substation) and rolling stock to achieve interoperability","type":"report"},"uris":[""]}],"mendeley":{"formattedCitation":"[55]","plainTextFormattedCitation":"[55]","previouslyFormattedCitation":"[54]"},"properties":{"noteIndex":0},"schema":""}[55]. Fig. 23 – Maximum current consumed by the train at nominal voltage. ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"European Committee for Electrotechnical Standardization","given":"","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issue":"August 2012","issued":{"date-parts":[["2013"]]},"title":"Railway Applications - Power supply and rolling stock - Technical criteria for the coordination between power supply (substation) and rolling stock to achieve interoperability","type":"report"},"uris":[""]}],"mendeley":{"formattedCitation":"[55]","plainTextFormattedCitation":"[55]","previouslyFormattedCitation":"[54]"},"properties":{"noteIndex":0},"schema":""}[55]The value of a in Fig 23, the knee point factor, for 25kV AC power supply systems is 0.9.Regenerative braking and on-board storageRegenerative braking (RB) has a significant role in energy saving of traction systems. Depending on the type of train, between 5% and 17% of energy can be recuperated. For example, the N700 series of Shinkansen has shown a 4.5% energy saving, the American Acela Express 8%, the Pendolino trains in UK 17%, and the New Delhi’s metro line 30%. RB is also beneficial for independently powered trains: the hybrid diesel locomotives for Indian Railways shown a fuel consumption reduced by 15%, and emissions reduced by 50% ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"URL":"","author":[{"dropping-particle":"","family":"Climate Technology Centre & Network","given":"","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issued":{"date-parts":[["0"]]},"title":"Regenerative braking for trains","type":"webpage"},"uris":[""]}],"mendeley":{"formattedCitation":"[57]","plainTextFormattedCitation":"[57]","previouslyFormattedCitation":"[56]"},"properties":{"noteIndex":0},"schema":""}[57].Regenerative braking is a mature technology and widely available in traction systems, however it is easier to use in AC electrification systems than DC ones. In fact, DC systems typically require a higher cost of investments for the inverting substations ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"URL":"","author":[{"dropping-particle":"","family":"Climate Technology Centre & Network","given":"","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issued":{"date-parts":[["0"]]},"title":"Regenerative braking for trains","type":"webpage"},"uris":[""]}],"mendeley":{"formattedCitation":"[57]","plainTextFormattedCitation":"[57]","previouslyFormattedCitation":"[56]"},"properties":{"noteIndex":0},"schema":""}[57].RB is more effective for rail vehicles with frequent stops, such as tram and metro lines. Almost all modern trains are equipped with a RB system, however the benefits are proportional to the frequency of stops. Some of the difficulties of implementation of RB in DC systems is the low voltage and the lack of possibility to feed current back to the public grid, especially in urban areas. In the MVDC-ERS concept these problems are mitigated, since the voltage is as high as of the AC systems and the traction substations are all bidirectional. The energy recuperated by the train can be injected to the electrical infrastructure, or stored on-board on an energy storage system. It was found that energy storage systems can achieve peak power reduction and enable catenary-free operations if needed. According to ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/TITS.2018.2886809","ISSN":"15580016","abstract":"Electric rail transit systems are the large consumers of energy. In trains with regenerative braking capability, a fraction of the energy used to power a train is regenerated during braking. This regenerated energy, if not properly captured, is typically dumped in the form of heat to avoid overvoltage. Finding a way to recuperate regenerative braking energy can result in economic as well as technical merits. In this comprehensive paper, the various methods and technologies that were proposed for regenerative energy recuperation have been analyzed, investigated, and compared. These technologies include: Train timetable optimization, energy storage systems (onboard and wayside), and reversible substations.","author":[{"dropping-particle":"","family":"Khodaparastan","given":"Mahdiyeh","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Mohamed","given":"Ahmed A.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Brandauer","given":"Werner","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Intelligent Transportation Systems","id":"ITEM-1","issue":"8","issued":{"date-parts":[["2019"]]},"page":"2831-2847","publisher":"IEEE","title":"Recuperation of regenerative braking energy in electric rail transit systems","type":"article-journal","volume":"20"},"uris":[""]}],"mendeley":{"formattedCitation":"[58]","plainTextFormattedCitation":"[58]","previouslyFormattedCitation":"[57]"},"properties":{"noteIndex":0},"schema":""}[58] the energy saving results obtained and presented in various publications is around 30%, depending on the type and storage technology used for energy storage system, which are mainly supercapacitors, batteries and flywheels. The advantages of supercapacitors and flywheels are: fast response, a long lifespan and a high power density. Among the batteries, the most popular are lithium-ion and lithium-titanate having the former a high energy density and the latter a high number of cycles.From this analysis, it is evident that regenerative braking has to be maintained with PETTs. This is generally not an issue, as all the power converter topologies used for PETTs are bidirectional and can easily control the power flow to the electrical infrastructure.Control and protection of traction convertersThere are several options for the DC-DC converters control implementation. The first choice is between analogue control and digital control. The advantages associated with analogue control are low price, low complexity, small printed circuit board (PCB) area required and high performance. However, analogue control relies on ICs developed by semiconductor manufacturers which greatly limits the control method flexibility and converter’s topology choice (no control IC can be found for the DAB converter for example). These disadvantages exclude the use of analogue control for the tasks that need to be completed in this project. Digital control allows a much greater flexibility and complexity of the control algorithms. A few examples of commonly used hardware platforms for digital control are: rapid prototyping systems (dSPACE for example ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/TCST.2017.2761866","ISSN":"1558-0865","abstract":"This paper presents an application of interconnection and damping assignment passivity-based control (IDA-PBC) principle to the port-controlled phasor Hamiltonian (PCPH) model of solid-state transformer (SST) (comprising of three stages, namely, ac/dc rectifier, dual active bridge converter, and dc/ac inverter). A PCPH model of SST is established for each individual stages using dynamic phasor concept. In comparison with other PBC approaches, IDA-PBC offers an additional degree of freedom to solve the partial differential equations. According to the target of the controller design at each stage, the desired equilibrium point of the system is obtained. The closed-loop system performance achieves regulation of constant output dc-bus voltage and unity input power factor. Large-signal simulation results for the full system validate the simplifications introduced to obtain the controller and verify the proposed controller. Robustness of the controller is demonstrated with 20% load disturbance and 10% input disturbance. For validation of the proposed approach and its effectiveness, hardware-in-loop simulation is carried out using Opal-RT and dSPACE simulators.","author":[{"dropping-particle":"V.","family":"Meshram","given":"Ragini","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Bhagwat","given":"Monika","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Khade","given":"Shubhangi","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Wagh","given":"Sushama R.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Stankovic","given":"Aleksandar M.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Singh","given":"Navdeep M.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Control Systems Technology","id":"ITEM-1","issue":"1","issued":{"date-parts":[["2019"]]},"page":"161-174","title":"Port-Controlled Phasor Hamiltonian Modeling and IDA-PBC Control of Solid-State Transformer","type":"article-journal","volume":"27"},"uris":[""]}],"mendeley":{"formattedCitation":"[59]","plainTextFormattedCitation":"[59]","previouslyFormattedCitation":"[58]"},"properties":{"noteIndex":0},"schema":""}[59]), digital signal processors (DSPs) and field programmable gate arrays (FPGAs).A rapid prototyping system like dSPACE has a large number of analogue to digital, digital to analogue and general-purpose IO interfaces to cover the requirements of almost any converter’s topology control system. Rapid prototyping systems are usually provided with a high-level graphical programming tool (like Simulink) that greatly reduces programming times. The major drawback of this approach is that system integration is limited. It may be difficult to add a Wi-Fi, CAN or other protocol-based connection to the control system developed. Also, the control system needs to be migrated to a custom hardware platform for production. The second choice for digital control implementation is the use of a DSP. DSPs are popular because they are easy to use, cheap and sufficiently performant for most control system’s requirements. A wide variety of programming languages generally familiar to engineers such as C, C++ or high-level graphical description languages (Simulink) accelerate and facilitate DSP programming. The third hardware platform option for digital control implementation are FPGAs ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/TII.2011.2123908","ISSN":"15513203","abstract":"The aim of this paper is to review the state-of-the-art of Field Programmable Gate Array (FPGA) technologies and their contribution to industrial control applications. Authors start by addressing various research fields which can exploit the advantages of FPGAs. The features of these devices are then presented, followed by their corresponding design tools. To illustrate the benefits of using FPGAs in the case of complex control applications, a sensorless motor controller has been treated. This controller is based on the Extended Kalman Filter. Its development has been made according to a dedicated design methodology, which is also discussed. The use of FPGAs to implement artificial intelligence-based industrial controllers is then briefly reviewed. The final section presents two short case studies of Neural Network control systems designs targeting FPGAs. ? 2011 IEEE.","author":[{"dropping-particle":"","family":"Monmasson","given":"Eric","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Idkhajine","given":"Lahoucine","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Cirstea","given":"Marcian N.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Bahri","given":"Imene","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Tisan","given":"Alin","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Naouar","given":"Mohamed Wissem","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Industrial Informatics","id":"ITEM-1","issue":"2","issued":{"date-parts":[["2011"]]},"page":"224-243","publisher":"IEEE","title":"FPGAs in industrial control applications","type":"article-journal","volume":"7"},"uris":[""]}],"mendeley":{"formattedCitation":"[60]","plainTextFormattedCitation":"[60]","previouslyFormattedCitation":"[59]"},"properties":{"noteIndex":0},"schema":""}[60]. The choice between FPGAs and DSPs has been widely debated in the past decade. Several comparisons between FPGAs and DSPs in applications such as synchronous motor control ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/ISIE.2010.5636605","ISBN":"9781424463916","abstract":"The aim of this paper is to present a Sensorless Speed Controller for a Synchronous Motor (SM). The estimation of the rotor position and speed is achieved using an Extended Kalman Filter (EKF), eliminating the need of their corresponding mechanical sensors. The developed controller has been implemented in a fully FPGA (Field Programmable Gate Array) based solution on the one hand and in a fully DSP (Digital Signal Processing) based solution on the other hand. Authors have compared and quantified the impact of the timing performance, in both cases, on the speed controller dynamic behavior and bandwidth. In this paper, the experimental validation of the Fully FPGA based solution is first discussed, followed by its comparison to the DSP solution. To prop up this comparison, experimental and simulation tests have been presented. ? 2010 IEEE.","author":[{"dropping-particle":"","family":"Idkhajine","given":"L.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Monmasson","given":"E.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Maalouf","given":"A.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE International Symposium on Industrial Electronics","id":"ITEM-1","issued":{"date-parts":[["2010"]]},"page":"2759-2764","publisher":"IEEE","title":"Extended Kalman filter for AC drive sensorless speed controller - FPGA-based solution or DSP-based solution","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[61]","plainTextFormattedCitation":"[61]","previouslyFormattedCitation":"[60]"},"properties":{"noteIndex":0},"schema":""}[61], Static Compensator (STATCOM) control ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/TII.2012.2222419","ISSN":"15513203","abstract":"Digital signal processors (DSPs) and field-programmable gate arrays (FPGAs) are predominant in the implementation of digital controllers and/or modulators for power converter applications. This paper presents a systematic comparison between these two technologies, depicting the main advantages and drawbacks of each one. Key programming and implementation aspects are addressed in order to give an overall idea of their most important features and allow the comparison between DSP and FPGA devices. A classical linear control strategy for a well-known voltage-source-converter (VSC)-based topology used as Static Compensator (STATCOM) is considered as a driving example to evaluate the performance of both approaches. A proof-of-concept laboratory prototype is separately controlled with the TMS320F2812 DSP and the Spartan-3 XCS1000 FPGA to illustrate the characteristics of both technologies. In the case of the DSP, a virtual floating-point library is used to accelerate the control routines compared to double precision arithmetic. On the other hand, two approaches are developed for the FPGA implementation, the first one reduces the hardware utilization and the second one reduces the computation time. Even though both boards can successfully control the STATCOM, results show that the FPGA achieves the best computation time thanks to the high degree of parallelism available on the device. ? 2005-2012 IEEE.","author":[{"dropping-particle":"","family":"Sepulveda","given":"Cristian A.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Munoz","given":"Javier A.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Espinoza","given":"José R.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Figueroa","given":"Miguel E.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Baier","given":"Carlos R.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Industrial Informatics","id":"ITEM-1","issue":"3","issued":{"date-parts":[["2013"]]},"page":"1351-1360","title":"FPGA v/s DSP performance comparison for a VSC-based STATCOM control application","type":"article-journal","volume":"9"},"uris":[""]}],"mendeley":{"formattedCitation":"[62]","plainTextFormattedCitation":"[62]","previouslyFormattedCitation":"[61]"},"properties":{"noteIndex":0},"schema":""}[62], artificial intelligence ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/FPL.2016.7577314","ISBN":"9782839918442","abstract":"Recurrent neural networks (RNNs) provide state-of-the-art accuracy for performing analytics on datasets with sequence (e.g., language model). This paper studied a state-of-the-art RNN variant, Gated Recurrent Unit (GRU). We first proposed memoization optimization to avoid 3 out of the 6 dense matrix vector multiplications (SGEMVs) that are the majority of the computation in GRU. Then, we study the opportunities to accelerate the remaining SGEMVs using FPGAs, in comparison to 14-nm ASIC, GPU, and multi-core CPU. Results show that FPGA provides superior performance/Watt over CPU and GPU because FPGA's on-chip BRAMs, hard DSPs, and reconfigurable fabric allow for efficiently extracting fine-grained parallelisms from small/medium size matrices used by GRU. Moreover, newer FPGAs with more DSPs, on-chip BRAMs, and higher frequency have the potential to narrow the FPGA-ASIC efficiency gap.","author":[{"dropping-particle":"","family":"Nurvitadhi","given":"Eriko","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Sim","given":"Jaewoong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Sheffield","given":"David","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Mishra","given":"Asit","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Krishnan","given":"Srivatsan","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Marr","given":"Debbie","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"FPL 2016 - 26th International Conference on Field-Programmable Logic and Applications","id":"ITEM-1","issue":"c","issued":{"date-parts":[["2016"]]},"page":"1-4","publisher":"EPFL","title":"Accelerating recurrent neural networks in analytics servers: Comparison of FPGA, CPU, GPU, and ASIC","type":"article-journal"},"uris":[""]},{"id":"ITEM-2","itemData":{"DOI":"10.1109/ISIE.2011.5984390","ISBN":"9781424493128","abstract":"In this paper two hardware applications of neural state estimator for the two-mass drive system are presented. One of them is realized in a Digital Signal Processor (DSP), and the second consists in parallel implementation of neural networks in a reconfigurable Field-Programmable Gate Array (FPGA) placed in CompactRIO controller. Described solutions of neural network implementations are used for the estimation of the load-side speed of an electrical drive with elastic joint. Several design and programming problems are presented. Developed neural estimators are tested in the laboratory drive. Application of the neural network with FPGA gives better results, especially on drive system transients. Obtained results show high accuracy of the load speed estimation with the presented neural estimator. High precision of calculation is also obtained in the presence of the load time constant changes. ? 2011 IEEE.","author":[{"dropping-particle":"","family":"Kaminski","given":"Marcin","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Orlowska-Kowalska","given":"Teresa","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"Proceedings - ISIE 2011: 2011 IEEE International Symposium on Industrial Electronics","id":"ITEM-2","issued":{"date-parts":[["2011"]]},"page":"1543-1548","publisher":"IEEE","title":"Comparison of DSP and FPGA realization of neural speed estimator for 2-mass system","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[63], [64]","plainTextFormattedCitation":"[63], [64]","previouslyFormattedCitation":"[62], [63]"},"properties":{"noteIndex":0},"schema":""}[63], [64] or signal processing applications ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/VLSI-SoC.2013.6673300","ISBN":"9781479905249","ISSN":"23248440","abstract":"A comparative study of Hierarchical Enumerative Coding (HENUC) for FPGA and DSP implementation is presented. HENUC is a lossless fixed-point entropy coding algorithm employed by a wavelet-based image encoder, which provides good compression performance for the locally stationary image data. It has been implemented in our previous work on an Altera's 40nm Stratix IV EP4SGX230 FPGA as a hardware IP accelerator in a Nios II based system. In this paper, we implemented it on a Texas Instruments's (TI) 40nm Integra C6A816x/AM389x DSP. We present experimental results regarding the execution time, resource utilization and core power consumption of the two implementations and we evaluate their throughput and power efficiency. Our results show that a highly parallelized FPGA implementation at 100MHz is 12.3x faster than a highly tuned DSP implementation running at 1.5 GHz and consumes 2.4x less power, they also show that the proposed algorithm is more suitable for hardware implementation. ? 2013 IEEE.","author":[{"dropping-particle":"","family":"Bai","given":"Yuhui","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Ahmed","given":"Syed Zahid","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Mhedhbi","given":"Imen","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Hachicha","given":"Khalil","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Champion","given":"Cedric","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Garda","given":"Patrick","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Granado","given":"Bertrand","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE/IFIP International Conference on VLSI and System-on-Chip, VLSI-SoC","id":"ITEM-1","issued":{"date-parts":[["2013"]]},"page":"318-321","title":"FPGA vs DSP: A throughput and power efficiency comparison for Hierarchical Enumerative Coding","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[65]","plainTextFormattedCitation":"[65]","previouslyFormattedCitation":"[64]"},"properties":{"noteIndex":0},"schema":""}[65] prove that FPGA devices drastically reduce execution times, increase controller bandwidth and increase throughput. Besides these advantages, FPGAs provide a greater number of digital IOs and parallel DSP blocks, allowing multiple high complexity control algorithms to be implemented on one device, reducing the number of ICs in the system. The increased performance of FPGAs is reflected however in much higher prices and in a more complex auxiliary circuitry (more power supplies with very tight tolerances to power the device, more PCB layers) that further increases the price of the system. Furthermore, unlike DSPs (C2000 family from Texas Instruments is a good example ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"Lee","given":"S W","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issue":"July","issued":{"date-parts":[["2014"]]},"page":"1-16","title":"Demystifying Type II and Type III Compensators Using Op- Amp and OTA for DC / DC Converters","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[66]","plainTextFormattedCitation":"[66]","previouslyFormattedCitation":"[65]"},"properties":{"noteIndex":0},"schema":""}[66]), FPGAs are not specifically designed for control systems lacking high performance internal Analog-Digital Converters (ADCs) or Pulse Width Modulation (PWM) generators. While ADCs can be added externally, the performance of dedicated PWM generator structures can’t be obtained on FPGAs, at least not with a significant amount of effort. Therefore, for implementing DC-DC converter’s control system, regardless whether is a DAB or other topology the first option is a DSP unless it is proved that such a device can’t achieve some specific performance parameters required.In the MVDC traction system, the control of DC voltage is an essential task, since it has a direct relation with power flow and power balance. In addition to voltage sensors of the primary loop, current sensors have to be used to implement an inner control loop and regulate the DC current.Regarding protection, two major contributors to Electromagnetic Interference (EMI) are high variations of the current that create overvoltage due to the stray inductances of current loops; and high variations of the voltage that create leakage current in the magnetic elements due to stray capacitive couplings. Overvoltages are produced in the DC-DC voltages also by the ringing effect. Therefore, protection circuitry is necessary for short circuit currents and overvoltages. In order to combat overvoltages, snubber circuits and active gate control could be used, considering not to increase number of components at the expense of significantly higher costs. The best solution is to choose components (including IGBTs and DC link capacitors) with low stray inductance (in the case of capacitors low ESL). Laminated DC-busbars can also reduce EMI, since they are designed with low stray inductance and resistance. More details about designing SSTs for reduced EMI can be found in ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/ITEC.2018.8450135","ISBN":"9781538630488","abstract":"The modern trend towards high-speed trains (HST) with distributed propulsion systems, demands high efficiency and high-power density traction systems. Line frequency transformers (LFTs) in railway traction systems are heavy and bulky, quite often necessitating power density to be compromised to achieve maximum efficiency of typically 90-92%. The advancements in power converter topologies, power switching devices and magnetic materials makes it possible to substitute massive LFTs with a new technology called solid-state transformers (SST) (also known as power electronic transformers (PET) or medium frequency transformers (MFT)) traction technology. This technology enables high power density systems with comparatively lower noise emissions which provide essential functionality without compromising efficiency. However, there are still major challenges to overcome associated with power converter connection on the high-voltage (HV) side, architecture modification and the compactness of the transformer design. This paper reviews the existing architectures and also introduces the new research possibilities especially in the power conversion stages, and the power switching devices. Finally, the design guide lines for high-power converters are presented.","author":[{"dropping-particle":"","family":"Ronanki","given":"Deepak","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Williamson","given":"Sheldon S.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2018 IEEE Transportation and Electrification Conference and Expo, ITEC 2018","id":"ITEM-1","issued":{"date-parts":[["2018"]]},"page":"858-862","publisher":"IEEE","title":"Topological Overview on Solid-state Transformer Traction Technology in High-speed Trains","type":"article-journal"},"uris":["",""]}],"mendeley":{"formattedCitation":"[67]","plainTextFormattedCitation":"[67]","previouslyFormattedCitation":"[66]"},"properties":{"noteIndex":0},"schema":""}[67]. The study in ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/ITEC.2018.8450135","ISBN":"9781538630488","abstract":"The modern trend towards high-speed trains (HST) with distributed propulsion systems, demands high efficiency and high-power density traction systems. Line frequency transformers (LFTs) in railway traction systems are heavy and bulky, quite often necessitating power density to be compromised to achieve maximum efficiency of typically 90-92%. The advancements in power converter topologies, power switching devices and magnetic materials makes it possible to substitute massive LFTs with a new technology called solid-state transformers (SST) (also known as power electronic transformers (PET) or medium frequency transformers (MFT)) traction technology. This technology enables high power density systems with comparatively lower noise emissions which provide essential functionality without compromising efficiency. However, there are still major challenges to overcome associated with power converter connection on the high-voltage (HV) side, architecture modification and the compactness of the transformer design. This paper reviews the existing architectures and also introduces the new research possibilities especially in the power conversion stages, and the power switching devices. Finally, the design guide lines for high-power converters are presented.","author":[{"dropping-particle":"","family":"Ronanki","given":"Deepak","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Williamson","given":"Sheldon S.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2018 IEEE Transportation and Electrification Conference and Expo, ITEC 2018","id":"ITEM-1","issued":{"date-parts":[["2018"]]},"page":"858-862","publisher":"IEEE","title":"Topological Overview on Solid-state Transformer Traction Technology in High-speed Trains","type":"article-journal"},"uris":["",""]}],"mendeley":{"formattedCitation":"[67]","plainTextFormattedCitation":"[67]","previouslyFormattedCitation":"[66]"},"properties":{"noteIndex":0},"schema":""}[67] summarises some important design considerations such as: minimizing distances between the conductors by using thin isolation; choosing insulation materials with high dielectric constant, breakdown strength and thermal conductivity; careful choice of DC link capacitors; careful choice of shape, location and routing of the conducting points to provide multi-layered current flow in opposite directions with equal strength; low impedance design of conductors (thin and flat with fewer holes and larger area of surface).Another protection challenge is the design of gate drives, since desaturation protection against short circuit and overcurrent needs MV diodes of higher costs, not to mention inconsistency of protection current caused by variations in temperature, voltage and other conditions. To address this issue, currently Rogowski coil-based protection circuits are under investigation ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/ECCE.2018.8558451","ISBN":"9781479973118","author":[{"dropping-particle":"","family":"Hu","given":"Boxue","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Lyu","given":"Xintong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Xing","given":"Diang","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Ma","given":"Dihao","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Brothers","given":"John","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Na","given":"Risha","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Wang","given":"Jin","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2018 IEEE Energy Conversion Congress and Exposition, ECCE 2018","id":"ITEM-1","issued":{"date-parts":[["2018"]]},"page":"2420-2427","publisher":"IEEE","title":"A Survey on Recent Advances of Medium Voltage Silicon Carbide Power Devices","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[68]","plainTextFormattedCitation":"[68]","previouslyFormattedCitation":"[67]"},"properties":{"noteIndex":0},"schema":""}[68].Potential benefits of using wide band-gap semiconductors in MVDC convertersThe design goal of MVDC traction converters are high efficiency and reliability. In addition to these characteristics, the DC-DC converters mounted on traction vehicles must have power density as high as possible (compactness), while capable sometimes of operation under harsh conditions. As Silicon (Si) semiconductors have already reached their full potential, new generation of semiconductors and switching devices using new WBG materials have been emerged to replace Si devices. Such WBG semiconductors are: SiC, Gallium Nitride (GaN) and diamond. They are used to develop IGBTs, MOSFETs, thyristors, JFETs, GTOs, BJTs and power diodes, which significantly improve the performance of power converters. GaN and SiC are currently the most mature among WBG semiconductors, therefore in this study only these two will be considered. Although GaN can achieve higher frequency and voltage, due to the lack of good bulk substrates and lower thermal conductivity, currently SiC is more promising. Some achievements in SiC technology include: bulk material growth, advances in SiC wafers, larger dielectric critical field, meaning a ten times higher blocking voltage for the same thickness ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/TPEL.2013.2268900","ISSN":"08858993","abstract":"Wide bandgap semiconductors show superior material properties enabling potential power device operation at higher temperatures, voltages, and switching speeds than current Si technology. As a result, a new generation of power devices is being developed for power converter applications in which traditional Si power devices show limited operation. The use of these new power semiconductor devices will allow both an important improvement in the performance of existing power converters and the development of new power converters, accounting for an increase in the efficiency of the electric energy transformations and a more rational use of the electric energy. At present, SiC and GaN are the more promising semiconductor materials for these new power devices as a consequence of their outstanding properties, commercial availability of starting material, and maturity of their technological processes. This paper presents a review of recent progresses in the development of SiC-and GaN-based power semiconductor devices together with an overall view of the state of the art of this new device generation. ? 2013 IEEE.","author":[{"dropping-particle":"","family":"Millan","given":"Jose","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Godignon","given":"Philippe","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Perpina","given":"Xavier","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Perez-Tomas","given":"Amador","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Rebollo","given":"Jose","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Power Electronics","id":"ITEM-1","issue":"5","issued":{"date-parts":[["2014"]]},"page":"2155-2163","title":"A survey of wide bandgap power semiconductor devices","type":"article-journal","volume":"29"},"uris":["",""]}],"mendeley":{"formattedCitation":"[69]","plainTextFormattedCitation":"[69]","previouslyFormattedCitation":"[68]"},"properties":{"noteIndex":0},"schema":""}[69]. Commercial Si IGBTs are limited to a blocking voltage of 6.5 kV and temperature of 200 ℃ (which implies complex and expensive cooling sometimes) in comparison to SiC devices, which have much higher thermal conductivity and can operate even above 300-400 ℃ with a melting point of 3000℃ ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/TPEL.2013.2268900","ISSN":"08858993","abstract":"Wide bandgap semiconductors show superior material properties enabling potential power device operation at higher temperatures, voltages, and switching speeds than current Si technology. As a result, a new generation of power devices is being developed for power converter applications in which traditional Si power devices show limited operation. The use of these new power semiconductor devices will allow both an important improvement in the performance of existing power converters and the development of new power converters, accounting for an increase in the efficiency of the electric energy transformations and a more rational use of the electric energy. At present, SiC and GaN are the more promising semiconductor materials for these new power devices as a consequence of their outstanding properties, commercial availability of starting material, and maturity of their technological processes. This paper presents a review of recent progresses in the development of SiC-and GaN-based power semiconductor devices together with an overall view of the state of the art of this new device generation. ? 2013 IEEE.","author":[{"dropping-particle":"","family":"Millan","given":"Jose","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Godignon","given":"Philippe","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Perpina","given":"Xavier","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Perez-Tomas","given":"Amador","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Rebollo","given":"Jose","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Power Electronics","id":"ITEM-1","issue":"5","issued":{"date-parts":[["2014"]]},"page":"2155-2163","title":"A survey of wide bandgap power semiconductor devices","type":"article-journal","volume":"29"},"uris":["",""]}],"mendeley":{"formattedCitation":"[69]","plainTextFormattedCitation":"[69]","previouslyFormattedCitation":"[68]"},"properties":{"noteIndex":0},"schema":""}[69]. WBG semiconductors enable the converters to operate at higher switching frequency (up to 100 kHz) while maintaining high energy efficiency. This decreases the size and weight of passive filters and heat-removal system and in consequence, increases the power density of the converters. SiC Schottky diodes have been commercialised since 2001 already and they are used in IGBT power modules too as freewheeling diodes. These IGBTs are the so called Si-SiC hybrid semiconductors and Japanese railways reported a reduced mass and volume of 60% in traction converters ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/MIE.2016.2588878","author":[{"dropping-particle":"","family":"Huber","given":"Jonas E","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Kolar","given":"Johann W","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Industrial Electronics Magazine","id":"ITEM-1","issue":"September","issued":{"date-parts":[["2016"]]},"page":"19-28","title":"Solid-State Transformers","type":"article-journal","volume":"10"},"uris":[""]}],"mendeley":{"formattedCitation":"[37]","plainTextFormattedCitation":"[37]","previouslyFormattedCitation":"[37]"},"properties":{"noteIndex":0},"schema":""}[37]. Also Mitsubishi Electric launched in 2015 traction inverters based only on SiC devices for the Japan-Tokyo 1.5?kV DC metro and a 30% energy consumption decrease was reported along a power loss reduction of 55% ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.7567/ssdm.2014.e-4-4l","author":[{"dropping-particle":"","family":"Hamada","given":"K.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Hino","given":"S.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Miura","given":"N.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Watanabe","given":"H.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Nakata","given":"S.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Suekawa","given":"E.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Ebiike","given":"Y.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Imaizumi","given":"M.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Umezaki","given":"I.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Yamakawa","given":"S.","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issued":{"date-parts":[["2017"]]},"page":"14-18","title":"3.3 kV/1500 A Power Modules for the World’s First All-SiC Traction Inverter","type":"article-journal"},"uris":["",""]}],"mendeley":{"formattedCitation":"[70]","plainTextFormattedCitation":"[70]","previouslyFormattedCitation":"[69]"},"properties":{"noteIndex":0},"schema":""}[70]. Two years later, in ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.23919/IPEC.2018.8507486","ISBN":"9784886864055","abstract":"This paper presents the development of a traction system for high-speed trains by adopting SiC power devices to pursue weight reduction and compactness of the system. We found the combination of the SiC applied conversion system with train-draft cooling system and 6-pole induction motors is a suitable approach to highlight the merits of SiC devices. The running tests of a prototype were conducted to confirm its sound performances. The developed traction system is to be installed in the latest-type Shinkansen train, or the Series N700S, which will debut in March 2018, and this SiC application to high-speed train's traction system is the first case over the world.","author":[{"dropping-particle":"","family":"Sato","given":"Kenji","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Kato","given":"Hirokazu","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Fukushima","given":"Takafumi","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2018 International Power Electronics Conference, IPEC-Niigata - ECCE Asia 2018","id":"ITEM-1","issued":{"date-parts":[["2018"]]},"page":"3478-3483","publisher":"IEEJ Industry Application Society","title":"Development of SiC Applied Traction System for Shinkansen High-speed Train","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[71]","plainTextFormattedCitation":"[71]","previouslyFormattedCitation":"[70]"},"properties":{"noteIndex":0},"schema":""}[71] the first traction system for high-speed trains was reported based on SiC devices combined with train-draft cooling system and a new series of 6-pole induction motors. Thanks to SiC technology, the main transformer and the conversion system could be installed in the same car due to compactness and to the 10% smaller new motors, an overall system weight reduction of 20% was achieved compared to the previous series of the train. In ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/IECON.2016.7793121","ISBN":"9781509034741","abstract":"This paper discusses the advancements in the development of the medium voltage solid state transformer (SST) based on 15 kV SiC MOSFET and JBS diode. Designed for 7.2 kV single phase distribution grid applications, the medium voltage SST converts high voltage AC to low voltage 240/120V ac. The use of ultra-high voltage SiC devices allows the simplification of the power conversion circuit topology. This paper presents the characteristics of the high voltage SiC MOSFET devices as well as the topology innovations to achieve ultra-efficient SST design. Specifically, three different designs are discussed which utilize three-stage, two-stage and single stage power conversion topologies to achieve the AC to AC conversion.","author":[{"dropping-particle":"","family":"Huang","given":"Alex Q.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Wang","given":"Li","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Tian","given":"Qi","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Zhu","given":"Qianlai","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Chen","given":"Dong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Yu","given":"Wensong","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IECON Proceedings (Industrial Electronics Conference)","id":"ITEM-1","issued":{"date-parts":[["2016"]]},"page":"6996-7003","publisher":"IEEE","title":"Medium voltage solid state transformers based on 15 kV SiC MOSFET and JBS diode","type":"article-journal"},"uris":["",""]}],"mendeley":{"formattedCitation":"[72]","plainTextFormattedCitation":"[72]","previouslyFormattedCitation":"[71]"},"properties":{"noteIndex":0},"schema":""}[72] a PETT was presented built with the earlier mentioned junction barrier SiC diodes and 15?kV/120?A SiC MOSFETs. At 1?MVA power, the achieved efficiency was 98% and the weight reduction 70%. A SiC MOSFET traction inverter was also operated in the Stockholm Metro System for 3 months and showed increased power density, achieving a reduction of 51% volume and 22% weight ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/VPPC.2018.8604975","ISBN":"9781538662038","abstract":"For the first time results are reported in literature of a successful field test using a silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (MOSFET) traction inverter operated in the field. The metro train has been operated over a period of 3 months on the Green Line in the Stockholm metro system. Increased traction converter power density with a volume reduction of 51 % as well as a weight reduction of 22 % have been achieved. Lower power losses allow the use of car motion cooling. From complementing measurements in the laboratory of silicon and SiC in the same power device package with varying switching frequencies considerably lower SiC temperatures can be reported.","author":[{"dropping-particle":"","family":"Lindahl","given":"Martin","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Velander","given":"Erik","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Johansson","given":"Mikael H.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Blomberg","given":"Anders","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Nee","given":"Hans Peter","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2018 IEEE Vehicle Power and Propulsion Conference, VPPC 2018 - Proceedings","id":"ITEM-1","issued":{"date-parts":[["2019"]]},"title":"Silicon carbide MOSFET traction inverter operated in the Stockholm metro system demonstrating customer values","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[73]","plainTextFormattedCitation":"[73]","previouslyFormattedCitation":"[72]"},"properties":{"noteIndex":0},"schema":""}[73].According to ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/TPEL.2013.2268900","ISSN":"08858993","abstract":"Wide bandgap semiconductors show superior material properties enabling potential power device operation at higher temperatures, voltages, and switching speeds than current Si technology. As a result, a new generation of power devices is being developed for power converter applications in which traditional Si power devices show limited operation. The use of these new power semiconductor devices will allow both an important improvement in the performance of existing power converters and the development of new power converters, accounting for an increase in the efficiency of the electric energy transformations and a more rational use of the electric energy. At present, SiC and GaN are the more promising semiconductor materials for these new power devices as a consequence of their outstanding properties, commercial availability of starting material, and maturity of their technological processes. This paper presents a review of recent progresses in the development of SiC-and GaN-based power semiconductor devices together with an overall view of the state of the art of this new device generation. ? 2013 IEEE.","author":[{"dropping-particle":"","family":"Millan","given":"Jose","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Godignon","given":"Philippe","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Perpina","given":"Xavier","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Perez-Tomas","given":"Amador","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Rebollo","given":"Jose","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Power Electronics","id":"ITEM-1","issue":"5","issued":{"date-parts":[["2014"]]},"page":"2155-2163","title":"A survey of wide bandgap power semiconductor devices","type":"article-journal","volume":"29"},"uris":["",""]}],"mendeley":{"formattedCitation":"[69]","plainTextFormattedCitation":"[69]","previouslyFormattedCitation":"[68]"},"properties":{"noteIndex":0},"schema":""}[69] SiC devices are developed for a large variety of applications and voltage ranges starting from JFETs, junction barrier diodes, IGBTs, MOSFETS and BJTs to SiC-GTOs. However, some of these devices are not as mature as others due to reliability problems. Theoretical studies show that SiC MOSFETs are a good candidate up to a 1015?kV breakdown voltage, while IGBTs are the devices with the highest potential for applications above 15?kV, due to their very good on-state performances. In ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.4028/MSF.821-823.847","author":[{"dropping-particle":"","family":"Brunt","given":"Edward","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Cheng","given":"Lin","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"O’Loughlin","given":"Michael","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Richmond","given":"James","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Pala","given":"Vipindas","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Palmour","given":"John","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Tipton","given":"Charles","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Scozzie","given":"Charles","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"Materials Science Forum","id":"ITEM-1","issued":{"date-parts":[["2015","6","1"]]},"title":"27 kV, 20 Ampere-rated 4H-SiC n-IGBTs","type":"article-journal","volume":"821-823"},"uris":["",""]}],"mendeley":{"formattedCitation":"[74]","plainTextFormattedCitation":"[74]","previouslyFormattedCitation":"[73]"},"properties":{"noteIndex":0},"schema":""}[74] a 27?kV SiC IGBT was reported as laboratory experiment and ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/ECCE.2018.8558451","ISBN":"9781479973118","author":[{"dropping-particle":"","family":"Hu","given":"Boxue","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Lyu","given":"Xintong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Xing","given":"Diang","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Ma","given":"Dihao","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Brothers","given":"John","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Na","given":"Risha","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Wang","given":"Jin","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2018 IEEE Energy Conversion Congress and Exposition, ECCE 2018","id":"ITEM-1","issued":{"date-parts":[["2018"]]},"page":"2420-2427","publisher":"IEEE","title":"A Survey on Recent Advances of Medium Voltage Silicon Carbide Power Devices","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[68]","plainTextFormattedCitation":"[68]","previouslyFormattedCitation":"[67]"},"properties":{"noteIndex":0},"schema":""}[68] mentions an engineering sample of a SiC GTO of 22?kV. Hitachi already commercialised 3.3 kV hybrid SiC IGBTs (as used in ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.7567/ssdm.2014.e-4-4l","author":[{"dropping-particle":"","family":"Hamada","given":"K.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Hino","given":"S.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Miura","given":"N.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Watanabe","given":"H.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Nakata","given":"S.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Suekawa","given":"E.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Ebiike","given":"Y.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Imaizumi","given":"M.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Umezaki","given":"I.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Yamakawa","given":"S.","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issued":{"date-parts":[["2017"]]},"page":"14-18","title":"3.3 kV/1500 A Power Modules for the World’s First All-SiC Traction Inverter","type":"article-journal"},"uris":["",""]}],"mendeley":{"formattedCitation":"[70]","plainTextFormattedCitation":"[70]","previouslyFormattedCitation":"[69]"},"properties":{"noteIndex":0},"schema":""}[70] and ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.23919/IPEC.2018.8507486","ISBN":"9784886864055","abstract":"This paper presents the development of a traction system for high-speed trains by adopting SiC power devices to pursue weight reduction and compactness of the system. We found the combination of the SiC applied conversion system with train-draft cooling system and 6-pole induction motors is a suitable approach to highlight the merits of SiC devices. The running tests of a prototype were conducted to confirm its sound performances. The developed traction system is to be installed in the latest-type Shinkansen train, or the Series N700S, which will debut in March 2018, and this SiC application to high-speed train's traction system is the first case over the world.","author":[{"dropping-particle":"","family":"Sato","given":"Kenji","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Kato","given":"Hirokazu","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Fukushima","given":"Takafumi","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2018 International Power Electronics Conference, IPEC-Niigata - ECCE Asia 2018","id":"ITEM-1","issued":{"date-parts":[["2018"]]},"page":"3478-3483","publisher":"IEEJ Industry Application Society","title":"Development of SiC Applied Traction System for Shinkansen High-speed Train","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[71]","plainTextFormattedCitation":"[71]","previouslyFormattedCitation":"[70]"},"properties":{"noteIndex":0},"schema":""}[71]) and their all SiC IGBT is on the way too, under development for production ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"URL":"","id":"ITEM-1","issued":{"date-parts":[["0"]]},"title":"3.3 kV Hybrid SiC IGBT commercialised and 3.3kV all SiC IGBT under developement","type":"webpage"},"uris":[""]}],"mendeley":{"formattedCitation":"[75]","plainTextFormattedCitation":"[75]","previouslyFormattedCitation":"[74]"},"properties":{"noteIndex":0},"schema":""}[75]. Paper ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/ECCE.2018.8558451","ISBN":"9781479973118","author":[{"dropping-particle":"","family":"Hu","given":"Boxue","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Lyu","given":"Xintong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Xing","given":"Diang","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Ma","given":"Dihao","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Brothers","given":"John","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Na","given":"Risha","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Wang","given":"Jin","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2018 IEEE Energy Conversion Congress and Exposition, ECCE 2018","id":"ITEM-1","issued":{"date-parts":[["2018"]]},"page":"2420-2427","publisher":"IEEE","title":"A Survey on Recent Advances of Medium Voltage Silicon Carbide Power Devices","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[68]","plainTextFormattedCitation":"[68]","previouslyFormattedCitation":"[67]"},"properties":{"noteIndex":0},"schema":""}[68] presents a survey on recent advances of MV SiC power devices. Beside the already mentioned advantages of SiC devices, it mentions some reports about lower on-state resistance, switching energy and cooling requirements However, higher voltage ratings and switching frequencies imply challenges in the packaging. To avoid overshoots and current imbalances mentioned in the previous chapter, the packaging must have low parasitic capacitance and inductance. In ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/ECCE.2017.8096699","ISBN":"9781509029983","abstract":"High-density packaging of fast-switching power semiconductors typically requires low thermal resistance and parasitic inductance. High-density packaging of high-voltage semiconductors, such as 10 kV SiC MOSFETs, has the added challenge of maintaining low electric field concentration in order to prevent premature dielectric breakdown. This work proposes a wire-bond-less, sandwich structure with embedded decoupling capacitors and stacked ceramic substrates in order to realize a high-density module capable of high-speed switching with low electric field concentration and EMI. This is the first time that these advanced packaging techniques have been applied to a 10 kV SiC MOSFET module.","author":[{"dropping-particle":"","family":"DIMarino","given":"Christina","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Johnson","given":"Mark","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Mouawad","given":"Bassem","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Li","given":"Jianfeng","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Boroyevich","given":"Dushan","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Burgos","given":"Rolando","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Lu","given":"Guo Quan","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Wang","given":"Meiyu","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2017 IEEE Energy Conversion Congress and Exposition, ECCE 2017","id":"ITEM-1","issued":{"date-parts":[["2017"]]},"page":"4003-4010","title":"Design of a novel, high-density, high-speed 10 kV SiC MOSFET module","type":"article-journal","volume":"2017-Janua"},"uris":["",""]}],"mendeley":{"formattedCitation":"[76]","plainTextFormattedCitation":"[76]","previouslyFormattedCitation":"[75]"},"properties":{"noteIndex":0},"schema":""}[76] a 57% loop inductance reduction was achieved only by adding decoupling capacitors inside the MOSFET module and ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/TPEL.2014.2352863","ISSN":"08858993","abstract":"Silicon (Si) insulated-gate bipolar transistors are widely used in railway traction converters. In the near future, silicon carbide (SiC) technology will push the limits of switching devices in three directions: higher blocking voltage, higher operating temperature, and higher switching speeds. The first silicon carbide (SiC) MOSFET modules are available on the market and look promising. Although they are still limited in breakdown voltage, these wide-bandgap components should improve traction-chain efficiency. Particularly, a significant reduction in the switching losses is expected which should lead to improvements in power-weight ratios. Nevertheless, because of the high switching speed and the high current levels required by traction applications, the implementation of these new modules is critical. An original method is proposed to compare, in terms of stray inductance, several dc bus-bar designs. To evaluate the potential of these new devices, a first set of measurements, based on a single-pulse test-bench, was obtained. The switching behavior of SiC devices was well understood at turn-off and turn-on. To complete this work, the authors use an opposition method to compare Si-IGBT and SiC-MOSFET modules in voltage source inverter operation. For this purpose, a second test-bench, allowing electrical and thermal measurements, was developed. Experimental results confirm the theoretical loss-calculation of the single-pulse tests and the correct operation of up to three modules directly connected in parallel. This analysis provides guidelines for a full SiC inverter design, and prospects for developments in traction applications are presented.","author":[{"dropping-particle":"","family":"Fabre","given":"Joseph","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Ladoux","given":"Philippe","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Piton","given":"Michel","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Power Electronics","id":"ITEM-1","issue":"8","issued":{"date-parts":[["2015"]]},"page":"4079-4090","publisher":"IEEE","title":"Characterization and Implementation of Dual-SiC MOSFET Modules for Future Use in Traction Converters","type":"article-journal","volume":"30"},"uris":[""]}],"mendeley":{"formattedCitation":"[77]","plainTextFormattedCitation":"[77]","previouslyFormattedCitation":"[76]"},"properties":{"noteIndex":0},"schema":""}[77] also reports such inductance reduction by doing different tests without and with decoupling capacitors A stacked substrate structure that improves not only the parasitic capacitance reduction but thermal performance as well was also presented in ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/ECCE.2017.8096699","ISBN":"9781509029983","abstract":"High-density packaging of fast-switching power semiconductors typically requires low thermal resistance and parasitic inductance. 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This is the first time that these advanced packaging techniques have been applied to a 10 kV SiC MOSFET module.","author":[{"dropping-particle":"","family":"DIMarino","given":"Christina","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Johnson","given":"Mark","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Mouawad","given":"Bassem","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Li","given":"Jianfeng","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Boroyevich","given":"Dushan","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Burgos","given":"Rolando","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Lu","given":"Guo Quan","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Wang","given":"Meiyu","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2017 IEEE Energy Conversion Congress and Exposition, ECCE 2017","id":"ITEM-1","issued":{"date-parts":[["2017"]]},"page":"4003-4010","title":"Design of a novel, high-density, high-speed 10 kV SiC MOSFET module","type":"article-journal","volume":"2017-Janua"},"uris":["",""]}],"mendeley":{"formattedCitation":"[76]","plainTextFormattedCitation":"[76]","previouslyFormattedCitation":"[75]"},"properties":{"noteIndex":0},"schema":""}[76]. The smaller dimensions of SiC devices brings also insulation issues, therefore ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/ECCE.2017.8096699","ISBN":"9781509029983","abstract":"High-density packaging of fast-switching power semiconductors typically requires low thermal resistance and parasitic inductance. High-density packaging of high-voltage semiconductors, such as 10 kV SiC MOSFETs, has the added challenge of maintaining low electric field concentration in order to prevent premature dielectric breakdown. This work proposes a wire-bond-less, sandwich structure with embedded decoupling capacitors and stacked ceramic substrates in order to realize a high-density module capable of high-speed switching with low electric field concentration and EMI. This is the first time that these advanced packaging techniques have been applied to a 10 kV SiC MOSFET module.","author":[{"dropping-particle":"","family":"DIMarino","given":"Christina","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Johnson","given":"Mark","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Mouawad","given":"Bassem","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Li","given":"Jianfeng","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Boroyevich","given":"Dushan","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Burgos","given":"Rolando","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Lu","given":"Guo Quan","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Wang","given":"Meiyu","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2017 IEEE Energy Conversion Congress and Exposition, ECCE 2017","id":"ITEM-1","issued":{"date-parts":[["2017"]]},"page":"4003-4010","title":"Design of a novel, high-density, high-speed 10 kV SiC MOSFET module","type":"article-journal","volume":"2017-Janua"},"uris":["",""]}],"mendeley":{"formattedCitation":"[76]","plainTextFormattedCitation":"[76]","previouslyFormattedCitation":"[75]"},"properties":{"noteIndex":0},"schema":""}[76] proposed a stacked insulation structure, reducing the strength of peak electric field by up to 40% compared to single substrates.The authors of ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/ECCE.2018.8558451","ISBN":"9781479973118","author":[{"dropping-particle":"","family":"Hu","given":"Boxue","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Lyu","given":"Xintong","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Xing","given":"Diang","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Ma","given":"Dihao","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Brothers","given":"John","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Na","given":"Risha","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Wang","given":"Jin","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2018 IEEE Energy Conversion Congress and Exposition, ECCE 2018","id":"ITEM-1","issued":{"date-parts":[["2018"]]},"page":"2420-2427","publisher":"IEEE","title":"A Survey on Recent Advances of Medium Voltage Silicon Carbide Power Devices","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[68]","plainTextFormattedCitation":"[68]","previouslyFormattedCitation":"[67]"},"properties":{"noteIndex":0},"schema":""}[68] also tested three SiC devices, two of them MOSFETs and based on the reports of the last few years defines the 3.3 kV rated SiC devices as the most mature ones currently, showing good static/dynamic performances, body diode surge current capability, avalanche capability and short-circuit ruggedness. In ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/ESARS.2015.7101518","ISBN":"9781479974009","ISSN":"21659427","author":[{"dropping-particle":"","family":"Casarin","given":"J.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Ladoux","given":"P.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Lasserre","given":"P.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"Electrical Systems for Aircraft, Railway and Ship Propulsion, ESARS","id":"ITEM-1","issued":{"date-parts":[["2015"]]},"page":"5-10","title":"10kV SiC MOSFETs versus 6.5kV Si-IGBTs for medium frequency transformer application in railway traction","type":"article-journal","volume":"2015-May"},"uris":[""]}],"mendeley":{"formattedCitation":"[78]","plainTextFormattedCitation":"[78]","previouslyFormattedCitation":"[77]"},"properties":{"noteIndex":0},"schema":""}[78] a 10?kV SiC MOSFET with 6.5 kV Si antiparallel diode are compared using a series-resonant DC/DC converter test bench. The results show a significant reduction of losses with the SiC module and in the conclusions, it is mentioned that 10?kV SiC modules without anti-parallel diodes are under development and tests are already undergoing. The SiC MOSFET with the highest voltage studied so far reaches 15?kV, which has been compared with the 15?kV SiC IGBT in ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/JESTPE.2016.2620991","ISSN":"21686785","abstract":"The 15-kV silicon carbide (SiC) MOSFET and 15-kV SiC IGBT are the two state-of-the-art high-voltage SiC devices. These high-voltage SiC devices enable simple two-level converters for a medium-voltage (MV) voltage source converter (VSC) topology compared with the complex three-level neutral point clamped and other multilevel topologies, which, otherwise, is required to realize for MV VSC with silicon devices. This paper characterizes the 15-kV SiC MOSFET module at 10- and 12-kV dc bus for two different configurations of the device under test. This paper also presents endurance test (continuous switching-mode experimental demonstration) of 15-kV SiC MOSFET for 10-kV output voltage for both a bidirectional and unidirectional dc-dc boost converter. Furthermore, this paper presents: 1) the switching loss comparison of 15-kV SiC MOSFET with 15-kV SiC IGBT for the same dv/dt condition; 2) the switching frequency limits of 15-kV SiC MOSFET for a dc-dc boost converter with a phase leg configuration at 10-kV output voltage; and 3) comparative evaluation of 15-kV SiC MOSFET and 15-kV SiC IGBT in a unidirectional dc-dc boost converter for 10 V output voltage.","author":[{"dropping-particle":"","family":"Vechalapu","given":"Kasunaidu","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Bhattacharya","given":"Subhashish","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Brunt","given":"Edward","non-dropping-particle":"Van","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Ryu","given":"Sei Hyung","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Grider","given":"Dave","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Palmour","given":"John W.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Journal of Emerging and Selected Topics in Power Electronics","id":"ITEM-1","issue":"1","issued":{"date-parts":[["2017"]]},"page":"469-489","publisher":"IEEE","title":"Comparative Evaluation of 15-kV SiC MOSFET and 15-kV SiC IGBT for Medium-Voltage Converter under the Same dv/dt Conditions","type":"article-journal","volume":"5"},"uris":["",""]}],"mendeley":{"formattedCitation":"[79]","plainTextFormattedCitation":"[79]","previouslyFormattedCitation":"[78]"},"properties":{"noteIndex":0},"schema":""}[79] and ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/ECCE.2014.6953428","ISBN":"9781479956982","abstract":"Advanced high-voltage (10 kV - 15 kV) silicon carbide (SiC) power MOSFETs described in this paper have the potential to significantly impact the system performance, size, weight, high-temperature reliability, and cost of next-generation energy conversion and transmission systems. In this paper, we report our recently developed 10 kV/20 A SiC MOSFETs with a chip size of 8.1 × 8.1 mm² and a specific on-resistance (R<inf>O</inf>N,SP) of 100 mΩ·cm² at 25°C. We also developed 15 kV/10 A SiC power MOSFETs with a chip size of 8 × 8 mm² and a R<inf>ON,SP</inf> of 204 mΩ·cm² at 25°C. To our knowledge, this 15 kV SiC MOSFET is the highest voltage rated unipolar power switch. Compared to the commercial 6.5 kV Silicon (Si) IGBTs, these 10 kV and 15 kV SiC MOSFETs exhibit extremely low switching losses even when they are switched at 2-3x higher voltage. The benefits of using these 10 kV and 15 kV SiC MOSFETs include simplifying from multilevel to two-level topology and removing the need for time-interleaving by improving the switching frequency from a few hundred Hz for Si based systems to ≥ 10 kHz for hard-switched SiC based systems.","author":[{"dropping-particle":"","family":"Pala","given":"Vipindas","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"V.","family":"Brunt","given":"Edward","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Cheng","given":"Lin","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"O'Loughlin","given":"Michael","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Richmond","given":"Jim","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Burk","given":"Albert","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Allen","given":"Scott T.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Grider","given":"David","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Palmour","given":"John W.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Scozzie","given":"Charles J.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2014 IEEE Energy Conversion Congress and Exposition, ECCE 2014","id":"ITEM-1","issued":{"date-parts":[["2014"]]},"page":"449-454","publisher":"IEEE","title":"10 kV and 15 kV silicon carbide power MOSFETs for next-generation energy conversion and transmission systems","type":"article-journal"},"uris":["",""]}],"mendeley":{"formattedCitation":"[80]","plainTextFormattedCitation":"[80]","previouslyFormattedCitation":"[79]"},"properties":{"noteIndex":0},"schema":""}[80]. The conclusion of the two studies was that SiC MOSFETs are better for low current applications and IGBTs for high current applications (Hitachi has two modules under development, one of 1,200?A and one of 1,800?A – both at 3.3?kV ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"URL":"","id":"ITEM-1","issued":{"date-parts":[["0"]]},"title":"3.3 kV Hybrid SiC IGBT commercialised and 3.3kV all SiC IGBT under developement","type":"webpage"},"uris":[""]}],"mendeley":{"formattedCitation":"[75]","plainTextFormattedCitation":"[75]","previouslyFormattedCitation":"[74]"},"properties":{"noteIndex":0},"schema":""}[75]). Also, the on-state resistance of MOSFETs becomes high above 15?kV. The articles categorise the SiC devices for future applications as follows: MOSFET up to 15kV, IGBT between 15-35?kV and GTOs above 35?kV. Another study, ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/TPEL.2014.2352863","ISSN":"08858993","abstract":"Silicon (Si) insulated-gate bipolar transistors are widely used in railway traction converters. In the near future, silicon carbide (SiC) technology will push the limits of switching devices in three directions: higher blocking voltage, higher operating temperature, and higher switching speeds. The first silicon carbide (SiC) MOSFET modules are available on the market and look promising. Although they are still limited in breakdown voltage, these wide-bandgap components should improve traction-chain efficiency. Particularly, a significant reduction in the switching losses is expected which should lead to improvements in power-weight ratios. Nevertheless, because of the high switching speed and the high current levels required by traction applications, the implementation of these new modules is critical. An original method is proposed to compare, in terms of stray inductance, several dc bus-bar designs. To evaluate the potential of these new devices, a first set of measurements, based on a single-pulse test-bench, was obtained. The switching behavior of SiC devices was well understood at turn-off and turn-on. To complete this work, the authors use an opposition method to compare Si-IGBT and SiC-MOSFET modules in voltage source inverter operation. For this purpose, a second test-bench, allowing electrical and thermal measurements, was developed. Experimental results confirm the theoretical loss-calculation of the single-pulse tests and the correct operation of up to three modules directly connected in parallel. This analysis provides guidelines for a full SiC inverter design, and prospects for developments in traction applications are presented.","author":[{"dropping-particle":"","family":"Fabre","given":"Joseph","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Ladoux","given":"Philippe","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Piton","given":"Michel","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Power Electronics","id":"ITEM-1","issue":"8","issued":{"date-parts":[["2015"]]},"page":"4079-4090","publisher":"IEEE","title":"Characterization and Implementation of Dual-SiC MOSFET Modules for Future Use in Traction Converters","type":"article-journal","volume":"30"},"uris":[""]}],"mendeley":{"formattedCitation":"[77]","plainTextFormattedCitation":"[77]","previouslyFormattedCitation":"[76]"},"properties":{"noteIndex":0},"schema":""}[77], presents a test-bench and a SiC MOSFET model in PSIM to efficiently compare different bus-bar designs and evaluate SiC switching behaviour. Furthermore, an additional test bench was developed to undertake thermal and electrical measurements and Si-IGBTs in comparison to SiC MOSFET modules for a VSI application. The simulation results about the impact of bus-bar design on the turn-off of SiC-MOSFETs show that SiC MOSFETs have lower turn-on energy than Si-IGBTs with same ratings. Then the paper presented different methods for measurement of losses. The results showed that SiC MOSFETs have 60% less power losses than Si-IGBT for 15 kHz switching frequency. Si-IGBT modules have the same losses of SiC MOSFETS only at 1 kHz switching frequency. For 20 kHz switching frequency the total loss reduction is 57% compared to Si-IGBT. However, at low frequency – 1 kHz - Si-IGBT modules have lower losses. It can be concluded that the experimental results confirm the losses reduction, operation at increased frequencies and junction temperatures. The analysis also provided useful guidelines for SiC inverter design in traction applications. Finally, the paper highlighted also the necessity of high current modules for traction applications. At the moment, commercially available 1.7 kV SiC devices already allow the design of traction inverters for metros and trams, as seen in ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.7567/ssdm.2014.e-4-4l","author":[{"dropping-particle":"","family":"Hamada","given":"K.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Hino","given":"S.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Miura","given":"N.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Watanabe","given":"H.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Nakata","given":"S.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Suekawa","given":"E.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Ebiike","given":"Y.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Imaizumi","given":"M.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Umezaki","given":"I.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Yamakawa","given":"S.","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issued":{"date-parts":[["2017"]]},"page":"14-18","title":"3.3 kV/1500 A Power Modules for the World’s First All-SiC Traction Inverter","type":"article-journal"},"uris":["",""]}],"mendeley":{"formattedCitation":"[70]","plainTextFormattedCitation":"[70]","previouslyFormattedCitation":"[69]"},"properties":{"noteIndex":0},"schema":""}[70] and ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.23919/IPEC.2018.8507486","ISBN":"9784886864055","abstract":"This paper presents the development of a traction system for high-speed trains by adopting SiC power devices to pursue weight reduction and compactness of the system. We found the combination of the SiC applied conversion system with train-draft cooling system and 6-pole induction motors is a suitable approach to highlight the merits of SiC devices. The running tests of a prototype were conducted to confirm its sound performances. The developed traction system is to be installed in the latest-type Shinkansen train, or the Series N700S, which will debut in March 2018, and this SiC application to high-speed train's traction system is the first case over the world.","author":[{"dropping-particle":"","family":"Sato","given":"Kenji","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Kato","given":"Hirokazu","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Fukushima","given":"Takafumi","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2018 International Power Electronics Conference, IPEC-Niigata - ECCE Asia 2018","id":"ITEM-1","issued":{"date-parts":[["2018"]]},"page":"3478-3483","publisher":"IEEJ Industry Application Society","title":"Development of SiC Applied Traction System for Shinkansen High-speed Train","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[71]","plainTextFormattedCitation":"[71]","previouslyFormattedCitation":"[70]"},"properties":{"noteIndex":0},"schema":""}[71].The work in paper ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"Salem","given":"Thomas E","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Wood","given":"Robert A","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issue":"5","issued":{"date-parts":[["2014"]]},"page":"2192-2198","publisher":"IEEE","title":"All-SiC Dual Module","type":"article-journal","volume":"29"},"uris":["",""]}],"mendeley":{"formattedCitation":"[81]","plainTextFormattedCitation":"[81]","previouslyFormattedCitation":"[80]"},"properties":{"noteIndex":0},"schema":""}[81] evaluates a 1,200?V/800?A all-SiC dual module designed for electric military vehicle under a 1000 hour operation test operated at 10 kHz frequency with different load profiles. During the test, it was observed that none of the measured characteristics suffered any significant unfavourable change more than 10% compared to their initial value. The length of the test represented 11,783 miles of usage, which corresponds to over a half of expected inverter lifecycle in such a vehicle. This validates also the reliability of SiC devices. In another paper, ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/JESTPE.2018.2886140","author":[{"dropping-particle":"","family":"Rothmund","given":"Daniel","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Member","given":"Student","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Guillod","given":"Thomas","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Member","given":"Student","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Bortis","given":"Dominik","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Kolar","given":"Johann W","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Journal of Emerging and Selected Topics in Power Electronics","id":"ITEM-1","issue":"2","issued":{"date-parts":[["2019"]]},"page":"779-797","publisher":"IEEE","title":"99.1% Efficient 10 kV SiC-Based Medium-Voltage ZVS Bidirectional Single-Phase PFC AC / DC Stage","type":"article-journal","volume":"7"},"uris":["",""]}],"mendeley":{"formattedCitation":"[82]","plainTextFormattedCitation":"[82]","previouslyFormattedCitation":"[81]"},"properties":{"noteIndex":0},"schema":""}[82], as part of a Swiss project titled ”SwiSS Transformer - P3: 99% Efficient Solid State SiC Transformer Cell Demonstrator” in the context of PETTs a 10kV SiC based PFC was studied. The authors designed a PFC of 25?kW achieving 99.1% efficiency at full load and a power density of 3.28kW/dm3. In ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/PEDG.2017.7972488","ISBN":"9781509053384","abstract":"State-of-the-art PWM AC/DC converters often suffer from high switching losses due to hard-switching and thus are limited in their efficiency and power density. In this paper, the concept of the integrated Triangular Current Mode (iTCM) operation is introduced, which enables soft-switching over the entire AC mains period and can overcome the limitation of PWM, resulting in a higher system performance. Thereby, an LC-circuit is added to the well-known full-bridge-based PWM AC/DC converter, which internally superimposes a high triangular current to the AC mains current in order to reverse the current direction in the semiconductors in each switching cycle and by this enabling soft-switching operation of all devices. In this paper, the iTCM concept is presented in detail and its performance is compared to the standard PWM and TCM approaches. Furthermore, the proposed iTCM concept is applied to a 10 kV SiC-MOSFET-based bidirectional 25kW single-phase AC/DC converter operated from the 6:6 kV medium-voltage AC grid. In this case, compared to PWM, the iTCM concept allows to increase the switching frequency by almost a factor of five while the total semiconductor losses are reduced by more than 40%.","author":[{"dropping-particle":"","family":"Rothmund","given":"Daniel","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Bortis","given":"Dominik","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Huber","given":"Jonas","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Biadene","given":"Davide","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Kolar","given":"Johann W.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"2017 IEEE 8th International Symposium on Power Electronics for Distributed Generation Systems, PEDG 2017","id":"ITEM-1","issue":"c","issued":{"date-parts":[["2017"]]},"page":"1-8","publisher":"IEEE","title":"10kV SiC-based bidirectional soft-switching single-phase AC/DC converter concept for medium-voltage Solid-State Transformers","type":"article-journal"},"uris":["",""]}],"mendeley":{"formattedCitation":"[83]","plainTextFormattedCitation":"[83]","previouslyFormattedCitation":"[82]"},"properties":{"noteIndex":0},"schema":""}[83] a 10?kV SiC based 25?kW single phase bidirectional AC/DC PETT was presented and the paper also introduced the concept of integrated Triangular Current Mode (iTCM) operation and demonstrated its superiority over PWM. With the iTCM concept they achieved a semiconductor losses reduction of 40% and an increased switching frequency as well as full range soft switching.Paper ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/ICCEP.2019.8890157","ISBN":"9781728113562","abstract":"In order to improve the energy efficiency of the railway traction power supply, a DC voltage of 9 kV has recently been proposed. Beyond train power supply, this new power system will allow to connect several sources and/or loads (AC power grid, energy storage, wind farm, solar panels, etc.). This new railway \"smart grid\" will require insulated DC-DC converters operating in a medium frequency range (from 10 to 20 kHz) to reduce the size of the passive components (mainly the transformer). In the voltage and power ranges targeted, this is now possible thanks to the arrival on the market of power modules based on SiC MOSFETs. Therefore, this paper focuses on the operation in ZVS mode of two power modules (1.7 kV / 1100 A and 3.3 kV / 750 A). The first part of the paper is devoted to the design of a driver for Zero Voltage Switching. In a second part, a test bench is presented. It allows to measure the switching energies in this operating mode. Finally, from these results, it is then possible to determine the efficiency of resonant DC/DC converters, which can be used in the MVDC power system.","author":[{"dropping-particle":"","family":"Fabre","given":"J.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Blaquière","given":"J. M.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Verdicchio","given":"A.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Ladoux","given":"P.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Sanchez","given":"S.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"ICCEP 2019 - 7th International Conference on Clean Electrical Power: Renewable Energy Resources Impact","id":"ITEM-1","issued":{"date-parts":[["2019"]]},"page":"470-477","title":"Characterization in ZVS Mode of SiC MOSFET Modules for MVDC Applications","type":"article-journal"},"uris":[""]}],"mendeley":{"formattedCitation":"[84]","plainTextFormattedCitation":"[84]","previouslyFormattedCitation":"[83]"},"properties":{"noteIndex":0},"schema":""}[84] studied two SiC modules, a 1.7?kV/1,100?A and a 3.3?kV/750?A in the context of the recently proposed MVDC-ERS of 9?kV in ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1109/TTE.2018.2826780","ISSN":"23327782","author":[{"dropping-particle":"","family":"Verdicchio","given":"Andrea","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Ladoux","given":"Philippe","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Caron","given":"Herve","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Courtois","given":"Christian","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"IEEE Transactions on Transportation Electrification","id":"ITEM-1","issue":"2","issued":{"date-parts":[["2018"]]},"page":"591-604","publisher":"IEEE","title":"New Medium-Voltage DC Railway Electrification System","type":"article-journal","volume":"4"},"uris":[""]}],"mendeley":{"formattedCitation":"[29]","plainTextFormattedCitation":"[29]","previouslyFormattedCitation":"[29]"},"properties":{"noteIndex":0},"schema":""}[29]. The paper proposed a driver for ZVS of the SiC MOSFETs and a test bench to define module losses. The experimental measurements on the test-bench included turn-off energy losses for both SiC modules (based on which the simulation model was designed). In the last section of the paper a 9kV/1.5kV ISOP PETT configuration was also presented, consisting of 6x360?kW modules. The obtained efficiency, based on simulations, was between 98.8% and 99.3%, depending on converter operation mode (Continuous Conduction Mode – CCM or Discontinuous Conduction Mode – DCM) and module output power. The study validated the efficiency of soft switching over hard switching in the case of the proposed configuration and the ZVS capabilities of the presented gate driver.As a summary, SiC semiconductors offers higher efficiency, better thermal characteristics and higher switching speeds with lower losses, all of these useful for MVDC-ERS traction. They can be already used for the tractions systems of light rail vehicles, and the future development of the technology will make them increasingly attractive also for other types of trains.ConclusionWhile PET-based systems are more expensive than traditional LFT-based systems due to the large number of high-voltage power devices and advanced cores used in MFTs, they have a number of attracting advantages. Firstly, the improved efficiency and power quality, secondly a redundant design, which improves availability, and thirdly the increased power density. However, the large number of components, reduces their reliability in some cases and requires complicated design and control strategies. For MVDC traction, LFT-based systems are not even an option, as the need of two converters and the possibility of choosing the intermediate AC frequency will certainly lead to MFTs for the higher achievable power density. Regarding the pros and cons of PET-based systems discussed, it is important to notice that the benefits are evident, while most drawbacks are technologies and materials dependent. A further development of power devices and materials, as well as investigation of topologies and control methods will probably mitigate most of the drawbacks.MVDC-ERS presents a concept of a new DC railway electrification system, based on the new technology that makes possible its implementation. Such a novel system will open new opportunities and functionalities of an interoperable smart DC grid. At the same time the new system will combine the advantages of various new technology and the advantages of current ERSs. The on-board PETTs will have to be redefined also for the new system and its needs. ReferencesADDIN Mendeley Bibliography CSL_BIBLIOGRAPHY [1]P. M. Kalla-Bishop, Future Railways and Guided Transport. 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