Spec Notes



POWER ELECTRONICSQUISTION BANK FOR MID - IS. NoQuestionMARKSCourse OutcomeBloomsTaxonomy LevelP.IUNIT -1POWER SEMI CONDUCTOR DEVICES & COMMUTATION CIRCUITS 1Differentiate power diode and signal diode?2 MC322.1Understand2.2.42Define latching current & holding current of a SCR.2 MC322.1Remember2.2.23Design Snubber circuit and write its operation5 MC322.1Create3.1.64Explain different methods to turn on the thyristor?3 MC322.1Understand2.2.25Define Thyristor turn off time and circuit turn off time.3 MC322.1Remember2.2.26Describe why circuit turn off time should be greater than the device turn-off time?5 MC322.1Remember2.3.27Illustrate the turn-on characteristics of SCR and mark the timings td, tr, ton5 MC322.1Analyze4.1.18List the factors that influence the turn-off time of a thyristor?2 MC322.1Remember2.2.29Sketch the V-I characteristics of SCR and mark the holding current and latching current in the characteristics.3 MC322.1Apply1.3.110Define string efficiency of SCRs connected in series.2 MC322.1Remember3.3.111Discuss why is pulse triggering preferred over RC triggering?5 MC322.1Remember2.2.412Categorize the different methods of firing circuits for forced commutated converter?2 MC322.2Analyze2.3.213Define commutation? What are the types of commutation?5 MC322.2Understand2.2.214 Compare natural commutation & forced commutation?3 MC322.2Understand2.2.415List the various forced commutation techniques used to turn off SCR.3 MC322.2Remember2.2.2UNIT – IIAC-DC CONVERTERS (1-PHASE & 3-PHASE CONTROLLED RECTIFIERS)1Construct phase controlled rectifier?5 MC322.3Create2.2.22Name some of the applications of phase controlled rectifier.2 MC322.3Remember4.1.13 Estimate the importance of freewheeling diode in phase controlled rectifier?3 MC322.3Evaluate2.3.24List the advantages of freewheeling diodes in a controlled in aControlled rectifier?2 MC322.3Remember1.3.15Define delay angle?2 MC322.3Remember2.2.26Design a single phase full wave mid-point converter with R-load and sketch he output waveforms with respect to supply voltages3 MC322.3Analyze2.3.17Define commutation angle or overlap angle?2 MC322.3Remember2.2.28 Illustrate the operation of a single phase half wave converter for R- load with neat circuit diagram and necessary waveforms.5MC322.3Apply2.3.29 Determine an expression for average voltage of single phase semi converters.3 MC322.3Apply2.4.410Describe the effect of the source inductance in full converter.2 MC322.3Understand1.3.111 Analyze the operation of three phase fully controlled bridge converter with RL loads.5MC322.3Analyze2.3.212Determine an expression for average voltage of single phase Full Converter with R load5 MC322.3Apply1.3.113 Analyze the operation of dual converter with neat sketch.5MC322.3Analyze2.3.214A single phase fully controlled converter is supplied at 220V, 50Hz. Determine the average load voltage when the firing angle is 450 for purely resistive load.5 MC322.3Evaluate3.1.615Explain six pulse converter? Write its advantages.5 MC322.3Understand2.2.216Sketch the four quadrants in which the dual converter operates?2 MC322.3Remember2.2.217Differences between non-circulating current mode & circulating current node of a dual converter.3 MC322.3Understand2.2.418Show the relation between the firing angles of two converters in a dualConverter.3 MC322.3Remember1.3.1UNIT-IIIAC-AC CONVERTERS (AC VOLTAGE CONTROLLERS)1Tell about ac voltage controller?2 MC322.4Remember2.2.22Define sequence control of ac voltage regulators?2 MC322.4Remember2.2.23Classify methods of control in ac voltage controllers?3 MC322.4Evaluate2.2.44 Describe What are the effects of load inductances on the performance of AC voltage controllers?5 MC322.4Understand1.3.15Show the applications of TRIAC2 MC322.4Apply3.1.16Compare between AC Voltage Controller and Cycloconverter?3 MC322.4Evaluate2.2.47An ac voltage controller uses a TRIAC for phase angle control of a resistive load of 100?. Calculate the value of delay angle for having an rms load voltage of 220 volts. Also calculate the rms value of TRIAC current. Assume the rms supply voltage to be 230V.5MC322.5Evaluate2.2.38A single phase full-wave AC voltage controller feeds a load of R=20Ω with an input voltage of 230V, 50Hz. Firing angle for both the thyristors is 45o. Calculaterms value of output voltageLoad power and input pfAverage and rms current of thyristors..5MC322.5Evaluate2.2.3POWER ELECTRONICSBIT BANK FOR MID – IUNIT – I1. A thyristor (SCR) is a [ c ]a) P-N-P deviceb) N-P-N devicec) P-N-P-N deviced) P-N device2. Which terminal does not belong to the SCR? [ c ]a) Anodeb) Gatec) Based) Cathode3. An SCR is a [b ]a) four layer, four junction deviceb) four layer, three junction devicec) four layer, two junction deviced) three layer, single junction device4. Choose the false statement. [a ]a) SCR is a bidirectional deviceb) SCR is a controlled devicec) In SCR the gate is the controlling terminald) SCR are used for high-power applications5. In the SCR structure the gate terminal is located [ b ]a) near the anode terminalb) near the cathode terminalc) in between the anode & cathode terminald) none of the mentioned6. The static V-I curve for the SCR is plotted for [ b ]a) Ia (anode current) vs Ig (gate current), Va (anode – cathode voltage) as a parameterb) Ia vs Va with Ig as a parameterc) Va vs Ig with Ia as a parameterd) Ig vs Vg with Ia as a parameter7. If the cathode of an SCR is made positive with respect to the anode & no gate current is applied then [c]a) all the junctions are reversed biasedb) all the junctions are forward biasedc) only the middle junction is forward biasedd) only the middle junction is reversed biased8. For an SCR in the reverse blocking mode, (practically) [a]a) leakage current does not flowb) leakage current flows from anode to cathodec) leakage current flows from cathode to anoded) leakage current flows from gate to anode9. With the anode positive with respect to the cathode & the gate circuit open, the SCR is said to be in the [ c ]a) reverse blocking modeb) reverse conduction modec) forward blocking moded) forward conduction mode10. For an SCR in the forward blocking mode (practically) [ b ]a) leakage current does not flowb) leakage current flows from anode to cathodec) leakage current flows from cathode to anoded) leakage current flows from gate to anode11.The value of anode current required to maintain the conduction of an SCR even though the gate signal is removed is called as the [ b ]a) holding currentb) latching currentc) switching currentd) peak anode current12. In the reverse blocking mode the middle junction (J2) has the characteristics of that of a [ b ]a) transistorb) capacitorc) inductord) none of the mentioned13. ________ are semiconductor thyristor devices which can be turned-on by light of appropriate wavelengths. [ d ]a) LGTOsb) LASERsc) MASERsd) LASCRs14.The MOSFET combines the areas of _______ & _________ [ a ]a) field effect & MOS technologyb) semiconductor & TTLc) mos technology & CMOS technologyd) none of the mentioned15. Which of the following terminals does not belong to the MOSFET? [ c ]a) Drainb) Gatec) Based) Source16. Choose the correct statement [ b ]a) MOSFET is a uncontrolled deviceb) MOSFET is a voltage controlled devicec) MOSFET is a current controlled deviced) MOSFET is a temperature controlled device17. Choose the correct statement(s) [ c ]i) The gate circuit impedance of MOSFET is higher than that of a BJTii) The gate circuit impedance of MOSFET is lower than that of a BJTiii) The MOSFET has higher switching losses than that of a BJTiv) The MOSFET has lower switching losses than that of a BJTa) Both i & iib) Both ii & ivc) Both i & ivd) Only ii18. Choose the correct statement [ c ]a) MOSFET is a unipolar, voltage controlled, two terminal deviceb) MOSFET is a bipolar, current controlled, three terminal devicec) MOSFET is a unipolar, voltage controlled, three terminal deviced) MOSFET is a bipolar, current controlled, two terminal device19. The arrow on the symbol of MOSFET indicates [ b ]a) that it is a N-channel MOSFETb) the direction of electronsc) the direction of conventional current flowd) that it is a P-channel MOSFET20. The controlling parameter in MOSFET is [ b ]a) Vdsb) Igc) Vgsd) Is21. In the internal structure of a MOSFET, a parasitic BJT exists between the [ b ]a) source & gate terminalsb) source & drain terminalsc) drain & gate terminalsd) there is no parasitic BJT in MOSFET22. In the transfer characteristics of a MOSFET, the threshold voltage is the measure of the [ a ]a) minimum voltage to induce a n-channel/p-channel for conductionb) minimum voltage till which temperature is constantc) minimum voltage to turn off the deviced) none of the above mentioned is true23.The output characteristics of a MOSFET, is a plot of [ b ]a) Id as a function of Vgs with Vds as a parameterb) Id as a function of Vds with Vgs as a parameterc) Ig as a function of Vgs with Vds as a parameterd) Ig as a function of Vds with Vgs as a parameter24.IGBT possess [ b ]a) low input impedanceb) high input impedancec) high on-state resistanced) second breakdown problems25. IGBT & BJT both posses ___ [ a ]a) low on-state power lossesb) high on-state power lossesc) low switching lossesd) high input impedance26 The three terminals of the IGBT are [ c ]a) base, emitter & collectorb) gate, source & drainc) gate, emitter & collectord) base, source & drain27. In IGBT, the p+?layer connected to the collector terminal is called as the [b ]a) drift layerb) injection layerc) body layerd) collector Layer28. The controlling parameter in IGBT is the [ b ]a) IGb) VGEc) ICd) VCE29. In IGBT, the n–?layer above the p+?layer is called as the [ a ]a) drift layerb) injection layerc) body layerd) collector Layer30. The voltage blocking capability of the IGBT is determined by the [d ]a) injection layerb) body layerc) metal used for the contactsd) drift layer31. The controlled parameter in IGBT is the [ c ]a) IGb) VGEc) ICd) VCE32. The structure of the IGBT is a [ c]a) P-N-P structure connected by a MOS gateb) N-N-P-P structure connected by a MOS gatec) P-N-P-N structure connected by a MOS gated) N-P-N-P structure connected by a MOS gate33. The major drawback of the first generation IGBTs was that, they had [ d ]a) latch-up problemsb) noise & secondary breakdown problemsc) sluggish operationd) latch-up & secondary breakdown problemsFill in the Blanks1. Silicon has ________________ leakage current. (less)2. Latching Current varying from ___________ to ______________. (1.5 to 2 times)3.dv/dt protection of SCR also known as _______________ method (Snubber circuit)4. Hot spot is ____________process (cumulative)5. Mostly we are using _________________ type MOSFET ( N type enhancement)6. Emitter direction depends up on the _______________ (direction of current)7. Intrinsic stand off ratio range_________________ (0.75 to 0.85)8. UJT turn off at ________________ ( Vin<VDD+ η VBB)9. UJT turn on at _______________ ( Vin >VDD + η VBB)10.UJT has a_______________________ oscillator (relaxation oscillator)11. The range of firing angle =______ (0-90?)12.Natural __________ technique used for turn off the SCR (commutation)13.Units of time constant _______ (seconds)14. Relaxation means ___________ (the time required to UJT conducts Off to ON state)15.Time constant at discharging the UJT ___ ( τ = R1C)16.UJT is _________ bridge rectifier because absence of gate terminal.(uncontrolled)17. Semiconductor device having negligible _____________losses.(switching)18.By making forward blocking and reverse blocking voltages equal for all the SCR’s is called________(Equalization).19.String efficiency equal to____________( Vs /n*Vd )20.Derating factor D=___________ (1- η)21.Series connection of (Rs)max ≤ _________. ( n VD - VS /(n-1) ?Ib max ) 22.Series connection of SCR, The value of (C)MIN ≥ ________________.[ (n-1)?QMAX / n VD – VS]23.Power across SCR =_________. (VD ? /R).24. The self distruction of unstabilized semi conductor device is called as____________. (Thermal runaway)25.Bringing the anode current is less then holding current is _______________. (Commutation)26.Natural commutation occurs at _____________.(AC supply)27.Forced commutation occurs at ______________.(DC supply)28. Voltage commutation is also known as ______________ ( impulse commutation)29. _______________ condition of class E commutation ( Ig- Ip < Ih)30. IGBT means _____________( insulated gate bi polar transistor)31. Transfer characteristics of IGBT plot between _______________parameters (Vge (Vs) Ic)32. Input terminals of IGBT ___________, ____________, and________. ( Gate , Emitter, Collector)33. combination of _________________ and _______________ forms IGBT ( MOSFET, BJT)34. SCR is a ________________ controlled device ( current)35. What are the terminals of MOSFET ________ ,______________, ____________ (drain , source, gate )36. GTO stands for ______________ ( Gate Turn off Thyrister)37. _________________ have less ON state voltage drop ( SCR)38. Reverse voltage applying across gate should be ______________ of anode voltage (1/3 to 1/5)39. UJT stands ________________ ( Uni Junction transistor)40. Power MOSFET is ____________ (voltage controlled device)41. Symbol of IGBT _______________42.Symbol of GTO__________________________43. Symbol of SCR ______________________44 Symbol of BJT _______________________45. Symbol of MOSFET _________________UNIT – II1. A voltage source Vs = Vm sinωt is connected in series with a resistance R and an SCR. At some firing angle delay of α a positive gate pulse is applied to the SCR which turns on the SCR. Considering ideal conditions, at the instant α the voltage at the resistor terminals Vo [c ]a) falls to zerob) falls to –Vm sin αc) rises to Vm sin αd) rises to Vm sin ωt2. The average output voltage is maximum when SCR is triggered at ωt = [b ]a) πb) 0c) π/2d) π/43.In the method of phase control, the phase relationship between ___ & ___ is controlled by varying the firing angle [ c ]a) supply current, supply voltageb) end of the load current, end of the load voltagec) start of the load current, start of the load voltaged) load current, load voltage4. In a single phase half-wave thyristor circuit with R load & Vs=Vm sinωt, the maximum value of the load current can be given by [ c ]a) 2Vm/Rb) Vs/Rc) Vm/2d) Vs/2?5.For a single phase thyristor circuit with R load & firing angle α, the conduction angle can be given by [ c ]a) π+αb) 2π+αc) π-αd) α6.A single-phase half-wave thyristor circuit with R load is triggered at an angle of α = 0°. As such, the maximum value of the average output voltage would be given by [ c ]Consider Vs = Vm sinωt.a) Vmb) 2Vm/πc) Vm/πd) Vm/α7.?single-phase full converter B-2 type connection has a RLE type of motor load connected. The minimum requirement to turn-on the device is [ b ]a) α > 30°b) Vm sinα > Ec) Vm sinα < Ed) α < 30°8.A single-phase full converter with B-2 type of connection has a continuous load current waveform. The thyristor pairs T3, T4 is triggered at ωt = [ c ]a) 0b) αc) π+αd) π-α9.The PIV for each diode in a single-phase, full converter with B-2 type of controlled rectifier isConsider supply voltage as Vs = Vm sinωt. [ b ]a) 2Vmb) Vmc) Vm/2d) Vm/√210.A single phase full converter, feeds power to a RLE load with R = 6 ? and E = 60 V. The supply voltage is 230 V AC and the firing angle is 50°. Find the power delivered to the battery. [ d ]a) 542 Wb) 100 Wc) 960 Wd) 730 W11. In a single phase full converter with resistive load and firing angle α, the load current is [ c ]a) zero at α, π+α, …b) remains zero for duration αc) Vm/R sinα at α, π+α, …d) remains zero for duration π-α12. In a single phase semi converter with resistive load and a firing angle α, each SCR and freewheeling diode would conduct for [ d ]a) α, 0°b) π-α, αc) π+α, αd) π-α, 0°13.. A single phase full converter has average & peak voltage values of 133 V and 325 V respectively. Find the value of the firing angle. [ c ]a) 40°b) 140°c) 50°d) 130°14. A freewheeling diode placed across a RL load provides [d ]a) fast turn-on timeb) slow turn-off timec) poor utilization factord) better power factor15. A single phase full converter has discontinues load current. The converter is supplying a dc shunt motor (R-L-E) load. When the current falls to zero the output voltage is [ d ]a) Zerob) Voc) Vmd) E16.?If in the below given converter configuration, any 3 of the 4 SCRs are replaced by diodes [a ]a) the average output voltage would increaseb) the average output voltage would decreasec) the average output voltage would not changed) the circuit would malfunction17.A single-phase symmetrical semi-converter employs [ a ]a) one SCR and one diode in each legb) two SCRs and two diodes in each legc) two SCRs in each legd) two diodes in each leg18. A single-phase asymmetrical semi-converter employs [ b ]a) one SCR and one diode in each legb) two SCRs in one leg and two diodes in the otherc) two SCRs in both the legsd) two diodes in both the legs19.?In any AC-DC circuit, the freewheeling action [ c ]a) improves the power handling capabilitiesb) increases the THDc) improves CDFd) all of the mentioned20.For the same triggering angle and ratings [ b ]a) a semi-converter operates at lower output voltage than a full converterb) a semi-converter operates at higher output voltage than a full converterc) a semi-converter has lower values of input p.f as compared to a full converterd) a semi-converter has more THD as compared to a full converter?21.A. three-phase, three-pulse, M-3 type controlled converter uses ____________ number of SCRs. [c ]a) 1b) 2c) 3d) 422. A three-phase, three-pulse, M-3 type controlled converter has firing angle for one of the SCRs set as 15°. This SCR would start conducting at [ d ]a) 0°b) 15°c) 30°d) 45°23. In a three-phase, three-pulse, M-3 type controlled converter T1 starts to conduct at 30 + n°. At what angles do T2 and T3 start to conduct? Assume that the conduction sequence is T1-T2-T3. [ b ]a) 2n° and 3n°b) 150 + n° and 270 + n°c) n° eachd) 30 + n° and 60 + n°24. A three-phase three pulse type controlled converter is constructed using 3 SCR devices. The circuit is supplying an R load with α < 30°. As such, each SCR device would conduct for [ b ]a) 60° each cycleb) 120° each cyclec) 180° each cycled) 360° each cycle25. Dual converters provide _______ [ c ]a) two quadrant operationb) three quadrant operationc) four quadrant operation26. A dual converters has _____________ [ c ]a) two full converters in seriesb) two half converters in seriesc) two full converters in anti-paralleld) two half converters in anti-parallelFill in the Blanks1.A freewheeling diode placed across a RL load provides __________________ (Better Power Factor )2.The PIV for each diode in a single-phase, full converter with B-2 type of controlled rectifier isConsider supply voltage as Vs = Vm sinωt. ____________ ( Vm )3. A. three-phase, three-pulse, M-3 type controlled converter uses ____________ number of SCRs ( 3 )4. In any AC-DC circuit, the freewheeling action _____________________ ( Improve CDF )5. Dual converters provide ________________ ( Four Quadrant Operation )6. A dual converters has _____________ (Two full converters in Anti – parallel )7. The major advantage of using dual converters is _____________ ( No mechanical switch is required to change the mode )8. The four quadrant operation of dual converters can be obtained by _____________ ( Changing the firing angle value )9.A single-phase semi-converter is having continuous conduction, as such each thyristor will conduct for an angle of _______________ ( π – α )10.The overlap angle of a phase controlled converter will increase ___________ ( If the firing angle is increased )11. All the modern AC-DC converters are using GTOs instead of SCRs because ______________ (GTO has reliable Commutation ) 12. Find the average output dc voltage of a single-phase semi-converter with Vs=230 V and firing angle of 30°. The converter is operating under continuous conduction. _____________ ( 193 V )UNIT – III1.Dual converters provide [ c ]a) two quadrant operationb) three quadrant operationc) four quadrant operationd) none of the mentioned2. A dual converters has [ c ]a) two full converters in seriesb) two half converters in seriesc) two full converters in anti-paralleld) two half converters in anti-parallel3. The major advantage of using dual converters is that [ c ]a) it is cheaply availableb) it has better pfc) no mechanical switch is required to change the mode of operationd) its operating frequency is very high4. The four quadrant operation of dual converters can be obtained by [ c ]a) moving the mechanical leverb) adding inductance to the circuitc) changing the firing angle valued) none of the mentioned5.?In the integral cycle control method of ac voltage controller [a ]a) the average power delivered to the load is controlledb) the instantaneous power delivered to the load is controlledc) the frequency of output voltage is controlledd) none of the mentioned6. In the integral cycle control of ac voltage controller, is the load is on for n cycles and off for m cycles, then the periodicity is given by? Consider the output is sinusoidal. [ b ]a) m/2π(m+n)b) n/2π(m+n)c) m/π(m+n)d) n/π(m+n)View Answer7. If k is the duty cycles of the controller, then the rms value of the output voltage in case of a integral cycle control circuit will be?Consider the input to be sinusoidal with peak value Vm and rms value Vs. [ c ]a) Vs x kb) Vs/kc) Vs x √kd) Vs8.Pulse gating is suitable for [ a ]a) R loads onlyb) R and RL loadsc) RL loads onlyd) all types of loads9. In continues gating [ b ]a) overlap angle is very hi9hb) SCR is heated upc) size of the pulse transformer is smalld) commutation cannot be achieved effectively10. High frequency gating uses a [ a ]a) train of pulsesb) continuous gating blockc) carrier signald) none of the aboveFill in the Blanks1. AC voltage controllers convert ___________________ ( Fixed AC to Variable AC)2. In AC voltage controllers the _____________ ( Variable AC with fixed Frequency can be obtained )3. Earlier then the semiconductor technology, ___________ devices were used for voltage control applications. (Tap Changing Transformers )4. The AC voltage controllers are used in __________ applications. ( Electric Heating)5. Control is achieved by adjusting ____________________ is in the principle of phase control. ( the firing angle of the devices )6. A single-phase half wave voltage controller consists of ______________ ( One SCR is anti-parallel with one Diode ) ................
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