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DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

ISO/WI NO: 41-REV: 1/EFFECTIVE DATE: 06/01/11

POWER ELECTRONICS LABORATORY

LAB MANUAL

B.E (MECHATRONICS) -1V SEMESTER

Prepared by: Edited by,

P. Rajasekaran M.E (Ph.D) Dr.N.Veerappan M.E,Ph.D. S.Anu.,M.E HOD - EEE

PREFACE

This Laboratory manual in Power electronics lab has been revised in order to be up to date with Curriculum changes, laboratory equipment upgrading.

This Laboratory provides ample opportunity for a good understanding of the power electronic components and to study the salient features of power diodes, power transistors and other members of thyristor family. This Laboratory also provides hands on understanding the use of semiconductor devices in the industrial applications in the field of Electrical, Electronics, Instrumentation and Control Engineering and the use of Power-electronic components in low as well as high power application.

Every effort has been made to correct all the known errors, if you find any additional errors or anything else you think is an error, please inform the HOD/EEE at eeedept@avit.ac.in.

The Authors thank all the staff members from the department for their valuable Suggestions and contributions.

The Authors

Department of EEE

INDEX

TABLE OF CONTENTS

|S.No |Experiment Name |Page no |

| |SCR, MOSFET & IGBT Characteristics - Study. | |

| |SCR half & fully controlled bridge rectifiers | |

| |UJT, R, RC Firing circuits for SCR. | |

| |SCR series inverter. | |

| |SCR DC Voltage Commutated chopper. | |

| |SCR DC Current Commutated chopper | |

| |Resonant dc-dc Converter buck regulator with ZCS | |

| |IGBT chopper | |

| |Single-phase cycloconvertor | |

| |Speed control of DC shunt motor using converter | |

| |Three phase fully controlled converter | |

| |IGBT based – Single phase PWM inverter | |

GUIDELINES FOR LABORATORY NOTEBOOK

The laboratory notebook is a record of all work pertaining to the experiment. This record should be sufficiently complete so that you or anyone else of similar technical background can duplicate the experiment and data by simply following your laboratory notebook. Record everything directly into the notebook during the experiment. Do not use scratch paper for recording data. Do not trust your memory to fill in the details at a later time.

Organization in your notebook is important. Descriptive headings should be used to separate and identify the various parts of the experiment. Record data in chronological order. A neat, organized and complete record of an experiment is just as important as the experimental work.

1. Heading:

The experiment identification (number) should be at the top of each page.

2. Objective:

A brief but complete statement of what you intend to find out or verify in the experiment should be at the beginning of each experiment

3. Diagram:

A circuit diagram should be drawn and labeled so that the actual experiment circuitry could be easily duplicated at any time in the future. Be especially careful to record all circuit changes made during the experiment.

4. Equipment List:

List those items of equipment which have a direct effect on the accuracy of the data. It may be necessary later to locate specific items of equipment for rechecks if discrepancies develop in the results.

5. Procedure:

In general, lengthy explanations of procedures are unnecessary. Be brief. Short commentaries along side the corresponding data may be used. Keep in mind the fact that the experiment must be reproducible from the information given in your notebook.

6. Data:

Think carefully about what data is required and prepare suitable data tables. Record instrument readings directly. Do not use calculated results in place of direct data; however, calculated results may be recorded in the same table with the direct data. Data tables should be clearly identified and each data column labeled and headed by the proper units of measure.

7. Calculations:

Not always necessary but equations and sample calculations are often given to illustrate the treatment of the experimental data in obtaining the results.

8. Graphs:

Graphs are used to present large amounts of data in a concise visual form. Data to be presented in graphical form should be plotted in the laboratory so that any questionable data points can be checked while the experiment is still set up. The grid lines in the notebook can be used for most graphs. If special graph paper is required, affix the graph permanently into the notebook. Give all graphs a short descriptive title. Label and scale the axes. Use units of measure. Label each curve if more than one on a graph sheet.

9. Results:

The results should be presented in a form which makes the interpretation easy. Large amounts of numerical results are generally presented in graphical form. Tables are generally used for small amounts of results. Theoretical and experimental results should be on the same graph or arrange in the same table in a way for easy correlation of these results.

10. Conclusion:

This is your interpretation of the results of the experiment as an engineer. Be brief and specific. Give reasons for important discrepancies.

LABORATORY SAFETY INFORMATION

Introduction

The danger of injury or death from electrical shock, fire, or explosion is present while conducting experiments in this laboratory. To work safely, it is important that you understand the prudent practices necessary to minimize the risks and what to do if there is an accident.

Electrical Shock

Avoid contact with conductors in energized electrical circuits. Electrocution has been reported at dc voltages as low as 42 volts. Just 100ma of current passing through the chest is usually fatal. Muscle contractions can prevent the person from moving away while being electrocuted.

Do not touch someone who is being shocked while still in contact with the electrical conductor or you may also be electrocuted. Instead, press the Emergency Disconnect . This shuts off all power, except the lights.

Make sure your hands are dry. The resistance of dry, unbroken skin is relatively high and thus reduces the risk of shock. Skin that is broken, wet or damp with sweat has a low resistance.

When working with an energized circuit, work with only your right hand, keeping your left hand away from all conductive material. This reduces the likelihood of an accident that results in current passing through your heart.

Be cautious of rings, watches, and necklaces. Skin beneath a ring or watch is damp, lowering the skin resistance. Shoes covering the feet are much safer than sandals.

If the victim isn't breathing, find someone certified in CPR. Be quick! If the victim is unconscious or needs an ambulance, contact the Department Office for help.

Fire

Transistors and other components can become extremely hot and cause severe burns if touched. If resistors or other components on your proto-board catch fire, turn off the power supply and notify the instructor. If electronic instruments catch fire, disconnect the power supply immediately. These small electrical fires extinguish quickly after the power is shut off. Avoid using fire extinguishers on electronic instruments.

Explosion

When using electrolytic capacitors, be careful to observe proper polarity and do not exceed the voltage rating. Electrolytic capacitors can explode and cause injury. A first aid kit is located on the wall near the door. Proceed to Student Health Services, if needed.

CIRCUIT DIAGRAM: CHARACTERISTICS OF SCR

[pic]

BASE DIAGRAM OF TY604

EXPT.NO:

DATE:

SCR, MOSFET & IGBT CHARACTERISTICS

SCR CHARACTERISTICS

AIM:

To study the V-I characteristics of S.C.R. and determine the Break over Voltage, Holding current & Latching current

APPARATUS REQUIRED:

| | | | |

|Sl.No. |NAME OF THE COMPONENTS |RANGE |QUANTITY |

|1 |SCR – TYN604 | | |

|2 | Power Supplies | | |

|3 | Wattage Resistors | | |

|4 |Ammeter | | |

|5 |Voltmeter | | |

|6 | Bread Board & Connecting Wires | |As required |

OBSERVATION TABLE:

Static V-I Characteristics of SCR

|Serial. |Anode to cathode |Anode current (Ia) |

|No. |voltage(Vak) |(Ampere) |

| |(Volt) | |

| | | |

| | | |

| | | |

| | | |

| | | |

|Serial. |Anode to cathode |Anode current (Ia) |

|No. |voltage(Vak) |(Ampere) |

| |(Volt) | |

| | | |

| | | |

| | | |

| | | |

| | | |

For Ig2 = ----- = Constant

For Ig1 = ----- = Constant

MODEL GRAPH

THEORY:

Silicon Controlled Rectifier (SCR): Thyristor (generally known as SCR) is a four layer, three junction, pnpn semiconductor switching device. It has three terminals; anode, cathode and gate. Basically, a thyristor consists of four layers of alternate p-type and n-type silicon semiconductors forming three junctions J1,J2 and J3. A gate terminal is usually kept near the cathode terminal. The terminal connected to outer p region is called anode (A), the terminated connected to outer n region is called cathode and that connected to inner p region is called the gate (G). The symbol of SCR is shown in figure.

A circuit diagram for obtaining static V-I characteristics of a thyristor is shown in Fig . The anode and cathode are connected to main source through the load. The gate and cathode are fed from a source Vs which gives positive gate current from gate to cathode. Fig , shows static V-I characteristics of a thyristor. Va is the anode voltage across thyristor terminals A, K and Ia is the anode current. Fig reveals that a thyristor has three basic modes of operation; namely, reverse blocking mode, forward blocking (off-state) mode and forward conduction (on-state) mode. These three modes of operation are now discussed below.

(A). When cathode is made positive with respect to anode with gate open, thyristor is reverse biased. Junctions J1, J3 are reverse biased whereas junction J2 is forward biased.

The device behaves like two diodes connected in series with reverse voltage appearing across them. A small leakage current of the order of a few mill amperes or few microamperes flows depending upon the SCR rating.. This is reverse blocking mode, called the off state of the SCR. If the reverse voltage is increase, then at a critical breakdown level, called reverse breakdown voltage VBR, an avalanche occurs at J1 and J3 and the reverse current increases rapidly. A large current associated with VBB gives rise to more losses in the thyristor. This may lead to thyristor damage as the junction temperature may exceed its permissible temperature rise. It should, therefore, be ensured that maximum working reverse voltage across a SCR does not exceed VBR.

(b). forward blocking mode: When anode is positive with respect to the cathode with gate circuit open, SCR is said to be forward biased. During this mode, junctions J1, J3 are forward biased but junction J2 is reverse biased. In this mode, a small current, called forward leakage current, flows.

In case the forward voltage is increased, ten the reverse biased junction J2 will have an avalanche breakdown at a voltage called forward break over voltage VBO. When forward voltage is less than VBO, thyristor offers high impedance. Therefore, a SCR can be treated as an open switch even in the forward blocking mode.

(c). Forward conduction mode: In this mode, SCR conducts currents from anode to cathode with a very small voltage drop across it. A SCR is brought from forward blocking mode to forward conduction mode by turning it on by exceeding the forward break over voltage or by applying a gate pulse between gate and cathode. In this mode, SCR is on state and behaves like a closed switch. Voltage drop across thyristor in the on state is of the order of 1 to 2V depending on the rating of thyristor. This voltage drop increases slightly with an increase in anode current.

In conduction mode, anode current is limited by load impedance alone as voltage drop across thyristor is quite small. This small voltage drop VT across the device is due ohmic drop in the four layers.

SPECIFIC TERMINOLOGY

Break over Current (IBO) − Principal current at the break over point

Break over Voltage (VBO) − Principal voltage at the break over point

Gate Trigger Current (IGT) − Minimum gate current required to maintain the SCR in

the on state

Holding Current (IH) − Minimum principal current required to maintain the SCR in

the on state

Latching Current (IL) − Minimum principal current required to maintain the SCR in the on state immediately after the switching from off state to on state has occurred and the triggering signal has been removed

On-state Voltage (VT) − Principal voltage when the SCR is in the on state

Gate Trigger Voltage (VGT) − Gate voltage required to produce the gate trigger current

On-state Current (IT) − Principal current when the SCR is in the on state

PROCEDURE:

Static V-I Characteristics of SCR

1. Connections as made as per the circuit diagram

2. Connect millimeter across G-K, across the thyristor (anode and cathode),

Across the supply terminals Vs to measure gate voltage Vg, Va and Vs.

(All in dc mode). An ammeter of the range (0-50) mA is connected to

Measure the load current Il.

3. Keep initially the gate potential Vg at very low value say around 0.4 Volts.

Vary the supply voltage Vs in steps and note whether ammeter shows any

Reading. For every step of Vs note the ammeter reading. Also note corresponding readings of Va respectively.

4. If the ammeter doesn’t indicate any reading, increase the gate potential Vg to

Some higher value says around 0.6 Volts & follows the procedure given in step

No. (3).

5. Further increase the gate potential to some higher values and repeat the

Procedure followed in step no. (3).

6. Tabulate the readings in the observation column.

7. Finally a graph is drawn between anode current (Ia = Il = load current)

And the device voltage Va respectively.

RESULT:

Thus the V-I characteristics of S.C.R. and the Break over Voltage, Holding current. & latching current has been determined.

QUESTIONS:

1. Explain the working operation of VI characteristics of S.C.R.

2. Define Holding current, Latching current, Break down voltage.

3. Explain the working operation of S.C.R. characteristics by using two transistors

Analogy.

4. What is meant by forward leakage current?

5. Mention the applications of S.C.R.

CIRCUIT DIAGRAM: CHARACTERISTICS OF MOSFET

MOSFET CHARACTERISTICS

AIM:

To obtain the steady state output side characteristics of the given MOSFET, for a specified value of gate source voltage

APPARATUS REQUIRED:

| | | | |

|Sl.No. |NAME OF THE COMPONENTS |RANGE |QUANTITY |

|1 |MOSFET-IRF740 | | |

|2 | Power Supplies | | |

|3 | Wattage Resistors | | |

|4 |Ammeter | | |

|5 |Voltmeter | | |

|6 | Bread Board | | |

|7 |Connecting Wires | | |

OBSERVATION TABLE:

FOR MOSFET

For VGS = -----, ------, ------, ------ = Constant

|Serial No. |Collector to emitter |Drain current (ID) |

| |voltage (VCE) (Volt) |(Ampere) |

| | | |

| | | |

| | | |

MODEL GRAPH:

MOSFET

[pic]

THEORY:

METALOXIDE SEMICONDUCTOR FIELD EFFECT TRANSISTOR (MOSFET): The circuit diagram to obtain the output characteristics is shown in figure power MOSFET is a voltage controlled device because the output current (drain current) can be controlled by gate source voltage (VGS).

The power MOSFET has three terminals called D, source S and gate G. The symbol of power MOSFET is shown in Fig. Here the arrow direction indicates the direction of electrons flow. Power MOSFET is unipolar device because its operation depends upon the flow of majority carrier’s only. It has very high input impedance, in the order of 109 ohm. The gate draws a very small leakage current, in the order of nano amperes. MOSFETs do not have problems of secondary breakdown. However, MOSFETs have the problems of electrostatic discharge and require special care in handling. In addition, it is very difficult to protect them under short – circuited fault conditions. Power MOSFETs are finding increasing applications in low power high frequency converters. The V I characteristics of MOSFET is shown in figure.

PROCEDURE:

Static V-I Characteristics of MOSFET

1. Connections as made as per the circuit diagram.

2. Connect Multimeter across G-K, across the MOSFET (source & drain) &

across the supply terminals Vs to measure gate voltage Vg, VDS , and Vs.

(all in dc mode) An ammeter of the range (0-50) mA is connected to

ensure the load current Il (drain current ID).

3. Keep initially the gate potential Vg at very low value. Vary the supply voltage Vs in steps and note whether ammeter shows any reading. For every step of Vs note the ammeter reading. Also note corresponding readings of VDS respectively.

4. If the ammeter doesn’t indicate any reading, increase the gate potential Vg to

some higher value & follow the procedure given in step no. (3).

CIRCUIT DIAGRAM: IGBT CHARACTERISTICS

5. Further increase the gate potential to some higher values and repeat the

Procedure followed in step no. (3).

6. Tabulate the readings in the observation column.

7. Finally a graph is drawn between load current (ID) and the device voltage

VDS respectively.

RESULT:

Thus the steady state output side characteristics of the given MOSFET, for a specified value of gate source voltage has been obtained.

QUESTIONS:

1. What is power MOSFET?

2. What are the applications of power MOSFET?

3. Compare MOSFET & BJT?

4. Compare MOSFET and BJT

5. Explain o/p & transfer characteristics of MOSFET

OBSERVATION TABLE:

FOR IGBT:

For VB = -----, ------, ------, ------ = Constant

|Serial No. |Source to Drain voltage |Drain current (ID) |

| |(VDS) (Volt) |(Ampere) |

| | | |

| | | |

| | | |

| | | |

| | | |

MODEL GRAPH:

IGBT

[pic]

IGBT CHARACTERISTICS

AIM:

To obtain the steady state output side characteristics of the given IGBT, for a specified value of base emitter voltage.

APPARATUS REQUIRED:

| | | | |

|Sl.No. |NAME OF THE COMPONENTS |RANGE |QUANTITY |

|1 |IGBT | | |

|2 | Power Supplies | | |

|3 | Wattage Resistors | | |

|4 |Ammeter | | |

|5 |Voltmeter | | |

| | | | |

|6 | Bread Board | | |

|7 |Connecting Wires | | |

THEORY:

INSULATED GATE BIPOLAR TRANSISTOR (IGBT): The circuit diagram to obtain the output characteristics of IGBT is shown in figure. The symbol of IGBT shown in Fig. IGBT is a new development in the area of power MOSFET technology. This device combines into it the advantages of both MOSFET and BJT. So an IGBT has high input impedance like a MOSFET and low-on state power loss as in a BJT. IGBT is free from second breakdown problem present in BJT. IGBT is also known as metal oxide insulated gate transistor (MOSIGT), conductively modulated field effect transistor (COMFET) or gain modulated FET (GEMFET). It is also called insulated gate transistor (IGT). The V I characteristics of MOSFET is shown in figure.

PROCEDURE

Static V-I Characteristics of IGBT

1. Connections as made as per the circuit diagram.

2. Connect multimeter across G-K, across the IGBT (collector and

Emitter), & across the supply terminals Vs to measure gate voltage

VBE , VCE , and Vs (all in dc mode) An ammeter of the range (0-50) mA

is connected to measure the load current Il (collector current IC).

3. Keep initially the gate potential VBE at very low value. Vary the supply voltage Vs in steps and note whether ammeter shows any Reading. For every step of Vs note the ammeter reading. Also note corresponding readings of VCE respectively.

4. If the ammeter doesn’t indicate any reading, increase the gate potential VBE

To some higher value & follow the procedure given in step no. (3).

5. Further increase the gate potential to some higher values and repeat the

Procedure followed in step no. (3).

6. Tabulate the readings in the observation column.

7. Finally a graph is drawn between load current (IC) and the device voltage

VCE respectively.

RESULT:

Thus the steady state output side characteristics of the given IGBT, for a specified value of base emitter voltage has been obtained.

QUESTIONS:

1. What is IGBT?

2. What are the applications of IGBT?

3. Compare MOSFET, BJT & IGBT?

4. Explain the working principle of IGBT

5. Explain o/p & transfer characteristics of IGBT.

CIRCUIT DIAGRAM: SINGLE PHASE HALF CONTROLLED BRIDGE RECTIFIER

P

T1 T3

230V, 50Hz

1φ AC Supply

D4 D2

N

230V/12V step down

UJT TRIGGERING CIRCUIT FOR SINGLE PHASE HALF CONTROLLED BRIDGE CONVERTER

Step down Transformer

EXPT.NO:

DATE:

SCR HALF & FULLY CONTROLLED BRIDGE RECTIFIERS

SINGLE PHASE HALF CONTROLLED CONVERTER

AIM:

To study the operation of single phase half controlled converter using R and RL load and to observe the output waveforms

APPARATUS REQUIRED:

| | | | |

|Sl.No. |NAME OF THE COMPONENTS |RANGE |QUANTITY |

|1. |Thyristor trainer kit | | |

|2. |SCR Triggering kit | | |

|3. |CRO | | |

|4. |Resistive load | | |

|5. |Multimeter | | |

|6 |Patch cards | | |

|7 |CRO probes | | |

OBSERVATION TABLE:

Half Controlled Bridge Rectifier Using R Load Vm = ________________

|Serial No. |Triggering angle ‘α’ |Output voltage |Output voltage |

| |degree |Voav |Voav |

| | |(volt) |(volt) |

| | |(measured) |(calculated) |

| | | | |

| | | | |

MODEL GRAPH:

Half Controlled Bridge Rectifier Using R Load

[pic]

FORMULA:

For Single Phase Half Controlled Bridge Rectifier

[pic]

THEORY:

Single Phase Half Controlled Bridge Rectifier (Single Phase Semi converter):

A semi converter uses two diodes and two thyristors and there is a limited control over the level of dc output voltage. A semi converter is one quadrant converter. A one-quadrant converter has same polarity of dc output voltage and current at its output terminals and it is always positive. It is also known as two-pulse converter.

Figure shows half controlled rectifier with R load. This circuit consists of two SCRs T1 and T2, two diodes D1 and D2. During the positive half cycle of the ac supply, SCR T1 and diode D2 are forward biased when the SCR T1 is triggered at a firing angle ωt = α, the SCR T1 and diode D2 comes to the on state. Now the load current flows through the path L - T1- R load –D2 - N. During this period, we output voltage and current are positive. At ωt = π, the load voltage and load current reaches to zero, then SCR T1 and diode D2 comes to off state since supply voltage has been reversed.

During the negative half cycle of the ac supply, SCR T2 and diode D1 are forward biased. When SCR T2 is triggered at a firing angle ωt = π + α, the SCR T2 and diode D1 comes to on state. Now the load current flows through the path N - T2- R load – D1 -L. During this period, output voltage and output current will be positive.

At ωt = 2π, the load voltage and load current reaches to zero then SCR T2 and diode D1 comes to off state since the voltage has been reversed. During the period (π + α to 2π) SCR T2 and diode D1 are conducting

PROCEDURE:

Single Phase Half Controlled Bridge Rectifier (Single Phase Semi converter)

1. Make the connections as per the circuit diagram.

2. Connect CRO and voltmeter across the load.

3. Keep the potentiometer at the minimum position.

4. Switch on the step down ac source.

5. Check the gate pulses at G1-K1 & G2-K2, respectively.

6. Observe the wave form on CRO and note the triggering angle ‘α’ and

7. Note the corresponding reading of the voltmeter. Also note the value of

8. Maximum amplitude Vm from the waveform.

9. Set the potentiometer at different positions and follow the step given in (6)

10. For every position.

11. Tabulate the readings in the observation column.

RESULT:

Thus the operation of single phase half controlled converter using R and RL load has studied and the output waveforms has been observed.

QUESTIONS:

1. What is meant by semi converter?

2. What is effect of freewheeling diode?

3. What are the advantages using FD?

4. What are fully controlled rectifiers?

5. What is the condition for different quadrant of operation

CIRCUIT DIAGRAM: SINGLE PHASE FULLY CONTROLLED CONVERTER: R, RL LOAD

[pic]

UJT TRIGGERING CIRCUIT FOR SINGLE PHASE FULLY CONTROLLED BRIDGE CONVERTER

SINGLE PHASE FULLY CONTROLLED CONVERTER

AIM:

To study the operation of single phase fully controlled converter using R and RL load and to observe the output waveforms

APPARATUS REQUIRED:

| | | | |

|Sl.No. |NAME OF THE COMPONENTS |RANGE |QUANTITY |

| |Thyristor trainer kit | | |

|2. |SCR Triggering kit | | |

|3. |CRO | | |

|4. |Resistive load | | |

|5. |Multimeter | | |

|6 |Patch cards | | |

|7 |CRO probes | | |

THEORY:

SINGLE PHASE FULLY CONTROLLED BRIDGE RECTIFIER

A fully controlled converter or full converter uses thyristors only and there is a wider control over the level of dc output voltage. With pure resistive load, it is single quadrant converter. Here, both the output voltage and output current are positive. With RL- load it becomes a two-quadrant converter. Here, output voltage is either positive or negative but output current is always positive. Figure shows the quadrant operation of fully controlled bridge rectifier with R-load.

OBSERVATION TABLE:

Fully Controlled Bridge Rectifier Using R Load Vm = _________

|Serial No. |Triggering angle ‘α’ degree |Output voltage |Output voltage |

| | |Voav |Voav |

| | |(volt) |(volt) |

| | |(measured) |(calculated) |

| | | | |

| | | | |

Fully Controlled Bridge Rectifier Using RL Load Vm = __________

|Serial No. |Triggering angle ‘α’ degree |Output voltage |Output voltage |

| | |Voav |Voav |

| | |(volt) |(volt) |

| | |(measured) |(calculated) |

| | | | |

| | | | |

| | | | |

| | | | |

Fig shows single phase fully controlled rectifier with resistive load. This type of full wave rectifier circuit consists of four SCRs. During the positive half cycle, SCRs T1 and T2 are forward biased. At ωt = α, SCRs T1 and T3 are triggered, and then the current flows through the L – T1- R load – T3 – N. At ωt = π, supply voltage falls to zero and the current also goes to zero. Hence SCRs T1 and T3 turned off. During negative half cycle (π to 2π),

SCRs T3 and T4 forward biased. At ωt = π + α, SCRs T2 and T4 are triggered, then current flows through the path N – T2 – R load- T4 – L. At ωt = 2π, supply voltage and current goes to zero, SCRs T2 and T4 are turned off. The Fig-3, shows the current and voltage waveforms for this circuit.

For large power dc loads, 3-phase ac to dc converters are commonly used. The various types of three-phase phase-controlled converters are 3 phase half-wave converter, 3-phase semi converter, 3-phase full controlled and 3-phase dual converter. Three-phase half-wave converter is rarely used in industry because it introduces dc component in the supply current. Semi converters and full converters are quite common in industrial applications. A dual is used only when reversible dc drives with power ratings of several MW are required.

The advantages of three phase converters over single-phase converters are as under:

In 3-phase converters, the ripple frequency of the converter output voltage is higher than in single-phase converter. Consequently, the filtering requirements for smoothing out the load current are less.

The load current is mostly continuous in 3-phase converters. The load performance, when 3-phase converters are used, is therefore superior as compared to when single-phase converters are used.

FORMULA:

For Single Phase Fully Controlled Bridge Rectifier

[pic]

MODEL GRAPH:

[pic]

PROCEDURE:

1. Single Phase Fully Controlled Bridge Rectifier

2. Make the connections as per the circuit diagram.

3. Connect CRO and multimeter (in dc) across the load.

4. Keep the potentiometer (Ramp control) at the minimum position (maximum

Resistance).

5. Switch on the step down ac source.

6. Check the gate pulses at G1-K1, G2-K2, G3-K3, & G4-K4 respectively.

7. Observe the waveform on CRO and note the triggering angle ‘α’ and

Note the corresponding reading of the multimeter. Also note the value of

Maximum amplitude Vm from the waveform.

8. Set the potentiometer at different positions and follow the step given in (6)

For every position.

9. Tabulate the readings in observation column.

10. Draw the waveforms observed on CRO.

RESULT:

Thus the operation of single phase fully controlled converter using R and RL load has been studied and the output waveforms has been observed.

QUESTIONS:

1. What is meant by semi converter?

2. What is effect of freewheeling diode?

3. What are the advantages using FD?

4. What are fully controlled rectifiers?

5. What is the condition for different quadrant of operation

CIRCUIT DIAGRAM: R – TRIGGERING CIRCUIT

[pic]

MODEL GRAPH: R – Triggering Circuit

EXPT.NO:

DATE:

R, R-C AND UJT FIRING CIRCUITS FOR SCR

AIM:

To study the operation of resistance, resistance capacitance and UJT triggering circuits of SCR

APPARATUS REQUIRED:

| | | | |

|Sl.No. |NAME OF THE COMPONENTS |RANGE |QUANTITY |

|1. |Transformer | | |

|2. |SCR – TY604 | | |

|3. |Resistor (3.3 Kohm, 100 Ohm/20W), | | |

|4. |. Capacitor | | |

|5. |UJT firing module | | |

|6 |CRO | | |

|7 |LOAD | | |

|8 |Multimeter | | |

CIRCUIT DIAGRAM: RC TRIGGERING CIRCUIT

MODEL GRAPH: RC TRIGGERING CIRCUIT

THEORY:

RESISTANCE TRIGGERING

Resistance trigger circuits are the simplest & most economical method. During the positive half cycle of the input voltage , SCR become forward biased but it will not conduct until its gate current exceeds Igmin . Diode D allows the flow of current during positive half cycle only. R2 is the variable resistance & R is the stabilizing resistance .R1 is used to limit the gate current.during the positive half cycle current Ig flows. Ig increases and when Ig= Igmin the SCR turns ON .The firing angle can be varied from 0 — 90° by varying the resistance R.

R —C TRIGGERING

By varying the variable resistance R, the firing angle can be varied from 0 —180° .In the negative half cycle the capacitance C charges through the diode D2 with lower plate positive to, the peak supply voltage Emax .This Capacitor voltage remains constant at until supply voltage attains zero value. During the positive half cycle of the input voltage , C begins to charge through R. When the capacitor voltage reaches the minimum gate trigger voltage SCR will turn on.

UJT TRIGGERING

The circuit for UJT trigger consists of UJT relaxation oscillator. The basic UJT relaxation oscillator is made as a line synchronized trigger circuit, with the addition of a diode rectifier and

a zener diode. A zener diode clips the control voltage to a fixed level. The capacitor will charge exponentially. When the voltage across the capacitor reaches the unijunction threshold voltage, the E-B,junction of UJT breaks down and. capacitor C discharges through UJT . SCR get gate pulse and turns on.

CIRCUIT DIAGRAM: UJT TRIGGERING CIRCUIT

MODEL GRAPH: UJT TRIGGERING CIRCUIT

Average value of output voltage [pic]

RMS value of output voltage =

PROCEDURE:

R Firing

1. Connections are made as shown in fig.

2. Switch on the power supply to the CRO.

3. Set the CRO to the line trigger mode.

4. Switch on power supply to the SCR trainer.

5. Observe the waveform on the CRO.

6. Study the waveforms for various firing angle by varying the pot in R trigger circuit.

7. Observe the range of firing angle control.

8. For any one particular firing angle plot the waveforms of the ac voltage, voltage across the load and the SCR.

9. Measure the average dc voltage across the load and rms value of the ac input voltage using a digital multimeter.

10. Calculate the dc output voltage using the equation.

[pic]

V - Vrms value of ac input voltage

Vm - .\/2Vrms

And compare the measured value

RC Firing

1. Connections are made as shown in fig.

2. Switch on the power supply to the CRO.

3. Set the CRO to the line trigger mode.

4. Switch on power supply to the SCR trainer.

5. Observe the waveform on the CRO.

6. Study the waveforms for various firing angle by varying the pot in R trigger circuit.

7. Observe the range of firing angle control.

8. For any one particular firing angle plot the waveforms of the ac voltage, voltage across the load and the SCR.

9. Measure the average dc voltage across the load and rms value of the ac input voltage usin g' a digital multimeter.

10. Calculate the dc output voltage using the equation.

UJT Firing

1. Connect A, K terminal of UJT triggering circuit to the gate cathode terminals of SCR.

2. Give a 24 V ac supply.

3. Observe the waveforms and plot it for one particular firing angle by adjusting the potentiometer and observe the range over which firing angle is controllable.

4. Observe that capacitor voltage is set at every half cycle.

RESULT:

Thus the operation of resistance, resistance capacitance and UJT triggering circuits of SCR has been studied.

And compare the measured value

QUESTIONS:

1. What are all the methods to trigger SCR.?

2. Which one is the most common & accurate method to turn on the SCR.

3. Explain the working of resistance firing circuit.

4. Explain the working of resistance- capacitor firing circuit.

5. What is meant by ramp control?

IRCUIT DIAGRAM: SERIES INVERTER

EXP NO:

DATE:

SERIES INVERTER

AIM:

To obtain variable AC from DC ripple input.

APPARATUS REQUIRED:

| | | | |

|Sl.No. |NAME OF THE COMPONENTS |RANGE |QUANTITY |

|1. |Module | | |

|2. |SCR | | |

|3. |Diode | | |

|4. |inductor | | |

|5. |capacitors | | |

THEORY:

In the series inverter, the commutating inductance and capacitance are in Series with the load. Thus the commutation circuit is part of the load. Fig shows the circuit diagram of series inverter. L and C are commutating components. T and T carry load current in positive and negative half cycles Operation of the circuit can be understood through following modes.

Mode - I

At the beginning of this mode, capacitor is charged to negative voltage as shown in waveforms of Fig. At t1 SCR T is triggered. The output current starts flowing through T and L-C-R circuit equivalent circuit-I in Fig show the current path. Because of the RLC circuit, the current increases sinusoid ally. The current becomes maximum when capacitor voltage is equal to VdC. Then the current reduces. At t current becomes zero. Hence T turns-off. The capacitor charges to the value higher than VdC. This charge is hold by the capacitor.

Model graph

OBSERVATION TABLE

|S.No |Amplitude (volt) |Ton (ms) |Toff (ms) |

| | | | |

Mode - II

This mode begins when SCR T is triggered at t3 Equivalent circuit-II in Fig shows the current path. The current starts flowing in opposite direction. Fig shows the negative half cycle of the current. The capacitor starts discharging in the RLC circuit. The current becomes maximum when capacitor voltage is zero. The current then starts reducing and becomes zero at t4 Therefore T2 turns off at t4. The Capacitor is charged to negative voltage. This charge is hold by the capacitor. The cycle repeats when T1 is triggered again. Fig shows output voltage waveform. Note that it is similar to output current for resistive load.

PROCEDURE:

1. To begin with switch on the power supply to the firing circuit check that

Trigger pulses by varying the frequency.

2. Connections are made as shown in the circuit diagram.

3. Now connect trigger outputs from the firing circuits to gate and cathode of

SCRs T1 & T2.

4. Connect DC input from a 30v/2A regulated power supply and switch on

The input DC supply.

5. Now apply trigger pulses to SCRs and observe voltage waveform across

The load.

6. Measure Vrms & frequency of o/p voltage waveform.

RESULT:

Thus the variable AC from DC ripple input has been obtained.

QUESTIONS:

1. What is meant by series inverter?

2. Give the classification of series inverter.

3. Give the frequency range at which the series inverter operate.

4. Explain the working of series inverter.

5. What are all the applications of series inverter?

CIRCUIT DIAGRAM: SCR DC VOLTAGE COMMUTATED CHOPPER

EXP NO:

DATE:

SCR DC VOLTAGE COMMUTATED CHOPPER

AIM:

To observe the operation of class D commutated technique.

APPARATUS REQUIRED:

|S.No |Name of the apparatus |Type |Range |Quantity |

|1 |Force commutation trainer kit | | | |

|2 |Patch cards | | | |

|3 |CRO | | | |

THEORY:

MODE-1

Main SCR is triggered to make source current to flow in two path one is load current and other path with triggering of SCR load get connected to supply and load voltage.

MODE-2

At a desired instant the auxiliary SCR is to be triggered for turning OFF the main SCR T1 with the switch ON, T2 reverse capacitance voltage appears across T1 which reverse biases it and turn it OFF.

MODE-3

SCR T2 turn OFF since the capacitance is slightly changed after the freewheeling diode set frequently forward biased.

OBSERVATION TABLE :

| | |T auxiliary time |

|S.NO |Vs in volts | |

| | | |

| | |Ton (ms) |Toff (ms) |

| | | | |

| | | | |

| | |T auxiliary time |

|S.NO |Amplitude | |

| | | |

| | |Ton (ms) |Toff (ms) |

| | | | |

| | | | |

NOTATIONS USED

Ig- gate current

It- thyristor current

Ic- capacitor current

Vc- capacitor voltage

Vt- thyristor voltage

Vo- output voltage

Ita- auxiliary thyristor current

PROCEDURE:

1) Patch the voltage commutated chopper as per the circuit diagram

2) Connect the CRO probe across the commutated chopper

3) Give the input dc voltage (0-30)v, 2amps from the external power supply.

4) Switch ON the trainer then switch ON the input dc supply circuit breaker.

5) After then switch ON the trigger OFF-ON position

6) From the load output waveform we can measure the turn on time and turn off time of main SCR as well as auxiliary SCR

7) Verify the unity and frequency of the triggering circuit using parts provided on the triggering circuit.

8) Also observe the voltage across main SCR and auxiliary SCR and load

9) Take the turn on and turn off time at main so auxiliary SCR from the capacitor waveform at various values of unity cycle and frequency and tabulate them

10) Also find out the peak value of current through the load.

OBSERVATION TABLE:

OUTPUT ACROSS CAPACITOR

|S.NO |Vs (volts) |Ip=VsVl/L |Main SCR turn on time |Main SCR turn off time |

| | | | | |

| | | | | |

OUTPUT ACROSS LOAD

|S.NO |Vs (volts) |Ip=VsVl/L |Main SCR turn on time |Main SCR turn off time |

| | | | | |

| | | | | |

PROCEDURE:

11) Patch the voltage commutated chopper as per the circuit diagram

12) Connect the CRO probe across the commutated chopper

13) Give the input dc voltage (0-30)v, 2amps from the external power supply.

14) Switch ON the trainer then switch ON the input dc supply circuit breaker.

15) After then switch ON the trigger OFF-ON position

16) From the capacitor output waveform we can measure the turn on time and turn off time of main SCR as well as auxiliary SCR

17) Verify the unity and frequency of the triggering circuit using parts provided on the triggering circuit.

18) Also observe the voltage across main SCR and auxiliary SCR and load

19) Take the turn on and turn off time at main so auxiliary SCR from the capacitor waveform at various values of unity cycle and frequency and tabulate them

20) Also find out the peak value of current through the capacitor.

WAVEFORM:

RESULT:

Thus the operation of class D commutated technique has been obtained.

QUESTIONS:

1. What is meant by commutation?

2. What are all the methods of commutation?

3. What is meant by voltage commutation?

4. Explain the working of voltage commutated chopper.

5. What are all the advantages and disadvantages of voltage commutated chopper

CIRCUIT DIAGRAM: SCR DC CURRENT COMMUTATED CHOPPER

EXP NO:

DATE:

SCR DC CURRENT COMMUTATED CHOPPER.

AIM:

To conduct and study current commutation chopper technique

APPARATUS REQUIRED:

|S.No |Name of the apparatus |Type |Range |

|1 |forced commutation trainer kit | | |

|2 |Patch cards | | |

|3 |CRO | | |

THEORY:

The power circuit diagram of current commutated chopper is represented T1 is the main thyristor the other component namely auxiliary T, capacitor C, inductor L, diode D1 and D2 exists commutation chopper FD is positive free wheeling diode and RC is the average resistor assumption for chopper are as load current is constant SCR diode and identical switches changing resistor R1 is so large.

PROCEDURE:

1. Patch the connections as circuit diagram

2. Connect the CRO probe across the capacitor

3. Switch on the trainer kit

4. From the capacitor waveform we can found the auxiliary SCR turn on time

OUTPUT ACROSS CAPACITOR

OUTPUT ACROSS LOAD

| |Amplitude (volt) |Ton (ms) |Toff (ms) | |

| | | | | |

|S.No |Amplitude (volt) |Ton (ms) |Toff (ms) | |

| | | | | |

WAVEFORM:

5. Switch on the DC output MCB and switch on the triggering circuit on/off switch

6. Observe the waveform across the main SCR auxiliary SCR and load.

RESULT:

Thus the current commutation chopper technique have been conducted.

QUESTIONS:

1. What is meant by current commutation?

2. What is meant by current commutated chopper?

3. What about the commutation time in voltage & current commutated chopper.

4. Explain the working of current commutated chopper.

5. Give the applications of current commutated chopper

CIRCUIT DIAGRAM: RESONANT DC TO DC CONVERTER

EXPT.NO:

DATE:

RESONANT DC TO DC CONVERTER

AIM:

To study the operation of DC to DC resonant converter

APPARATUS REQUIRED:

| | | | |

|Sl.No. |NAME OF THE APPARATUS |RANGE |QUANTITY |

|1. |Resonant DC to DC converter triggering module | | |

|2. |Resonant DC to DC converter power module | | |

|3. |CRO | | |

|4. |CRO probes | | |

|5. |Patch cards | | |

OBSERVATION TABLE:

|S.NO |Vdc (Input voltage) v |Vd (Peak voltage) V |Vd (on-Time) T sec |Vgs (on-time) T |

| | | | |sec |

| | | | | |

MODEL GRAPH:

PROCEDURE:

1. Make the connections as per the circuit diagram.

2. Switch ON the triggering module.

3. Set the carrier wave switching frequency is equal to resonant frequency.

4. Switch ON the power module.

5. Observe the output voltage and current waveforms.

6. By varying the reference signal the output voltage control is achieved.

7. Switch OFF the trainer. Change the LC value and observe the voltage waveforms.

RESULT:

Thus the operation of DC to DC resonant converter has been studied.

QUESTIONS:

1. What is meant by resonant converter?

2. What is the need for resonant converter?

3. Give the classification of ZCS.

4. Explain the working of ZCS.

5. Give the advantages & limitations of ZCS.

CIRCUIT DIAGRAM OF IGBT CHOPPER (I & IV QUADRANT OPERATION)

CIRCUIT DIAGRAM OF IGBT CHOPPER (II & III QUADRANT OPERATION)

EXP NO:

DATE:

IGBT CHOPPER

AIM:

To conduct the operation of four quadrants IGBT chopper with bipolar switching and unipolar switching.

APPARATUS REQUIRED:

|S.No |Name of the apparatus |Type |Range |Quantity |

|1 |IGBT module | | | |

|2 |Chopper control module | | | |

|3 |CRO | | | |

|4 |Rheostat | | | |

|5 |Multimeter | | | |

APPARATUS REQUIRED:

THEORY:

The type of chopper is obtained by connectivity type A type B chopper is parallel. The output voltage Vo is always positive because of the presence of freewheeling diode across the load. When chopper CH2 ON free wheeling diode conduct output voltage Vo=0 and incase chopper CH2 is ON or diode.

PROCEDURE:

For bipolar switching

1. Using the chopper module, and referring to the mimic diagram, connect the circuit as per the circuit diagram.

i) Connect B11 to V+1 using patch chords.

TABULATION: FIRST AND FOURTH QUADRANT

|S.NO |Vo |Ton (ms) |T (ms) |α = Ton/T |Vo= |

| | | | | | |

| | | | | | |

| | | | | | |

| | | | | | |

| | | | | | |

TABULATION: SECOND AND THIRD QUADRANT

|S.NO |Vo |Ton (ms) |T (ms) |α = Ton/T |Vo= |

| | | | | | |

| | | | | | |

| | | | | | |

| | | | | | |

| | | | | | |

ii) Connect B12 to B21 using patch chords.

iii) Connect B23 to V-1 using patch chords.

iv) Connect V+2 to B31 using patch chords.

v) Connect B32 to B41 using patch chords.

vi) Connect V-2 to B43 using patch chords.

2. Connect the R-load between B12 to B33.

3. Connect the gating signals from the chopper control module to the chopper module using the signal cable provided.

4. Connect the power cables for both the modules.

5. Select bipolar voltage switching mode, mode III by setting SW3 in the control module at position.

6. Keeping pulse release ON/OFF switch SW4, in the control module in the off position. Switch ON ac mains to the CRO, control module and chopper module.

7. Switch ON SW! in chopper module to establish dc link voltage.

8. Release the gating signals by switching on SW$ in the control module.

9. Observe the load voltage waveforms through CRO.

10. Vary the duty cycle ratio and measure Ton, Toff, average dc output voltage and tabulate them.

For unipolar voltage switching

1. Follow the steps 1 to 4 in bipolar voltage switching.

2. Select the unipolar switching mode, by setting the mode switch SW3 at position IV in the chopper control module.

3. Follow the remaining steps.

RESULT:

Thus the four quadrant chopper was constructed and the operation of the chopper has been obtained from the output waveform.

QUESTIONS:

1. Explain the principle of dc chopper operation

2. Describe the various types of chopper configuration

3. What is meant by IGBT CHOPPER?

4. Explain the working of IGBT chopper

5. Where we are using this two quadrant IGBT chopper.

CIRCUIT DIAGRAM: - SINGLE PHASE CYCLOCONVERTER

[pic]

EXP NO:

DATE:

SINGLE PHASE CYCLOCONVERTER

AIM:

To study the operation of single phase Cycloconverter.

APPARATUS REQUIRED:

|S.No |Name of the apparatus |Type |Range |Quantity |

|1 |Cycloconverter module | | | |

|2 | Loading rheostat | | | |

|3 |CRO | | | |

|4 |Inductance | | | |

|5 |probes | | | |

THEORY:

Cycloconverter directly changes frequency changes that convert ac power at one frequency to ac power at another frequency by ac to ac conversion without an intermediate conversion link. The majority of Cycloconverter are naturally commutated. Some Cycloconverter need forced commutatory circuit.

1) Step-down Cycloconverter→Natural commutation.

2) Step-up Cycloconverter→Forced commutation.

Itable

|Sl.No |Amplitude (V) |Frequency(Hz) |Ton(ms) |Toff(ms) |

| | | | | |

| | | | | |

| | | | | |

| | | | | |

| | | | | |

The Principle of operation of Single phase Cycloconverter can be explained with the circuit diagram. The SCR T1 and T2 form positive polarity of output voltage and T3, T4 produce negative polarity of the load voltage. The positive group SCR’s T1 and T2 are gated together depending upon polarity one of them will conduct Dc output voltage of impulse Cycloconverter.

PROCEDURE:

1. Patch the firing circuit unit as per the Patching diagram

2. Switch on the Firing circuit unit through the power on Indicator switch providing the front panel.

3. Verifying the test point through the CRO Whether it is Proper or not.

4

. Then press soft start switch.

5. Study and observe the various stages of waveform through the appropriate test point.

6. Observe the firing pulse output and their phase sequence Through the corresponding terminal using dual in CRO.

7. Now switch off the firing circuit and patch the power circuit as show in the patching diagram, also interlink the firing unit and power unit as Shown in the patching diagram .

8. Connect the CRO probe across the load Resistor (It may be a fixed orVariable Resistor)

9. Switch on both the firing and power unit and observe the Cycloconverter output in the CRO and change the firing angle through the firing angle variation (0-180°) pot meter

10. Repeat the experiment for the various values frequency divider output, Observe and trace the Cycloconverter output and note down the voltage and current reading for various value of R.

RESULT:

Thus the output waveform of the single phase mid point Cycloconverter was studied and observed.

QUESTIONS:

1. What is meant by cycloconverter.

2. Give the classification of cycloconverter

3. Explain the operation of cycloconverter.

4. Which commutation is employed in cycloconverter.

5. Give its applications

CIRCUIT DIAGRAM: SINGLE PHASE FULLY CONTROLLED CONVERTER FED DC MOTOR

[pic]

EXP NO:

DATE:

SPEED CONTROL OF DC SHUNT MOTOR USING CONVERTER

AIM:

To study the open loop speed control of DC motor using field control and armature control.

APPARATUS REQUIRED:

|S.No |Name of the apparatus |Type |Range |Quantity |

|1 |DC motor speed controller | | | |

| |trainer. | | | |

|2 |DC motor-generator setup | | | |

|3 |Connecting wires | | | |

|4 |probes | | | |

PROCEDURE:

1. Connect the armature of the DC motor across the banana connectors A,AA and field of the DC motor across the connectors F,FF.

2. Keep the rotary switch S3 in position for open loop study.

3. Connect the field of generator to the connectors provided at the right side panel of the trainer. It provides a fixed DC of 180V for the generator field.

4. Keep the switch S1 in the position PV to read speed.

Model graph

5. Connect the armature of the DC motor across the banana connectors A,AA and field of the DC motor across the connectors F,FF.

6. Keep the rotary switch S3 in position for open loop study.

7. Connect the field of generator to the connectors provided at the right side panel of the trainer. It provides a fixed DC of 180V for the generator field.

8. Keep the switch S1 in the position PV to read speed.

FOR FIELD CONTROL METHOD

1. Keep the switch S2 position INT for internal supply and the armature controlled pot at maximum position.

2. Keep the switch S5 in variable position.

3. Switch ON the power ON/OFF switch and check whether it glows. Switch ON

4. Switch ON the MCB which provides 230v AC to the converter circuit of DC motor field and armature.

5. Initially note down the speed on the digital meter.

6. Vary the field control pot in steps up to maximum and note the speed. the variation in speed is due to variation in the field current

7. Bring the field control port to minimum position and switch OFF the MCB and then the power ON/OFF switch.

FOR ARMATURE CONTROL METHOD

1. Keep the SPDT switch S2 in INT position and switch S5 in fixed position. Keep the armature control pot in minimum position .

2. Switch on the power on/off switch and check whether it glows. switch on both the pulse on/off switches s6 and S7.

3. Switch on the MCB which provides 230v a.c to the converter circuit of d.c motor field and armature.

4. Initially note down the speed on the digital voltmeter.

5. Vary the armature control pot unto maximum value in steps and note down the speeds. the variation in speed is due to the variation in armature voltage.

6. Bring the armature control pot to minimum position and then switch off the MCB and then the power on/off switch.

RESULT:

Thus the open loop speed control of DC motor using field control and armature control have been studied.

QUESTIONS:

1. What are the different speed control methods?

2. Difference between field control and armature control method.

3. Why speed control is necessary.

4. What is open loop speed control?

5. What is closed loop speed control?

Circuit diagram

[pic]

EXPT.NO:

DATE:

THREE PHASE FULLY CONTROLED BRIDGE RECTIFIER

AIM:

To study the operations and the performance of the three phase fully controlled converter with resistive and inductive load.

APPARATUS REQUIRED:

1. PC

2. Pspice

THEORY:

Three phase converter are extensively used in industrial applications up to the 120KW level, where two-quadrant.

A) WITH RESISTIVE LOAD

The circuit shows a fully converter circuit with resistive load. The load is fed via a three phase Half-wave connection, the return path being via another half –wave connection to one of the three supply lines, no neutral being required.

The circuit consists of two groups of SCRs, positive group and negative group. The positive group SCRs are turned ON when the supply voltage is positive and negative group SCRs are turned on when the supply voltage are negative. If SCR T1 is triggered at a particular instant, it can conduct provided there is a return path for the current. Since phase B is the maximum negative, the return path should be to phase B. That means SCR T5 must be triggered simultaneously with SCR T1. similarly, when phase B has the highest value, SCR-T2 and SCR-T6 and when phase C has the highest value SCR T3 must be triggered simultaneously.

Model graph

.

OPERATIONS:

It can be classified as

i. continuous conduction mode (0≤α≤π/3)

ii. Discontinuous conduction mode(π/3≤α≤2π/3)

α is firing angle of thyristor

i) CONTINUOUS CONDUCTION MODE: (0≤α≤π/3)

When the phase a and phase B are all over to conduct at“ between zero to π/3, it continuous to conduct by 60 when the phase C is fired. The condition is shifted from SCR T5 to SCR T6. The phase A & C conducts after another 60 after which it is replaced by phases B and C when phase B voltage assumes greater value than C or A. Hence load current is continuous for α between 0 and π/3.

ii) DISCONTINUOUS CONDUCTION MODE (π/3≤α≤2π/3)

When (π/3≤α≤2π/3), the phase A and B conducts up to angle π after which both the thyristor T1 and T5 are commutated off due to natural commutation and after 60 when T6 and T1 are fired, Phase A and C conducts also up to angle π, hence load current, remains zero from angle π to the next firing pulse and becomes discontinuous.

V0 (theoretical) = 3√2VScosα = 1.35 VScosα

PROCEDURE:

1. Open capture CIS from start up or from the short cut.

2. Create a new project using analog or mixed – Signal circuit Wizard.

3. Add the necessary library to the project.

4. Select the required devices from place part and give the connections.

5. Create a new simulation profile and simulate the project.

6. Verify the voltage across different terminals from the output waveforms through Pspice A/D

RESULT:

The operation and the performance of 3 phase fully controlled converter with resistive and inductive load was studied.

QUESTIONS:

1. What is the firing angle of a thyristor.

2. At what firing angle load current is continuous.

3. When the load current remains zero.

4. At what firing angle load current is discontinuous

5. Give the application of three phase converter.

CIRCUIT DIAGRAM

TABULAR COLUMN:

|S.no |Output voltage (v) |Time (ms) |

| | | |

| | | |

| | | |

| | | |

EXP NO:

DATE:

IGBT BASED – SINGLE PHASE PWM INVERTER

AIM:

To study the behavior of IGBT based single-phase full-bridge inverter connected to R load.

PARATUS REQUIRED:

|SI.NO |APPARATUS REQUIRED |RANGE |QUANTITY | |

|1. |PWM module | | | |

|2. |Multi meter | | | |

|3. |CRO | | | |

|4. |Connecting probes | | | |

MODULE DETAILS:

This unit consists of two parts:

(a) Control Circuit and

(b) Power Circuit.

A) CONTROL CIRCUIT:

This is based on 89C52 Microcontroller. 2 X 16 line LCD display to indicate and monitor the Parameters and type of modulation. The following modulation techniques are incorporated:

a) Single pulse modulation

b) Sine triangle modulation

c) Multi pulse modulation

d) Trapezoidal modulation

Model graph

d) Trapezoidal modulation

e) Stair case modulation

5 keys: SET, INC, DEC, FRQ/DTY and RUN/STOP to vary and set the parameters. opto coupler based isolation circuit to drive 4 IGBTs connected as 1-ph. Bridge Inverter.

B) POWER CIRCUIT:

This unit consists of 4 IGBT’s unit built in diodes of rating 19A/600V. All the devices are mounted on proper heat-sink and protected by snubber circuit and fuse. All the terminals are brought out on the front panel. In the input side a switch and a fuse are provided for DC input 24V @ 2A. The frequency can be varied from 20Hz to 100Hz. The duty can be varied from 0% to 100%. Carrier frequency – 9 pulses per each half cycle

PROCEDURE:

A. CONTROL CIRCUIT

1. Switch ON the mains supply of the controller unit. The LCD display shows 1-ph PWM inverter with modulation type and M- (Duty cycle or modulation index) 00 and F-100 Hz and in OFF position.

2. When M-00 Blinks, press INC key to set the duty cycle from 00- 100%.

3. Press FRQ/DTY key and select F-100. When F-100 blinks, use INC and DEC key to increase or decrease the frequency from 20Hz to 100Hz.

4. After setting the duty cycle and frequency, press RUN/STOP key. Now the driver O/Ps pulses are available at O/Ps are comes to OFF with soft stop.

5. Set the modulation type to other type and check the outputs

6. Check the driver outputs for different types of modulation. Make sure that the driver outputs are proper before connecting to the power circuit.

NOTE: The SET key works only when it is in OFF position. This is to avoid change of modulation type when the power circuit is ON.

B. POWER CIRCUIT

1. Make the connections as given in the circuit diagram.

2. Connect DC supply from 30V/2A regulated power supply unit.

3. Connect a resistive load – 50 ohms or 100 ohms 2 Amps Rheostat at load terminals.

4. Connect driver output signals to the Gate and Emitter of corresponding IGBTs.

5. Switch ON the DC supply.

6. Switch ON the driver outputs and observe the output voltage across the load.

RESULT:

The behavior of IGBT based single phase full bridge inverter was studied.

QUESTIONS:

1. What is meant by inverter?

2. What are the two main types of inverter?

3. Discuss how output power in single-phase full bridge inverter is doubled than that of single phase half bridge inverter.

4. How to overcome the problem of half-bridge using full bridge.

5. What is meant by feedback diodes

-----------------------

D3

D2

D1

-

+

24V,D.C

Vo

D4

T1

T2

T3

T4

50(/5A

C1

C2

t

t

Vref

Vcar

Vo

................
................

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