EE56 Power Electronics

EINSTEIN COLLEGE OF ENGINEERING Sir.C.V.Raman Nagar, Tirunelveli-12

Department of Electrical & Electronics Engineering

Subject Code & Name: EE56 – Power Electronics Laboratory

Name : ………………………………………

Reg.No. : ………………………………………

Branch : ………………………………………

Year & Semester : ………………………………………

Sub Code: EE56, Power Electronics Lab

Page 2 of 62 ©Einstein College of Engineering

EINSTEIN COLLEGE OF ENGINEERING

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGG

CLASS & SEM : III EEE, V SEMESTER

BRANCH : ELECTRICAL AND ELECTRONICS ENGINEERING

SUBJECT : POWER ELECTRONICS LABORATORY

SUB.CODE : EE56

LIST OF EXPERIMENTS

S.NO. EXPERIMENTS PAGE.NO.

1 Characteristics of SCR 1

2 Characteristics of TRIAC 7

3 Characteristics of MOSFET and IGBT 13

4 Transient characteristics of SCR and MOSFET 23

5 Three phase fully controlled converter 31

6 Three phase half controlled converter 37

7 Step down and Step up MOSFET based choppers 42

8 IGBT based single phase PWM inverter 48

9 IGBT based three phase PWM inverter 56

10 Series, Parallel resonant converters 62



INDEX

S.No.

Expt.

Date

Name of the Experiment

Marks

Staff

Signature

1

2

3

4

5

6

7

8

9

10



Ex:No: Date:

1. CHARACTERISTICS OF SCR AIM:

To obtain the V-I characteristics of SCR (Silicon Controlled Rectifier) and to measure the breakdown voltage and holding current values.

APPARATUS REQUIRED:

S.No Apparatus Range Type Quantity 1 Ammeter (0-50)mA MC 2 2 Voltmeter (0-30)V MC 1 3 RPS (0-30)V - 1 4 Resistors 1KΩ, 1MΩ - 1 5 SCR TN4004 - 1 6 Bread Board - - 1 7 Wires - - Few

THEORY:

An SCR is a three terminal, four layer latching device. The three terminals are anode, cathode and gate. When the anode is more positive w.r.t the cathode, junctions j1, j3 are forward biased and the junction j2 is reverse biased. Only a small leakage current flows through the device. The device is said to be in the forward blocking state or OFF state. When the anode to cathode voltage is increased to break-over value, the junction j2 breaks down and device starts conducting. The anode current must be more than a value known as latching current in order to maintain the device in the ON state. Once SCR starts conducting, it behaves like a conducting diode and gate has no control over the device.

Fig.1. Schematic Symbol Fig.2. Block Construction



TABULATION:

S.No IG = mA IG = mA

VAK (V) IA (mA) VAK (V) IA (mA)



The device can be turned OFF only by bringing the device current below a value known as holding current. The forward voltage drop across the device in the ON state is around one volt. When the cathode voltage is made positive w.r.t the anode voltage the junction j2 is forward biased and the junction’s j1 and j3 are reverse biased. The device will be in the reverse blocking state and small reverse leakage current flows through the device. The device can be turned ON at forward voltages less than break over voltage by applying suitable gate current.

PROCEDURE:

1. Connections are made as shown in the circuit diagram. 2. Switch ON the power supply. 3. Keep the gate current (IG) as certain value. 4. Now slowly increase the Anode–Cathode voltage (VAK) by varying the pot till the

SCR gets ON. Now note down the anode current IA. 5. Find out the break over voltage (VBR) and latching current (IL) values. 6. Now reduce VAK till the SCR gets turn OFF and measure the SCR holding current

(IH) value. 7. For various gate currents take the readings and tabulate it.

RESULT:



DISCUSSION QUESTIONS:

1. What is thyristor?

2. What are the different families of thyristor devices?

3. What are the modes of an SCR?

4. Define Latching current (IL).

5. Define Holding current (IH). Which will be larger either IL or IH?

6. What are the different methods to turn ON the SCR?



CIRCUIT DIAGRAM:

MODEL GRAPH:



Ex:No: Date:

2. CHARACTERISTICS OF TRIAC AIM:

To obtain the V-I characteristics of TRIAC for both forward and reverse conduction.

APPARATUS REQUIRED:

S.No Apparatus Range Type Quantity 1 Kit module - - 1

2 Voltmeter (0-30)V MC 1

3 Ammeter (0-200)mA MC 1

4 Patch chords - - Few

THEORY:

A TRIAC is a bidirectional thyristor (it can conduct in both directions) with three terminals. It is used extensively for control of power in AC circuit. When in operation, a TRIAC is equivalent to two SCRs connected in anti-parallel. Its three terminals are usually designated as MT1, MT2 and gate.

Fig.1. Schematic Symbol Fig.2. Block Construction

The V-I characteristics of a TRIAC is based on the terminal MT1 as the reference point. The first quadrant is the region wherein MT2 is positive w.r.t MT1 and vice-versa for the third quadrant. The peak voltage applied across the device in either direction must be less the break over voltage in order to retain control by the gate. A gate current of specified amplitude of either polarity will trigger the TRIAC into conduction in either quadrant, assuming that the device is in a blocking condition initially before the gate signal is applied. The characteristics of a TRIAC are similar to those of an SCR, both in blocking and conducting states, except for the fact that SCR conducts only in the forward direction, whereas the TRIAC conducts in both the directions.



TABULATION:

1. MT2 positive with respect to MT1 negative

IG = mA

VA (V) IA (mA)

2. MT2 negative with respect to MT1 positive

IG = mA

VA (V) IA (mA)



PROCEDURE:

1. Connections are made as per the circuit diagram. 2. Keep in position minimum so IS and VA across MT1 and MT2 are zero. 3. Switch on the supply. 4. Allow low voltage between MT1 and MT2 increase VA so IA increases. Repeat it till the

device turn ON. 5. Slowly increases gate to MT1 voltage set particular IG = 18mA. 6. Keep IG constant and increases VA in step by step when VA increases. IA increases

slightly when break over is reached voltage get decreases but current increases sharply. 7. For reverse characteristics, change the connection to make MT1 positive with respect to

MT2 and repeat the same procedure.

RESULT:




1. What is TRIAC?

2. TRIAC is only used in AC circuits. Justify.

3. How does a TRIAC work?

4. Draw the equivalent circuit for TRIAC?

5. What are the differences between SCR and TRIAC?

S.No SCR TRIAC



MOSFET

CIRCUIT DIAGRAM:

MODEL GRAPH:

Output Characteristics Transfer Characteristics



Ex:No: Date:

3. CHARACTERISTICS OF MOSFET AND IGBT AIM:

To obtain steady state output characteristics and transfer characteristics for both MOSFET and IGBT.

APPARATUS REQUIRED:

S.No Apparatus Range Type Quantity 1 Kit module - VPET202A 1


3 Ammeter (0-200)mA MC 1

4 RPS (0-30)V - 2

4 Patch chords - - Few THEORY: MOSFET

a) Output characteristics:

It indicate the variation of drain current ID as a function of drain–source voltage VGS as a parameter. For low values of VDS, the graph between ID–VDS is almost linear; this indicates a constant value of on resistance RDS = VDS / ID. For given VGS, if VDS is increased, output characteristic is relatively flat indicating that drain current is nearly constant.

b) Transfer characteristics:

This characteristic shows the variation of drain current ID as a function of gate-source voltage VGS. Threshold voltage VGST is an important parameter of MOSFET. VGST is the minimum positive voltage between gate and source to induce n-channel. Thus, for threshold voltage below VGST, device is in the OFF-state. Magnitude of VGST is of the order of 2 to 3V.

IGBT

a) Output characteristics:

Output characteristics of an IGBT show the plot of collector current IC versus Collector-Emitter voltage VCE for various values of Gate-Emitter voltages. In the forward direction, the shape of the output characteristics is similar to that of BJT. But here the controlling parameter is Gate-Emitter voltage VGE because IGBT is a voltage controlled device. When the device is OFF, junction j2 blocks forward voltage and in case reverse voltage appears across collector and emitter, junction j1 blocks it. VRM is the maximum reverse breakdown voltage.



TABULATION:

MOSFET:

Output Characteristics

VGS = V VGS = V VGS = V

VDS (V) ID (mA) VDS (V) ID (mA) VDS (V) ID (mA)

Transfer Characteristics

VDS = V VDS = V VDS = V

VGS (V) ID (mA) VGS (V) ID (mA) VGS (V) ID (mA)



b) Transfer characteristics:

The transfer characteristics of an IGBT is a plot of collector current IC versus Gate-Emitter voltage VGE. This characteristic is identical to that of power MOSFET. When VGE is less than the threshold voltage VGET, IGBT is in the OFF-state.

MOSFET

PROCEDURE:

a) Output Characteristics:

1. Connections are made as per the circuit diagram. 2. Gate-Source voltage (VGS) is kept at a constant value greater than the threshold value

of the device. 3. Drain-Source voltage (VDS) is varied in steps and the corresponding drain current (ID)

is noted down. 4. The procedure is repeated by keeping the Gate-Source voltage (VGS) at some other

constant value.

b) Transfer Characteristics:

1. Drain-Source voltage (VDS) is kept at a constant value. 2. Gate-Source voltage (VGS) is varied in steps and the corresponding drain current (ID)

is noted down. 3. The procedure is repeated by keeping the Drain-Source voltage (VDS) at some other

constant value.



IGBT

CIRCUIT DIAGRAM:

MODEL GRAPH:

Output Characteristics Transfer Characteristics



IGBT

PROCEDURE:

a) Output Characteristics:

1. Connections are made as per the circuit diagram. 2. Gate-Emitter voltage (VGE) is kept at a constant value. 3. Collector-Emitter voltage (VCE) is varied in steps and the corresponding collector current

(IC) is noted down. 4. The procedure is repeated by keeping the Gate-Emitter voltage (VGE) at some other

constant value.

b) Transfer Characteristics:

1. Collector–Emitter voltage (VCE) is kept at a constant value. 2. Gate–Emitter voltage (VGE) is varied in steps and the corresponding collector

current (IC) is noted down. 3. The procedure is repeated by keeping the Collector-Emitter voltage (VCE) at some

other constant value.



TABULATION:

IGBT:

Output Characteristics

VGE = V VGE = V VGE = V

VCE(V) IC (mA) VCE (V) IC (mA) VCE (V) IC(mA)

Transfer Characteristics

VCE = V VCE = V VCE = V

VGE(V) IC (mA) VGE (V) IC (mA) VGE (V) IC (mA)



RESULT:




1. What are the different types of Power MOSFET?

2. Power MOSFET is a voltage controlled device? Why?

3. Name the three regions of operation in a MOSFET.

4. Define threshold voltage.

5. Define Pinch off Voltage.

6. Compare Power MOSFET’s with BJT’s.



CIRCUIT DIAGRAM:

Turn-ON characteristics of SCR:

Turn-OFF characteristics of SCR:



Ex:No: Date:

4. TRANSIENT CHARACTERISTICS OF SCR AND MOSFET

AIM:

To obtain the transient characteristics of SCR and MOSFET under turn ON and turn OFF conditions.

APPARATUS REQUIRED:

S.No Apparatus Range Type Quantity 1 Kit module - VPET-216 1

2 CRO - - 1



5 Power chord - - 1

THEORY:

SCR

a) Turn-ON characteristics:

A forward biased thyristor is usually turned ON by applying a positive gate voltage between gate and cathode. Thyristor turn ON time is defined as the time during which it changes from forward blocking state to final ON state. Total turn ON time can be divided into three intervals; 1. Delay time (td) 2. Rise time (tr) 3. Spread time (tp).

Delay time is measured from the instant at which gate current reaches 0.9 Ig to the instant at which anode current reaches 0.1 Ia.

Rise time is the time taken by the anode current to rise from 0.1 Ia to 0.9 Ia. Spread time is the time taken by the anode current to rise from 0.9 Ia to Ia.

b) Turn-OFF characteristics:

Thyristor turn-OFF means that it has changed from ON to OFF state and is capable of blocking the forward voltage. This dynamic process of the SCR from conduction state to forward blocking state is called turn OFF process. The turn OFF time is divided into two intervals; Reverse Recovery time trr and Gate Recovery time tgr. The time required for the reversed anode current to recover to zero or nearly zero value. The charges around junction j2 of SCR are trapped and these only by recombination. This recombination of charges between t3 and t4 is called gate recovery time.



MODEL GRAPH:



MOSFET

a) Turn-ON characteristics:

The turn ON time is defined as the sum of turn ON delay time and rise time of the device.

During turn ON delay time tdn, the input capacitance charges to gate threshold voltage VGST and the drain current is zero.

During rise time period, gate voltage rises to VGSP which is the gate source peak voltage.

This voltage is sufficient to drive the MOSFET into ON state. Then drain current increases from zero to full value of current ID.

Thus the total turn ON time is ton = tdn + tr. The turn ON time can be reduced by using low impedance gate drive circuit.

b) Turn-OFF characteristics:

The turn OFF process is initiated by the removal of gate source voltage VGS at time t1, because MOSFET is a majority carrier device. The turn OFF time is the sum of turn OFF delay time tdf and fall time tf.

During this period tdf, the input capacitance discharges from over drive gate voltage V1 to VGSP but the drain current ID does not change.

During fall time tf, the input capacitance again discharges from VGSP to threshold voltage

VGST. Then drain current fall from ID to zero. So when VGS ≤ VGST, power MOSFET turn OFF is completed. Toff = tdf + tf.

SCR

PROCEDURE:

1. Connections are made as per the circuit diagram. 2. Switch ON the trainer power ON switch. 3. Switch ON the gate ON/OFF switch. 4. Observe the waveform in the following manner.

To observe the input square wave connect the CRO between the input and GND terminals.

To view gate voltage connects CRO between gate and cathode. To view output voltage connects CRO across the load resistor.

5. From the output waveform note down the values. 6. Plot the graph for voltage versus time.



CIRCUIT DIAGRAM:

MODEL GRAPH:



MOSFET

PROCEDURE:

1. Connections are made as per the circuit diagram. 2. Switch ON the trainer power ON switch. 3. Switch ON the gate ON/OFF switch. 4. Observe the waveform in the following manner.

To observe the input square wave connect the CRO between the input and GND terminals.

To view gate voltage connects CRO between gate and source terminals. To view output voltage connects CRO across the load resistor.

5. From the output waveform note down the values. 6. Plot the graph for voltage versus time.

RESULT:




1. What are the biasing methods of SCR?

2. Define SCR turn ON time.

3. Mention the three intervals of SCR turn ON process.

4. Define SCR turn OFF time.

5. Define circuit turn OFF time.

6. Why circuit turn OFF time is greater than the SCR turn OFF time?



CIRCUIT DIAGRAM:

MODEL GRAPH:



Ex:No: Date:

5. THREE PHASE FULLY CONTROLLED CONVERTER

AIM:

To study the operation of three phase SCR fully controlled converter using VPET-215 module.

APPARATUS REQUIRED:

S.No Apparatus Range Quantity 1 Kit module VPET-215 1

2 Multimeter - 1

3 Pulse chords - Few

4 Power chord - 1

5 CRO - 1

6 Connecting wires - Few

THEORY:

A three-phase fully-controlled bridge rectifier can be constructed using six SCRs. The bridge circuit has two halves, the positive half consisting of the SCRs T1, T3 and T5 and the negative half consisting of the SCRs T2, T4 and T6. At any time, one SCR from each half conducts when there is current flow. The SCRs are triggered in the sequence T1, T2, T3, T4, T5, T6 and T1 and so on. When the SCRs are fired at 0o firing angle, the output of the bridge rectifier would be the same as that of the circuit with diodes. For instance, it is seen that D1 starts conducting only after θ = 30o. In fact, it can start conducting only after θ = 30o, since it is reverse-biased before θ = 30o. The bias across D1 becomes zero when θ = 30o and diode D1 starts getting forward biased only after θ =30o.

For α = 0o, T1 is triggered at θ = 30o, T2 at 90o, T3 at 150o and so on. For α = 60o, T1 is triggered at θ = 30o + 60o = 90o, T2 at θ = 90o + 60o = 150o and so on. Note that positive group of SCRs are fired at an interval of 120o. Similarly, negative group of SCRs are fired with an interval of 120o. But SCRs from both the groups are fired at an interval of 60o. This means that commutation occurs every 60o, alternatively in upper and lower group of SCRs. Each SCR from both groups conducts for 120o.



TABULATION:

S.No Firing Angle (deg) Measured Voltage (V) Calculated Voltage (V)

MODEL CALCULATION:



FORMULAE USED:

Average output voltage,

Vo = ( 3√3 Vm / Π ) *cosα

Where,

Vm = Peak phase voltage, Volts α = Firing angle, degrees

PROCEDURE:

1. Switch ON the power supply ON/OFF switch. 2. Switch ON the pulse ON/OFF switch. 3. Vary the firing angle step by step in the range 180° – 0°. 4. For each firing angle observe the output waveform through CRO. 5. Tabulate the readings.

RESULT:




1. What is a three phase controlled rectifier?

2. What are the advantages of three phase controlled rectifiers?

3. What are the classifications of three phase controlled rectifier?

4. What are the advantages of six pulse converter?

5. Write down the expression for average output voltage of three phase full converter.

6. What are the effects of source impedance in the controlled rectifiers?



CIRCUIT DIAGRAM:

MODEL GRAPH:



Ex:No: Date:

6. THREE PHASE HALF CONTROLLED CONVERTER

AIM:

To study the operation of three phase SCR half controlled converter using VPET-218 module.

APPARATUS REQUIRED:

S.No Apparatus Range Quantity 1 Kit module VPET-218 1

2 Multimeter - 1

3 Pulse chords - -

4 Power chord - 1

5 CRO - 1

6 Connecting wires - Few

THEORY:

Three phase half controlled bridge rectifier circuit consists of three SCRs in three arms and three diodes in the other three arms.The output voltage V0 across the load terminals is controlled by varying the firing angles of SCRs T1, T2, T3. The diodes D1, D2 and D3 provide merely a return path for the current to the most negative line terminal. For firing angle less than 30°, the output terminal voltage of the converter is always positive, and the freewheeling diode does not come into operation. As the firing angle is retarded beyond this point, so the load current starts to freewheel through the diode for certain periods, thus cutting off the input line current, and preventing the output terminal load voltage from swinging into the negative direction. Hence the effect of the freewheeling diode is to cause a reduction of ripple voltage of the output terminals and at the same time to divert the load current away from the input lines.



TABULATION:

S.No Firing Angle (deg) Measured Voltage (V) Calculated Voltage (V)

MODEL CALCULATION:



FORMULAE USED:

Average output voltage,

Vo = ( 3√3 Vm / 2Π ) * (1+cosα)

Where,

Vm = Peak phase voltage, Volts

α = Firing angle, degrees

PROCEDURE:

1. Switch ON the power supply ON/OFF switch. 2. Switch ON the pulse ON/OFF switch. 3. Vary the firing angle step by step in the range 180° – 0°. 4. For each firing angle observe the output waveform through CRO. 5. Tabulate the readings.

RESULT:




1. What is the condition for load current should be discontinuous?

2. What is the output ripple voltage frequency of three phase half wave converters?

3. What are the two modes of operation present in the three phase half controlled rectifiers?

4. What is the use of freewheeling diode present in the three phase half controlled rectifiers?

5. What is the condition for the output voltage should be negative?



CIRCUIT DIAGRAM:

Boost Converter:

Buck Converter:



Ex:No: Date:

7. STEP DOWN AND STEP UP MOSFET BASED CHOPPERS

AIM:

To examine the closed loop response of DC-DC Buck and Boost converters using VSMPS-07A module.

APPARATUS REQUIRED:

S.No Apparatus Range Quantity 1 Kit module VSMPS-07A 1

2 Patch chords - Few

3 Voltmeter (0-30)V 2

4 CRO - 1

THEORY:

This experiment is intended to study the closed loop operation of Buck-Boost converter. The set voltage to the PWM generator is set at 1V. Feedback voltage from Buck-Boost converter power circuit is connected to the PWM generator circuit. On varying the DC input voltage slowly from 0 to 15V, the output voltage is measured as constant. These values are tabulated.

PROCEDURE:

1. Switch ON AC power supply. 2. Switch ON the power ON/OFF switch. 3. View the carrier signal in the CRO at T3. 4. Set switch SW1 in downward direction. 5. Set switch SW2 in downward direction for Boost converter / Set switch SW2 in upward

direction for Buck converter. 6. View the PWM signal in the CRO at T1. 7. Vary the SET VOLTAGE ADJUST POT from min to max and set the PWM signal at

desired duty cycle ratio. 8. Note down the ton and T values. 9. Switch ON the variable DC supply and set the voltage at 15V. 10. Check all the test point waveforms.



MODEL GRAPH:

Boost Converter :

Buck Converter :

TABULATION:

Input Voltage = V

Boost Converter Buck Converter

Set Voltage

(mV)

PWM

Voltage (V)

Output

Voltage (V)

Set Voltage

(mV)

PWM

Voltage (V)

Output

Voltage (V)



11. View the device current IQ across I1 and I2. 12. View the diode D current across I3 and I4. 13. View the inductor current IL across I3 and I7. 14. View device voltage across I2 and I3. 15. View the rectified voltage across I5 and I8. 16. View the inductor voltage across I7 and I8. 17. Connect CRO across P5 and P6 output terminals of trainer module and view the output

voltage. 18. View the feedback signal at T6. 19. For each input voltage value, tabulate the measured output voltage values.

RESULT:




1. What is a DC chopper?

2. What are the different types of chopper configuration?

3. What is meant by step-down and step-up chopper?

4. Write down the expression for average output voltage for step-down and step-up choppers?

5. Define switched mode regulator.



CIRCUIT DIAGRAM:



Ex:No: Date:

8. IGBT BASED SINGLE PHASE PWM INVERTER

AIM:

To study the operation of the single phase bridge inverter using IGBT, with Sinusoidal Pulse Width Modulation technique.

APPARATUS REQUIRED:

S.No Apparatus Quantity 1 Single phase IGBT PWM inverter 1

2 CRO 1

3 RL load 1

THEORY:

It consists of four IGBTs S1, S2, S3, S4 and four inverse parallel diodes D1, D2, D3, D4. The diodes are essential to conduct the reactive current, and thereby to feed back the stored energy in the inductor to the DC source. These diodes are known as feed back diodes. For many industrial applications the output AC voltage of the inverter must be sinusoidal in shape and the amplitudes and frequency must be controllable. This is achieved by PWM of the inverter switches.

The switching sequence of the inverter switches in this case, is obtained by comparing a sinusoidal control signal, of adjustable amplitude and frequency with a fixed frequency triangular carrier. The frequency of the triangular carrier wave determines the switching frequency of the inverter switches. The frequency of the sinusoidal control signal decides the fundamental frequency of the inverter output voltage, and is also called the modulating frequency. The sinusoidal pulse width modulation can be programmed to have either bipolar voltage switching or unipolar voltage switching. The unipolar voltage switching has the advantage of effectively doubling the switching frequency as compared to the bipolar voltage switching.



MODEL GRAPH:

Variation of Output Voltage with Modulaton Index



FORMULAE USED: ma = Vsine / Vtri

Vo = ma x Vs

Where, ma = Modulation index

Vsine = Amplitude of the sine wave

Vtri = Amplitude of the triangular wave Vo = Output voltage

Vs = DC supply voltage

PROCEDURE:

1. Ensure that the circuit breaker and pulse release ON/OFF toggle switch are in OFF position.

2. Connect the R-L load across the output terminals Lo and No provided in the front panel. Include an ammeter to measure the current and voltmeter to measure the voltage.

3. Connect an AC input at the input terminals L and N provided in the front panel. 4. With the pulse ON/OFF switch and circuit breaker in OFF condition give the power to

the inverter module. This will ensure the control power supply to all the control circuitry. 5. Set the amplitude of the reference sine wave to minimum value. 6. Keeping the pulse release ON/OFF switch in OFF position, switch ON the power supply

to the bridge rectifier. 7. Release the gating signals to the inverter switches by turning ON the pulse release

ON/OFF switch. 8. Observe the triangular carrier and the reference sine waveforms on the CRO. Measure the

amplitude and the frequency of the triangular carrier through CRO and note it down. Adjust the sine wave frequency to about 50Hz.

9. Connect the CRO probes to observe the load voltage and current waveforms. 10. Observe the load voltage and load current waveforms. Sketch the waveforms on a graph

sheet to scale for one cycle period of the inverter output frequency. Measure the amplitude of the voltage pulses.

11. Measure the output voltage either by using a digital multimeter. 12. Calculate the modulation index ma and the rms output voltage Vo. 13. Increase the amplitude of the reference sine wave and note down its value. 14. Repeat steps 8 to 13 for various amplitude of reference sine wave and tabulate the

readings. Plot the characteristics of modulation index versus output voltage.



TABULATION:

S.No Vtri (V) Vsine (V) ma Vo measured (V) Vo calculated (V)

MODEL CALCULATION:



RESULT:




1. What is the function of an inverter?

2. What are the different types of inverters?

3. Why thyristors are not preferred for inverters?

4. What is meant by PWM control?

5. What are the different types of PWM control?

6. What are the advantages of PWM control?



CIRCUIT DIAGRAM:



Ex:No: Date:

9. IGBT BASED THREE PHASE PWM INVERTER

AIM: To study the operation of IGBT based three phase inverter and its switching.

APPARATUS REQUIRED:

S.No Apparatus Range Quantity

1 Kit module PEC16HV2-A PEC16HV2-B

1 1

2 3 phase lamp load - 1

3 CRO - 1

THEORY:

The most frequently used three phase inverter circuit of three legs, one for each phase. For this configuration, output transformer is not required. Also, this circuit uses six IGBTs. The inverter configuration is also termed as six step bridge inverter. In inverter terminology, a step is defined as a change in the firing from one IGBT to the next IGBT in proper sequence. For one cycle of 360°, each step would be of 60° for a six step inverter. This means that IGBT’s would be gated at regular intervals of 60°.

Basically, there are two possible schemes of gating the IGBT. In one scheme, each IGBT conducts for 180° and in the other scheme, each IGBT conducts for 120°. In 180° mode operation, pair in each leg, i.e. T1, T4; T3, T6; and T5, T2 are turned ON with the time interval of 180°. It means that IGBT T1 conducts for 180° and IGBT T4 for the next 180° of a cycle. IGBTs in the upper group, i.e. T1, T3, T5 conduct at an interval of 120°. It means that if IGBT T1 is fired at 0°, then T3 must be triggered at 120° and T5 at 240°. Same is true of lower group of IGBT.



MODEL GRAPH:



PRECEDURE:

1. Switch ON power ON/OFF switch of power module. O.C LED glows. 2. Press the O.C reset switch. Now LED is switched OFF. 3. Press the DC ON/OFF button. LED glows to indicate the DC supply to the circuit. 4. Switch ON power ON/OFF switch to the digital inverter controller module. 5. Select the 180 degree mode of operation using the press button. 6. CRO must be isolated 7. Using CRO view the output voltage across the load terminals. 8. Observe the output waveform. 9. Press the RST button to reset the system.

RESULT:




1. What is the use of three phase inverter?

2. Define step.

3. What are the different conduction methods of three phase inverter?

4. What is the function of capacitor connected at the input terminal of an inverter?

5. What is the function of feedback diodes in an inverter?

6. What is the switching sequence for three phase inverters in 180° conduction?



CIRCUIT DIAGRAM:

SERIES RESONANT CONVERTER:

MODEL GRAPH:



Ex:No: Date:

10. SERIES, PARALLEL RESONANT CONVERTERS

AIM: To study the series and parallel loaded resonant converter using VPET-315 module.

APPARATUS REQUIRED:

S.No Components Range Type Quantity

1 Kit module - VPET-315 1


3 Ammeter (0-2)A MC 1


5 9 pin D connector - - 1

6 CRO - - 1

THEORY:

Series resonant converter

The resonant converters are defined as the combination of converter topologies and switching strategies that result in zero voltages and/or zero current switching. The series resonant converter consist of one or two half bridges forming a half or full bridge converter. Between the output terminals, a series resonant circuit is connected. This series resonant circuit consists of an inductor, capacitor and resistor, with one or more of these elements actually being part of the load. Usually, at least the resistor is part of the load.

An AC power can be delivered to the load, due to the resonant behavior of the circuit. If a DC load is used, the resistor can be replaced by a rectifier connected to the DC load. If the load is directly connected to the resonant circuit, i.e. without a rectifier in between, it is referred to as a series resonant DC to DC converter.



TABULATION:

Resonant frequency = KHz

S.No Switching frequency (fs) Output Voltage (V) Output Current (A)

CIRCUIT DIAGRAM:

PARALLEL RESONANT CONVERTER:



Parallel resonant converter

The parallel load resonant converter is similar to the previously investigated series resonant converter. In the case of parallel resonant converter, the output rectifier is connected in parallel with the resonant capacitor. Since the resonant capacitor represents a voltage source to the rectifier, the output filter of the rectifier must be a current source, i.e. inductive. The rectifier represents a non linear load. Usually a transformer is connected between the resonant circuit and the rectifier in order to adapt the load voltage to the DC link voltage used. A transformer can also be used to provide a galvanically isolated output voltage, which is desired in some applications.

The resonant inductor current is not determined by the rectifier output current for the parallel resonant converter. The rectifier output voltage is dependent on the resonant capacitor voltage for the parallel resonant converter. For the parallel resonant converter, continuous current operation above resonance results in turn-ON at ZCS conditions since the resonant current commutates from the freewheeling diodes to the power transistors naturally. In this case, natural commutation means that the commutation takes place at the zero crossing of the resonant inductor current. Transistor turn-OFF is not performed under neither ZCS or ZVS conditions, unless loss less turn-OFF snubbers are used.

Series resonant converter

PROCEDURE:

1. Initially keep all switches in OFF position. 2. Initially keep frequency adjustment pot in minimum position. 3. Power ON the main switch. 4. Check the test point waveforms w.r.t ground. 5. Connect the 9 pin D connector from PWM output to PWM input. 6. Connect the connector P to P1 and P6 to P7. 7. Connect the connector P10 to P4 and P8 to P11. 8. Connect the current sensing resistor across the connector P2 and P3. 9. Connect voltmeter across the connector P5 and P12. 10. Connect the R-load across the connector P5 and P12 through ammeter. 11. Power ON the S1 switch. 12. Adjust “FREQUENCY ADJUST” pot and set the switching frequency. 13. Connect the CRO to the connector T15 w.r.t driver circuit ground to observe the switch

voltage. 14. Connect the CRO to the connector P2 (+) and P3 (-) to observe the current waveform. 15. Similarly, note the switch voltage and current waveforms for various switching frequency

and tabulate the corresponding load voltage and current.



MODEL GRAPH:

TABULATION:

Resonant frequency = KHz

S.No Switching frequency (fs) Output Voltage (V) Output Current (A)



Parallel resonant converter

PROCEDURE:

1. Initially keep all switches in OFF position. 2. Initially keep frequency adjustment pot in minimum position. 3. Power ON the main switch. 4. Check the test point waveforms w.r.t ground. 5. Connect the 9 pin D connector from PWM output to PWM input. 6. Connect the connector P to P1 and P6 to P7. 7. Connect the connector P9 to P4, P8 to P10 and P10 to P11. 8. Connect the current sensing resistor across the connector P2 and P3. 9. Connect voltmeter across the connector P5 and P12. 10. Connect the R-load across the connector P5 and P12 through ammeter. 11. Power ON the S1 switch. 12. Adjust “FREQUENCY ADJUST” pot and set the switching frequency. 13. Connect the CRO to the connector T15 w.r.t driver circuit ground to observe the switch

voltage. 14. Connect the CRO to the connector P2 (+) and P3 (-) to observe the current waveform. 16. Similarly, note the switch voltage and current waveforms for various switching frequency

and tabulate the corresponding load voltage and current.

RESULT:




1. What are the types of resonant switch DC-DC converters?

2. What is meant by Zero Current Switching?

3. What is meant by Zero Voltage Switching?

4. Define resonant converters.

5. What is meant by series resonant converter?

6. What are the conditions for resonant circuit behaves like a capacitive load and

inductive load in a series resonant converter?

Documents

EE56 Power Electronics