power electronics lab manual

SUDHARSAN ENGINEERING COLLEGE,

SATHIYAMANGALAM.

DEPARTMENT OF

ELECTRICAL AND ELECTRONICS

ENGINEERING

VII – SEMESTER

POWER ELECTRONICS & DRIVES

SUBJECT CODE: EE 1405

LAB MANUAL

PREPARED BY: APPROVED BY:

Mr. G. SARAVANA VENKATESH

(AP / EEE) (HOD / EEE)

ANNA UNIVERSITY

THIRUCHIRAPALLI

Subject Name : Power Electronics Lab

Subject Code : EE 1405

Semester : VII

Branch : EEE

Course Duration : JULY 2010 – DEC 2010

Staff in – charge : Mr. G.Saravana Venkatesh

LIST OF EXPERIMENTS

1. Single Phase Semi-converter with R and R-L loads for continuous and discontinuous

conduction modes

2. Single Phase Full-converter with R and R-L loads for continuous and discontinuous

conduction modes

3. Three phase full-converter with R-L load

4. IGBT based Single phase inverters.

5. Volts/Hz control of VSI fed three phase induction motor drive.

6. Single phase AC voltage controller

7. Simulation of open loop speed control of converter fed DC motor drive using MATLAB

8. Simulation of open loop speed control of chopper fed DC motor drive using MATLAB

9. Step down chopper

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1. SINGLE PHASE HALF CONTROLLED CONVERTERS WITH R & R-L

LOADS FOR CONTINUOUS AND DISCONTINUOUS CONDUCTION

MODES

AIM:

To study the half controlled and fully controlled converter with Resistive &

Resistive and inductive load.

APPARATUS REQUIRED:

1) Device module.

2) R, RC, UJT/555 firing circuit module.

3) Loading rheostat.

4) Load inductance.

5) CRO.

6) Digital multimeter.

THEORY:

Semi converter

Controlled rectifiers are those whose output voltage can be controlled by

varying the firing angle of the SCR. During the positive half-cycle. SCR1 & D2

are forward biased and starts conducting when trigger pulses are given

simultaneously. During negative half-cycle SCR2& D1 are forward biased and it

starts conducting. In the trigger circuit synchronization must be obtained from the

supply voltage other than SCR voltage and trigger pulse must be continuous

during the conduction period.

PROCEDURE:

Semi converter:

1. Connect the cathodes of SCR1 and SCR3 together, and the anodes of

two diodes together connect the anode of SCR1 and the cathode of diode

SUDHARSAN ENGINEERING COLLEGE, SATHIYAMANGALAM 3

D4 together. Also connect the anode of SCR3 and D2 together.

2) Connect the 24V AC input to the bridge circuit.

3) Connect the load consisting of L and R across the output terminals of the

bridge converter.

4) Connect the gating signals to the SCRs from the bridge firing circuit

module, with G1K1 to SCR1 and G2K3 to SCR3 as marked in the circuit.

5) Switch on + 24AC provided in the firing circuit.

6) Ensure proper connection of the circuit as shown in figure.

7) Switch ON power supply to CRO and the input power module.

8) Connect the CRO probes to observe the waveforms of the input ac

voltage, output voltage and voltage across any one of the SCR.

9) Adjust the firing angle delays to about 600 and plot the waveforms to scale

on a graph sheet.

10) Remove the CRO probes from the circuit and connect them to observe the

load voltage (VL) and load current (IL) waveforms. For this, connect the

CRO ground terminal to (-) end of the load and channel-1 probe to positive

end of the load.channel-2 probe to the common terminal of the inductance

and resistance marked ‘0’ in the circuit. The voltage across the load

resistance is proportional to the load current.

11) Plot the load voltage and load current waveforms to scale in the graph

sheet in time synchronization with the AC input voltage.

12) Measure the average DC output voltage and rms AC input voltage with a

digital multimeter. Switch off power supply to the circuit.

13) Calculate the DC output voltage.


CIRCUIT DIAGRAM:


RESULT:

The operation of half controlled and fully controlled converter with

Resistive & Resistive and inductive load have been studied.

Signature of the Staff


2. SINGLE PHASE FULL CONTROLLED CONVERTERS WITH R & R-L

LOADS FOR CONTINUOUS AND DISCONTINUOUS CONDUCTION

MODES

AIM:

To study the half controlled and fully controlled converter with Resistive &

Resistive and inductive load.

APPARATUS REQUIRED:

1) Device module.

2) R, RC, UJT/555 firing circuit module.


4) Load inductance.

5) CRO.


THEORY:

Fully Controlled Converter

The single phase fully controlled rectifier consists of 4 SCRs and load R.

During the positive half-cycle SCR1&2 are forward –biased and when this SCR is

fired simultaneously at a firing angle the load is connected to the input supply.

During the negative half-cycle the SCRs 3&4 are forward biased and SCRs 1&2

are turned off due to line or natural commutation.

PROCEDURE:


1)Form the single-phase bridge circuit. Connect the cathode of SCRs 1&3

together. Connect the anodes of SCRs 2&4 together. Connect the anode

of SCR1 to cathode of SCR4.Connect the anode of SCR3 to the cathode

of SCR2.


2)Connect the gating signals to the SCRs from the firing circuit module.

Connect 24V ac input to the bridge circuit.

3)Connect the CRO probes to observe the output load voltage and the

voltage across SCR2.

4)Switch on the power supply to CRO and input power module. Switch on

24V ac in the firing circuit module and 24V ac input to the bridge

circuit. Draw the input ac line waveform on a graph sheet to suitable scale,

since SCR2 conducts only during positive half cycles, the output load

voltage waveforms can be easily synchronized with the ac waveform

drawn.

5) Vary the firing angle by adjusting the pot provided in the bridge firing

circuit module and observe the waveform.

6) Adjust the firing angle to 30 degrees. Observe the waveforms. Draw the

voltage waveforms across the load and SCR2, on the graph sheet.

7) Measure the dc output voltage with the digital multimeter and rms value of

the ac voltage to the bridge circuit for various firing angles.

8) Calculate the output dc voltage and compare with the measured one.

CIRCUIT DIAGRAM:



Fully Controlled Converter with Resistive Load


RESULT:

The operation of half controlled and fully controlled converter with

Resistive & Resistive and inductive load have been studied.



3. THREE- PHASE FULLY CONVERTERS WITH R-L-E LOADS

AIM:

To study the operation of three- phase fully controlled converter with

RLE Loads

APPARATUS REQUIRED:

1) Device module.

2) Firing circuit module.


4) Load inductance.

5) CRO.


THEORY:

The three-phase circuit consists of two groups of SCRs, positive group

and negative group. The positive group SCRs are turned on when the supply

voltages are 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, SCRT2 and T6 and when phase C has the highest T3 must be triggered

simultaneously.

PROCEDURE :

1) Connect the full converter circuit as shown in the circuit.

2) Connect the load across the output terminals of the power citcuit.

3) Keep the MCB in off position.

4) Give the 3- phase supply to control unit. Observe the signals from test

points and from firing pulses terminals with the help of CRO.

5) Connect the firing pulses terminals to gate and cathode terminals of


respective thyristors.

6) Observe the output waveforms for various firing angle.


RESULT:

Thus the operation of three- phase fully- controlled converter with RLE load has been

studied.



4. IGBT BASED SINGLE PHASE PWM INVERTER

AIM:

To study the operation of the single phase bridge inverter using IGBT, with

sinusoidal pulse width modulation.

APPARATUS REQUIRED:

1) Single phase IGBT PWM inverter

2) CRO

3) R-L Load.

THEORY:

DC to AC converters are known as inverters. The function of an inverter is

to change the DC input voltage to a symmetrical output voltage of desired

magnitude & frequency. The output voltage could be fixed or variable at a fixed

or variable frequency. Varying the input DC voltage and maintaining the gain of

the inverter constant can obtain a variable output voltage. On the other hand if

the DC input voltage is fixed and it is not controllable a variable output voltage

can be obtained by varying the gain of the inverter, which is normally

accomplished by pulse width modulation (PWM) controlled within the inverter.

The inverter gain may be defines as the ratio of Ac output voltage to DC input

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 a

voltmeter to measure the voltage.

3) Connect the ac input at the input terminals L and N provided in the front

panel.

4) With the pulse release 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 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 frequency of the triangular carrier

through CRO and note it down. Adjust the sine wave frequency to about

50 Hz.

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 an analog meter or a digital

multi-meter.

11) Calculate the modulation index ma and the rms output voltage Vo.

m a = V control / V tri

= Amplitude of the sine wave / Amplitude of the triangular wave

Vo = m a Vs / _ 2

1)Increase the amplitude of the reference sine wave and note down its

value.

2)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.


SINGLE PHASE PWM INVERTER WAVE FORMS


RESULT:

The operation of the single-phase bridge inverter using IGBT, with

sinusoidal pulse width modulation has been studied.



5. VOLTS/HZ CONTROL OF VSI FED THREE PHASE INDUCTION

MOTOR DRIVE

AIM:

To control the speed of the induction motor by (a) varying the voltage with

fixed frequency (b) varying the frequency with fixed voltage.

APPPARATUS REQUIRED:

1) Three-phase IGBT PWM inverter kit

2) 1 H.P. – 3- Phase induction motor

3) Braking resistance

4) Isolation transformer

5) CRO

6) Tachometer

THEORY:

Inverters produce a sinusoidal ac output whose magnitude and frequency

can be controlled. The dc voltage is obtained by rectifying and filtering the line

voltage most often by the diode rectifier circuits. In an ac motor load, the voltage

at its terminals is desired to be sinusoidal and adjustable in its magnitude and

frequency. This is accomplished by means of the inverters, which accepts a dc

voltage as the input and produces the desired ac voltage input. In PWM

inverters, the input dc voltage is essentially constant in magnitude. DC voltage is

obtained by a diode rectifier, which is used to rectify the line voltage. The inverter

must control the magnitude and the frequency of the ac output voltages. This is

achieved by PWM of the inverter switches and hence such inverters are called

PWM inverters.

PROCEDURE:

1) Keep the main switch in off position initially.

2) Keep the MCB in off position. Check whether the kit is disconnected

from the supply or not.


3) Connect the braking resistance to the terminals RB1 and RB2.

4) Connect the 1- HP 3 phase induction motor across the output terminals of

inverter, as per the following procedure:

R phase of motor –U

Y phase of motor –V

B phase of motor –W

5) Switch on the main supply.

6) Switch on the pulse release switch.

7) Keep the frequency pot of the control voltage is in constant position.

Amplitude pot of the control voltage is the variable one.

Switch on the MCB. Now, voltmeter shows the output voltage of the bridge

rectifier.

8) For particular amplitude of control voltage with fixed frequency, the motor

picks up speed and it runs.

9) Measure the speed of the motor using Tachometer.

10) For various position of amplitude pot of reference sine wave, measure the

speed.

11) Find out the output voltages across u-v, v-w and w-u with the help of

multimeter.

12)Calculate the modulation index and the output voltage. The modulation

index is given by ma = Amplitude of sine wave/ Amplitude of triangular

wave.

13) Increase the amplitude of the reference wave and calculate the

modulation index. Then plot the characteristics of modulation index versus

output voltage.

14)Follow the same procedure keeping voltage as fixed and varying the

frequency. Also, the speed of the motor is controlled by varying both the

voltage and frequency.

15) Also, draw the graph between speed and voltage for voltage control and

speed versus V/f for V/f control.


TABULAR COLUMN:


RESULT:

Thus the speed of the induction motor is controlled using IGBT PWM

Inverter was studied.



6. SINGLE PHASE AC VOLTAGE CONTROLLER.

AIM:

To study the operation of single-phase ac voltage regulator with R load.

APPARATUS REQUIRED:

1) Device module

2) R, RC &UJT Firing circuit module

3) CRO

4) R load

THEORY:

The AC regulators are used to obtain a variable AC output voltage from a

fixed AC source. A single phase AC regulator is shown in the figure. It consists of

two SCRs connected in anti-parallel. Instead of two SCRs connected in antiparallel,

a TRIAC may also be used. The operation of the circuit is explained with

reference to RL load. During positive half-cycle SCR-1 is triggered into

conduction at a firing angle _. The current raises slowly due to the load

inductance. The current continues to flow even after the supply voltage reverses

polarity because of the stored energy in the inductor. As long as SCR-1

conducts, conduction drop across it will reverse bias SCR-2.Hence SCR-2 will

not turn on even if gating signal is applied. SCR-2 can be triggered into

conduction during negative half cycle after SCR-1 turns off.

PROCEDURE:

1) Connect the two SCRs in antiparallel as shown in the figure. Connect the

anode of SCR- .to the cathode of SCR-2.Connect the cathode of SCR-1 to

the anode of SCR-2.

2) Connect the load as shown in the figure.

3) Connect 24V AC to the circuit using patch cords.


4) Connect the gating signals (G1, K1) from the UJT trigger circuit to SCR-1

and (G2, K2) to SCR-2.

5) Switch on 24V AC supply.

6) Connect the CRO probes to observe the input AC voltage and the load

voltage waveforms.

7) Switch on power to CRO and on 24V ac to the circuit.

8) Select suitable voltage sensitivity and time base setting on the CRO. Use

line trigger mode.

9) Observe the waveforms. Vary the firing angle delay and study the

waveforms. For a particular firing angle, plot the waveforms on a graph

sheet to scale. Also plot the load current waveforms in synchronization

with the load voltage.

CIRCUIT DIAGRAM:

MODEL GRAPH:


RESULT:

The operation of single-phase ac voltage regulator with R, R-L load has been

studied.



7) SIMULATION OF OPEN LOOP SPEED CONTROL OF CONVERTER FED DC

MOTOR DRIVE USING MATLAB

OBJECTIVE

To simulate and analyze the performance of converter fed dc motor drive using

Matlab/Simulink.

REQUIREMENTS

1. Block parameter: GTO, DC Machine, AC Voltage source, DC voltage source

2. Source Block parameters : Pulse generator, Load Torque (Constant )

3. Function Block parameters: Product, Sum, Bus Selector, Relay, Gain

4. De-multiplexer

5. Connecting Elements

6. Scope

SYSTEM DESCRIPTION

1. Converter is used to get the variable D.C voltage from A.C source of fixed voltage.

2. Converter fed D.C drive also known as Static Ward Leonard drives.

3. II Quadrant operation demands that field winding of the motor is energized from a

single-phase, or three-phase, full converter.

4. Converter with α1 < 90 deg operates the motor in forward motoring mode in

Quadrant I

5. Converter with α1 > 90 deg and with field excitation reversed operates the motor in

forward regenerative braking mode in Quadrant IV.

6. As thyristors are capable of conducting current only in one direction, the rectifier is

capable of providing current only in one direction.


OPERATION PROCEDURE

Step - 1: Start Matlab and open Simulink

Step - 2 Open New Model Window and save

Step - 3: Drag all the required blocks from the Simulink library

Step - 4: Connect all the blocks and complete the system design

Step - 5: Set firing angles to all the converters with required delay. Set AC source

voltage at 220 V(50 Hz), DC source voltage at ----, simulation stop time at ----s and

Load torque initial and final values at --- N.m., --- N.m respectively.

Step - 6: Start running simulation and wait for the completion of the Simulation stop

time

Step - 7: Observe the behavior of waveforms of the motor speed, armature current,

field current and Electromagnetic torque.

Step - 8: Save the model and waveforms

Step - 9: Close Simulink window and Exit Matlab.

SIMULINK MODEL DIAGRAM


Figure: Converter fed DC Motor Drive

SIMULATION RESULTS AND ANALYSIS

The following parameters of the Dual converter fed DC motor drive can be observed

on the scope. The parameters are

a. motor speed,

b. Armature current

c. Field current and

d. Electromagnetic torque

1. Converter works as a rectifier and provide control of D.C voltage in either

direction, allow motor control in quadrants I and IV.

2. The rotor speed starts increasing gradually from zero and reaches its maximum

value at the end of simulation time.

3. It is also observed on the scope that field current is constant throughout the

simulation time.

SIMULATION WAVEFORMS

CONCLUSION

In this drive experiment converter fed DC motor Drive has been modeled using

Matlab/Simulink and the performance of the modeled system for the following

parameters have been observer on the scope and the behavior of the system is also

discussed. The parameters are

a. AC Source Voltage : 220 V

b. DC Source Voltage : ------V

c. Load Torque Initial Value : -----N.m.

d. Load Torque Final Value : -----N.m


e. Simulation time : -----sec

8) SIMULATION OF OPEN LOOP SPEED CONTROL OF CHOPPER FED DC

MOTOR DRIVE USING MATLAB

OBJECTIVE

To simulate and analyze the performance of the chopper fed dc motor drive using

Matlab/Simulink.

REQUIREMENTS

1. Block parameters :Separately Excited DC motor, Voltage source

2. Source block parameters : Constant, Pulse generator

3. GTO

4. Connecting elements

5. Scope

SYSTEM DESCRIPTION


1. The DC motor is fed by the DC source through a chopper which consists of GTO

thyristor. The motor drives a mechanical load characterized by inertia J, friction

coeficient B, and load torque TL.

2. The hysteresis current controller compares the sensed current with the reference

and generates the trigger signal for the GTO thyristor to force the motor current to

follow the reference.

3. The speed control loop uses a proportional-integral controller which produces the

reference for the current loop. Current and Voltage Measurement blocks provide

signals for visualization purpose. During torque regulation the speed controller is

disabled.

4. Time based generator having a pulse width of 50 with phase delay of 0 sec is used.

This phase delay varies for all the GTO pairs. Time-based is recommended for use

with a variable step solver.

OPERATION PROCEDURE

STEP – 1: Start Matlab and open simulink tool boxes.

STEP – 2: Open new model window and save.

STEP – 3: Draw all the required blocks from simulink library.

STEP – 4: Connect all the blocks and complete the system design.

STEP – 5: Set load torque value at ----Nm, simulation time = -----s.

STEP – 6: Start running the simulation and wait the for completion of the simulation

stop time.

STEP - 7: Using the scope observe the behavior of waveforms of the armature and

field Current, Electromagnetic torque and rotor Speed.

STEP – 8: Save the model and waveform.

STEP – 9 : Close simulink window and exit matlab.

SIMULINK MODEL DIAGRAM


Figure: Chopper fed dc motor drive

CHOPPER FED DC MOTOR DRIVE SIMULATION

1. In this experiment, a DC supply voltage of ----V is used. The GTO firing angles are

kept at ----deg and -----deg .

2. The GTO is triggered by applying the phase delay to the pulse generator. To

shorten the starting time, a very light load was chosen. Since only the speed is

controlled, the field current is maintaining at constant.

RESULTS AND ANALYSIS

The following parameters of the chopper fed DC drive can be observe on thescope.

The parameters are

a. Rotor speed,

b. Armature current,

c. Field currents,

d. Electromagnetic torque.


1. Motor starting: Start the simulation. Observe the motor current, voltage, and speed

during the starting on the scope. The end of the simulation time (----s), the system has

reached its steady-state.

2. The motor is coupled to a linear load, which means that the mechanical torque of

the load is proportional to the speed. The armature current follows the current

reference very well, with fast response time and small ripples.

3. Response to a change in reference load torque:

4. Restart the simulation and observe the drive response to successive changes in

speed reference and load torque.

SIMULATED WAVEFORMS

CONCLUSION

In this experiment, Chopper fed DC motor drive has been modeled using

Matlab/Simulink and the performance of the modeled system for the following

parameters have been observed on the scope and the behaviour of the system is also

discussed.

The parameters are

a. Voltage : 230 V

b. Load torque range : ---- Nm to ---- Nm

c. Firing angle : ----and -----degrees.

d. Simulation time : -----s


9. A.STEP DOWN CHOPPER

AIM:

To study the Step down chopper. (Buck converter).

APPARATUS REQUIRED:

· VPET 350 module.

· Patch chords.

THEORY:

A buck converter (dc-dc) is a step-down converter. (Shown in Fig.1.). Only

a switch is shown, for which a device belonging to transistor family is used. Also

a diode (termed as free wheeling) is used to allow the load current to flow

through it, when the switch (i.e., a device) is turned off. The load is inductive (RL)

one. In some cases, a battery (or back emf) is connected in series with the

load (inductive). Due to the load inductance, the load current must be allowed a


path, which is provided by the diode; otherwise, i.e., in the absence of the above

diode, the high-induced emf of the inductance, as the load current tends to

decrease, may cause damage to the switching device. If the switching device

used is a thyristor, this circuit is called as a step-down chopper, as the output

voltage is normally lower than the input voltage. Similarly, this dc-dc converter is

termed as buck one, due to reason given later. The output voltage and current

waveforms of the circuit (Fig. 1) are shown in Fig. 2. The output voltage is same

as the input voltage, i.e. when the switch is ON, during the period, . The switch is

turned on at, and then turned off at . This is called ON period. During the next

time interval, the output voltage is zero, i.e., as the diode, now conducts. The

OFF period is, with the time period being . The frequency is with T kept as

constant, the average value of the output voltage is,

.

Normally, due to turn-on delay of the device used, the duty ratio (k) is not zero,

but has some positive value. Similarly, due to requirement of turn-off time of the

device, the duty ratio (k) is less than 1.0. So, the range of duty ratio is reduced. It

may be noted that the output voltage is lower than the input voltage. Also, the

average output voltage increases, as the duty ratio is increased. So, a variable

dc output voltage is obtained from a constant dc input voltage. The load current

is assumed to be continuous as shown in Fig. 2. The load current increases in

the ON period, as the input voltage appears across the load, and it (load current)

decreases in the OFF period, as it flows in the diode, but is positive at the end of

the time period, T.

PROCEDURE:

1) Initially keep all the switches in the OFF position

2) Initially keep duty cycle POT in minimum position

3) Connect banana connector 24V DC source to24V DC input.

4) Connect the driver pulse output to MOSFET input. (G to G, S to S).

5) Switch ON the main supply.

6) Check the test point waveforms with respect to ground.

7) Switch ON the S1 switch and then Switch ON S2.

8) Vary the duty cycle POT and tabulate the TON , TOFF & output voltage.

9) Trace the waveforms of Vo & iO.


· Draw the graph for Vo Vs Duty cycle, k

CIRCUIT DIAGRAM:

I. Fig.1.Buck converter

MODEL GRAPH:

Waveforms for CCM

Output Voltage Vs Duty Cycle


RESULT:

Thus the Buck converter was studied.


power electronics lab manual

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input ac voltage

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bridge firing circuit