manual_pE

POWER ELECTRONICS LAB MANUAL

Department of Electrical and Electronics Engineering – SMVEC, Puducherry

1

Exp.No.1 CHARACTERISTICS OF SCR, MOSFET AND IGBT AIM:

To study the characteristics of SCR, MOSFET and IGBT.

To draw the V-I characteristics of SCR and Break down voltage

To draw the input and output characteristics 0f MOSFET & IGBT APPARATUS:

1. Characteristics of SCR, MOSFET and IGBT study unit.

2. Ammeters 0-500mA-1 no

Ammeters 0-50mA-2 no

Ammeter 0-10mA-2 no

3. Voltmeter 0-50V-2no

4. CRO

5. Connecting wires

A) V-I CHARACTERISTICS OF SCR CIRCUIT DIAGRAM:



2

WAVE FORMS:

TABULAR COLUMN:

IG =__4___mA

S.NO VAK IA

PROCEDURE: 1. Connections are made as per the circuit diagram.

2. Gate current is kept at constant fixed value by varying the Gate source, potentiometer.

3. Anode Cathode source is varied from its min. value in steps and readings of VAK & IA

are noted down at each step by observing the gate current IG , At Break down voltage

the gate current raises rapidly(to be observed in Ammeter IG ) and Anode Cathode

Voltage is falls down suddenly (to be observed in Volt meter VAK).

4. The Break down voltage, Anode current at which sudden rising starts will be noted .

5. Repeat the steps 2-4 for other constant gate current.

6. Graph is drawn between VAK & IA for different values of gate currents. IG1 & IG2 .



3

B) CHARACTERISTICS OF MOSFET

CIRCUIT DIAGRAM:

WAVEFORMS:

TABULAR COLUMN:

VDS =__4___V

S.NO VGS ID



4

VGS =__4___V

S.NO VDS ID


2. VGS is kept at constant fixed value by varying the Gate supply.

3. Drain Source supply is varied from its min. value in steps and readings of VDS & ID

4. Are noted down at each step by observing the VGS constant.

5. Graph is drawn between VDS & ID for different values of Gate Source Voltages

VGS1 & VGS2.

6. VDS is kept at constant fixed value by varying the Drain resistance using potentio

meter.

7. Gate Source supply is varied from its min. value in steps and readings of VGS & ID

are noted down at each step by observing the VDS constant.

8. Graph is drawn between VGS & ID for different values of Drain Source Voltages

VDS1 & VDS2.

C) CHARACTERISTICS OF IGBT CIRCUIT DIAGRAM:



5

WAVE FORMS:

TABULAR COLUMN: VCE =__4___V S.NO VGE IC

VGE =__4___V S.NO VCE IC


2. VGE is kept at constant fixed value by varying the Gate supply.

3. Drain Source supply is varied from its min. value in steps and readings of VCE & IC are

noted down at each step by observing the VGE constant.

4. Graph is drawn between VCE & IC for different values of Gate Emitter Voltages



6

VGE1 & VGE2.

5. VCE is kept at constant fixed value by varying the Drain resistance using potentio meter.

6. Gate Source supply is varied from its min. value in steps and readings of VGE & IC are

noted down at each step by observing the VCE constant.

7.Graph is drawn between VGE & IC for different values of Collector Emitter Voltages

VCE1 & VCE2.

PRECAUTIONS: 1. Check the SCR.MOSFET & IGBT for the performance before making connections

2. Check the Battery supplies V1 & V2,R1 & R2.

3. Make fresh connections before you make a new experiment.

4. Keep all knobs at min. position before you switch ON the supply.

5. Show connections to the lab faculty before you start the experiment.

RESULT: The Characteristics of SCR, MOSFET and IGBT are studied and the graphs were

Plotted

CONCLUSION: 1. Break down voltage of SCR, Anode current sudden raise is observed.

2. MOSFET input & out characteristics as per the graph is observed.

3. IGBT‘s transfer & collector characteristics are observed.

VIVA-VOCE: 1. What is difference between SCR & Thyristor ?

2. What is meant by Triggering?

3. What is holding current, Latching current?

4. What is Depletion mode in MOSFET?

5. What are the differences between SCR, MOSFET & IGBT?

6. What are the advantages of IGBT over BJT & MOSFET?



7

Exp.No.2.A GATE FIRING CIRCUITS (R, RC & UJT)

AIM: To study the performance of various turn-on methods of thrusters by it’s gate

terminal.

To prove that the firing angle range for R-triggering is 0 to 900

To prove that the firing angle range for RC-triggering is 0 to 1800

To prove that the firing angle range for UJT-triggering ramp triggering.

To observe the magnitude & wave forms of input and output in CRO

To draw the wave forms of input and output drawn on graph sheet.

APPARATUS:

1. RC-Firing circuit study unit.

2. UJT-Firing circuit study unit

3. Thyristor-TYN612-1 no

4. Rheostat-50 ohms

5. CRO

6. Connecting wires

R-FIRING CIRCUIT

CIRCUIT DIAGRAM:



8

WAVEFORMS:


2. The main supply is switched ON and triggering circuit is switched ON

3. Wave forms across the load are observed in CRO values are noted down and tabulated

for different firing angles.

4. The out put wave forms are plotted on the graph sheet.

TABULAR COLUMN: Vm = ______ s.no Firing angle

(α) Vdc

(theoretical)

Vdc

(Practical) Vrms

(theoretical) Vrms

(Practical)



9

THEORETICAL CALICULATIONS:

Vd.c = tdtSinVT

V mavg ωωπ

α.

1∫=

= )1(2

απ

CosVm +

Va.c = tdtSinVT

V mrms ωωπ

α.

1 22∫=

=2/1

22

)(2

+−ααπ

πSinVm

RC-FIRING CIRCUIT

CIRCUIT DIAGRAM:



10

WAVE FORMS:

TABULAR COLUMN: Vm = ______ s.no Firing angle

(α) Vdc

(theoretical)

Vdc

(Practical) Vrms

(theoretical) Vrms

(Practical)








11

UJT-FIRING CIRCUIT CIRCUIT DIAGRAM:

WAVEFORMS:



12






PRECAUTIONS: 1. Check all the SCR’s for the performance before making connections

2. Check the firing circuits trigger outputs and its relative phase sequence.


4. Preferably work at low voltages (30-40V) for every new connection after careful

Verification raised to the max. ratings.



RESULT: The performance of R,RC & UJT Firing circuits with R -load are studied and out put

wave forms for different firing angles are drawn on the graph sheet.

CONCLUSION: R-Triggering circuit works for firing angle range 0 to 90 degrees,

RC-Triggering circuit works for firing angle range 0 to 180 degrees and UJT Firing circuit

works for instant triggering.

VIVA-VOCE:

1. What is the range of firing angle in R-Triggering? 2. What is the range of firing angle in RC-Triggering?

3. What is meant by Ramp Triggering?

4. What are the advantages of UJT-firing circuit over R & RC-triggering?

5. What is the importance of 1:1 pulse transformer?



13

Exp.No: 3.A VOLTAGE COMMUTATED CHOPPER

AIM:

To construct a voltage commutated chopper circuit and study its time ratio (TRC)

controls.

APPARATUS REQUIRED:

Chopper power module, chopper firing unit, rheostat 100 ohm/ 2amp, CRO, patch

cards, multimeter etc.

THEORY: Chopper converts fixed DC voltage to a variable DC voltage through the use of

semiconductor devices. The DC to DC converters have gained popularity in medium

industry. Some practical applications of DC to DC converter include armature voltage

control of DC motors converting one DC voltage level to another level, and controlling DC

power for wide variety of industrial processes. The time ratio controller (TRC) is a

form of control for DC to DC conversion

. Time ration controller (TRC) or chopper is basically a thyristor switch. The switch is

closed and opened periodically such that the load is connected to, and disconnected from,

the supply alternatively. Thus the average voltage impressed on the load is controlled by

controlling the ratio of ON state interval to one cycle duration.

The average output voltage of the chopper is given by

Var = (TON/T) V

Where V is the input voltage, TON is the time duration of chopper. The ratio TON/T is

called the duty ratio chopper. The most important factor that governs the performance of the

chopper is the duty ratio. The duty ratio can be controlled in many ways, such as by

changing the ON period duration by keeping the frequency constant or by changing

frequency keeping the ON period constant. The third alternative method is to change both

ON period and frequency. Changing the frequency of the chopper introduces different

harmonics at different frequencies. At some frequency of operation the harmonic contents



14

are larger than the tolerable limits. Therefore fixed frequency choppers with a variable ON

period technology are generally used.

Chopper circuit shown is class-D commutation circuit here an auxiliary thyristor is

used to turn OFF the main SCR TM. It is assumed that the capacitor C is initially charged to

voltage Ec with the polarity shown. When TM is turned on, the capacitor will discharge

through it, and through inductor L. At the end of discharge cycle the capacitor will discharge

through TM and will turn it OFF. Since a reverse voltage is applied across the TM

immediately after turning on the SCR, this phenomenon is known as voltage commutation.

PROCEDURE:

1. Circuit connections are made as shown in the circuit diagram by connecting

rheostat as the load. The gate cathode terminals of the 2 SCR’s are connected to

the respective points on the firing module.

2. Check all the connections and confirm connections made are correct before

switching on the equipment.

3. Keeping duty cycle knob at minimum position & input voltage at zero switch on

the firing and then power circuit.

4. Now gradually increase the input voltage upto 30V.

5. Keeping frequency constant vary duty cycle of the chopper firing circuit in steps

and note down corresponding load voltage for each step.

6. The output wave forms are seen on a CRO.

7. Keeping duty cycle at minimum position gradually decrease the input voltage.

DC CHOPPER CIRCUIT DIAGRAM

D12

TAGA

C

LOAD 100 ohm / 2A

RHEOSTATE

TM

GM

DF

L1

L2

ON

DC SUPPLY

30V / 1A



15

8. Switch OFF the power circuit & firing unit. Remove the patch cords.

OBSERVATIONS:

FREQUENCY = ___________ Hz

Sl.NO

DUTY CYCLE

LOAD

VOLTAGE IN

VOLTS

1

2

3

4

5

6

MODEL GRAPH:

RESULT:

DC Chopper is constructed and its performance is studied.



16

Ex.No:3.B CURRENT COMMUTATED CHOPPERS

AIM:

To construct a current commutated chopper circuit and study its time ratio (TRC)

controls.

APPARATUS REQUIRED:

Chopper power module, chopper firing unit, rheostat 50 ohm/ 5 W, CRO, patch

cards, multimeter etc.

THEORY: Chopper converts fixed DC voltage to a variable DC voltage through the use of

semiconductor devices. The DC to DC converters have gained popularity in medium

industry. Some practical applications of DC to DC converter include armature voltage

control of DC motors converting one DC voltage level to another level, and controlling DC

power for wide variety of industrial processes. The time ratio controller (TRC) is a

form of control for DC to DC conversion

. Time ration controller (TRC) or chopper is basically a thyristor switch. The switch is

closed and opened periodically such that the load is connected to, and disconnected from,

the supply alternatively. Thus the average voltage impressed on the load is controlled by

controlling the ratio of ON state interval to one cycle duration.

The average output voltage of the chopper is given by

Var = (TON/T) V

Where V is the input voltage, TON is the time duration of chopper. The ratio TON/T is

called the duty ratio chopper. The most important factor that governs the performance of the

chopper is the duty ratio. The duty ratio can be controlled in many ways, such as by

changing the ON period duration by keeping the frequency constant or by changing

frequency keeping the ON period constant. The third alternative method is to change both

ON period and frequency. Changing the frequency of the chopper introduces different

harmonics at different frequencies. At some frequency of operation the harmonic contents



17

are larger than the tolerable limits. Therefore fixed frequency choppers with a variable ON

period technology are generally used.

Chopper circuit shown is class-B current commutation circuit. In this circuit source

voltage Vs charges capacitor C to voltage Vs with the top side positive as shown. Main

thyristor T1 and auxiliary thyristor TA are OFF. Positive direction of capacitor voltage and

capacitor current ic is marked. When T1 is tuned ON a constant current Io is established in

the load circuit. Here, for simplicity, load current is assumed constant. For initializing the

commutation of main thyristor T1, auxiliary thyristor TA is triggered. With main thyristor

T1 is ON, a resonant current ic begin to flow from C through TA, L and back to C. Then the

capacitor is charged to –Vs, resonant current ic now build through L, D and T1. As this

current Ic grows opposite to forward thyristor current of T1, net forward current iT1 = Io - ic

begins to decreases. Finally, when ic in the reverse direction attains the value Io, forward

current in T1 (iT1 = Io – I0) is reduced to zero and the device is turned OFF. For reliable

commutation, peak resonant current Ip must be greater then load current Io. As thyristor is

commutated by gradual built up of resonant current in the reverse direction, this method is

called current commutation or resonant-pulse commutation.

Circuit Diagram for Dc Current

Commutated Chopper

TA

G1

D1

T1

G1 Io

CA

LOAD 500 E/ 0.6A

RHEOSTATE

L

DF

12

C

OND2

DC INPUT

80V / 1A



18

PROCEDURE:

1. Switch on the chopper firing circuit, check for the firing pulses.

2. Circuits connections are made as shown in the circuit diagram by connecting rheostat as

load with input DC voltage at 24V.

3. The gate cathode terminals of the 2 SCR’s are connected to the respective points on the

firing module.

4. Check all the commutation and confirm connections made are correct before switching

on the equipments.

5. Switch on the DC power supply to the chopper and also firing circuit.

6. Keeping frequency constant vary the duty cycle of the chopper firing circuit in steps and

note down corresponding load voltage for each step.

7. The output wave forms are seen on a CRO.

8. Keeping frequency constant vary duty cycle of the chopper firing circuit in steps and

note down corresponding load voltage for each step.

9. Plot a graph of duty cycle against load voltage.

10. Tabulate theoretical and practical values. (Refer given table)

11. A graph of Vdc(av) verses duty cycle is plotted.

12. Draw the following wave forms.

i. Load voltage waveform.

ii. Voltage across the capacitor.

TYPICAL EXPERIMENTAL OBSERVATIONS:

1. Y = ______ V

2. VOLTS/DIV =

3. Therefore V = ________ V

4. TB = DIV

5. Time period, T = X * TB

6. ON time TON = t1 x TB

7. Frequency, F = (1/T)

8. Duty cycle = TON / T

9. Theoretical load voltage Vdc(av) = [TON / T] (V)



19

FOR R LOAD

Use R2 = 500 ohm

Time period, T = X * TB

T = 4 DIV x 5 ms/DIV = 20ms

Frequency F = 1/T = 1/20 ms = 50Hz.

TABULAR COLUMN:

Sl.NO

No.OF t1

DIV

DUTY CYCLE

IN %

LOAD VOLTAGE IN VOLTS

THEORITICAL PRACTICAL

1 0.4 10

2 0.8 20

3 1.2 30

4 1.6 40

5 2.0 50

6 2.4 60

7 2.8 70

8 3.2 80

9 3.6 90

MODEL GRAPH:

RESULT:

Current commutated Chopper is constructed and its performance is studied.



20

Exp.No: 4.A SINGLE PHASE SEMI CONVERTER

AIM: To study the performance of single phase Half controlled bridge converter.

To prove that the Half controlled converter works in only one quadrant.

To observe the magnitude & wave forms of input and output in CRO

To draw the wave forms of input and output drawn on graph sheet.

APPARATUS: 1. Single phase fully controlled bridge kit 2. Single phase fully controlled bridge firing kit

3. Thyristors-TYN612-2 no

4. Diodes –IN 4007-2 no

5. Rheostat-50 ohms

6. Loading inductor

7. CRO

8. Connecting wires CIRCUIT DIAGRAM:

SINGLE PHASE HALF CONTROLLED BRIDGE CONVERTER WITH R-LOAD



21

WAVE FORMS:

TABULAR COLUMN: Vm = ______

S.NO FIRING ANGLE (α)

V avg (practical)

Vavg (theoreticall)

1 2 3 4 5

0

30

60

90

150


Vd.c = tdtSinVT

V mavg ωωπ

α.

1∫= for R-Load

= )1( απ

CosVm +



22

PRECAUTIONS: 1. Check all the SCR’s for the performance before making connections



4. Preferably work at low voltages (30-40V) for every new connections after careful

verification raised to the max. ratings.


6. Show connections to the lab faculty before you start the experiment. PROCEDURE: 1. Connections are made as per the circuit diagram.

2. Firing pulses are applied for the respective SCR’s from the firing circuit.

3. The main supply is switched ON and triggering circuit is sitched ON

4. Wave forms across the load are observed in CRO values are noted down and tabulated for

different firing angles.


6. Similarly RL-load steps of the above are repeated.

7. Wave forms are observed in CRO

RESULT: The performance of Single phase Half controlled bridge converter of R & RL-load are studied and out put wave forms for different firing angles are drawn on the graph sheet. CONCLUSION: The Single phase Half controlled bridge converter will act in I-quadrant only for firing angles 0< α <180degrees. QUESTIONS FOR VIVA-VOCE: 1. How many quadrants does a Half controlled rectifier works?

2. What is meant by Line commutation?

3. How the thyristers get commutated?

4. Does a Half controlled rectifier work as inverter?

5. What are the merits & demerits of half controlled rectifier over fully controlled rectifier?



23

Exp.No: 4.B 1-PHASE FULLY CONTROLLED CONVERTER AIM:

To convert AC supply to variable DC supply by changing the firing angles of thyristers.

To observe the input and output waveforms by using CRO & calculate voltage

and currents for different firing angles.

To draw the input and output waveforms for different firing angles.

APPARATUS: 1. Thyristors-4 no

2. Single phase fully controlled bridge firing kit

3. Rheostat-50 ohms

4. Loading inductor 10mH, 25mH&50mH

5. CRO

6. Connecting wires

CIRCUIT DIAGRAM: SINGLE PHASE FULLY CONTROLLED BRIDGE CONVERTER WITH R-LOAD

SINGLE PHASE FULLY CONTROLLED BRIDGE CONVERTER WITH RL-LOAD



24

WAVE FORMS: SINGLE PHASE FULLY CONTROLLED BRIDGE CONVERTER WITH R-LOAD

SINGLE PHASE FULLY CONTROLLED BRIDGE CONVERTER WITH RL-LOAD



25

TABULAR COLUMN : Vm = ______

S.NO FIRING ANGLE (П)

V avg (practical)

Vavg (theoreticall)

1

0

2

30

3

60

4

90

5

150



26


Vd.c = tdtSinVT

V mavg ωωπ

α.

1∫= for R-Load

= )1( απ

CosVm +

Vd.c = tdtSinVT

V mavg ωωαπ

α.

1∫

+= for RL-Load

= απCos

Vm2

PRECAUTIONS:

1. Check the working condition of all the SCR’s before connecting them in the circuit.



4. Preferably work at low voltages (30-40V) for every new connections after careful

Verification raised to the max. Ratings.




2. Firing pulses are applied for the respective SCR’s from the firing circuit.

3. The main supply is switched ON and triggering circuit is sitched ON

4. Wave forms across the load are observed in CRO values are noted down and tabulated for

different firing angles.


6. Similarly RL-load steps of the above are repeated.

7. Wave forms are observed in CRO RESULT: The performance of Single phase Fully controlled bridge converter of R & RL-load are

studied and out put wave forms for different firing angles are drawn on the graph sheet.



27

CONCLUSION: The Single phase Fully controlled bridge converter will act as a rectifier

for firing angles 0< α <90degrees, and act as a inverter for firing angles ranging from 90 < α

< 180 degrees and out put voltages of desired magnitude can be obtained by varying the

firing angle α.

QUESTIONS FOR VIVA-VOCE:

1.How many quadrants does a Full controlled rectifier works ?

2.What is meant by Line commutation ?

3.How the thyristers get commutated ?

4.When a full controlled rectifier work as inverter ?

5.What is the change observed in wave forms for R-load & RL-load



28

Exp.No: 5.A THREE PHASE SEMI CONVERTER

AIM:

To study the Three Phase semi converter characteristic by observing input and output

voltage waveform

APPARATUS: 1. Three phase semi controlled bridge kit

2. Three phase semi controlled bridge firing kit


6. Loading inductor

7. CRO

8. Connecting wires THEORY:

3-phase semi-converters are three phase half controlled bridge controlled rectifiers

which employ three thyristors and three diodes connected in the form of a bridge

configuration. Three thyristors are controlled switches which are turned on at appropriate

times by applying appropriate gating signals. The three diodes conduct when they are

forward biased by the corresponding phase supply voltages.

3-phase semi-converters are used in industrial power applications up to about 120kW

output power level, where single quadrant operation is required. The power factor of 3-phase

semi-converter decreases as the trigger angle α increases. The power factor of a 3-phase

semi-converter is better than three phase half wave converter.

The figure shows a 3-phase semi-converter with a highly inductive load and the load

current is assumed to be a constant and continuous load current with negligible ripple.



29

CIRCUIT DIAGRAM:

Thyristor 1T is forward biased when the phase supply voltage anv is positive and greater than

the other phase voltages bnv and cnv . The diode 1D is forward biased when the phase

supply voltage cnv is more negative than the other phase supply voltages.

Thyristor 2T is forward biased when the phase supply voltage bnv is positive and greater

than the other phase voltages. Diode 2D is forward biased when the phase supply voltage

anv is more negative than the other phase supply voltages.

Thyristor 3T is forward biased when the phase supply voltage cnv is positive and greater

than the other phase voltages. Diode 3D is forward biased when the phase supply voltage

bnv is more negative than the other phase supply voltages.

The figure shows the waveforms for the three phase input supply voltages, the output

voltage, the thyristor and diode current waveforms, the current through the free wheeling

diode mD and the supply current ai . The frequency of the output supply waveform is 3 Sf ,

where Sf is the input ac supply frequency. The trigger angle α can be varied from

0 00 to 180 .

During the time period 7

6 6t

π πω ≤ ≤

i.e., for 0 030 210tω≤ ≤ , thyristor 1T is forward

biased. If 1T is triggered at 6

tπω α = +

, 1T and 1D conduct together and the line to line

supply voltage acv appears across the load. At 76

tπω =

, acv starts to become negative



30

and the free wheeling diode mD turns on and conducts. The load current continues to flow

through the free wheeling diode mD and thyristor 1T and diode 1D are turned off.

If the free wheeling diode mD is not connected across the load, then 1T would continue to

conduct until the thyristor 2T is triggered at 56

tπω α = +

and the free wheeling action is

accomplished through 1T and 2D , when 2D turns on as soon as anv becomes more negative

at 76

tπω =

. If the trigger angle

3πα ≤

each thyristor conducts for 23π

radians ( )0120



31

and the free wheeling diode mD does not conduct. The waveforms for a 3-phase semi-

converter with 3πα ≤

is shown in figure

We define three line neutral voltages (3 phase voltages) as follows



32

sin ;RN an mv v V tω= = Max. Phase VoltagemV =

2

sin3YN bn mv v V tπω = = −

( )0sin 120YN bn mv v V tω= = −

2

sin3BN cn mv v V tπω = = +

( )0sin 120BN cn mv v V tω= = +

( )0sin 240BN cn mv v V tω= = −

The corresponding line-to-line voltages are

( ) 3 sin6RB ac an cn mv v v v V tπω = = − = −

( ) 53 sin

6YR ba bn an mv v v v V tπω = = − = −

( ) 3 sin2BY cb cn bn mv v v v V tπω = = − = +

( ) 3 sin6RY ab an bn mv v v v V tπω = = − = +

Where mV is the peak phase voltage of a star (Y) connected source.

TO DERIVE AN EXPRESSION FOR THE AVERAGE OUTPUT VOLTAGE OF

THREE PHASE SEMICONVERTER FOR 3πα >

AND DISCONTINUOUS

OUTPUT VOLTAGE

For 3πα ≥ and discontinuous output voltage: the average output voltage is found from

( )7

6

6

3.

2dc acV v d t

π

πα

ωπ

+

= ∫

( )7

6

6

33 sin

2 6dc mV V t d t

π

πα

πω ωπ

+

= − ∫



33

( )3 31 cos

2m

dc

VV α

π= +

( )31 cos

2mL

dc

VV α

π= +

The maximum average output voltage that occurs at a delay angle of 0α = is

3 3 mdm

VV

π=

The normalized average output voltage is

( )0.5 1 cosdcn

dm

VV

Vα= = +

The rms output voltage is found from

( ) ( )

17 26

2 2

6

33 sin

2 6mO RMSV V t d t

π

πα

πω ωπ

+

= −

∫

( )

123 1

3 sin 24 2mO RMSV V π α απ

= − +

For 3πα ≤ , and continuous output voltage

Output voltage 3 sin6O ab mv v V tπω = = +

; for to

6 2t

π πω α = +

Output voltage 3 sin6O ac mv v V tπω = = −

; for

5 to

2 6t

π πω α = +

The average or dc output voltage is calculated by using the equation

( ) ( )5

62

6 2

3. .

2dc ab acV v d t v d t

ππα

π πα

ω ωπ

+

+

= + ∫ ∫

( )3 31 cos

2m

dc

VV α

π= +



34

( )0.5 1 cosdcn

dm

VV

Vα= = +

The RMS value of the output voltage is calculated by using the equation

( ) ( ) ( )

15 262

2 2

6 2

3. .

2 ab acO RMSV v d t v d t

ππα

π πα

ω ωπ

+

+

= +

∫ ∫

( )

12

23 23 3 cos

4 3mO RMSV Vπ α

π = +

Table Firing Scheme with R Load

Result:

Firing Angle (α˚)

DC Output Voltage (Vdc) (Volts)

Theoretical Practical 0 18 36 54 72 90 108

115.2 120



35

Exp.No: 5.B THREE PHASE FULLY CONTROLLED CONVERTER

AIM:

To study the Three Phase fully converter characteristic by observing input and output

voltage waveform

APPARATUS: 1. Three phase fully controlled bridge kit

2. Three phase fully controlled bridge firing kit


6. Loading inductor

7. CRO

8. Connecting wires Theory:

Three phase full converter is a fully controlled bridge controlled rectifier using six

thyristors connected in the form of a full wave bridge configuration. All the six thyristors are

controlled switches which are turned on at a appropriate times by applying suitable gate

trigger signals.

The three phase full converter is extensively used in industrial power applications

upto about 120kW output power level, where two quadrant operation is required. The figure

shows a three phase full converter with highly inductive load. This circuit is also known as

three phase full wave bridge or as a six pulse converter.

The thyristors are triggered at an interval of 3π

radians (i.e. at an interval of 060 ).

The frequency of output ripple voltage is 6 Sf and the filtering requirement is less than that

of three phase semi and half wave converters.



36

CIRCUIT DIAGRAM:

At 6

tπω α = +

, thyristor 6T is already conducting when the thyristor 1T is turned

on by applying the gating signal to the gate of 1T . During the time period

to 6 2

tπ πω α α = + +

, thyristors 1T and 6T conduct together and the line to line supply

voltage abv appears across the load.

At 2

tπω α = +

, the thyristor 2T is triggered and 6T is reverse biased immediately and 6T

turns off due to natural commutation. During the time period 5

to 2 6

tπ πω α α = + +

,

thyristor 1T and 2T conduct together and the line to line supply voltage acv appears across

the load.

The thyristors are numbered in the circuit diagram corresponding to the order in which they

are triggered. The trigger sequence (firing sequence) of the thyristors is 12, 23, 34, 45, 56,

61, 12, 23, and so on. The figure shows the waveforms of three phase input supply voltages,

output voltage, the thyristor current through 1T and 4T , the supply current through the line

‘a’.

We define three line neutral voltages (3 phase voltages) as follows

sin ; Max. Phase VoltageRN an m mv v V t Vω= = =



37

( )02sin sin 120

3YN bn m mv v V t V tπω ω = = − = −

( ) ( )0 02sin sin 120 sin 240

3BN cn m m mv v V t V t V tπω ω ω = = + = + == −

Where mV is the peak phase voltage of a star (Y) connected source.

The corresponding line-to-line voltages are

( ) 3 sin6RY ab an bn mv v v v V tπω = = − = +

( ) 3 sin2YB bc bn cn mv v v v V tπω = = − = −

( ) 3 sin2BR ca cn an mv v v v V tπω = = − = +

iG1

iG2

iG3

iG4

iG5

iG6

(30 + )0 α600

600

600

600

600

(360 +30 + )0 0

α

T1 T2 T3 T4 T5 T6 T1 T2T6

t

t

t

t

t

t

Gating (Control) Signals of 3-phase full converter



38

To derive an expression for the average output voltage of three phase full converter

with highly inductive load assuming continuous and constant load current

The output load voltage consists of 6 voltage pulses over a period of 2π radians, hence the

average output voltage is calculated as

( )

2

6

6. ;

2dc OO dcV V v d t

π α

π α

ωπ

+

+

= = ∫

3 sin6O ab mv v V tπω = = +

2

6

33 sin .

6dc mV V t d t

π α

π α

πω ωπ

+

+

= + ∫



39

3 3 3cos cosm mL

dc

V VV α α

π π= =

Where mLV 3 Max. line-to-line supply voltagemV= = The maximum average dc output voltage is obtained for a delay angle α = 0,

( )max

3 3 3m mLdmdc

V VV V

π π= = =

The normalized average dc output voltage is

cosdcdcn n

dm

VV V

Vα= = =

The rms value of the output voltage is found from

( ) ( )

12

22

6

6.

2 OO rmsV v d t

π α

π α

ωπ

+

+

=

∫

( ) ( )

12

22

6

6.

2 abO rmsV v d t

π α

π α

ωπ

+

+

=

∫

( ) ( )

12

22 2

6

33 sin .

2 6mO rmsV V t d t

π α

π α

πω ωπ

+

+

= +

∫

( )

121 3 3

3 cos 22 4mO rmsV V α

π

= +

Table Firing Scheme with R Load

Result:

Firing Angle (α˚)

DC Output Voltage (Vdc) (Volts)

Theoretical Practical 0 18 36 54 72 90 108

115.2 120



40

Exp.No: 6.A SINGLE PHASE VOLTAGE SOURCE INVERTER

Aim:

To construct a Voltage Source Inverter and to study its Performance.

Apparatus:

Inverter Module, Variable DC power supply, AC voltmeter, CRO. Rheostat and patch

cards etc.

Name of the Equipment Specifications Quantity

1.Input:

Input through Reguleted power supply.

DC Regulated Power supply - 0 -

30V/2A

-1no

2. Control & power module: Voltage Source Inverter module -1no.

3. Output (load): Rheostat - 100 ohm/2A. -1no.

4. Measuring Instruments: 1. Oscilloscope

2. AC Voltmeter

-1no.

-1no.

5. Connecting wires: Patch cords for connecting.

INTRODUCTION:

Inverters convert DC power to AC power at a desired output voltage and frequency

and in most of the inverters both are required to be controlled. AC output voltage is built by

using semiconductor devices as switches and hence circuits with fewer components have

non-sinusoidal output wave form.

Inverters are used for (i) Variable speed AC' motor drives.

(ii) Induction heating.

(iii) Aircraft power supplies

(iv) UPS for important applications such as Computers.



41

In Voltage Source Inverter power module four IGBT's are used. The devices arc

placed inside and the terminals are to front panel.

SPECIFICATIONS:

SINGLE PHASE VOLTAGE SOURCE INVERTER:

SL.NO. Devices / parameters Ratings

1

IGBTS IRGP30B120KD-E(With ultra soft recovery diode) 04nos

VCES 1200V VCE(ON) 2.28V IC 25 Amps VGE 15V DIODES: IF 30A

2 Max. allowable average Current 2A DC 3 Max. allowable dc supply voltage 60V DC

4 Input power supply 230V 5 Operating frequency 25Hz to 50Hz

FRONT PANEL DETAILS OF PWM INVERTER MODULE:

1. DC Power on/off switch.

2. Mains power on/off switch.

3. Four IGBTs are mounted on heat sink are connected to the terminals of the front panel.

4. A knob is provided for the frequency control (25 Hz to 50 Hz).

5. Four output pulses connected to the terminals of front panel and marked as G1, G2, G3 &G4.

Theory

A device that converts DC power in to AC power at output voltage and frequency is called

an inverter. Some industrial applications of inverters are for adjustable speed AC drives,

inductive heating, stand by aircraft supplies, UPS, HVDC, transmission lines etc. Schematic

diagram of a single phase inverter is given in the fig. The current can be supplied to the load

by proper gating the IGBTs. Only two IGBTs will be on at any one time. Load voltage is

PWM signal.



42

A voltage fed inverter(VFI) or Voltage source Inverter(VSI) is one in which the DC source

has small or negligible impedeence. In other words, a voltage source inverter has stiff DC

voltage source at its input terminals.

PROCEDURE:

1. Circuit connections are made as shown in the circuit diagram.

2. Connect DC Input from Regulated power supply.

3. Connect Rheostat (100 ohm/2A) as load.

4. Check all the connections and confirm connections made are correct before: switching on the equipments.

5. Switch on firing circuit switch.

6. Keep the Frequency at minimum position. Switch on the DC power on/off switch,

7. Observe the load voltage waveforms using CRO,

8. Vary the frequency of the inverter circuit, observe the Load Voltage wave forms

9. Note down the output voltage using AC Voltmeter.

10. Tabulate the readings in the table.

11. Switch off all the switches.

12. Remove the connections.

TABULAR COLUMN:

SLNo. Frequency in Hz

Output Voltage using AC Voltmeter

1. 2. 3. 4.

Result:

Voltage Source Inverter is constructed and its performance is studied.



43



44

TYPICAL LOAD VOLTAGE WAVE FORMS AT LOW FREQUENCY:

T F=1/T AT HIGHER FREQUENCY:

T



45

Exp.No: 6.B SINGLE PHASE CURRENT SOURCE INVERTER

AIM:

To construct an inverter and to study its Performance.

APPARATUS: Inverter Module, DC power supply. CRO, AC voltmeter, patch cards etc.

SPECIFICATIONS:

SINGLE PHASE CURRENT SOURCE INVERTER POWER MODULE

SL.NO. Devices / parameters Ratings 1

Main Thyristors: (Marked A.C,G) VRRM 1200V VDRM 1200V ITRMS 25 Amps ITAV 16Amps Turn off time 20 us

2 Commutating capacitance 2.2 µF,250 V 3

Max. allowable average Current at any duty cycle

2A DC

4 Max. allowable dc supply voltage 60V DC SINGLE PHASE CURRENT SOURCE INVERTER FIRING UNIT

SL. No. Parameters Particulars 1 Input power supply: 230 V from the mains for the power

supply 2 Output: Isolated gate signals for4 SCRs 3 Gate drive current: 200 mA. 4 Operating Frequency: 25 Hz to 50 Hz

INTRODUCTION:

Inverters convert DC power to AC power at a desired output voltage and frequency

and in most of the inverters both are required to be controlled. AC output voltage is built by

using thyristors as switches and hence circuits with fewer components have non-sinusoidal

output wave form.

Inverters are used for (i) Variable speed AC motor drives.

(ii) Induction heating.



46

(iii) Aircraft power supplies

(iv) UPS for important applications such as computers.

In single phase current source inverter power module consists of one capacitor, and four SCR’s.The devices are placed inside and the terminals are to front panel.

FRONT PANEL DETAILS OF INVERTER POWER MODULE:

1. DC Power on/off switch.

2. Four Thyristor are marked as T1 T2, T3. T4, are mounted on heat sink are connected to the terminals of the front panel and marked as A, C, G on front panel.

INVERTER FIRING UNIT:

1. Power ON/OFF Switch with indicator.

2. A knob is provided for the frequency control.

3. Four output pulses.

RECOMMENDED FOR THE EXPERIMENTS:

Name of the equipment Specifications Quantity 1. Input source: DC power supply Output: 0 - 30 V/2 A -1 no 2. Control modules: Inverter module -1 no. 3- Output load: Rheostatc – 100 ohm/2A -1 no.

4. Measuring instruments: 1. Oscilloscope 2. AC Voltmeter

-1 no. -1 no.

5. Connecting wires: Patch cords for connecting.

THEORY:

A device that converts DC power in to AC power at output voltage and frequency is

called an inverter. A current source inverter has greater simplicity, better controllability,

higher regenerative capability and ease of protection. In current source inverters, input

current is constant but adjustable. The amplitude of output current from CSI is independent

of load. However, the magnitude of output voltage and its waveform output from CSI is

dependent upon the nature of load impendence. The DC input to CSI is from regulated

power supply.



47

A CSI converts the input DC current to an AC current at its output terminals. The

output frequency of AC current depends upon the rate of triggering the SCRs. The amplitude

of AC output current can be adjusted by controlling the magnitude of DC input current.

A CSI does not require any feedback diodes, whereas these are required in a VSI.

Commutation circuit is simple, as it contains only capacitors. As power semi-conductors in a

CSI have to withstand reverse voltage, devices such as GTOs. power transistors, power

MOSFETs cannot be used in CSI.

The CSIs find their use in the following applications:

1) Speed control of AC Motors

2) Induction heating

3) Lagging Var compensation

4) Synchronous motor starting

Power circuit diagram for a single phase CSI with resistive load R is shown. The source for

this inverter is a constant but adjustable DC current source. Capacitor C in parallel with load

is used for storing the charge for force commutating the SCRs. The Thyristors Tl to T4 are

the four power switches. These SCRs gated in pairs; T1, T2 & T3, T4.

PROCEDURE:

1. Circuit connections are made as shown in the circuit diagram by connecting rheostats100Ω/2A as loads with input DC voltage at 30 V.

2. Connect respective firing pulses to respective SCRs.

3. Check all the connections and confirm connections made are correct before switching on the equipments.

4. Switch on the inverter firing unit.

5. Switch on the DC power supply

6. Vary the frequency of the inverter circuit in steps.

7. For each step observe load voltage wave forms on CRO.



48

8. Vary the frequency of the inverter circuit in steps. For each step note download voltage.

9. Tabulate the readings in the table (refer given table).

TYPICAL EXPERIMENTAL OBSERVATIONS:

Sl. No. Frequency In Hz Load Voltage Using AC Voltmeter

1. 2. 3. 4. 5.

RESULT:

Single phase Current Source Inverter (CSI) is constructed and its performance is studied.

TYPICAL LOAD VOLTAGE WAVE FORMS AT LOW FREQUENCY:

T F=1/T AT HIGHER FREQUENCY:

T



49

manual_pE

Documents

relative phase

electronics

careful verification

dc motors

gate cathode

time ration

average voltage

put wave forms