PE Manual 10ECL78

Sri Adichunchanagiri Shikshana Trust(R)

SJB INSTITUTE OF TECHNOLOGY BGS HEALTH AND EDUCATION CITY

Kengeri, Bengaluru-560060

7th SEMESTER

POWER ELECTRONICS LAB MANUAL

(10ECL78)

DEPARTMENT OF ELECTRONICS AND COMMUNICATION

SJB INSTITUTE OF TECHNOLOGY BENGALURU -560060

NAME : ________________________

USN : ________________________

SECTiON : ________________________

Power Electronics Lab Manual-10ECL78 2013-14

CONTENTS

Sl.

No. Topics Page No.

1 List of Experiments 1

2 Examination Questions 2

3 Component and devices 4

4 Static characteristics of SCR 7

4 Static characteristics of DIAC 9

5 Static characteristics of Power MOSFET 11

6 Static characteristics of Power IGBT 13

7 RC triggering circuit 15

8 AC voltage controller 18

9 UJT firing circuit 20

10 Controlled rectifier with R & RL load 22

11 Commutation circuits 24

12 Inverters 26

13 DC Chopper (Jones chopper) 28

14 Speed control of DC motor 30

15

16

17

18

Digital Firing circuit

Speed Control of Stepper Motor

Introduction of ORCAD 16.5 Use, circuit design

& Simulation

Converter Circuits Using ORCAD Pspice

32

33

36

41

19 Theory & Working operations 53

20 Viva Questions 58


1 Dept. of ECE, SJBIT, Bangalore.

POWER ELECTRONICS LAB (10ECL78)

List of VTU Experiments:

1. Static characteristics of SCR & DIAC.

2. Static characteristics of MOSFET & IGBT.

3. Controlled HWR & FWR using RC triggering

4. SCR turn off circuits using (i) LC circuits (ii) Auxiliary Commutation.

5. Synchronized UJT firing circuit for HWR & FWR circuits.

6. Generation of firing signals for thyristors /TRIACs using digital circuits /

Microprocessors.

7. AC voltage controller using TRIAC-DIAC combination.

8. Single phase Fully Controlled Bridge Converter with R & RL loads.

9. Voltage (Impulse) commutated chopper-both frequency & variable frequency

operations.

10. Speed control of a separately excited DC motor.

11. Speed control of Universal motor & single-phase induction motor.

12. Parallel/Series Inverters.

13. Speed control of a stepper motor.



EXAMINATION QUESTIONS

1. Obtain the VI characteristics of a given SCR by conducting a suitable experiment & find

the holding current, latching current & forward resistance.

2. Conduct a suitable experiment to obtain the VI characteristics of a unidirectional four-

layer device for two gate currents. Determine breakdown voltage & holding current, for

both the cases.

3. Conduct a suitable experiment to obtain the VI characteristics of the Bi-directional switch

experimentally. Determine the holding current & break down voltage in 1st & 3

rd

coordinate.

4. Conduct the suitable experiment to draw VI characteristics of the given IGBT. Using that

find the threshold voltage & Trans- resistance of the IGBT.

5. Conduct a suitable experiment to draw VI characteristics of the given MOSFET. Using

that find the threshold voltage & drain resistance of the MOSFET.

6. Design and conduct to obtain triggering input voltage by using RC triggering circuit for

HWR.

7. Design and conduct to obtain triggering input voltage by using RC triggering circuit for

FWR

8. Design and conduct an experiment to obtain synchronized triggering pulse to turn- on

SCR in Half wave with resistive load. Show the load voltage and trigger pulse

waveforms.

9. Design and conduct an experiment to obtain synchronized triggering pulse to turn- on

SCR in Full wave with resistive load. Show the load voltage and trigger pulse

waveform.

10. Conduct a suitable experiment on Half controlled bridge rectifier with resistive

load/RL load. Plot the output DC voltage V/S delay angle graph.

11. Conduct a suitable experiment to obtain output voltage waveform of full controlled

bridge using R-L load. Plot the output DC voltage V/S delay angle graph. i) Without

freewheeling diode, ii) With freewheeling diode.

12. Conduct the suitable experiment to obtain output voltage waveform using jones chopper.



13. Conduct the suitable experiment to turn off SCR using LC circuit and Auxiliary

Commutation.

14. Rig up and test the chopper circuit to produce variable DC output. Draw the output

voltage V/S duty cycle graph.

15. Conduct a suitable experiment on a chopper to convert constant DC voltage to variable

DC voltage with a duty cycle of ------ Check the result with theoretical value.

16. Conduct a suitable experiment to obtain AC output using Series Inverter.

17. Conduct a suitable experiment to verify the operating principle of a Parallel Inverter.

18. Setup the circuit to control RMS voltage across incandescent lamp using Triac- Diac

combination, plot the graph of load voltage V/S delay angle

19. Conduct a suitable experiment to determining the speed control of DC motor using semi

converter and plot delay angle V/S speed.

20. Conduct a suitable experiment to determine the speed control of a universal motor using

AC voltage controller.

21. Rig up test a chopper circuit to variable DC output using Digital firing circuit, draw the

output voltage V/S duty cycle graph.



G (Gate)

A K

(Anode) (Cathode)

G (Gate)

MT2 MT1 (Main (Main terminal-2) terminal-1)

K A G

MT1 MT2 G

D (Drain)

G

Gate S (Source) G D S

C (Collector)

G

Gate

E (Emitter) G C E

MT2 MT1 MT2 MT1

(Main (Main OR

terminal-2) terminal-1)

B2 (Base-2)

E

(Emitter)

B1 (Base-1)

COMPONENTS & DEVICES

(1) Thyristor (SCR-Silicon controlled rectifier): TYN-410 /TYN-610 / TYN-612

(2) Triac: BT-136 / BT-139

(3) MOSFET: IRF-450 / IRF-740 / IRF-40/ IRF-42

(4) IGBT (Insulated Gate Bipolar transistor): IRG4BC200 / IRG4BC20S

(5) Diac: DB-32C

(6) Diodes: IN-4007 A K

(7) Zener diodes: DZ-15 A K

(8) UJT (Uni Junction Transistor): 2N2646

TYN

612

BT

136

IRF

740

IRG4

BC20

Bottom view In order to identify the terminals go in clockwise after the notch

B2 B1 E

2N

26

46 Notch



Primary

winding

230V

1:1:1 pulse

Transformer

- +

12V

0

12V

10mH - 5mH - 0 - 5mH - 10mH

115V

60V

30V

0

30V

60v

115V

(9) Isolation Transformer: 230V/115V-60V-30V-0-30V-60V-115V with 2A

(10) Pulse Transformer-1:1 and 1:1:1

In order to identify the primary & secondary windings, check the continuity.

(11) Power (Wattage) resistors: 100/5W, 500/5W, 1K/5W

(12) Potentiometers (POTS): 4.7K, 10K, 100K, 1M

(13) Rheostats: 50/25W, 100/25W, 200/25W.

(14) Capacitors: Disc type:0.1F, 0.01F,

Electrolytic type:1F, 10F,47F, 6.8F/100V & 100F/100V

High voltage handling capacitor: 100nF/200V, 100nF/600V

(15) Step down Transformers:

230V / 12V-0-12V (500mA),

230V / 24V-0-24V

(16) Inductors: 10mH, 100mH, 250H, 500H:

Mutual inductor coil:

Secondary windings

with different tapings

1:1 pulse

Transformer

Green coloured

(Thick) Resistors 500

Polarity will

be there

Primary

winding 230V

Secondary

winding



Symbol Physical appearance

(17) Fuses: 1A, 2A, 5A & 6A

(18) Single phase converter Triggering unit:

(19) DC Chopper Triggering unit:

(20) DC Motor: Separately Excited Dc Motor:

(21) Induction Motor:

1 Converter Triggering

unit: 900

ON / OFF 1200 600

Trigger O/Ps 1500

300

G K T1

1800 00

T1’ Test Points

T2 Gnd 1 2 3

T2’ 4 5 6 7

POWER DC Chopper Triggering unit:

10% 90% Min Max DUTY CYCLE FREQUENCY

ON / OFF

Trigger O/Ps

G K

Test Points

TMAIN Gnd 1 2 3

TAUX 4 5 6 7

POWER

M Armature

side

Field side

M



EXPERIMENT-1

Static characteristics of SCR

AIM :- a) To Plot the VI characteristics of SCR.

b) To obtain the device parameters.

COMPONENTS REQUIRED: SCR (TYN-612), Resistors, Milli-ammeters (0-50mA,0-100mA),

Voltmeter, Power supplies & connecting board.

CIRCUIT DIAGRAM:-

PROCEDURE:

(1) Make the connections as shown in the figure. (2) Keep the gate current (IG) at a constant value (say 5mA).

(3) Now vary the anode supply voltage (VAA) in steps.

(4) Correspondingly note down the ammeter (IA) & Voltmeter (VAK) readings, till the SCR turns on, which can be observed by sudden increase in anode current & drop in anode to cathode voltage.

Readings are tabulated.

(5) Repeat the above procedure for different values of gate currents & plot the graph.

(6) From the graph find out Forward Break-over voltage (VFBO) & the forward resistance of the SCR.

1k (0-50mA)

A

IG VGG

0-30V

(0-100mA) 500 / 5W

A

V

IA

VAK (0-60V )

A

K G VAA 0-30V

TYN- 612

TYN

612

K A G

SCR IA

IL

IH

V-I (Static) Characteristics of SCR:

VFBO VAK

VKA VRBO

-IA

Forward Blocking

Region

Reverse Blocking

Region

Breakdown

Region

Forward

Conduction

Region

IG3 > IG2 > IG1

IG2 > IG1

IG1 = 0



PROCEDURE FOR FINDING LATCHING CURRENT (IL):

(1) Turn on the SCR as explained above, which is indicted by sudden increase in IA & drop in VAK. (2) Increase the anode current slowly, by increasing the anode supply VAA, & the gate supply (VGG)

should be turned on & off repeatedly, for each increased value of anode current.

(3) When the anode current goes below the latching current, the SCR turns off, if the gate supply is

turned off. (4) Adjust the anode current, such that the SCR continues to conduct even after the gate supply is

switched off. This minimum value of the anode current indicated by the milli ammeter gives the

Latching current (IL). Indicate this on the graph.

PROCEDURE FOR FINDING HOLDING CURRENT (IH):

(1) Turn on the SCR as explained above, which is indicted by sudden increase in IA & drop in VAK.

(2) Now switch off the gate supply (VGG) permanently.

(3) Then reduce the anode current (IA) slowly till the SCR turns off, by decreasing the anode supply VAA.

(4) When the anode current drops below the Holding current, the SCR turns off, hence observe the

anode current, just before it suddenly returns to zero (5) Note down this value, which gives the Holding current (IH). Indicate this on the graph.

TABULAR COLUMN:

IG = mA IG = mA VAK ( in volts) IA (in mA) VAK ( in volts) IA (in mA)

RESULT: The static characteristics of SCR are conducted & the following values are calculated using its

graph.

The break-over voltages are: VBFO1= & VBFO2=

Latching Current (IL) =

Holding Current (IH) =

Forward resistance = Rf = VAK / IA =



EXPERIMENT-2

Static characteristics of DIAC

AIM:- To Plot the VI characteristics of DIAC.

COMPONENTS REQUIRED: DIAC (BT-136), Milli-ammeters (0-100mA), Power supplies &

connecting board.

CIRCUIT DIAGRAM:-

MT2 MT1 (Main (Main

terminal-2) terminal-1)

V-I Characteristics of DIAC:-



Procedure:

1. Connect the circuit as per the circuit diagram.

2. Change the voltage Vs in steps till 30V and observe VB01, the start of break over voltage.

3. Change the voltage Vs in steps in the negative direction till -30V and observe VB02, the start

of break over voltage.

4. Note down the voltage Vo and Current I and plot the graph.

Tabular Column:

Mode-I : Mode-III : Vo ( in volts) I (in mA) V0( in volts) I (in mA)

RESULT:-

The static characteristic of DIAC is conducted & the following values are calculated using its

graph.

The break-over voltages are : VBO1=

VBO2=



EXPERIMENT-3

Static characteristics of power MOSFET

AIM:- To Plot the VI characteristics of Power MOSFET.

COMPONENTS REQUIRED: MOSFET (IRF-40), Resistors (500 / 5W, 1K),

Milli-ammeter (0-100mA), Voltmeters (0-30V, 2nos), Power supplies & connecting board.

CIRCUIT DIAGRAM:

PROCEDURE:

(a) OUTPUT CHARACTERISTICS:

(1) Make the connection as shown in the fig.

(2) Keep the gate–source voltage (VGS) constant (say at 3.5V).

(3) Vary the supply voltage VDD in steps and note down the corresponding drain current (ID),

Drain-Source voltage (VDS) and tabulate the result.

(4) Repeat the above procedure for different values of gate–source voltage (VGS).

(5) From the readings draw the output characteristics & calculate the drain resistance rd,

which is given by, rd = VDS (in volts) / ID (in mA)

TABULAR COLUMN:

Ref VDD

VGS1 = V VGS2 = V VGS3 = V

VDS (in volts) ID(in mA) VDS (in volts) ID(in mA) VDS (in volts) ID(in mA) 0V

0.5V 2V

4V

6V 8V

10V

15V

20V 25V

30V

G D S

IRF

740

MOSFET VGG

0-30V

1K

VGS

0-30V

(0-100mA) 500/ 5W

A

V

ID

VDS (0-30V)

D

S

G

IRF

40 / 42

V

VDD 0-30V



b) TRANSFER CHARACTERISTICS:


(2) Keep the Drain–source voltage (VDS) constant (say at 10V). (3) Vary the gate supply voltage VGG in steps and note down the corresponding drain current (ID),

Gate-Source voltage (VGS) and tabulate the result.

(4) Repeat the above procedure for different values of Drain–source voltage (VDS).

(6) From the readings draw the transfer characteristics & calculate the trans-conductance gm, which is

given by gm = ID (in mA) /VGS (in volts)

TABULAR COLUMN:

Ref

VGG VDS1 = 5 V VDS2 = 8 V

VGS (in volts) ID(in mA) VGS (in volts) ID(in mA)

RESULT:- The static characteristics of MOSFET is conducted & the following values are calculated using its graph.

(a) Drain resistance = rd = VDS (in volts) / ID(in mA) =

(b) Trans-conductance = gm = ID(in mA) /VGS (in volts) = mhos

(c) Amplification factor = = rd * gm =

(d) VGS(th)=Threshold voltage = V

ID

(in mA)

VT VDS (in volts)

VGS4

VGS3

VGS2

VGS1

Active region

Cut-off region

VGS(th) VGS (in volts)

ID (in mA)

Transfer Characteristics

of MOSFET



EXPERIMENT-4

Static characteristics of power IGBT

AIM:- To Plot the VI characteristics of Power IGBT.

COMPONENTS REQUIRED: IGBT (IRG4BC200), Resistors (500 / 5W, 1K),

Milli-ammeter (0-100mA), Voltmeters (0-30V, 2nos), Power supplies & connecting board.

CIRCUIT DIAGRAM:

PROCEDURE:

(a) OUTPUT CHARACTERSTICS.


(2) Keep the Gate–Emitter voltage (VGE) constant ( say at 5V).

(3) Vary the supply voltage VCC in steps and note down the corresponding collector current

(IC) & the Collector-Emitter voltage (VCE) and tabulate the result.

(4) Repeat the above procedure for different values of Gate–Emitter voltage (VGE).

(5) From the readings draw the output characteristics & calculate the Collector resistance rC,

which is given by, rC = VCE (in volts) / IC (in mA)

TABULAR COLUMN:

Ref

VGG VGE1 = V VGE2 = V

VCE (in volts) IC (in mA) VCE (in volts) IC (in Ma) 0V

0.5V

2V

4V

6V

8V 10V

15V

20V

25V

30V

VGG 0-30V

IC

(in mA)

VT VCE (in volts)

VGE4 = 5.2V

VGE3 = 5.15V

VGE2 = 5.1V

VGE1 = 5.05V

G C E

IRG4

BC200

0

IGBT

1K

VGE

0-10V

(0-100mA) 500/ 5W

A

V

IC

VCE (0-30V)

C

E

G

IRG4

BC-200

V

VCC 0-30V

IGBT



(b) TRANSFER CHARACTERISTICS:


(2) Keep the Collector–Emitter voltage (VCE) constant (say at 10V).

(3) Vary the gate supply voltage VGG in steps and note down the corresponding collector

current (IC), Gate-Emitter voltage (VGE) and tabulate the result.

(4) Repeat the above procedure for different values of Collector–Emitter voltage

(VCE).

(5) From the readings draw the transfer characteristics & calculate the trans-resistance

rm, which is given by rm = VGE (in volts) / IC (in mA)

TABULAR COLUMN:

Ref

Vcc VCE1 = V VCE1 = V

VGE (involts) IC (in mA) VGE (involts) IC (in mA)

RESULT:- The static characteristics of IGBT is conducted & the following values are calculated using its

graph.

(a) Collector resistance = rc = VCE (involts) / IC (in mA) =

(b) Trans-resistance = rm = VGE (involts) / IC (in mA) =

(c) VGS(th)=Threshold voltage = V

VGE(th) VGE (in volts)

IC (in mA)

Transfer Characteristics

of IGBT



EXPERIMENT-5

RC Triggering Circuit

AIM:- a) To study the working of Half wave and Full wave controller rectification using

RC triggering.

b) To plot the response curve Vdc v/s α

c) To draw the waveforms at different points.

COMPONENTS REQUIRED: SCR (TYN-612), Diodes (IN-4007), Resistors (500 / 5W, 1K),

Pot (4.7K), CRO with probes, Transformer & connecting board.

CIRCUIT DIAGRAM OF

RC TRIGGERING FOR HWR:

D1: Prevents the breakdown of the gate to cathode junction during the negative half cycle of the I/P D2: It allows the capacitor to charge in the in the negative direction (there by it introduces the phase shift

between capacitor voltage & the supply voltage)

DESIGN: Let us assume that Vs = 24V, Vg (min) = 0.5V, Ig (min) =4mA, VD1 = 0.7V, Ig (max) = 500mA.

The thyristor turns on when the capacitor voltage reaches to the minimum triggering voltage (Vgt), which

is given by: VC = Vg (min) + VD1

Therefore the maximum value of Rv is obtained from the equation given by:

Vs > Ig(min) * RV + Vc. Where Vs is the instantaneous supply voltage. But Vc = Vg (min) + VD1

Rv < Vs – V g (min) – V D1 = 24V – 0.5V – 0.7V = 5.7K Choose RV = 4.7K. (POT)

I g (min) 4mA

Also Rmin > Vs = 24V = 48 Choose Rmin = 100. I g (max) 500mA

RC > 1.3 T = 4 C > 1.3 T ( Since f =50Hz, T = 20mS)

2 w 2R

C = 1.3* 20m > 2.76 F Choose C = 4.7 F

2*4.7K

C

4.7F D1

230V

AC I/P

12V

0V

D2

V

o

R

L

Vo

RL=500

Rmin

100 Rv

4.7K

A

VSCR G

K



D1

PROCEDURE: (Same for both HWR & FWR circuits)


(2) Apply the AC input voltage through the step down transformer.

(3) Observe the waveforms at different points of the circuit, like Vo, VSCR, VC etc.

(4) The delay angle is varied using the pot (RV) & the waveforms for different values of

delay angle () are observed & traced.

RC TRIGGERING FOR FWR:

DESIGN:

Let Vs = 48V, then Vdc = 2 Vm/ = 30V.

Designing of Rmin is same as HWR, Rmin = 100

Rv < Vs – V g t = 30V – 0.5V 10K Choose RV = 10K. (POT)

I g (min) 3mA

To find C use the relation given by: RC > 50 T C > 50 T 50*20m 50F

2 2R 2*10K

Hence choose C = 47 F

TABULAR COLUMN:

α in degrees VL (volts)

A TYN-410

SCR

K G

IN-4007

IN-4007

D2

230V AC I/P

C

47F

12V

12V

Rmin

100

Rv

10K VSCR

Vo RL=500/

5W

VL

Vm /

0 900 1800 in degrees



Vs

Vm

2 3 4 t

( +)

2 (2 +)

3 (3 +)

4 t

( +)

2 (2 +)

3 (3 +)

4 t

WAVE FORMS:

RESULT: RC triggering circuit for HWR & FWR are designed & waveforms at different points

are observed.

Vs

Vm

2 3 4 t

2

(2 +) 3 4 t

Output for RC-triggering for HWR:

can be varied from 0 to 1800

VSCR

2

(2 +) 3 4 t

Vo

VSCR

Output for RC-triggering for FWR:

can be varied from 0 to 1800

Vo



AC

Mains

150V/ 230V

0V

Rmin=100/5W

1M

DB32C

C=100nF/200V

MT2

BT-136

MT1 G

EXPERIMENT-6

AC Voltage Controller AIM: a] To study the speed control of universal motor using Triac-Diac combination.

b] To study the working principle phase control of Triac (light dimmer)

APPARATUS REQUIRED: Triac (BT-136), Diac (DB32C), Rheostat-200, Resistors-

100/5W, Capacitor-100nF/200V, Pot-1M, Isolation Transformer,

Power Scope, Multi meter, Patch chords & Connecting board.

CIRCUIT DIAGRAM:

PROCEDURE:

(1) Rig up the circuit as shown in the figure.

(2) Apply 230V from the secondary of the transformer, observe the waveforms across the

load, Capacitor & Triac.

(3) Now vary the pot & measure the O/P RMS voltage across the load using a multi meter

(in AC range) & correspondingly measure the delay angle using Power Scope.

(4) Calculate the theoretical O/P RMS voltage, for every delay angle measured using the

formula:

(5) Compare the theoretical O/P voltage with the practical values.

(6) Draw a graph of Vo(rms) versus delay angle ()

Vo

Lamp/motor

VT2T1

1

V0(rms) = Vs - + Sin (2)

2



Vo(rms)

Delay angle ()

2 3 t

( +) (2 +) t

VC

Vo

( +)

2 (2 +) t

VT1T2

TABULAR COLUMN:

Delay angle () measured from the CRO

Delay angle

() in degrees Vo(rms) Theoretical =

VS1/ ( - + ½ sin [2]}1/2

Vo(rms) practical

Measured using multimeter

EXPECTED WAVEFORMS:

IDEAL GRAPH:

RESULT: An AC voltage controller is studied & its O/P rms voltage is calculated & verified

for different values of delay angle.

Vo(rms) V/S Delay angle()

( +) 2

(2 +) 3 t

VS

Vm



A

VSCR

G K

IZ-15V

B2

2N2646

B1

RL=500

/ 5W

R2

1K

A

VSCR

G K

IZ-15V

B2

2N2646

B1

RL=500

/ 5W

R2

1K

Pulse Transformer

Pulse Transformer

EXPERIMENT-7

UJT Firing Circuit

AIM:- To study the UJT triggering circuit for HWR & FWR circuits

COMPONENTS REQUIRED: SCR (TYN-612), UJT (2N2646), Resistors (500/5W, 1K,

330, 100, Pot (10K), CRO with probes, Transformer & connecting board.

CIRCUIT DIAGRAM:

UJT TRIGGERING CIRCUIT

FOR HWR CIRCUIT:

Designing: (Same for both HWR & FWR): Let Secondary voltage of the transformer

Vs = 48V, Is = 50mA, Vz = 15V, = 0.66, tg = 50S & T = 5mS

Hence Vdc = 2 Vm/ = 30V.

Then Rs = Vs –Vz = 30 – 15 = 300 Choose Rs = 330. Is 50m

Let C = 0.47F, then R1 = tg / C = 50*10-6

/ 0.47* 10-6

= 106. Choose R1 = 100.

We know that for an UJT relaxation Oscillator T = RC ln(1/1-)

R = T /{ C ln(1/1-)} = 5*10-3 /{0.47*10

-6 ln (1/1-0.66)} 10K.

Hence Choose RV = 10K (pot) in series with a 100 resistor.

R2 = 104 / Vz = 10

4 / (0.66 * 15) 1K. Hence choose R2 = 1K. Choose RL = 500 /5W

CIRCUIT DIAGRAM:

UJT triggering circuit

for FWR circuit:

D1

IN-4007

IN-4007

D2

230V AC I/P

12V

12V C

0.47F

Rmin

100

Rv

10K

E

Vo Rs = 330

D1

IN-4007

D2

IN-4007

230V AC I/P

12V

12V C

0.47F

Rmin

100

Rv

10K

E

Vo

Rs = 330



PROCEDURE: (Same for both HWR & FWR):


(2) Apply the AC input voltage through the step down transformer.

(3) Observe the waveforms at different points of the circuit, like Vdc, Vo, VSCR,VC, Vz etc.

(4) The delay angle is varied using the pot (RV) & the waveforms for different values of

delay angle () are observed & traced.

WAVEFORMS OF UJT

TRIGGERING CIRCUIT:

RESULT: UJT triggering circuit for HWR & FWR are designed & waveforms at different points

are observed.

2 (2 +) 3 4 t

Vo

VSCR

2 (2 +) 3 4 t

2 (2 +) 3 4 t

Vo

VSCR

2 (2 +) 3 4 t

FOR HWR

CIRCUIT

FOR FWR

CIRCUIT

Vin Vm

2 3 4 t Vdc

Vm

2 3 4 t

VZ

2 3 4 t

Vc

2 3 4 t VB1

2 3 4 t



K K

EXPERIMENT-8

CONTROLLED RECTIFIER WITH R& RL LOAD

AIM:- To study the Half Controlled & Full Controlled Rectifier circuits for R & RL loads

COMPONENTS REQUIRED: SCR (4 Nos-TYN-612), Diodes (2 Nos- IN5402), Converter Firing

circuits, Resistor (500/ 10W), Inductor 10mH, CRO with probes, Voltmeter & patch cords.

CIRCUIT DIAGRAM: HALF CONTROLLED RECTIFIER (SEMI CONVERTER) FOR R AND

RL LOAD:

PROCEDURE: (Common for both Semi & Full Converters):

(1) Rig up the circuit as shown in the figure.

(2) Apply some input voltage (say 30V) through the isolation transformer. Then switch on the triggering circuit

(3) Display the output on the CRO & observe the rectified voltage.

(4) Now vary the firing angle () in steps & note down the corresponding output voltage using a voltmeter.

(5) The theoretical output voltage is calculated using the formula given by: Vo(avg)= [Vm /](1+Cos ).

(6) Compare the practical readings with the theoretical values.

(7) Repeat the above procedure for RL load & observe the effect of the Free Wheeling Diode.

TABULAR COLUMN:

in degrees Vo(Practical) Vo(Theoretical)=[Vm / ] (1+ Cos ).

Isolation

Transformer

230V

AC I/P

30V

0V

RL

500

/5W

K

G T2 A

D1 A

K

G

T1 A

D2 A

Vo CRO &

Voltmeter

R

FWD

L



Vo O/P for R load & RL load with FWD

2 3 t

Vg1

(2 +) t

Vg2

( +) t

Vo O/P for RL load without FWD

CIRCUIT DIAGRAM OF FULL CONTROLLED RECTIFIER :( FULL CONVERTER) FOR

R & RL LOADS:

TABULAR COLUMN:

in degrees Vo(Practical) Vo(Theoretical) = [Vm / ] (1+ Cos ).

RESULT: The Half controlled (Semi converter) & Full controlled (Full converter) rectifiers are studied for both R & RL load.

Isolation Transformer

230V

AC I/P

30V

0V

RL

500

K

G T2 A

K

G T1

1 A

K

G

T1 A

K

G

T12

A

( +) 2 (2 +) 3

t

( +) 2 (2 +) 3 t

VS Vm

Vo(avg)

2Vm /

0 900 1800 in degrees

Ideal graph of delay angle ()&

the output average voltage Vo(avg):

EXPECTED WAVEFORMS OF A

CONVERTER:

FWD



RL

1K

L 10mH

C

10F Vs

10V

toff

EXPERIMENT-9

Commutation Circuits

AIM:- To study the different commutation circuits.

COMPONENTS REQUIRED: SCR (2 Nos-TYN-612), Diodes (2 Nos- IN5402), Firing circuits,

Rheostat (1K/ 5W), CRO with probes & patch cords.

Self Commutation with LC in shunt with thyristors (CLASS-B Commutation):

L-C or C switched by an auxiliary SCR (Class D):

A

TYN-612 G K

Ig

VT

VL

t

t

t



Turn off times of different commutation circuits:

Class-B Class-D

Theoretical

Turnoff time

toff = (πLC)/2 toff = 0.693 R1C

Practical

Turnoff time

Result: Class B and Class D Commutation circuits are constructed & their turn off times is

verified.

Procedure:

(1) Make the circuit as shown in the figure.

(2) Apply a DC voltage using Vs (say 10V).

(3) Switch on the triggering circuit unit & observe

the voltage across the load, thyristors &

capacitors in CRO & then trace them.

(4) Measure the turn off time & verify it using

appropriate formulae.

(5) Repeat the above procedure for all the

Commutation circuits.



Vs

10V

C1

RL=50

Vo

C2

O/P Voltage across load (For low frequency):

O/P Voltage across load (For High frequency):

G

D1

L

Vs

10V

C RL

50

D2

EXPERIMENT-10

INVERTERS

AIM:- To study the performance of Series & Parallel inverter circuits.

COMPONENTS REQUIRED: SCR (2 Nos-TYN-410), Diodes (2 Nos- IN5402), Firing circuits,

Rheostat (50/ 25W), CRO with probes & patch cords.

CIRCUIT DIAGRAM:

Series Inverter:

PROCEDURE: (Same for both series & parallel Inverters):

(1) Rig up the circuit as shown in the fig.

(2) Switch on the DC supply & apply some voltage (say 10V) to the circuit.

(3) Now switch on the triggering circuit & observe the O/P voltage across the load.

(4) Measure the frequency of the O/P voltage, if this frequency increases above the resonant

frequency of the circuit, commutation failure occurs.

(5) Then switch off the DC supply, change the triggering angle & Load resistance & again

switch on the circuit to get the inverter O/P.

(6) Measure the minimum & maximum range of the O/P frequency.

CIRCUIT DIAGRAM: Parallel Inverter:

K A

G T1

A

T1 D1

G K

A

T2 D2

G K

t

t

T2 K A

Vo

O/P Voltage waveform:

t



TABULAR COLUMN:

𝐹𝑟 =1

2𝜋 1

𝐿𝐶−𝑅2

4𝐿2

Type of the Inverter Theoretical Frequency Practical Frequency

Series Inverter:

Fmin=

Fmax=

Parallel Inverter:

Fmin=

Fmax=

RESULT:

The Series & Parallel Inverters are constructed & their performance is studied.



Vs

10V

RL

500

T1

C 1F T2

L D

10mH

Vo

EXPERIMENT-11

Voltage (Impulse) Commutated Chopper

AIM: To study the performance of a Chopper using Jones chopper circuit.

Apparatus required: SCR (2 Nos-TYN - 612), Diodes (1No - IN5402), Chopper Triggering

unit, VRPS, Resistor-500/5W, CRO with Probes & patch chords.

Circuit Diagram:

Procedure:

(1) Rig up the circuit as shown in the figure

(2) Apply a DC voltage using VRPS (say 10V)

(3) Switch on the Chopper Triggering circuit & observe the voltage across the load on CRO.

(4) Measure the on & off periods of the output voltage & calculate the duty cycle (D), using

it, the output average voltage can be calculated, which is given by: Vo(avg) = Vs * D.

(5) Measure the output average voltage using a multi-meter (keeping it in DC range),

compare that with the theoretical value.

(6) Repeat the above procedure for different values of firing angle () & frequency.

Tabular Column: For Duty cycle variation: Vs=10V

Firing

Angle ()

Ton Toff D = Ton. .

Ton + Toff

Vo(avg) (Theoretical)

= D * Vs

Vo(avg) (Practical)

(Multi-meter reading)

Vo t Ton Toff



Vo(avg)

Duty

Cycle (D)

For Frequency variation: Vs=10V

Frequency Ton Toff D = Ton. .

Ton + Toff

Vo(avg) (Theoretical)

= D * Vs

Vo(avg) (Practical)

(Multi-meter reading)

Expected Graph:

Result: A DC Chopper is constructed & its performance is studied.



A RL Armature

500/5W side

AA

F

Field side

FF

AC

Mains

60V 0V

K G K G

T1 T2

A A

D2 D1

EXPERIMENT-12

SPEED CONTROL OF DC MOTOR

Aim: To study the speed control of a separately excited DC motor using a Semi converter

Apparatus required: SCRs –2 Nos (TYN-410), Diodes –2 Nos (IN 5402), A Separately excited

DC motor, Rheostat-50, Power Scope, Tachometer, Isolation Transformer, Multi meter,

Connecting board & Patch chords.

Circuit Diagram:

Procedure:

(1) Switch on the triggering circuit & observe the triggering pulses generation from it.

(2) Rig up the circuit as shown in the fig. With R-load only. Connect the triggering circuit to

the SCRs.

(3) Apply 30V from the secondary of the transformer & observe the O/P voltage waveform

across the load resistor (RL), on the CRO.

(4) Now switch off the Mains & then Triggering circuit & replace the load resistor (RL) by

the motor as shown in the fig.

(5) Switch on the Field supply & mains, then switch on the Triggering circuit

(6) Now observe the running of the motor.

(7) Vary the firing angle () in steps & note down the corresponding speed of the motor

using a Tacho-meter.

(8) Tabulate the readings & plot the graph of delay angle () versus speed.

NOTE: While Switching on, the AC mains is switched on first & then the firing circuit. While

switching off the circuit, switch off the mains first, then the firing circuit should be switched off.

Tabular Column: Delay angle ()

in degrees Vo(avg)

(Measured using multi meter )

Speed (in rpm) Measured using Tacho-meter

M Vo



Vo(avg)

& Speed

0o 90

o 180

o Delay angle ()

2 3 t

Vg1

(2 +) t Vg2

( +) t

Expected waveforms:

Ideal Graph:

Result: The Speed control of a DC motor is studied & the graph of O/P average voltage & its

speed are plotted for different values of delay angle.

Vo(avg) & Speed V/S Delay angle()

( +) 2 (2 +) 3 t

VS

Vm



Preset

CLK

Reset

Reset

Ō

A Ā

Load

B

B

A Ā

En

Sync Signal (~8V) DC 5V Supply

TP

TN

TM TA

EXPERIMENT: 13

DIGITAL FIRING CIRCUIT

Aim: To study the performance of a Digital Firing circuit.

Block Diagram:

Procedure:

Waveforms:

Flip-

Flop

Clock Generator (Astable

Multivibrator)

N-Bit

Counter

Logic Circuit and

Modulator +

Driver Stage

Carrier Frequency Oscillator

ZCD (Zero

Crossing Detector)

(1) Switch on the Mains supply.

(2) Observe the AC reference compare it with ZCD O/P A & reset O/P.

(3) Choose the selector switch of the Logic circuit to get either converter mode or chopper mode.

(4) Vary the firing angle/ duty cycle & observe the change in the pulse width

at the O/P (5) If TP & TN are observed then Converter triggering pulses can be observed

& if TM

& TA are observed then Chopper triggering pulses can be observed.

(6) This Digital circuit can be used as triggering circuit for converter or chopper.

Synchronous

Sine wave & DC

reference Signal

A

Ā

ZCD O/P C

C

Down Counting

Counter O/P

maximum

B

B

fc

when G1

Y=0 G2

When G1

Y= 1 G2



EXPERIMENT-14

SPEED CONTROL OF STEPPER MOTOR

AIM: To rig up and verify operation of Stepper Motor.

COMPONENTS REQUIRED: Stepper Motor Controller (SMC), Stepper Motor Module.

CIRCUIT DIAGRAM:

PROCEDURE:

1. Connect the controller o/p A1, A2, B1, B2 to A1 A2 B1 B2 i/ps (respectively) of the

Stepper Motor Module.

2. Connect +ve common terminal to +ve supply.

3. Switch on the power supply to the unit. It displays S-00.

4. Press SET on SMC.

5. Display shows “rpm”(Rev Per Sec).

6. Press ENT for “Speed MODE”.

7. Display “00”.

8. Press INC key to set rpm.

9. Press ENT

10. Displays DR FR (Direction of rotation).

11. Press INC/DEC to change direction of rotation.

12. Press ENT.

13. Displays HF ST or FL STEP.(Step size Half or Full)

14. Use INC/DEC to select step size.

15. Press ENT.

16. Then it displays n…….. Rpm set for speed mode.

17. Press Run/Stop for running or stopping the motor.



STEP MODE:

1. Switch on the power supply.

2. Display shows S 00

3. Press SET.

4. Display shows rpm.

5. Press INC/DEC to change to step mode

6. Follow similar steps as above from step 7 for setting the parameters for step mode.

7. In the last display shows S……. Steps set.

8. Run/Stop will make the motor to run by respective steps.

TABULAR COLUMN: Speed Mode.

Sl. No RPM set Time for full

Rotation

No of Rotations Practical RPM

TABULAR C OLUMN: Step Mode [Step angle =1.8 ± 0.1] (Non cumulative)

Sl. No No of Steps Type of Step Half or

Full

Theoretical

Degrees

NOTE: Step Lle =1.8 + 0.1 (Non cumulative)

Steps/ revolution =200



SWITCHING LOGIC SEQUENCE:

Full step

A1

(RED)

A2

(GREEN)

B1

(BLUE)

B2

(BLACK)

0

0

1

1

1

1

0

0

0

1

0

1

1

0

0

1

Half step

A1

(RED)

A2

(GREEN)

B1

(BLUE)

B2

(BLACK)

0

0

1

1

1

0

0

0

1

0

0

0

0

0

1

1

0

0

0

0

1

1

1

0

1

1

1

0

0

0

0

0

RESULT: The operation of a Stepper motor is studied and the speed control is verified.



INTRODUCTION OF ORCAD 16.5, USE, CIRCUIT DESIGN & SIMULATION

Step 1: Software opens by clicking an option “CAPTURE LITE” in the start menu.

Step 2: To start with a PSpice project:

Go to “File” menu. Select “New Project” option.

Choose “analog or mixed A/D” option and specify the project name and its location and

click Ok



Step 3: Once the step (2) is completed the following window appears. Choose “Create a blank

project” option.

Step 4: Create the circuit by placing all its parts using “Part” option from “Place” menu. In this

way a complete electrical circuit can be formed.



Step 5: After completing the circuit, make the simulation profile using “New Simulation Profile”

command from “PSpice” menu.

Step 6: Go to “Edit Simulation Profile” in “PSpice” menu, simulation settings window will

open. Go to “Analysis” and set the simulation parameters as shown below.



Step 7: Place the markers (voltage or current) near the required component on the circuit by

using command “MARKERS” from “PSpice” menu.

Step 8: Run the simulation by using command “RUN” from “PSpice” menu.



Step 9: And the results will be plotted.



CONVERTER CIRCUITS USING ORCAD PSPICE

1. AC voltage controller using triac – diac combination.

Output Waveforms:

12k

0

Vs

FREQ = 50VAMPL = 230v

VOFF = 0

R4

50

C

48uf

Triac

V+ V-



2. Controlled Rectifiers with R & RL Loads. 2. a. Half bridge controlled rectifier (semi converter) for R load

Output Waveforms:

D1N914

Vpulse1

TD = {talpha+1/(2*f )}

TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5

V

D1N914

Vpulse

TD = {talpha}

TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5

1k

V

2N1595

PARAMETERS:talpha = {alpha/(360*f )}alpha = 90f = 60v rms = 120

Vs

FREQ = {f }VAMPL = 30v

VOFF = 0

2N1595



2. b. Half bridge controlled rectifier (semi converter) for RL load without freewheeling diode

Output Waveforms:

500Vs


VOFF = 0

L1

0.5H

1

2

D1N914

Vpulse

TD = {talpha}

TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 52N1595 Vpulse1


TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5

2N1595

D1N914

V




2. c. Half bridge controlled rectifier (semi converter) for RL load with

freewheeling diode

Output Waveforms:

V

Vpulse1


TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5Vpulse

TD = {talpha}

TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5

500Vs


VOFF = 0

2N1595

L1

0.5H

1

2


2N1595



2. d. Full controlled rectifier for R load

Output Waveforms:

Vs


VOFF = 0

PARAMETERS:talpha = {alpha/(360*f )}alpha = 90f = 60

R1

500

Vpulse

TD = {talpha}

TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5Vpulse1


TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5

0

Vpulse2

TD = {talpha}

TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5Vpulse3


TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5

0

V

V



2. e. Full controlled rectifier for RL load

Output Waveforms:

Vs


VOFF = 0


R1

500

Vpulse

TD = {talpha}

TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5Vpulse1


TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5

0

Vpulse2

TD = {talpha}

TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5Vpulse3


TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5

0

L1

0.5H

V



2. f. Full controlled rectifier for RL load with freewheeling diode

Output Waveforms:

Vs


VOFF = 0


R1

500

Vpulse

TD = {talpha}

TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5Vpulse1


TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5

0

Vpulse2

TD = {talpha}

TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5Vpulse3


TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5

0

L1

0.5H

D

V



3. COMMUTATION CIRCUITS

3. a. Self Commutation with LC in shunt with thyristor (CLASS-B

Commutation)

Output Waveforms:

V3

5Vdc

R

1k

C1

5uF

L1

0.5H

1

2PARAMETERS:talpha = {alpha/(360*f )}alpha = 60f = 60

V

2N1595

V2

TD = {talpha}

TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5

V-

V+



3. b. L-C or C switched by an auxiliary SCR (Class D Commutation)

Output Waveforms:

R

1k

X2

2N1595

VC1

1uF

D2

D1N914


V-

L2

10uH

1

2

V+

D1

D1N914

V2

TD = {talpha}

TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5

2N1595

Vpulse1


TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5

L1

0.5H

1 2

V3

5Vdc



4. Voltage (Impulse) commutated chopper

Output Waveforms:

2N1595

Vpulse

TD = {talpha}

TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5

D

VC

1uf1.5kVs

10Vdc


Vpulse1


TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5

L

10mH

1 2



5. Inverters 5. a. Series Inverter

Output Waveforms:


2N1595

Vs

10Vdc

Vpulse

TD = {talpha}

TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5C

10uf

D

Vpulse1


TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5

V+

C1

10uf

R2

100

D1

V-

L2

10mH

1

2

L1

10mH

1

2



5. b. Parallel Inverter

Output Waveforms:

2N1595

R3

500

Vpulse2

TD = {talpha}

TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5


Vpulse3


TF = 0.1uPW = {0.5/f }PER = {1/f }

V1 = 0

TR = 0.1u

V2 = 5

TX2

L4

300uH

1 2VC

6.8uf

Vs

10v



Theory & working operations about the experiments:

Thyristor (Silicon Controlled Rectifier-SCR):

It is a four layer (PNPN), three junction & three terminal semiconductor device which

can be used as a controlled uni-directional switch. It has three terminals called Anode (A),

Cathode (K) & Gate (G). Due to its uni-direction property it can be used as controlled rectifier.

Due to the gate terminal its conduction can be controlled. Hence it is mainly used in controlled

rectifiers (converters), Inverters, AC voltage controllers, cyclo-converters etc.

TRIAC:

It is a four layer, three junction & three terminal semiconductor device which can be used

as a controlled bi-directional switch. It has three terminals called Main terminal-1 (MT1), Main

terminal-2 (MT2) & Gate (G). It can be considered as equivalent to two thyristors connected in

anti-parallel combination. The TRIAC can be operated in four modes depending upon the

voltage applied to its main terminals & gate terminal. The mode which requires minimum gate

current to turn is considered as most sensitive mode of TIAC. Due to its bi-directional property,

it can be used to control the AC power, hence it is used as AC voltage controllers.

MOSFET (Metal Oxide Semiconductor Field Effect Transistor):

It is a type of uni-polar transistor, which can be used as a fast acting switch. It is a

voltage controlled device, whose conduction can be controlled using gate voltage. It has three

terminals called Drain (D), Source (S) & Gate (G). Due to the semiconductor layer at its gate

terminal, it offers very high input impedance & low output impedance. The conduction loss of

the MOSFET is less compared to BJT, but power handling capacity of it is less.

IGBT (Insulated Gate Bipolar Transistror):

It is a latest power electronic device, which is obtained by combining the advantages of

BJT & MOSFET. It has three terminals called Emitter (E), Collector (C) & Gate (G).It is a bi-

polar switch, having low on state drop & high switching speed. It’s a voltage controlled device

having almost flat temperature coefficient & it does not have second break down problem. But it

is a costly device. It is used in UPS systems, AC motor drives, Choppers etc.

RC Triggering:

The process of turning on of the thyristor is called as Triggering. The best way of

triggering the thyristor is by applying gate current, which is called as Gate triggering. R

triggering can be used to control the thyristor triggering from 0 to 900 only. But in RC triggering

AC voltage is used to trigger the thyristor with the help of Resistance & Capacitance, hence it

can be used to control the thyristor triggering from 0 to 1800. This possible due to the charging

of the capacitor, which introduces a phase shift between voltage & current. The triggering angle

can be controlled by varying the R value.

Working operation:

During the negative half cycle of the supply voltage, the capacitor charges through diode

D2 (to –Vs) & during this the output voltage will be zero. During the next positive half cycle, the

capacitor discharges through resistor & starts charging in the positive direction. As this positive

voltage reaches the minimum gate voltage required to trigger the thyristor, the diode D1 gets

forward biased & allows the capacitor to discharge through it, hence the thristor gets sufficient



gate current & it gets triggered. The triggering of the Thyristor can be controlled from 0 to 1800,

by raring the resistance value.

UJT Triggering:

UJT is a Uni-junction Transistor, which exhibits negative resistance region (Increase in

the voltage decreases the current). Hence it can be used as Relaxation Oscillator to generator saw

tooth waves & short durational spikes (pulses). Due to this property it is used as a triggering

circuit for thyristors. When the UJT & SCR both are triggered using the same AC vaoltage, it is

called as Synchronous UJT Triggering circuit. In Asynchronous UJT Triggering they are

triggered using two different voltages.

Working operation: AC input voltage is stepped down using transformer, then it is rectified

using a rectifier. This rectified (DC) voltage is regulated using a zener diode. This regulated

voltage is applied as DC supply voltage for UJT circuit. Here UJT is used as a Relaxation

Oscillator, hence it behaves like a open switch until its emitter voltage reaches peak voltage of it

& as its emitter voltage reaches peak voltage level UJT turns on & it behaves like a closed

switch. This is achieved by charging the capacitor through the resistor. For this the regulated

zener voltage is used. As the capacitor discharges reaches peak voltage of UJT, it turns on &

provides a path for discharging. This discharging of the capacitor takes place very fast, hence a

short duration spike gets developed across its base terminal. This short duration spike (pulse) is

applied to the gate terminal of the thyristor, through 1:1 pulse transformer (which is used for

isolation) to trigger the thyristor. The charging of the capacitor can be controlled by varying the

resistance value & there by the conduction of the thyristor can be controlled.

Single Phase Half controlled & Fully controlled converters:

Converter is basically a controlled rectifier, which gives variable DC voltage. Depending

upon the polarity of the output voltage & current (Quadrants) obtained they are classified as 1

Quadrant, 2 Quadrant & 4 Quadrant converters. Single phase half controlled converter is a single

Quadrant converter & single phase fully controlled converter is a 2 Quadrant converter.

Both of them work in the similar fashion. But half controlled converter uses 2 diodes & 2

thyristors, on the other hand Fully controlled converter uses 4 thyristors. Output voltage is same

in both the cases for R load. But for RL load, the output voltage will have small negative voltage

in case of Fully controlled converters. This negative voltage occurs due to the inductive load &

this can be eliminated using Free wheeling Diode (FWD). These converters are mainly used in

DC drives, power supplies, HVDC systems stc.

Working operation of Half controlled converter: During the positive half cycle, T1-D1 gets

forward biased, by controlling the firing angle of T1, this half cycle can be controlled. Similarly

during the negative half cycle of the I/P, T2-D2 gets forward biased, now T2 can be controlled by

varying the firing angle. Thus the negative half cycle can be controlled. Due to the bridge

configuration the output voltage will be always positive. This positive voltage can be controlled

using the delay angle.

Working operation of Fully controlled converter:

Same as Half controlled converter, but the firing of T1 &T’1 should be done simultaneously.

And the firing of T2 &T’2 should be done simultaneously.



SCR Commutation Circuits:

Commutation is the process of turning off of the thyristor. A conducting thyristor can be

turned off by making the current through it to fall below Holding current (which is called as

Current Commutation) or by applying a large negative voltage across it (which is called as

Voltage Commutation). Mainly there are 2 types of Commutation methods called Natural

Commutation & Forced Commutation. In Natural Commutation the conducting thyristor gets

turned off due to the AC supply applied to it. But in Forced Commutation the Input voltage will

be DC, hence some external components are used to turn off the thyristor.

CLASS-B Commutation: (Self Commutation by parallel L & C)

It is also a type of current Commutation circuit, in which the L & C are connected in

parallel to the thyristor. The main advantage of this circuit is that it is very simple, but the main

disadvantage of this circuit is that its turn off time is fixed. Here R, L & C are selected such that

the circuit is always under damped. This circuit is mainly used in parallel inverters.

In this case the thyristor is connected across the series combination of L & C, hence

when the thyristor was off, the capacitor gets charged to the supply voltage, & as the thyristor is

turned on it discharges through L & SCR. As the capacitor discharges, it gets charged in the

opposite direction, and as the capacitor gets fully charged in the opposite direction it again

discharges, through the thyristor but in the opposite direction. Hence after some time the current

through the thyristor drops to zero (due to opposing currents), thus causes current commutation

& turns off the thyristor.

CLASS-C Commutation: (Complimentary Commutation) In this method an extra thyristor is used to turn off the conducting thyristor, hence one

thyristor will be on at a time & the other being off, thus it is called as Complimentary

Commutation circuit. It is a type of voltage commutation circuit.

In this case when one of the thyristor is conducting, the other will be off. Hence the

capacitor gets charged & this stored energy can be used to turn off the conducting thyristor,

whenever it is required. The main advantage of this circuit is that, its simple construction, but its

major disadvantage is that the load current will be discontinuous.

AC Voltage Controller using TRIAC-DIAC combination

AC Voltage Controller is a circuit, which controls the AC voltage without change in the

frequency. As it controls AC voltage it is mainly used in Light control, fan regulator, AC motor

speed control etc. It uses a TRIAC-DIAC combination, in which DIAC helps in trigger the

TRIAC. DIAC can be triggered using R-C combination.

Working operation: Initially the TRIAC will be off, hence the I/P current flows towards the

capacitor through resistor & charges it. As the capacitor gets charged to the minimum voltage

required to turn on DIAC, the DIAC turns on. Now the capacitor discharges through DIAC

towards gate of the TRIAC & helps in triggering it. Then the output voltage is obtained & it can

be controlled using the pot. Since DIAC & TRIAC both are bi-directional, output can be

controlled in both the directions.

DC Chopper:

It is a circuit, which converts fixed DC to variable DC. It is DC equivalent to

transformer. It uses thyristors with forced commutation. The circuit & working of a Jones



chopper is similar to a Class-D commutation circuit. It produces square wave form, whose on &

off periods can be controlled to control the output DC voltage. We control the output DC voltage

in two ways, namely-fixed frequency & variable frequency operations. In fixed frequency

operations, the duty cycle of the output is varied to control it. In variable frequency operations,

the duty cycle is kept constant & frequency of the output wave is varied.

Inverters:

It converts DC signal into AC signal of desired amplitude & frequency. It uses thyristors

with forced commutation. They are mainly used in UPS, Stand by power supplies etc.

Depending upon the commutating elements, they are classified as series & parallel inverters.

Series Inverter: In this case the commutating elements are placed in series with the thyristors. It

uses two Thyristors with two sets of commutating elements. It uses current commutation for the

thyristors. When one thyristor is fired, the other turns off due to the energy stored in the

commutating elements & vice versa. Thus it produces a wave which looks like spike of longer

duration, but if it is properly filtered, then almost sine wave can be obtained.

Parallel Inverter: In this case the commutating elements are placed in parallel with the

thyristors. It uses voltage commutation for the thyristors.

Working operation: When one thyristor is on (say T1), the current flows through half of the

transformer, T1 & inductor and causes the capacitor to charge to 2Vs. This voltage gets applied

across the conducting thyrisor T2 & turns it off due to voltage commutation. Now the capacitor

discharges through L & T2, and gets charged in the opposite direction. Now the capacitor

becomes ready for the commutation of T2 & it can be done whenever T1 is fired again. This

continues producing a slightly tilted square wave across the output.

Note: In case of inverters, the thyristors are connected with anti parallel diodes to provide

alternative path for reverse current, which can occur due to inductive loads.

Speed Control of DC motor:

DC motor is a device, which uses DC voltage to convert electrical energy into

mechanical energy. Mainly there are two types of DC motors, namely: Separately excited DC

motors & Self-excited DC motors. In case of Separately excited DC motor, the field winding

will be excited using a separate supply, but in case of Self excited DC motors the field winding

will not be there separately.

A Separately excited DC motor can be controlled in two ways, namely: Armature

control, Field control. Incase of Armature control, the armature current is varied to control its

Torque & speed. But in field control, the field current is varied to control its speed. A semi

converter can be used to control the armature voltage & there by its current can be controlled,

this in turn controls the speed of the motor.

Speed Control of Universal motor:

Universal motor is basically a series wound motor, capable of working under both AC &

DC inputs. When it works on DC, it is controlled by armature control & it can be done using a

converter and when it works on AC, it is controlled by stator voltage, which can be done using a

AC voltage controller (using two thyristors connected back to back or using a TRIAC). The

speed of the motor can be controlled by varying the firing angles of thyristors.



Speed Control of Induction motor:

It a type of AC motor, which works with AC input. It has two parts, called Stator

(primary winding) & rotor (secondary winding). These stator & rotors are electrically isolated &

the current through stator induces current into the rotor, hence the name Induction motor. The

speed of the motor is controlled by stator voltage control & this can be achieved by using an AC

voltage controller, having two thyristors connected back to back or using a TRIAC. The speed of

the motor is controlled by varying the firing angles of the thyristors, which in turn varies output

rms voltage.

Speed Control of Stepper motor:

A Stepper motor changes its speed in steps. It basically converters an electronic pulse

into appropriate mechanical movement. Thus it provides precision positioning & speed control

without the use of feedback sensor. Each revolution of the stepper motor’s shaft made up of a

series of discrete individual steps. A step is the angular rotation produced by the output shaft

when the motor receives a step pulse. The number of pulses can control positioning & speed of

the motor precisely. The rotor of the motor produces a torque due to the interaction between the

magnetic fields in the stator & rotor. The stepper motors are mainly used in Robotics, machine

tools, disk drives & programmable controllers.



POWER ELECTRONICS LAB - VIVA QUESTIONS

(01) What is an SCR?

(02) Why Silicon is used in SCR?

(03) What are Latching & Holding currents? Distinguish them.

(04) What is Break over voltage (VBO)?

(05) Explain the procedure used for finding Latching & Holding currents?

(06) What is the significance of wattage resistors?

(07) Give the applications of SCR.

(08) What are the current & voltage ratings of SCR?

(09) What is the difference between Converter grade & Inverter grade SCRs?

(10) Explain the regions in which SCR can be operated.

(11) What is TRIAC? How it differs from SCR?

(12) In how many modes TRIAC can be operated?

(13) In which of the modes the TRIAC is most sensitive? What is the basis?

(14) How many layers are there in TRIAC?

(15) Give the applications of TRIAC.

(16) What is MOSFET?

(17) What are the types of MOSFETs we have?

(18) What are Drain resistance, trans-conductance & amplification factors of MOSFET.

(19) What is the meaning of Negative temperature coefficient of resistance?

(20) Give the applications of MOSFET.

(21) What is an IGBT?

(22) Compare its features with MOSFET & BJT.

(23) Give the advantages & applications of IGBT.

(24) How many types of IGBT’s are available?

(25) Why we call IGBT as majority carrier device?

(26) What is Triggering?

(27) What are the methods of triggering an SCR?

(28) What is the limitation of R triggering?

(29) How RC triggering is better than R triggering?

(30) What is the range of R triggering & RC triggering?

(31) What is meant by synchronized triggering?

(32) What is relaxation oscillator?

(33) What is UJT? How it differs from BJT?

(34) Why UJT is used in relaxation oscillator?

(35) In what region of its characteristics, the UJT is operated for relaxation oscillator

(36) What is the range of in case of UJT triggering?

(37) What is the advantage of UJT triggering over other triggering circuits?

(38) What is the role of Zener diode in this circuit?

(39) What is a pulse transformer? Why it is used in UJT triggering circuit?

(40) What is the role of resistor connected in series with the POT?

(41) What is Commutation?

(42) What is Natural Commutation & Forced Commutation.

(43) How the commutation can be achieved practically?

(44) What are the circuit elements required for Commutation?

(45) What is the difference between current & voltage Commutation?



(46) Give the types of Forced Commutation circuits.

(47) What is the advantage of Class-B Commutation over Class-A Commutation?

(48) What is the advantage of Class-C Commutation over Class-B Commutation?

(49) What is the advantage of Class-D Commutation over Class-C Commutation?

(50) What is Auxiliary voltage commutation?

(51) What is an AC voltage controller? Give its application.

(52) What is the role of Diac in AC voltage controller?

(53) What are the factors on which the charging of the capacitor depends?

(54) What are the different types of AC voltage controllers we have?

(55) What is the difference between on off controller & phase controller?

(56) What is a Converter? What is the difference between converter & rectifier?

(57) What is the difference between Fully controlled & Half controlled converters?

(58) What is the effect of inductance on the load circuit?

(59) What is freewheeling/ Fly wheeling diode?

(60) What is the effect of Freewheeling diodes on the load?

(61) What is a Dual Converter? Give its applications.

(62) What is a Series Converter? Give its applications.

(63) In what way the Free wheeling diodes are different from ordinary diode?

(64) Give the classification of converters based on the quadrant operation

(65) Give the applications of controlled rectifiers?

(66) What is a DC Chopper? Give its applications.

(67) What is the principle of a Chopper?

(68) Give the classification of choppers.

(69) Give the classification of choppers based on quadrant operation.

(70) What are the types of controlling we have for choppers?

(71) What is meant by separately excited DC motor?

(72) What are methods of speed control of DC motor?

(73) What method is implemented in this experiment?

(74) What are the applications of DC motor?

(75) What are the different types of DC motors?

(76) What is an Universal motor?

(77) What are the methods of speed control of universal motor?

(78) What are the applications of Universal motor?

(79) What is a stepper motor?

(80) Give the applications a stepper motor.

(81) What is an Inverter?

(82) What is the principle of an Inverter?

(83) What is the difference between series & parallel inverters?

(84) What is the use of Fly back diodes used in the Inverters?

(85) Give the applications of inverters.

(86) Which inverter circuit gives a square wave output?

(87) How to get sine wave from the square wave obtained from the Parallel Inverter?

(88) Which inverter gives an approximate sine wave output?

(89) Compare a series inverter with parallel inverter?

(90) How the Inverters are classified?

(91) What is meant by dv/dt & di/dt ratings?

(92) What is a Snubber circuit? How it eliminates voltage & current transients?



(93) How do you protect SCR against high voltage & currents?

(94) What is the purpose of a Fuse? How does it protects a circuit?

(95) What is PIV rating of a Thyristor?

(96) What is GTO? How it differs from SCR?

(97) Give the advantage & disadvantages of GTO.

(98) What are Harmonics? Why they will get introduced in power electronic circuits

(99) What is a Cyclo-converter? Give its applications.

(100) What is the difference between Un-controlled, Controlled & Fully controlled

devices. Give examples for them.

(101) What is stepper motor?

(102) Why is stepper motor also called digital motor?

(103) How many steps are covered in one revolution?

(104) What is step angle?

(105) What are the applications of stepper motor?

PE Manual 10ECL78

Documents

static characteristics

rc triggering circuit

triggering input voltage

suitable experiment

breakdown voltage

speed control of dc

ac voltage controller

commutation circuits