17YEX501/ Power Electronics (Common to Batch 2017,2018 Programme: B.

Tech
Electrical & Electronics Engineering)

Unit – I
Two Marks Question

Q.No. Question Marks KL CO

1 Why IGBT is very popular nowadays? 2 k1 co1

2 What are the different methods to turn on the thyristor? 2 k1 co1

3 What is the difference between power diode and signal diode? 2 k1 co1

4 IGBT is a voltage controlled device, Why ? 2 k1 co1

5 Power MOSFET is a voltage controlled device, Why ? 2 k1 co1

6 Power BJT is a current controlled device 2 k1 co1

7 What are the different types of power MOSFET? 2 k1 co1

8 How can a thyristor turned off? 2 k1 co1

9 Define latching current 2 k1 co1

10 Define holding current 2 k1 co1

11 What is a snubber circuit? 2 k1 co1

12 What losses occur in a thyristor during working conditions? 2 k1 co1

13 Define hard-driving or over-driving 2 k1 co1

14 Define circuit turn off time 2 k1 co1

Why circuit turn off time should be greater than the thyristor turn-off
15 2 k1 co1
time?

What is the turn-off time for converter grade SCRs and inverter
16 2 k1 co1
grade SCRs?

Big Question (Marks ≥5 & ≤15)

Q.No. Question Marks KL CO

 1 Explain the structure and operation of turn on and turn of
8 k1 Co1
characteristics of SCR

2 Describe the methods of turn-on mechanism of SCR 7 k2 Co1

3 Explain the turn off characteristics of SCR 8 k3 Co1

4 Discuss the transfer, output and switching characteristics of IGBT 8 k2 Co1

5 Draw and explain the Static VI characteristics of SCR with all its
7 k3 Co1
operating modes

6 Compare any six salient features of MOSFET with IGBT 8 k2 Co1

7 Discuss the operation of power MOSFET and explain the transfer,

7 k1 Co1
output and switching characteristics of power MOSFET

8 Differentiate natural commutation and forced commutation 8 k2 Co1

9 State the Applications and Role of Power Electronics 7 k2 Co1

10 Draw and explain Turn On Dynamic Characteristics of SCR. 8 k2 Co1

11 Draw and explain Turn Off Dynamic Characteristics of SCR 7 k2 Co1

*Marking Scheme is depending upon the faculty.

Unit – II
Two Marks Question

Q.No. Question Marks KL CO

1 Define holding current. 2 k2 co2

2 What is a snubber circuit? 2 k2 co2

3 What losses occur in a thyristor during working conditions? 2 k2 co2

4 Define circuit turn off time. 2 k2 co2

Why circuit turn off time should be greater than the thyristor turn-off
5 2 k2 co2
time?

6 What are the advantages of GTO over SCR? 2 k2 co2

 7 Mention some of the applications of controlled rectifier. 2 k2 co2

8 Define latching current 2 k2 co2

9 How can a thyristor turned off? 2 k2 co2

10 What is commutation? 2 k2 co2

Big Question (Marks ≥5 & ≤15)

Q.No. Question Marks KL CO

1 Briefly discuss the Resistance triggering of SCR 8 k1 Co2
2 Explain the Class B type of Commutation 7 k2 Co2
3 Explain the Class A type of Commutation 8 k3 Co2
4 Explain the types of Protection of Thyristor 8 k2 Co2
5 Explain single phase Half wave thyristor controlled rectifier 7 k3 Co2
6 Explain the different turn ON methods of SCR. 8 k2 Co2
7 Explain the Class C Complementary commutation of thyristor 7 k1 Co2
8 Briefly discuss the RC triggering of SCR 7 k1 Co2
9 Compare MOSFET and BJT 8 k2 Co2

Unit – III
Two Marks Question

Q.No. Question Marks KL CO

1 What is the function of freewheeling diodes in controlled rectifier? 2 k3 co3

Compare the semi controlled converter with Full controlled phase

2 2 k3 co3
converter

3 What is the advantage of Dual converter 2 k3 co3

4 Mention some of the applications of controlled rectifier 2 k3 co3

5 What is the function of freewheeling diodes in controlled rectifier? 2 k3 co3

6 What is meant by delay angle? 2 k3 co3

 What are the advantages of single phase bridge converter over single
7 phase 2 k3 co3
mid-point converter?

8 What is commutation angle or overlap angle? 2 k3 co3

Give an expression for average voltage of single-phase semi

9 2 k3 co3
converters

Big Question (Marks ≥5 & ≤15)

Q.No. Question Marks KL CO

1 Explain the working of single phase dual converter with circuit co3
8 k1
diagram and waveforms

2 Explain the operation of three phase half wave controlled converter co3
with 7 k2
inductive load. Sketch the associated waveforms.

3 With necessary circuit and waveforms, explain the principle of co3

operation of Single
phase controlled bridge rectifier feeding R-L load and derive the 8 k3
expression for the
average output dc voltage.

4 Explain the operation of Single phase semi converter with RLE load. co3
Sketch the 8 k2
associated waveforms

5 Explain the effect of source inductance in the operation of single co3

phase fully
controlled converter, indicating clearly the conduction of various 7 k3
thyristors during one
cycle.

6 Explain the operation of single phase dual converter with circulating co3
and non 8 k2
circulating current type
 7 A single phase full converter feeds power to RLE load with R=6 ohm, co3
L = 6mH and E=60V. The as source voltage is 230 V, 50 Hz. For
7 k1
continuous conduction find the average value of load current for a
firing angle delay of 50 degree.

8 with a neat circuit diagram and necessary waveforms explain working co3
7 k1
of single phase fully controlled bridge converter feeding RL load.
*Marking Scheme is depending upon the faculty.

Unit – IV
Two Marks Question

Q.No. Question Marks KL CO

Why diodes should be connected in antiparallel with the switch in

1 2 k1 co4
inverter circuits?

2 Compare CSI and VSI 2 k1 co4

3 What are the disadvantages of PWM control? 2 k1 co4

4 What is meant a series inverter? 2 k1 co4

5 What are the applications of a series inverter? 2 k1 co4

6 How is the inverter circuit classified based on commutation circuitry? 2 k1 co4

7 What are the applications of a CSI? 2 k1 co4

8 What is meant by PWM control? 2 k1 co4

9 Why thyristors are not preferred for inverters? 2 k1 co4

10 What is the Main drawback of half bridge Inverter. 2 k1 co4

Big Question (Marks ≥5 & ≤15)

Q.No. Question Marks KL CO

1 Explain Single phase full bridge Inverter with circuit Diagram and
8 k1 co4
output
 waveforms.

2 Explain 3phase voltage source Inverter with 180 degree mode of

operation 7 k2 co4
showing all the operating stages

3 Explain Single phase Half bridge Inverter with circuit Diagram and
output 8 k3 co4
waveforms.

4 Explain 3phase voltage source Inverter with 120-degree mode of

operation 8 k2 co4
showing all the operating

5 List down the applications of an inverter? Also explain the

requirement of 7 k3 co4
Inverter in all the applications.

6 Compare CSI and VSI 8 k2 co4

7 Draw the circuit diagram of current source inverter and explain its
operation with 7 k1 co4
relevant waveforms.

8 Describe the working of a single phase full bridge inverter supplying

R, RL loads 7 k1 co4
with relevant circuit and waveforms.

9 Draw the circuit diagram of current source inverter and explain its
operation with 8 k3 co4
relevant waveforms.

10 What is the need for controlling the output voltage of inverters?

Classify the various
8 k2 co4
techniques adopted to vary the inverter gain and brief on sinusoidal
PWM.

11. Write a note on the classification of Inverters. 7 k3 co4

*Marking Scheme is depending upon the faculty.
Unit – V
Two Marks Question

Q.No. Question Marks KL CO

1 What are the two types of control strategies? 2 k1 co5
2 What are the two types of TRC? 2 k1 co5
3 What is meant by FM control in a dc chopper? 2 k1 co5
Write down the expression for the average output voltage for step
4 2 k1 co5
down and step up chopper
What are the different types of chopper with respect to commutation
5 2 k1 co5
process?
6 What are the advantages of current commutated chopper? 2 k1 co5
7 What is meant by unidirectional or half-wave ac voltage controller? 2 k1 co5
What are the disadvantages of unidirectional or half-wave ac voltage
8 2 k1 co5
controller?
9 What is meant by bidirectional or full-wave ac voltage controller? 2 k1 co5
10 What is meant by cyclo-converter? 2 k1 co5

Big Question (Marks ≥5 & ≤15)

Q.No. Question Marks KL CO

1 Discuss the principle of operation of DC-DC step down chopper with
8 k1 co5
suitable waveforms. Derive the expression for its average dc voltage
2 A step down dc chopper has input voltage of 230v with 10 ohm load,
voltage drop across chopper is 2v, when it is on. For a duty cycle of
7 k2 co5
0.5. Calculate i) average and rms value of output voltage ii) power
delivered to the load.
3 Explain the two quadrant dc chopper operation with RLE load using
8 k3 co5
suitable waveforms.
4 Explain time ratio control and current limit control strategies. 8 k2 co5
5 Explain Class C and Class D chopper 7 k3 co5
6 Explain class A and Class B chopper. 8 k2 co5
7 Derive the equation for the average voltage of a half wave AC
7 k1 co5
voltage Regulator.
 8 With the necessary circuit diagram and waveforms, explain the
principle of operation of single phase ac voltage controller having
only thyristor feeding resistive load by on-off control and phase 7 k1 co5
control. Derive the expression for rms value of output voltages in
both cases
9 Draw the circuit diagram of three phase to single phase
8 k3 co5
cycloconverter and explain its operation with waveforms
10 Explain the operation of single phase half wave phase controller and
single phase full wave phase controller with circuit diagrams and 8 k2 co5
waveforms
*Marking Scheme is depending upon the faculty.