Power Electronics - May 2016

Electronics and Comm. Engg. (Semester 7)

TOTAL MARKS: 100
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any four from the remaining questions.
(3) Assume data wherever required.
(4) Figures to the right indicate full marks.

Answer the following in brief:

1 (a) (i) What is commutation in SCR circuits? Explain self commutation in SCR circuits.(4 marks) 1 (a) (ii) Compare SCR and TRIAC.(4 marks)

Answer the following:

1 (b) (i) List the various turn on methods of SCR. Explain resistance triggered circuits.(3 marks) 1 (b) (ii) Explain how fly wheel diode improves the power factor of the systems.(3 marks) 2 (a) Explain the operation of single phase fully controlled bridge converter with inductive load. Draw the associated waveforms.(7 marks)

Solve any one question from Q2(b) & Q2(c)

2 (b) What are the needs of series and parallel operations of thyristor? Explain the problems with series and parallel operations of thyristor and possible solutions(7 marks)

Define the following terms for SCR.

2 (c) (i) Latching and holding current (ii) dv/dt and di/dt rating.(4 marks) 2 (c) (ii) Thermal and current rating(3 marks)

Solve any two question from Q3(a), Q3(b) & Q3(c), Q3(d)

3 (a) Explain the principle of an inverter. With help of neat diagram and associated waveform explain the operation of single phase half bridge voltage source inverter.(7 marks) 3 (b) Explain the principle of operation of step up Chopper with resistive load. Differentiate between constant frequency and variable frequency operation of this chopper.(7 marks) 3 (c) Explain the circuit diagram and operation of three phase bridge inverter. Draw phase and line voltage waveforms on the assumption that each thyristor conducts for 120° and resistive load is star connected.(7 marks) 3 (d) With the help of a neat circuit diagram and associated waveforms, discuss the operation of Buck converter. List the advantages and disadvantages of this type of converter.(7 marks)

Solve any two question from Q4(a), Q4(b) & Q4(c), Q4(d)

4 (a) What is forced commutation? With help of circuit diagram and necessary waveform explain the complementary commutation(7 marks) 4 (b) Explain the construction and characteristics of GTO. Compare the turn on and turn off method of GTO with SCR.(7 marks) 4 (c) Draw a circuit diagram for ramp and pedestal trigger circuit used for the single phase semi converter. Describe its operation with appropriate waveforms.(7 marks) 4 (d) Write short note on IGBT.(7 marks)

Solve any two question from Q5(a), Q5(b) & Q5(c), Q5(d)

5 (a) Explain the circuit diagram and working of single phase semi converter with freewheeling diode.(7 marks) 5 (b) Write short note Uninterrupted Power Supply.(7 marks) 5 (c) Write short note on four quadrant Type E chopper.(7 marks) 5 (d) Write short notes on dielectric heating and induction heating.(7 marks)