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Power Electronics : Question Paper May 2016 - Electronics and Comm. Engg. (Semester 7) | Gujarat Technological University (GTU)
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## 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)

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