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Power Electronics : Question Paper Dec 2015 - Electronics & Telecomm (Semester 6) | Pune University (PU)
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## Power Electronics - Dec 2015

### Electronics & Telecom Engineering (Semester 6)

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.

### Solve any one question from Q1 and Q2

1 (a) What are phase controlled converter? Explain with circuit diagram working of 1ϕ Half controlled converter with suitable load. Draw suitable waveforms & comment on p.f.(7 marks) 1 (b) What is inverter? Explain with diagram 3ϕ voltage controlled inverter with star load (R). Comment on waveforms & Duty cycle.(7 marks) 1 (c) What is IGBT? Explain with characteristics.(6 marks) 2 (a) What is the need of dual converters in the industries? Explain with diagram & waveforms, working of 1ϕ dual converter with highly inductive load.(7 marks) 2 (b) Explain with circuit diagram & waveforms working of 1ϕ Full controlled converter with RL load? Justify what is Inversion & Rectification mode with waveforms.(7 marks) 2 (c) What is bridge Inverter? Explain with circuit diagram & waveforms.(6 marks)

### Solve any one question from Q3 and Q4

3 (a) What are DC-to-DC converters? Explain with circuit diagram & waveforms working of 4 Quadrant chopper? State its applications.(9 marks) 3 (b) What is AC to AC controller? Explain with circuit diagram working of 1ϕ AC full wave AC to AC controller with balanced star Load (R).(9 marks) 4 (a) i) What is chopper? Explain in brief.
ii) A DC chopper has a resistance of 10W & input voltage is 220V. When the chopper switch remains ON its voltage drops to 2V. & chopping frequency is 1KHz. If the Duty cycle is 50% Determine,
1) Average o/p volt
2) RMS o/p voltage
3) Chopper freq
4) Input resistance of chopper
(10 marks)
4 (b) Explain with circuit diagram & waveforms working of TRIAC based AC power controller ckt. Comment on p.f. Justify why SCR based controllers are preferred over TRIAC based controllers.(8 marks)

### Solve any one question from Q5 and Q6

5 (a) Explain with block schematic working of off-line UPS. State its specifications & applications.(8 marks) 5 (b) What are speed control techniques of DC Motors? Explain with circuit diagram working of 1ϕ separately Excited DC Motor with Inductive Load. Comment on p.f.(8 marks) 6 (a) Compare ON-Line UPS with Off-Line UPS. Justify why ON-Line is better than Off-Line with technical reasons.(8 marks)

### Write short notes on:

6 (b) (i) Battery charger(4 marks) 6 (b) (ii) Electronic Ballast(4 marks)

### Solve any one question from Q7 and Q8

7 (a) What are resonant converters? Explain with circuit diagram & waveform working of ZVS?(8 marks) 7 (b) A Snubber circuit is used in SCR circuit for protection of di/dt, dv/dt. The value of RLC being 4Ω, 6μH, & 6μF respectively & Supply being 400V. Find the maximum permissible value of dv/dt. Assume the load resistance to be 10Ω.(8 marks) 8 (a) Compare Linear, switched mode & Resonant converter based power Supplies.(6 marks)

### Write short notes on:

8 (b) (i) HVDC(3 marks) 8 (b) (ii) Induction Heating(3 marks) 8 (b) (iii) Protection circuits(3 marks)