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)