Power Electronics-1 - Dec 2015

Electronics Engineering (Semester 6)

TOTAL MARKS: 80
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Assume data if required.
(4) Figures to the right indicate full marks. 1 (a) Draw and explain gate characteristics of SCR.(5 marks) 1 (b) Differentiate between symmetrical IGBT and asymmetrical IGBT.(5 marks) 1 (c) Draw output voltage waveform for the circuit given below. Draw waveform with scale. (5 marks) 1 (d) Explain in brief why harmonic neutralisation in necessary in the output of inverter.(5 marks) 2 (a) Explain the working of dual converter with all far quadrants of operation. Draw circuit diagram and waveforms.(10 marks) 2 (b) Draw and explain of working of buck boost converter with the help of circuit diagram and waveforms. Derive the relation for output voltage.(10 marks) 3 (a) Explain three phase bridge inverter with 120° conduction mode. Draw circuit diagram and waveforms.(10 marks) 3 (b) With the help of circuit diagram and waveforms explain bi-directional AC control circuit using TRAC & DIAC.(10 marks) 4 (a) Explain semiconverter circuit for the conversion of AC to DC. Draw waveforms for α=60°. Explain how it eliminates the need of prewheeling diode in case of R-L Load to increase the power factor.(10 marks) 4 (b) Explain class D communicate circuit with the help of circuit diagram and waveforms.(10 marks) 5 (a) Explain in detail SOA of MOSFET.(5 marks) 5 (b) Explain multiple pulse width modulation to control the output of inverter with sine wave as a reference signal.(10 marks) 5 (c) What do you understand by cycloconverter. Draw single phase cycloconverter with circuit diagram and waveforms.(5 marks) 6 (a) Draw and explain three phase fully controlled bridge rectifier with R load in continuous mode. Derive the relation for output voltage.(10 marks) 6 (b) A single phase semiconverter is operated from 120V 50HZ ac. supply. The load resistance is 10ohm. If the average output voltage is 25% of the maximum possible average output voltage. Determine.
i) Firing angle
ii) RMS and average output current
iii) RMS and average Thysistor current.(10 marks)