University of Mumbai 2007-6th Sem B.E Electrical and Electronics Engineering Power Electronics - Question Paper

(a)    Draw and explain Gate characteristics of SCR.

(b)    Explain the triggering methods for an SCR

(c)    Compare properties of power BJT, power MOSFET and IGBT on application point of view,

(d)    Explain with neat diagram working principle of an inverter.

(e)    Explain how SCR is suitable than BJT, with suitable example.

2.    (a) Sketch l-V characteristics of typical TRIAC. Explain it's four quadrant operation. 10 (b) Explain the buck regulator with help of circuit diagram and its waveform. Also 10

derive the equation of output voltage.

3.    (a) Draw and explain the circuit diagram for the synchronized UJT triggering with associate 10

voltage waveform. Explain the necessity of synchronization.

(b) Explain the different methods to achieve harmonic reduction in three phase inverters. 10

4.    (a) Draw circuit diagram of Parallel inverter driving highly inductive load. Explain its 10

feedback mode of operation.

(b) Explain constructional features and working principle of IGBT. Give applications 10 of IGBT

5. (a) Draw a neat circuit diagram of one quadrant controlled bridge rectifier and ex- 10 plain Its working. Draw the waveforms for

(i)    Supply voltage    (iii) Load voltage for a = 45

(ii)    Load current    (iv) Source current, consider contineous load current.

(b) Explain the importance of isolation in gate drive circuits.    10

6. (a) Single phase full-bridge inverter has a resistive load R = 3 fl and the d.c. input 10 voltage = 50 V.

Calculate :

(i)    the RMS output voltage at the fundamental frequency

(ii)    the output power (p₀)

(iii)    Average and peak currents of each thyristor

(iv)    Peak reverse-blocking voltage of each thyristor.

(b) Draw the circuit for 1 $ AC regulator and explain its operation with appropriate 10 waveforms.