MORE IN Power Electronics
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INSTRUCTIONS
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary

1(a) Explain the different types of power electronic converter circuits with neat circuit diagram and input and output waveforms. Also mention its application.
8 M
1(b) Write the symbol and characteristic features of the following devices:
i) BJT ii) TRIAC iii) GTO iv) MOSFET.
8 M
1(c) Discuss the peripheral effects of power electronic converters. Also write the remedies.
4 M

2(a) For the circuit shown in Fig. Q2(a), BJT is specified to have β in the rang of 12 to 75. If Vcc = 40 V, Rc=1.5 Ω, VB = 6 V, VCE(sat)=1.2 V and VBE(sat) = 1.6 V and Rb=0.7 Ω. Calculate : i) Overdrive factor ODF ii) Forced Bf iii) Total power dissipational (PT).

7 M
2(b) With the transient model of MOSFET explain swiching characteristics.
6 M
2(c) What is the need for isolation for gate drive circuits? Discuss the different methods of providing isolation of gate drive circuits from power circuits?
7 M

3(a) Explain the V-1 characterists of SCR by clearly indicating different states on characteristics. Also explain different modes of operation.
6 M
3(b) With two transistor analogy of a thyristor obtain the equation for anode current.
6 M
3(c) An SCR employs an R-triggering as shown in Fig. Q3(c) With Ig(min) = 0.1 mA and Vg(min) = 0.5 V. The diode is silicon and the peak amplitude of the input voltage is 24 volts. Determine the triggering angle α for R = 100 kω and Rmin = 10kω.

4 M
3(d) A SCR has a di/dt = 50A/μsec and dv/dt = 150 V/μsec. It operates on a 100 V, calculate the snubber circuit elements using approximate expressions.
4 M

4(a) With necessary circuit and waveforms explain the principle of operation of single phase semiconverter. Also derive an expression for the average output voltage.
6 M
4(b) With neat circuit diagram explain the opetating principle of dual converter with and without circulating current.
8 M
4(c) A single phase half wave controlled rectifier is used to supply power to 10 ω load from 230V, 50Hz supply at a firing angle of 30°: . Calculate (i) average output voltage (ii) effective output voltage (iii) average load current.
6 M

5(a) What is the necessary condition for successful commutation of SCR? Compare between forced and natural commutation.
6 M
5(b) With necessary circuit waveforms explain the working of complementary commutation. Also perform circuit analysis.
8 M
5(c) For the impulse commutated thyristor of circuit Fig.Q5(c), determine the turn-off time of the circuit, if Vs = 200 V, R = 10 ω C= 5 μF and Vc (t=0) = Vs. Also derive te equations used.

6 M

6(a) With the help of neat circuit and relevant waveforms explain the working of ON-OFF control, for single phase AC voltage controller with resistive load. Also derive an expression for RMS output voltage.
8 M
6(b) A 1 ϕ half wave ac voltage controller has an input voltage of 120 V, 60 Hz and a load resistance of 10 Ω. The firing angle of thyristor is 60°. Find
i) RMS output voltage ii) Input power factor iii) Average input current.
8 M
6(c) What is the problem caused by sharp single pulse triggering in a 1 ϕ AC voltage controller when the load is inductive? How can this be solved?
4 M

7(a) Briefly explain the clalssification of choppers with circuit, waveforms and quadrant diagrams.
8 M
7(b) For the chopper shown in below Fig. Q7(b), DC source voltage is 200 V, load resistanace is 20 ω . Consider the voltage drop of 4 V across chopper when it is ON. For a duty cycle of 0.3, calculate (i) Average and rms value of output voltage.

4 M
7(c) Explain the operation of step down chopper with RL load. Also derive an expression of peak-peak output ripple currrent.
8 M

8(a) Explain the principle of single phase half bridge inverter with suitable circuit and waveforms.
10 M
8(b) Explain the performance parameters of inverter.
4 M