Anna University Chennai 2005 B.E Electrical and Electronics Engineering SEMESTER V EE 332 - POWER ELECTRONICS - Question Paper

B.E. ELECTRICAL AND ELECTRONICS ENGINEERING
SEMESTER V
EE 332 - POWER ELECTRONICS
Time : three Hrs Max. Marks: 100
PART - A (10 x two = 20 Marks)
1. elaborate the differences ranging from Transistor & SCR?
2. discuss latching current and holding current of thyristor.
3. What is natural or line commutation?
4. Why is power factor of semiconverter better than full converter?
5. elaborate the differences ranging from free wheeling diode and feedback diode?
6. elaborate the main differences ranging from voltage source inverter and current source
inverter?
7. elaborate the advantages and disadvantages of AC voltage controllers?
8. discuss time ratio control of choppers.
9. Draw the load voltage waveform for a = 150o.
10. discuss the principle of operation of step up chopper.
PART - B (5 x 16 = 80 Marks)
11. A dc battery is charged through a resistor R as shown in fig.1. Derive an expression
for the avg. value of charging current in terms of Vm, E, R on the assumption
that SCR is fired continuously.
a. For an ac source voltage of 230V, 50Hz obtain the value of avg. charging
current for R = 8O and E = 150V
b. obtain the power supplied to battery and dissipated in the resistor.
c. compute supply PF.
Fig. 1
12.a) For 3 phase thyristor controlled half wave rectifier feeding load R as shown in
fig. 2. Show that the avg. output voltages are provided by
Vo = (3v3 Vm Cos a) / 2p for 0 = a = p/6
Vo = (3/2p) Vm [1+cos (a + p/6)] for p/6 = a = 5p/6
Where Vm is the maximum value of phase voltage and a is the firing angle delay.
Fig. 2
(OR)
12.b) A half controlled three phase bridge rectifier is supplied at 220v from a source of
reactance 0.24O/phase. Neglecting resistance and device volt drops determine
mean load voltage for level load current of 40A at a firing delay angle of 45º and
90º.
13.a) discuss the operation of single phase replaced MC Murray half bridge inverter
(OR)
13.b)i) discuss the operation of replaced series inverter with neat diagram. Derive an
expression for the output frequency of the inverter.
ii) What is the difference ranging from series and parallel inverter?
14.a) discuss the operation of voltage commutated chopper with neat diagram and
waveforms. Derive expressions for commutating capacitor (C) and commutating
inductor (L).
(OR)
14.b) For a current commutated chopper peak commutating current is twice the maximum
possible load current. The source voltage is 230V dc and main SCR turn of time is
30µsec. The circuit turn off time is twice device turn off time. For maximum load
current of 200A compute.
(i) Values of the commutating inductor and capacitor
(ii) Maximum capacitor voltage
(iii) Peak commutating current
15.a) discuss the operation of multistage sequence control of ac voltage controllers with
neat diagram.
(OR)
15.b) discuss the operation of single phase to single phase step down cyclo converter
with voltage and current waveforms for
(i) Continuous load current
(ii) Discontinuous load current
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Earning:   Approval pending.