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Mumbai University Electronics (Semester -VII)
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Solution for Power Electronics 2
December 2015
Index
Q.1)
a) …………………………………………………………………………. N.A
b) …………………………………………………………………………. 2
c) …………………………………………………………………………. 2-3
d) …………………………………………………………………………. 4
e)………………………………………………………………………….. 4
Q.2)
a) …………………………………………………………………………. 5
b) …………………………………………………………………………. N.A
Q.3)
a) …………………………………………………………………………. 6-7
b) …………………………………………………………………………. N.A
Q.4)
a) …………………………………………………………………………. N.A
b) …………………………………………………………………………. 7-10
c) ………………………………………………………………………….. 10-12
Q.5)
a) ………………………………………………………………………….12-15
b) …………………………………………………………………………. 15-19
Q.6)
a) …………………………………………………………………………. 19-20
b) ………………………………………………………………………….20-22
c) …………………………………………………………………………. 22-23
Mumbai University Electronics (Semester -VII)
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Q1)
(a) What are the advantages of SVM over the conventional sine wave PWM?
Explain .
ANs : N.A
(b) List the merits and demerits of online and offline UPS.
Ans:
(c) Explain regenerative braking for DC motors.
Ans:
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Mumbai University Electronics (Semester -VII)
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(d) Explain in brief the effect of source inductance in single phase fully
controlled bridge rectifier.
Ans:
(e) Explain the concept of UPS and give classification of UPS system.
Ans:
Types of UPS:
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Q2)
(a) Explain clearly the steps involved in space Vector Modulation for
three phase voltage source inverse
Ans:
Switching states for SVM controlled 3 ɸ VSI
(b) A single phase full-wave mid-point converter with free wheeling
diode as shown below in Fig Q2 (b) is supplied from a 120V,50 Hz
supply with a source inductance of 0.33 mHenry .Assuming that the
load current is continuous at 4V .find the overlap angle for.
i) Transfer of current from a conducting thyristor to the commutating
diode.
ii) From the commutating diode to a thyristor when the fring angle is
15 degree.
Ans: N.A
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Q3)
(a) Derive and explain the state-space model of Buck converter.
Ans:
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(b) Explain the PI(Proportional +Integral) control of DC-DC converter
with the help of neat diagram.
Ans: N.A
______________________________________________________________
Q4)
(a) Derive the expression for output voltage and current for a single phase
fully controlled bridge rectifier with the source inductance using
equivalent circuit.
Ans: N.A
(b) What are SMPS? Give classification and explain any SMPS circuit in
detail.
Ans:
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When the switch is on ,it connects the unregulated dc input Vin as it is to the
input of the filter and the filter input is disconnected from the dc input voltage
Vin when the switch is open circuited.
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Complete switched Mode Regulator.
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(c) Draw and explain the battery charging circuit involving power
electronics system.
Ans:
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(a) Ckt diagram of a simple battery (b) Waveform of battery charger
charger circuit
Battery Charging Regulator:
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_______________________________________________________________
Q5)
(a) A separately excited DC motor is supplied from 230V ,50 Hz source
through a 10 single-phase half wave controlled converter .Its field is
fed through single-phase semi-converter with zero degree firing angle
delay. Motor resistance =0.70 Ω ,Motor constant =0.5 volts sec/rad.
for a rated load torque of 15NM at 1000 rpm and for continuous
ripple –free current,determine:
i) Firing angle delay of the armature converter.
ii) RMS value of thyristor and freewheeling diode current.
iii) Input power factor of the armature current.
Ans: note: Similar sum
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Mumbai University Electronics (Semester -VII)
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Mumbai University Electronics (Semester -VII)
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(b) Explain various methods of speed control for 3-phase induction motor.
Ans:
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Stator Volatge control
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Stator voltage and frequency Control
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Operation
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Q6) Write notes on:
(a) Comparison of fly-back and forward converters used in SMPS.
Ans:
Flyback
The flyback topology is essentially the buck-boost topology that is isolated by
using a transformer as the storage inductor. The transformer not only provides
isolation, but by varying the turns ratio, the output voltage can be adjusted.
Since a transformer is used, multiple outputs are possible. The flyback is the
simplest and most common of the isolated topologies for low-power
applications. While they are well suited for high-output voltages, the peak
currents are very high, and the topology does not lend itself well to output
current above 10A.
One advantage of the flyback topology over the other isolated topologies is that
many of them require a separate storage inductor. Since the flyback transformer
is in reality the storage inductor, no separate inductor is needed. This, coupled
with the fact that the rest of the circuitry is simple, makes the flyback topology a
cost effective and popular topology.
Forward
The forward converter is really just a transformer isolated buck converter. Like
the flyback topology, the forward converter is best suited for lower power
applications. While efficiency is comparable to the flyback, it does have the
disadvantage of having an extra inductor on the output and is not well suited for
high voltage outputs. The forward converter does have the advantage over the
flyback converter when high output currents are required. Since the output
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current is non-pulsating, it is well suited for applications where the current is in
excess of 15A
(b) Power electronics application in induction heating
Ans: Electronic Application in induction heating are as follows:
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Mumbai University Electronics (Semester -VII)
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(c) Slip power recovery scheme for induction motor using Kramer Drive
below sbu-synchronous speed.
Ans:
Mumbai University Electronics (Semester -VII)
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