Solution for Power Electronics 2 - BRAINHEATERS · Mumbai University Electronics (Semester -VII)

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



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:





(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:



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



Q3)

(a) Derive and explain the state-space model of Buck converter.

Ans:



(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:



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.



Complete switched Mode Regulator.



(c) Draw and explain the battery charging circuit involving power

electronics system.

Ans:



(a) Ckt diagram of a simple battery (b) Waveform of battery charger

charger circuit

Battery Charging Regulator:



_______________________________________________________________

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







(b) Explain various methods of speed control for 3-phase induction motor.

Ans:



Stator Volatge control



Stator voltage and frequency Control



Operation



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



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:





(c) Slip power recovery scheme for induction motor using Kramer Drive

below sbu-synchronous speed.

Ans:



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Solution for Power Electronics 2 - BRAINHEATERS · Mumbai University Electronics (Semester -VII)

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