Download AKTU B-Tech 6th Sem 2015-2016 EEE 602 Power Electronics Question Paper

Download AKTU (Dr. A.P.J. Abdul Kalam Technical University (AKTU), formerly Uttar Pradesh Technical University (UPTU) B-Tech 6th Semester (Sixth Semester) 2015-2016 EEE 602 Power Electronics Question Paper

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B.TECH.
Theory Examination (Semester?VI) 2015-16
POWER ELECTRONICS
T ime : 3 Hours Max. Marks : 100
Section-A
1. Attempt all parts of the following : (2X10=20)
(a) What is primary breakdown in semiconductor devices?
(b) Explain the signi?cance of latchng and holding current.
(c) What is the difference between voltage and current
controlled semiconductor devices?
((1) De?ne the term commutation.
(e) Enlist different swtichjng limits ofpower BJT.
(1) P.T.O.

(f)
(g)
(h)
G)
What is need of series and parallel operation of
thyristors?
Discuss the merits and demerits of four quadrant chop-
per over single quadrant chopper.
Compare natural and forced commutation.
Discuss the applications of ac voltage controllers.
Discuss drawbgacks 0f cyclo-converter.
Section-B
Attempt any ?ve questions from this section. (5X10=50)
(a)
(b)
(C)
Draw the static V?I characteristics of the SCR and explain
its modes of operation.
De?ne di/dt and dv/dt ratings of SCR. How is SCR
protected against these?
Obtain the expression of input power factor for a single-
phase half?wave controlled recti?er feeding a purely
resistive load.
(2)

(d)
(e)
(f)
(g)
CD
With the help of Vittical section diagram describe the
operation of IGBT, discuss its merits and demerits with
respect to other self?commutating power semiconductor
devices. What is latch-up in IGBT? How it is avoided?
Calculate the number of SCRs, each with rating of 500
V, 75A required in each branch of a series and parallel
combination for a circuit With the total voltage and cur-
rent ratings of 7.5 kV and 1000 A. Assume derating
factor of 14%
Discuss the two transistor analogy of a thyristor. Using
this model, describe the various mechanism of turning-
on a thyristor.
What is do chopper? Describer the various types of
chopper con?gurations with appropriate Diagrams.
A single phase ?lll wave ac controller operates from 230
V 50 Hz mains and feeds a resistive load whose value
varies between 1.15 ohms and 2.30 ohms. Calculate:
(i) RMS current rating of each SCR
(ii) Average current rating of each SCR
(iii) The maximum load power for on = n/4
(3) P.T.O.

Section-C
Note : Attempt any two questions from this section. (2X15=30)
3.
Explain operation of a single-phase fully controlled bridge
converter feeing a highly inductive load. Draw waveforms of
output voltage, load current and source current.
What are dual converters? Explain the operation of three-
phase dual converter using circulating current mode of opera-
tions. How are ?ring angles of two converters controlled?
What is pulse Width modulation? Explain sinusoidal pulse Width
modulation used in P.W.M. inverters. What are the advantages
of P. W. M. inverters?
(4)