Code No: A55B2 R 20A
BVRAJU INSTITUTE OF TECHNOLOGY, NARSAPUR
(UGC - AUTONOMOUS)
III B.Tech I Semester Regular Examinations, Jan/Feb 2024
POWER ELECTRONICS
(Electrical and Electronics Engineering)
Time: 3 Hours Max Marks: 70
Note: This Question Paper contains two Parts A and B
Part A is compulsory which carries 10 marks. Five questions from five units. Answer all
questions in Part A at one place only.
Part-B consists of 5 Questions (numbered from 2 to 11) carrying 10 marks each. Each of these
questions is from one unit and may contain a, b, c as sub-questions. For each question there will
be an either/or choice (that means there will be two questions from each unit and the student
should answer only one question).
PART – A (5x2 = 10 Marks)
1 Marks Bloom CO
Level
a Draw the gate characteristics of SCR. 2 L1 CO1
b What is the maximum peak inverse voltage of single phase full wave 2 L3 CO2
midpoint converter that appears across the device in blocking state
for a supply voltage of 200V.
c A three-phase, three-pulse, M-3 type controlled converter has firing 2 L3 CO3
angle for one of the SCRs set as 15°. This SCR would start
conducting at how many degrees.
d If a step-up chopper’s switch is always kept open then (ideally) how 2 L3 CO4
much is the output voltage.
e A single phase half bridge inverter has load R = 2 Ω and a dc 2 L3 CO5
voltage source Vs/2 = 115 V. Find the power delivered to the load
due to the fundamental component.
PART – B (5x12 = 60 Marks)
Marks Bloom CO
Level
2 Define MOSFET, Draw the V-I AND switching Characteristics of 12 L2 CO1
MOSFET in detail.
OR
3 Explain any two forced commutation methods with neat waveforms 12 L2 CO1
and derive its relative expressions.
***
4 Explain single-phase semi converter with R-L Load, draw input and 12 L3 CO2
output wave forms and derive its Average, RMS values and power
factor.
OR
5 Explain the operation and derive the expression of the rms value of 12 L3 CO2
output voltage for a single-phase two pulse M-2 type controlled
rectifier with RL load and continuous load current along with
associated waveforms.
***
6 For a 3-phase Full wave bridge converter, draw the output voltage 12 L4 CO3
waveforms for a firing angle delay of 45 degrees indicating the
conduction of its various elements on the assumption of continuous
output current. Hence obtain an expression for the output voltage in
terms of AC supply voltage and firing angle delay.
OR
7 A three-phase half-wave-controlled converter is fed from a 3-phase, 12 L4 CO3
400 V source and is connected to a load which takes a constant
current of 36 A. Find the value of average output voltage and
average current rating of SCR for a firing angle of 30°.
***
8 Describe the principle of step-up chopper. Derive an expression for 12 L3 CO4
the average output voltage in choppers, and determine the range of
off-periods for the gate signal if step-up chopper has output voltage
of two to four times the input voltage, for chopping frequency of 2
KHz.
0R
9 Explain the operation of bridge type 1-phase step down 12 L3 CO4
cycloconverter with RL load for continuous and discontinuous load
currents.
***
10 Explain with neat sketches the operation of 180 degrees conduction mode 12 L3 CO5
3-Ø VSI with Y connected R load.
OR
11 A 3-phase VSI is supplied from a 600V DC source. For a star 12 L3 CO5
connected resistance load of 20 ohms per phase, Determine the rms
value of load current and the load power for 120 degrees mode.
***
