M.Sc. (Semester (CBCS) Examination Nov/Dec-2018
Electronics
POWER ELECTRONICS
Time: 2½ Hours Max. Marks: 70
Instructions: Answer five questions.
All questions are compulsory.
Figures to the right indicate full marks.
Q.1 Choose correct answer. 14
A device that converts DC power into AC power is called as
Chopper Inverter
Rectifier None of these
A Dual convertor is a convertor.
One quadrant Two quadrant
Four quadrant Three quadrant
The free-wheeling action takes place through in asymmetrical
configuration.
a SCR and a diode only a pair of diodes
two SCRs and one diode a SCR and two diodes
The step-down chopper feeds DC motor with no voltage drop. If the source
voltage is 200 V and duty cycle is 0.5. The output voltage of this chopper

200 V 150 V
250 V 100 V
The class-A choppers has operation.
One quadrant Two quadrant
Four quadrant All of these
In cycloconverter output is controlled by controlling the angle of
the thyristors.
conduction delay
both a b extinction
The single phase bidirectional controller delivers maximum power for α is
equal to radian.
0
− α
The output voltage of single phase bridge inverter is wave.
square sine
triangular ramp
The is used to prevent short circuiting in cycloconverters.
free wheeling diode intergroup reactor
switch semiconductor switches
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10) The of the following techniques is used to reduce the harmonics
in Inverters.
Stepped wave inverter PWM
EAC both a and b
11) The class C chopper is also called as chopper.
Two quadrant class B Single quadrant class A
Two quadrant class A Single quadrant class B
12) In AC voltage controller is the SCRs are switched on for 20 cycles and off
for 20 cycles then the duty cycle would
4.0 0.20
1.0 0.50
13) Rectifiers can be used for
dc motor drivers variable speed drives
four quadrant operation all of these
14) In bidirectional AC voltage controlling the firing angle must be greater than

load of angle
conduction angle
Q.2 Answer any four of the following questions. 08
Compare the current source inverter and voltage source inverter.
Define choppers and give its classification.
Give the techniques of power factor improvement.
Describe applications of cycloconverters.
Explain class A chopper
Answer any two of the following questions. 06
Explain the Class C chopper.
Explain the working principle of phase angle control in AC voltage
controllers.
Explain current source inverter.
Q.3 Answer any two of the following questions. 08
Explain single phase dual converter.
Describe in detail the classification of Inverters.
Explain working principle of AC chopper.
Answer any one of the following questions. 06
Explain step-up chopper
Describe single phase full bridge inverter
Q.4 Answer any two of the following questions. 10
Explain single phase full controlled bridge rectifier.
Explain working of single phase bidirectional controller.
Explain harmonic reduction techniques for inverter.
Answer any one of the following questions 04
Explain effect of duty cycle on ac voltage controllers.
Explain multiphase chopper.
Q.5 Answer any two of the following questions. 14
Explain three phase dual converter.
State the advantages disadvantages of unidirectional and bidirectional
controllers.
Explain three phase fully controlled bridge rectifier.