Hall Ticket No Question Paper Code: AEE010
INSTITUTE OF AERONAUTICAL ENGINEERING
(Autonomous)
Four Year B.Tech V Semester End Examinations (Regular) November, 2018
Regulation: IARE R16
POWER ELECTRONICS
Time: 3 Hours Max Marks: 70
Answer ONE Question from each Unit
All Questions Carry Equal Marks
All parts of the question must be answered in one place only
UNIT I
1. Distinguish between the power MOSFET and BJT.
The trigger circuit of a thyristor has a source voltage of 15V and line has a slope of -120V per
ampere. The minimum gate current to turn-on the SCR is 25mA. Compute the
i. Source resistance required in the gate circuit
ii. The trigger voltage and trigger current for an average gate power dissipation of 0.4Watts.
2. Explain the various types of commutation circuits for SCR.
For an SCR, gate-cathode characteristics is given by Vg=1+10Ig. Gate source voltage is a rectangular
pulse of 15V with 20μ sec duration. For an average gate power dissipation of 0.3W and
a peak gate drive power of 5W, compute
i. The resistance to be connected in series with the SCR gate,
ii. The duty cycle of the triggering pulse.
UNIT II
3. Explain the working of a single phase fully controlled bridge converter in the inversion mode.

With suitable circuit topology, voltage and current waveforms, reflect the effect of input source
impedance on the average output of a single phase fully controlled converter.
4. Discuss the various performance factors of line commutated converters.
A single phase fully controlled bridge converter supplies an inductive load. Assume that the
output current is virtually constant, and is equal to Id, determine the following performance
parameters. The supply voltage is 230V and firing angle is maintained at radians.
i. Average output voltage
ii. Supply RMS
iii. fundamental power factor.
iv. Voltage ripple factor.
Page 1 of 2
UNIT III
5. Describe the operation of single phase full wave AC voltage controller with the help of voltage
and current waveforms.
A single phase voltage controller is employed for controlling the power flow from 230V, 50 Hz
source into a load circuit consisting of R=3
and
Calculate
i. The control range of firing angle
ii. The Maximum value of rms load current
6. Explain the principle of operation and working of single phase to single phase step-up cycloconverter.

Explain the advantages and disadvantages of Cycloconverter and AC Voltage controller.

UNIT IV
7. Explain the current limit control method of the output voltage control of choppers. A step up
chopper is used to deliver load voltage of 500 V from a 220 V DC source. If the blocking period
of the thyristor is 80 s. Compute the required pulse width.
Explain the working of a Cuk converter with a neat circuit diagram and associated voltage and
current waveforms.
8. Describe the working principle of buck-boost converter with necessary circuit and waveforms.

For type A chopper feeding RLE load, obtain maximum value of average current rating for the
thyristor in case load current remains constant.
UNIT V
9. Discuss the functioning of three phase voltage source inverter in 120 degree operating mode with
relevant waveforms and obtain the expression for voltage.
A single phase full bridge inverter is fed from a DC source such that fundamental component of
output voltage is 230V. Find the RMS value of thyristor and diode current for R=2
load.

10. Compare the Voltage Source and Current Source Inverters.
Explain the working of a basic parallel inverter with neat circuit and related circuit voltage and
current waveforms.