JNTU B.Tech III POWER ELECTRONICS Previous Question Paper (February - 2023 - R16)

List out at least two merits of IGBT over MOSFET.

Define the different ratings of SCR.

What are the advantages of freewheeling diode?

How four quadrant operation is possible with 1-ph fully controlled converters?

Define AC voltage controller.

What are the limitations of a cycloconverter compared ac voltage controller?

Write few applications of choppers.

What is the Current limit control of choppers?

How quality of an inverter output voltage can be measured?

What type of commutation is used in basic series inverter?

Discuss the need for parallel connections of SCRs with necessary diagrams.

Design RC firing circuit for SCR at a load resistance of 25 ohms.

Draw and explain dynamic characteristics of SCR during turn off.

Draw and explain the transfer and output characteristics of n-channel enhancement type MOSFET’s.

Explain the operation of 1-ph half controlled bridge rectifier with RLE load and derive expression for average output voltage.

A 1-ph semi-converter delivers power to RL load with R= 5 Ω, L = 10 mH. The a.c. supply voltage is 230 V, 50 Hz. For the continuous conduction, find the average value of output voltage and current for the firing angle of 45°.

A 3-ph fully controlled bridge rectifier is operating from a 400V, 50 Hz supply. The load is highly inductive and continuous current constant. Find load voltage at firing angle 45°.

Explain the operation of single phase fully controlled converter with RL load. Derive the output voltage and current expressions for firing angle of 45°.

Discuss the voltage control methods employed in ac voltage controllers with waveforms.

A three-phase resistive load is to be controlled by three Triacs from a 415V supply. If the load is 15 kW, determine the required ratings of Triacs. If thyristors were used instead of Triacs, determine their rating.

Describe the working principle of 1-ph to 1-ph step-down midpoint type cycloconverter with waveforms for R load.

A single phase bidirectional controller supplies a resistance load of R = 10 Ω. Determine the output voltage and power consumed by the load at i) α = 30° ii) α = 75° and iii) α = 120°.

Describe the Morgan chopper with associated voltage and current waveforms.

Enumerate the merits of Morgan chopper compared to Jones chopper.

Explain the operation of a step down chopper with RLE load. Derive the necessary output voltage and current expressions.

A step-down chopper is fed from a 220 V DC source to deliver a load voltage of 100 V. If the non-conduction time of transistor is 100μs. The required pulse width would be?

Describe sinusoidal PWM control of single phase VSI with the help of suitable waveforms.

A square wave inverter has a dc source of 125 V, an output frequency of 60 Hz, and an RL series load with R = 20 Ω, and L = 25 mH. Determine i) an expression for load current, ii) rms load current and iii) average source current.