Power Electronics (EX-502) - Important Questions

Explain the different methods to turn on (trigger) a thyristor.

Explain the need for commutation in thyristor/SCR circuits and the different commutation techniques used to turn off the thyristor.

Describe the modes of operation of a thyristor/SCR with the help of its static V-I characteristics.

Compare power BJT, power MOSFET and IGBT.

Describe the advantages of IGBT over other power electronic devices.

What is commutation? Explain Class B commutation with circuit diagram and waveforms.

Explain the working of GTO with its VI characteristics.

Explain different types of SCR firing circuits.

Explain the different methods to turn on (trigger) a thyristor / SCR.

Explain the different types of over-current and over-voltage protection for SCR.

Explain the role and applications of major power semiconductor devices (Power MOSFET, IGBT, GTO, SCR/DIAC).

Describe LASCR. Give its industrial applications. With neat circuit diagram explain how UJT firing circuit will generate pulse for an SCR.

Explain the working of a single-phase fully controlled / full-wave bridge controlled rectifier with waveforms for R / RL load

Explain the working / operation of a single-phase fully controlled (full-wave bridge) converter with RL load, circuit diagram and waveforms including load voltage and SCR voltage.

Explain what is meant by rectification mode and inversion mode in a single-phase fully controlled converter.

What is the function of freewheeling diodes in a controlled rectifier?

Draw voltage and current waveforms for single-phase half-bridge rectifier with RLE load

Explain the function and effect of a freewheeling diode on controlled rectifier / converter performance including power factor improvement.

Explain what is meant by rectification mode and inversion mode in a single-phase fully controlled converter

Draw and explain voltage and current waveforms for continuous load current in a single-phase full-bridge converter with RLE load, including inversion mode $\alpha > 90^{\circ}$

Explain the working of three-phase full converter for a firing delay angle of 45 degrees

Compute firing angle delay for single-phase full converter with RLE load given supply, load and EMF.

Derive the output voltage and current expressions for firing angle of 45 degrees.

Explain the effect of source impedance on the performance of a single-phase fully controlled bridge converter.

Explain the working of a three-phase bridge voltage source inverter in $120^{\circ}$ conduction mode with star-connected resistive load and waveforms.

Explain the working of a three-phase bridge voltage source inverter in $180^{\circ}$ conduction mode with waveforms.

Explain the working of a three-phase bridge / voltage source inverter in $180^{\circ}$ conduction mode with resistive load, with waveforms.

Explain the operation/working of single-phase current source inverter, including its merits and demerits

Explain the working and principle of operation of a current source inverter (CSI), including single-phase commutated CSI with R load and auto-sequential commutated inverter.

Explain the working of self cumulated inverters.

Explain the principle of operation of McMurray and McMurray-Bedford (modified McMurray half-bridge) inverter.

What is an inverter ? list a few industrial applications of inverter?

Draw and explain the operation of three-phase series-inverter circuit.

For a single-phase square-wave inverter with DC source and series RL load, derive the load current expression and find RMS load current and average source current.

Differentiate / compare between voltage source inverter and current source inverter.

Explain the operation of single pulse modulation of a single-phase inverter with neat diagram.

For a type-A (R-L-E) chopper with given $V_s, T, T_{on}, R, L, E$, determine whether load current is continuous, calculate average output current, and compute steady-state maximum and minimum load currents.

Explain the working of Type-C chopper with circuit and waveform.

Explain the working of step-up chopper with circuit diagram and waveforms and derive the expression for output voltage.

Explain the working / operation of step-up chopper with neat circuit diagram and waveforms and derive expression for output voltage.

Explain the operation of step-up and step-down chopper with circuit diagram, waveforms, duty cycle and output voltage expression.

Describe the Morgan (Morgen) chopper with associated voltage and current waveforms.

Numerical on step-up chopper to find switching frequency / on-off time / duty cycle from given source voltage, load voltage and on/off time with continuous inductor current.

Numerical problem on step-down DC chopper with resistive load to find average output voltage, RMS output voltage and efficiency.

Describe the operation of Morgan chopper with voltage and current waveforms.

Write short notes on Jones chopper and current limit control of DC-DC converter.

For a DC on-off (type-A R-L) chopper with given source voltage, frequency/duty cycle, $R$ and $L$, compute the maximum and minimum load currents.

Explain the working principle of a single-phase bridge-type step-down cycloconverter with circuit diagram and input-output waveforms (e.g., output frequency $f/2$ for resistive load).

Single-phase full-wave AC voltage controller feeding resistive load: given input voltage and load power, find thyristor firing delay angle and input power factor.

Describe the working of a two-stage sequence control of AC voltage controller for R-L load.

Explain the working of a single-phase full-wave AC voltage controller / regulator feeding an R-L (inductive) load.

Explain the operating principle of a single-phase to single-phase step-up cycloconverter using midpoint (and bridge) configuration with circuit diagram and waveforms.

Explain the working of the buck-boost regulator/converter with the help of circuit diagram and relevant waveforms.

For a single-phase voltage controller with on-off control (4 cycles on, 3 cycles off), $230\,V$ input and $10\,\Omega$ resistive load, determine RMS output voltage, input power factor, and average and RMS thyristor current.

What are dual converters? Explain the operation of three phase dual converter using circulating current mode of operations. How are firing angles of two converters controlled?

Describe the operating principle of a single-phase to single-phase step-up cycloconverter with mid-point and bridge configurations, circuits and waveforms.

Explain the working of a three-phase to single-phase cycloconverter.

Single-phase half-wave AC voltage controller with resistive load: given supply voltage and delay angle, determine rms output voltage, input power factor and average input current.

Write short notes on AC voltage controllers (as part of choice among topics including harmonics, GTO, forced commutation).