Anna University
Department of Electrical and Electronics Engineering
EE2301 Power Electronics
5th Semester
Regulation 2008
Unit I
1. (a) Discuss the different modes of operation of thyristor with the help of its static V-I characteristics. (8)
(b) Explain why triac is rarely operated in I quadrant with -ve gate current & in III quadrant +ve gate current. (8)
2.(a) Describe the structure of an IGBT. (8)
(b) Draw the simplified model of a MOSFET to show the interelectrode capacitance. (8)
3. Explain the four modes of operation of a TRIAC. Compare their sensitivity. (16)
4. Draw the dynamic characteristics of SCR during turn-on and turn-off and explain. (16)
5. Describe any one driver circuit and snubber circuit for MOSFET. (16)
6. Write short notes on:
(a) Snubber circuit of BJT (8)
(b) commutation circuit of SCR (8)
7. (a) Draw and explain the forward characteristics of SCR using two transistor model of
SCR.(10) (b) Compare any six salient features of MOSFET & IGBT. (6)
Unit II
1. Discuss the operation of single phase half controlled rectifier with inductive load. Derive the average output voltage equation. (16)
2. Explain the principle of operation of single phase dual converter with neat power circuit diagram. (16)
3. Explain the operation of three phase half controlled rectifier supplying R- load with neat waveforms. Derive an expression for the average output voltage. (16)
4. With necessary circuit and waveforms explain the principle of operation of single Phase fully controlled converter. Derive the expression for average output voltage. (16)
5. Explain the effect of source inductance in the operation of single phase fully controlled converter. Derive the expression for its output voltage. (16)
6. Explain the operation of three -phase full converter. Derive expression for its average output voltage. (16)
7. A Single phase semiconverter is operated from 120 V, 50 Hz ac supply. The load current with an average value Idc is continues and ripple free firing angle α=π/6, Determine
(i) Displacement factor
(ii) Harmonic factor of input current
(iii) Input power factor (16)
Unit III
1. Derive the expression for the output voltage of a step-up chopper & explain its control strategies. (16)
2. Discuss the principle of operation of DC-DC step-down chopper with suitable waveform. Derive an expression for its average DC output voltage. (16)
3. A step-up chopper has input voltage 220 V and output voltage of 660 V. if the non-conducting time of thyristor chopper is 100 µs, compute the pulse width of output voltage. In case pulse width is halved for constant frequency operation, find the new output voltage. (16)
4. Explain the various modes of operation of Boost DC – DC converter with necessary waveforms. (16)
5 (a) A DC chopper an input voltage of 200 V and a load of 20 Ω resistance.When chopper is ON, its voltage drop is 1.5 V and the chopping frequency is 10 kHz .If the duty cycle is 80% .
Find (1) Average output voltage.
(2) RMS output voltage.
(3) Chopper on time. (12)
(b) Explain about Type – E chopper. (4)
6. Classify the basic topologies of switching regulators and explain the operation of buck regulator with continuous load current using suitable waveform(16)
Unit IV
1. Explain the principle of operation of three phase inverter with 180° conduction mode With necessary waveforms and circuits. (16)
2. Describe the functioning of three phase voltage source inverter supplying a balanced star - connected load in 120° operating mode. (16)
3. (a) Describe any one PWM technique used in inverter in detail.(8)
(b) Explain the working principle of single phase current source inverter. (8)
4. (a) Write short note on series resonant inverter.(8)
(b) Explain how inverter can be controlled using multiple and sine PWM technique. (8)
5. Explain the operation of single phase commutated current source inverter with R load. (16)
6. Explain, different methods of voltage control adopted in an inverter with suitable waveforms. (16)
Unit V
1. Explain the working principle of multistage sequence control of AC Voltage controller. (16)
2. Explain the principle of single phase to single phase step down a Cycloconverter with power circuit and waveforms. (16)
3. Discuss the operation of on-line & Off-line UPS with block diagram. (16)
4. Describe the operation of single phase full wave ac voltage controller with the help of voltage and current waveform. Also derive the expression for average value of output voltage.(16)
5. Explain with waveforms the principle of working single phase to single phase step up Cycloconverter. List the factors that affect the performance of Cycloconverter. (16)
6. Write short note on the following:
(a) UPFC (8)
(b) Static VAR compensator. (8)