DHANALAKSHMI COLLEGE OF ENGINEERING DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

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1 DHANALAKSHMI COLLEGE OF ENGINEERING DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING Power Diode EE2301 POWER ELECTRONICS UNIT I POWER SEMICONDUCTOR DEVICES PART A 1. What is meant by fast recovery diode? (N/D-04) 2. What is meant by reverse recovery time? (A/M-06) Power BJT 3. What are the advantages of GTO over BJT? (N/D-04) 4. What are the advantages of MOSFET over BJT? (A/M-08) 5. Why is a BJT called as a current controlled device? SCR 6. Draw the V I characteristics of SCR and mark the holding current and the latching current on the characteristics. (N/D-04) 7. Define Holding Current and Latching Current of SCR (A/M-08) 8. Define String Efficiency of SCRs connected in series (A/M-05) 9. List out the various advantages of GTO over SCR. (A/M-04) 10. What are the various factors that influence the turn-off time of a thyristor? (N/D-06) 11. What is meant by turn off time of a converter grade SCR? 12. What is meant by turn off time of an inverter grade SCR? 13. What are the different methods of turning on of a thyristor? Power MOSFET 14. Why are MOSFETs not preferred for low frequency applications? (M/J-06) 15. Define Pinch Off Voltage of a MOSFET (N/D-07) Power IGBT 16. Why are IGBTs becoming more popular in their applications in controlled converters? 1

2 TRIAC 17. What are the advantages of a TRIAC? Power BJT PART B 1. Explain the switching operation of a BJT with relevant waveforms, indicating clearly the turn on time, turn off time and their components. (16) (N/D-07) 2. Compare the performance characteristics of MOSFET with BJT. (8) (A/M-08) Power MOSFET 3. Explain in detail, the operation of a power MOSFET. Also explain the transfer characteristics, output characteristics and switching characteristics of the power MOSFET. (16) (N/D-07) 4. Compare the salient features of MOSFET with IGBT. (8) (M/J-07) Power IGBT 5. Explain the transfer, output and switching characteristics of IGBT.(A/M-08, N/D-12) SCR 6. Explain in detail, the structure of SCR and its turn on and turn off operations. (N/D-12) 7. Explain in detail, the forward characteristic of SCR using two transistor model of SCR. (16) (M/J-07) 8. Differentiate natural commutation from forced commutation. (8) (A/M-08) 9. Explain in detail, the operation of a driver circuit and a snubber circuit for power MOSFET. (16) (N/D-09) 10. Explain in detail, the different types of commutation circuits. (16) TRIAC 11. Explain in detail, the various modes of working of TRIAC. (16) (A/M-10) 2

3 Two pulse converter UNIT II PHASE CONTROLLED CONVERTERS PART A 1. What is meant by two pulse converter? (N/D-11) 2. What is meant by full converter? (N/D-04) 3. What is meant by delay angle of converters? (N/D-03) 4. Define Firing Angle (A/M-04) 5. What is meant by inversion mode of rectifier? (A/M-08) 6. List out the applications of phase controlled converters. (N/D-06) 7. What is meant by freewheeling diode? (J-06) 8. What is meant by half controlled rectifier? (A-01) 9. What is meant by commutation? 10. What is meant by forced commutation? 11. What is meant by natural commutation? 12. Define Commutation Angle or Overlap Angle 13. Performance characteristics 14. Define Displacement Factor and Total Harmonic Distortion (M/J-07) 15. Define Harmonic Factor of the input current (N/M-04) 16. Effect of source inductance 17. What are the effects of source impedance in a controlled rectifier? (N/D-06) Two pulse converter PART B 1. Explain in detail, the operation of a single phase half controlled rectifier with R load. Also derive an equation for the average output voltage. (16) (A/M-08) 2. Explain in detail, the principle of operation of a three phase fully controlled bridge rectifier feeding RL load and derive an expression for the average output voltage. (16) (M/J-07) 3. A single phase fully controlled bridge is connected to RLE load. The source voltage is 230 V, 50 Hz. The average load current of 10 A continuous over the working range, R= 0.4 Ω and L = 2 mh. Determine the following: 3

4 a) Firing angle for E = 120 V b) Firing angle for E = 120 V (16) (N/D-07) 4. (i) Describe the operation of a single phase two pulse bridge converter using four SCRs with relevant waveforms. (8) 5. (ii) Explain the working of the above converter mode with RLE load. (8)(N/D-06) 6. A single phase two pulse converter feeds power to RLE load with R = 6 Ω, L = 6 mh, E = 60 V, AC source voltage is 230 V, 50 Hz for continuous condition. Find the average value of load current for a firing angle of 50º, if one of the four SCRs gets open circuited. Find the new value of average load current assuming the output current as continuous. (16) (N/D-06) 7. Explain in detail, the principle of operation of a two quadrant two pulse converter in the rectifying mode and inverting mode of operations. (16) (N/D-12) 8. A resistive load of 10 Ω is connected to a half wave rectifier SCR circuit to 220 V, 50 Hz, single phase source. Calculate the power delivered to the load for a firing angle of 60º. Find also the value of input power factor. (16) 9. Explain in detail, the operation of a single phase half wave and full wave ac voltage controllers. (16) Three pulse converter 10. Explain with neat sketch the operation of a three phase half controlled rectifier supplying R load. Also derive an expression for the average output voltage. (16) (A/M-08) Effect of source inductance 11. Explain in detail, the effect of source inductance in controlled rectifiers. (16) Performance characteristics 12. For a single phase full converter having highly inductive load, derive the following: a) Displacement factor b) Supply power factor c) Harmonic factor d) Current distortion factor (16) 4

5 UNIT- III DC TO DC CONVERTERS PART A Chopper 1. Define Duty Cycle of DC chopper (N/D-06, N/D-07) 2. What is meant by DC chopper? (N/D-07) 3. What are the applications of DC choppers? Time ratio and current limit control 4. What are the control strategies used in chopper? (N/D-03) 5. What are the disadvantages of FM scheme used in chopper? (N/D-04) 6. What are the methods of controlling the output voltage of a chopper? (A/M-05) 7. Differentiate constant frequency control strategy from variable frequency control strategy of varying the duty cycle of DC choppers. (N/D-06) 8. What is meant by time ratio control of DC DC converter? (M/J-06) 9. What is meant by pulse width modulation control in DC Chopper? (M/June 07 Buck regulator 10. What are the different types of switching regulators used in DC choppers? 11. What is meant by buck regulator? (M/J-07) Buck boost regulator 12. What are the advantages and disadvantages of a buck-boost regulator? (A/M-05) Chopper classification 13. What are the classifications of DC to DC converter depending upon the directions of current and voltage? (M/J-06) SMPS 14. What are the applications of SMPS? 5

6 PART B Step down chopper 1. Explain the principle of operation of a DC-DC step down chopper with suitable waveforms. Also derive an expression for its average DC output voltage. (16) (N/D-06) 2. A step down DC chopper has input voltage of 230 V with 10 Ω load resistor connected, voltage drop across chopper is 2 V when it is ON. For a duty cycle of 0.5, calculate the following: a) Average and r.m.s values of output voltage b) Power delivered to the load (16) (N/D-06) Step up chopper 3. Describe the principle of a step-up chopper. Also derive an expression for the average output voltage in terms of dc input voltage and duty cycle. (16) (N/D-03) 4. Explain in detail, the operation of a step-up chopper and drive an expression for its output voltage. (16) (N/D-04) Chopper classification 5. Explain in detail, the operation of class-c and class-d choppers. (16) (A/M-05) 6. In a type A chopper, the input supply voltage is 230 V, the load resistance is 10 Ω and there is a voltage drop of 2 V across the chopper thyristor, when it is on. For a duty ratio of 0.4, calculate the average and r.m.s values of the output voltage. Also find the chopper efficiency. (16) (A/M-05) Buck converter 7. Draw the circuit diagram of a buck converter and explain its operation with equivalent circuit for different modes and waveforms. (16) Boost converter 8. Explain in detail, the operation of boost regulator with neat diagrams and waveforms. (16) Buck- boost converter 9. Describe in detail, the principle of operation of buck- boost converter with a neat circuit diagram. (16) (N/D-06) SMPS 10. Explain in detail, the operation of a resonant switching based SMPS. (16) (A/M-08) 6

7 11. A DC chopper has an input voltage of 200 V and a load of 20 Ω resistance. When the chopper is on, its voltage drop is 1.5 V and the chopping frequency is 10 khz. If the duty cycle is 80%, determine the following: a) Average output voltage b) RMS output voltage c) Chopper on time (16) 7

8 UNIT IV INVERTERS PART A Single phase inverter A single phase full bridge inverter has a resistive load of R = 10 Ω and an input voltage V dc of 100 V. Find the rms output voltage at fundamental frequency. (N/D-03) List out the industrial applications of inverters. (A/M-04) What is meant by inverter? What are the applications of inverter? PWM technique What is meant by PWM? Define Modulation Index of PWM What is the need for voltage control in an inverter? What are the advantages of current source inverter? (A/M-05) (N/D-05) (M/J-06) (M/J-07) What are the advantages of PWM inverter? (A/M 08) What are the advantages of PWM control? Current source inverter Differentiate VSI from CSI. What is meant by current source inverter? (N/D-03, N/D-06, N/D-07) (A/M-08) PART B Single phase inverter 1. Describe in detail, the operation of a single phase half bridge inverter supplying RL load with a neat sketch and waveforms. (16) (N/D-05) 2. Explain in detail, the principle of operation of a single phase half bridge inverter. (16) 3. Describe in detail, the working of a single phase full bridge inverter supplying R, RL loads with relevant circuit and waveforms. (16) (N/D-06, N/D-07) 8

9 Three phase inverter 4. Explain in detail, the functioning of a three phase voltage source inverter supplying a balanced star connected load in 120º operating mode. (16) (A/M 08) 5. Explain in detail, the three phase voltage source inverter, using transistors operating in 180 º conduction mode with a neat diagram and waveforms. Also obtain the expression for r.m.s value of output voltage. (16) (A/M-05, A/M-07) PWM techniques 6. Explain in detail, the different methods of voltage controls used in inverters. (16) (N/D-03) 7. Explain in detail, the various PWM techniques. (16) (N/D-06) 8. Explain in detail, the following PWM techniques used in inverter: a) Sinusoidal PWM b) Multiple PWM (16) (M/J-07) 9. Explain in detail, the SVPWM. (16) 10. Explain in detail the different methods of controlling the output voltage of inverters. (16) Series inverter 11. Describe in detail, the operation of a series inverter. (16) (N/D-03) 12. Explain in detail, the series resonant inverter. (16) (N/D-05) 9

10 UNIT V AC TO AC CONVERTERS PART A AC voltage controller 1. What is meant by AC voltage controller? (M/J-10) 2. What are the applications of AC voltage controllers? (N/D-12) 3. What are the various types AC voltage controllers? (M/J-13) 4. What is meant by unidirectional or half-wave AC voltage controller? (N/D-11) 5. What is meant by bidirectional or half-wave AC voltage controller? (N/D-10) Cycloconverter 6. What is meant by cycloconverter? (N/D-12) 7. Write the principle of operation of a cycloconverter. (N/D-12) 8. What are the two types of cycloconverters? 9. What are the applications of cycloconverters? 10. What is meant by negative converter group in a cycloconverter? 11. What is meant by positive converter group in a cycloconverter? Matrix converter 12. What by matrix converter? (M/J-13) AC voltage controller PART B 1. Explain in detail, the operation of 1ф AC voltage controller with RL load. (16) (N/D-07) 2. Explain in detail, the principle of operation of a single phase ac voltage controller feeding R load by on-off control and phase control. Also derive an expression for the r.m.s value of the output voltage in both the cases. (16) (M/J-07) 3. For a single phase AC voltage controller feeding a R load, draw the waveforms of source voltage, output voltage, source current and output current. Also explain its working with reference to waveforms. (16) (N/D-07) 10

11 Cycloconverter 4. Compare the operation of three phase cycloconverter with single phase cycloconverter with neat circuit diagram s and waveforms. (16) (N/D-12) Multistage sequence control 5. Explain in detail, the operation of multistage control of AC voltage controllers with neat diagram. (16) Multi stage sequence control 6. Explain in detail, the two stage sequence control of voltage controller with R load. (16) Matrix converter 7. Explain in detail, the operation of matrix converter. (16) 11

11. Define the term pinch off voltage of MOSFET. (May/June 2012)

11. Define the term pinch off voltage of MOSFET. (May/June 2012) Subject Code : EE6503 Branch : EEE Subject Name : Power Electronics Year/Sem. : III /V Unit - I PART-A 1. State the advantages of IGBT over MOSFET. (Nov/Dec 2008) 2. What is the function of snubber circuit?