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EE2301 Power Electronics - University Questions Collections
#1


Anna University
Department of Electrical & Electronics Engineering


Department : B.E EEE
Semester : V
Year : 3rd yr
Regulation : 2008
Subject Code : EE2301
Subject Name : Power Electronics

Content : Power Electronics University Question collected from Various Previous Year Question Paper

UNIT I
POWER SEMICONDUCTOR DEVICES
PART A


1. Draw the V-I characteristics of SCR and mark the holding current and latching current in the characteristics. (Nov/Dec04)
2. What are the advantages of GTO over BJT? (Nov/Dec 04)
3. Define: holding current and latching current of SCR (Apr/May 08)
4. Define: string efficiency of SCRs connected in series (Apr/May 05)
5. What is fast recovery diode? Mention its uses. (Nov/Dec 04)
6. Distinguish between holding current and latching current of SCR. (Nov/Dec 05)
7. Why is pulse triggering preferred over RC triggering? (Nov/Dec 05)
8. What is reverse recovery time? (Apr/May06)
9. Mention any two advantages of advantages of GTO over SCR. (Apr/May 04)
10. Why MOSFETs are not preferred for low frequency applications? (May/June 06)
11. Why are IGBT becoming popular in their application to controlled converters? (Nov/Dec06)
12. What are the factors that influence the turn-off time of a thyristor? (Nov/Dec 06)
13. Draw the turn on characteristics of SCR and mark the timings td ,tr and ton. (May/June 07)
14. In TRIAC which of the modes the sensitivity of gate is high. (Nov/Dec 07)
15. Define the term pinch off voltage of MOSFET. (Nov/Dec 07)
16. What are the advantages of MOSFET with BJT? (Apr/May 08)


PART B

1. Explain the structure and operation of turn on and turn of characteristics of SCR. (Model I / AU)
2. (i) Describe the any two methods of turn-on mechanism of SCR.
(ii) Explain the turn off characteristics of SCR. (Model II / AU)
3. Discuss the transfer, output and switching characteristics of IGBT. (Model II / AU )
4. Explain the switching performance of BJT with relevant waveforms indicating clearly the turn on, turn off times and their components. (Nov / Dec 07)
5. (i) Draw and explain the forward characteristics of SCR using two transistor model of SCR.
(ii) Compare any six salient features of MOSFET with IGBT. ( May/June 07 )
6. (i) Compare the performance characteristics of MOSFET with BJT.
(ii) Briefly discuss the R-C triggering of SCR. (April/may 08)
7. Discuss the operation of power MOSFET and explain the transfer, output and switching characteristics of power MOSFET. (Nov/Dec 07)
8. Differentiate natural commutation and forced commutation. (Apr/May 08)
9. Explain the operation of driver and snubber circuits for power MOSFET. (Model AU
10. Explain with diagram the various modes of working of TRIAC (Model AU)

UNIT II
PHASE CONTROLLED CONVERTERS


PART - A
1. What is two pulse converters? (Model AU)
2. What is full converter? Mention its uses. (Nov/Dec 04)
3. What is a delay angle of converters? (Nov/Dec 03)
4. What is the principle of phase control half wave rectifier? (Nov/Dec 04)
5. What is the function of freewheeling diode in Semi converter? AU/ME–Jan 05, 06 )
6. Draw the three phase half wave converter. (Model AU)
7. Write the expression for 3Φ full converter with RL load. (Model AU)
8. What is meant by full controlled rectifier? ( Model AU)
9. Define: firing angle α (Apr/May 04)
10. List the merits of phase control. (Apr/May 04)
11. Why the power factor of semiconverter better than full Converter? (April/May 08)
12. What is the inversion mode of rectifiers? April/May 08
13. Define the terms: displacement factor, total harmonic distortion. May/June 07
14. Under what conditions a single phase fully controlled converter gets operated as an inverter. Nov/ Dec 07
15. State the principle of phase control in AC-DC converter. Nov/ Dec 07
16. It is required to operate a single phase full converter in the inverter mode with RLE load. Should the average output voltage be more or less than E during inverter operation? Why? Nov/Dec 06
17. List various applications of phase controlled converters. Nov/Dec 06
18. What is freewheeling diode and what is the purpose? (ME/Jan 06 & AU model I)
19. Define displacement factor. (AU model I)
20. Is the input power factor of fully controlled converter is less than that of half controlled converter? Justify your answer. AU model II
21. What are the applications of AC voltage controllers? AU model II
22. Define: distortion factor. AU model III
23. What is a AC voltage controller? AU model III
24. What are the effects of source impedance in the controlled rectifiers? Nov/Dec 06
25. What is meant by half controlled rectifier? MKU/ Apr 01
26. For the single phase fully controlled bridge converter having load of ‘R’, determine the average output voltage if the supply is 230V, 50 Hz, single phase AC and the firing angle is 60ᵒ. AU/Dec 04
27. Mention the function of free-wheeling diode in controlled rectifier circuits. AU/Dec 06
28. Define: harmonic factor of the input current. AU/May 04

PART B

1. Discuss the operation of single phase half controlled rectifier with R load. Also derive the average output voltage equation. April/May 08
2. Explain the operation of three phase half controlled rectifier supplying R load with neat sketch. Also derive an expression for the average output voltage. April/May 08
3. With necessary circuit and waveforms, explain the principle of operation of three phase fully controlled bridge rectifier feeding R-L load and drive the expression for the average output voltage. May/June 07
4. With necessary circuit and waveforms, explain the principle of operation of single phase ac voltage controller feeding R load by on-off control and phase control. Derive the expression for rms value of output voltage in both cases. May/June 07
5. For the single phase fully controlled bridge is connected to RLE load. The source voltage is 230 V, 50 Hz. The average load current of 10A continuous over the working range. For R= 0.4 Ω and L = 2mH, Compute
(a) firing angle for E = 120V
(b) firing angle for E = -120V Nov/Dec 07
6. For a single phase Ac voltage controller feeding a R load draw the waveforms of source voltage, output voltage, source and output current. Describe its working with reference to waveforms drawn. Nov/Dec 07
7. i) Describe the operation of single phase two pulse bridge converter using 4 SCRs with relevant waveforms. Nov/Dec 06
ii) Discuss the working of the above converter mode with RLE load. Nov/Dec 06
8. i) A single phase two pulse converter feeds power to RLE load with R= 6Ω, L= 6mH, E= 60V, AC source voltage is 230V, 50Hz for continuous condition. Find the average value of load current for a firing angle of 50ᵒ. In case one of the 4 SCRs gets open circuited. Find the new value of average load current assuming the output current as continuous. Nov/Dec 06
ii) Draw the possible configurations of a single phase AC voltage controller and compare them. Nov/Dec 06
9. Discuss with the aid of schematic diagram and waveforms, the principle of operation of a two quadrant two pulse converter in the rectifying and inverting mode of operation. AU/Model I
10. Draw the circuit diagram and explain the operation of three pulse half controlled rectifier. AU/ Model I
11. Draw the power circuit diagram of a 6 pulse two quadrant converter circuit. Explain the operation of the circuit with necessary wave forms. AU/Model II
12. i) Draw the schematic diagram of a single phase half controlled thyristor bridge converter and explain the operation of this system. AU/Model II
ii)The full wave controlled bridge rectifier has an ac Input of 120V rms at 60Hz and a 20Ω load resistor. The delay angle is 40ᵒ. Determine 1) Average load voltage 2) Average load current and 3)RMS load voltage. AU/Model II
13. i) Explain the effect of source inductance in controlled rectifiers.
ii) Drive the expressions for average output voltage and rms output voltage of single phase semiconductor. AU/Model III
14. Explain the operation of single phase half wave and full wave ac voltage controllers. AU/Model III
15. For a single phase full converter having highly inductive load, drive the following:
i) Displacement factor. ii) Supply power factor. iii) Harmonic factor. iv) Current distortion factor AU/Model III
16. A resistive load of 10Ω is connected through a half-wave SCR circuit to 220V, 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. AU/Model II

UNIT- III
DC TO DC CONVERTERS

PART- A
1. What are the control strategies of chopper? Nov/Dec 03
2. Mention the disadvantages of FM scheme used in chopper Nov/Dec 04
3. What are the methods of controlling the output voltage of a chopper? Apr/May 05
4. What are the advantages and disadvantages of buck-boost regulator? Apr/May 05
5. Define: duty cycle of dc chopper Nov/Dec 06,07
6. Differentiate between constant frequency and variable frequency control strategies of
varying the duty cycle of DC choppers. Nov/Dec 06
7. What is meant by time ratio control in dc-dc converter? May/June 06
8. What are the classification of dc to dc converter depending upon the directions of current
and voltage? May/June 06
9. What is meant by buck regulator? May/June 07
10. What is meant by pulse width modulation control in dc chopper? May/June 07
11. What is DC chopper? Nov/Dec07
12. What is two quadrant DC chopper? Apr/May 08
13. What is time ratio control in chopper? Apr/May 08

PART – B

1. i) Describe the principle of step-up chopper. Derive an expression for the average output voltage in terms of input dc voltage and duty cycle. State the assumptions made.
ii) A step-up chopper supplies a load of 480 V from 230 V dc supply. Assuming the non conduction period of the thyristor to be 50 microsecond, find the on time of the thyristor. Nov/Dec 03
2. For a type A chopper ( first quadrant ), express the following variable as a function of VS, R and duty cycle δ in case the load is resistive. Nov/Dec 03
3. Explain the operation of the step-up chopper and drive an expression for its output voltage. Nov/Dec 04
4. With the help of power circuit diagrams, discuss the operation of class-C and class- D choppers Apr/May 05
5. In a type A chopper, the input supply voltage is 230 V the load resistance is 10Ω 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. Apr/May05
6. i) Draw the circuit diagram of a buck converter and explain its operation with equivalent circuit for different modes and waveforms. Nov/Dec 05
ii) Design the filter components for a buck converter which has an input voltage of 12 V and output voltage of 5 V. the peak to peak output ripple voltage is 20 mV and peak to peak ripple current of inductor is limited to 0.8 A. the switching frequency is 25 KHz. Nov/Dec 05
7. i) Discuss the principle of operation of DC-DC step down chopper with suitable waveforms. Derive an expression for its average DC output voltage. Nov/Dec 06
ii) 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: 1) Average and r.m.s values of output voltage 2) Power delivered to the load Nov/Dec 06
8. i) Discuss the need for resonant switching in SMPS. Nov/Dec 06
ii) Describe briefly the principle of operation of buck- boost converter with a neat circuit. Nov/Dec 06
9. Draw the circuit of buck regulator and explain its working principle with necessary waveforms. Derive the expression for peak to peak ripple voltage of the capacitor that is present across the load. May/Jun 07
10. Draw the circuit of cuk regulator and explain its working principle with necessary waveforms in detail. May/Jun 07
11. A step up chopper has input voltage of 220 V and output voltage of 660 V. If the nonconducting time of thyristor chopper is 100 micro sec compute the pulse width of output voltage. In case the pulse width is halved for constant frequency operation , find
the new output voltage. Nov/Dec 07
12. Classify the basic topologies of switching regulators and explain the operation of buck regulators with continuous load current using suitable waveforms. Nov/Dec 07
13. Discuss the operation of the resonant switching based SMPS. Apr/May 08
14. i) A dc chopper has an input voltage of 200 V and a load of 20 Ω resistances. 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. Apr/May 08
1) Average output voltage
2) RMS output voltage
3) Chopper on time
ii) Explain about type- E chopper. Apr/May 08

UNIT IV
INVERTERS

PART A
1. A single phase full bridge inverter has a resistive load of R = 10 Ω and the input voltage Vdc of 100 V. Find the rms output voltage at fundamental frequency. Nov/Dec 03
2. List the application of CSI Nov/Dec 04
3. Distinguish between VSI and CSI Nov/Dec 03,06,07
4. List a few industrial applications of inverters. Apr/May 04
5. What is the purpose of connecting diode in antiparallel with thyristors in inverter? Apr/May 04
6. What is PWM? List its various techniques. Apr/May 05
7. What are the main differences between current driven and voltage driven inverter? Apr/May 05
8. Define modulation index of PWM. What is its use? Nov/Dec 05
9. What is the need for voltage control in an inverter? May/Jun 06
10. What are the modulation techniques used in an inverter?
(or)
List different methods of controlling the output voltage of inverters. May/Jun 06
11. Define modulation index in PWM employed in inverter. May/Jun 07
12. Mention any two advantages of current source inverter. May/Jun 07
13. Define the term inverter gain Nov/Dec 07
14. What is a current source inverter? Apr/May 08
15. What are the advantages of PWM inverter? Apr/May 08

PART B

1. Describe the operation of series inverter. What are its advantages? Nov/Dec03
2. State different methods of voltage control in inverters. Describe about SPWM control in inverter. Nov/Dec 03,07
3. i) Explain the principle of operation of single phase half bridge inverter. Nov/Dec 04
ii) The single phase half bridge inverter has a resistive load of 2.4 Ω and the dc input voltage is 48 V. determine the r.m.s output voltage at the fundamental frequency, output power and the total harmonic distortion. Nov/Dec 04
4. i) Describe with a neat sketch and waveform the operation of a single phase half bridge inverter supplying RL load. Nov/Dec 05
ii) Discuss the application of PWM technique in the inverter, bring out its use. Nov/Dec 05
5. With neat diagram and waveform, explain three phase voltage source inverter, using transistors operating in 180ᵒ conduction mode. Also obtain the expression for rms value of output voltage. Apr/May 05,07
6. With aid of circuit diagram and relevant waveforms, explain the operation of PWM inverters. Nov/Dec 05
7. i) Compare CSI with VSI. Nov/Dec 05
ii) Explain the operation of a single phase capacitor commutated CSI with R load with equivalent circuit and output waveform. Nov/Dec 05
8. Explain using a diagram the operation of a series inverter. Bring out its limitations, develop the circuit of a modified series inverter. Nov/Dec 06,May/Jun 06
9. i) With a neat diagram explain the single pulse width modulation method of voltage control of inverters. May/Jun 06
ii) Discuss a few applications for inverters. May/Jun 06
10. i) Describe the working of a single phase full bridge inverter supplying R, RL loads with relevant circuit and waveforms. Nov/Dec 06,07
ii) What is PWM? List the various PWM techniques and explain any one of them. Nov/Dec 06
11. With a neat circuit and relevant waveforms discuss the operation of an ideal single phase CSI. Nov/Dec 06
12. Explain the following PWM techniques used in inverter.
i) Sinusoidal PWM
ii) Multiple PWM May/June 07
13. Discuss the functioning of three phase voltage source inverter supplying a balanced star connected load in 120ᵒ operating mode. Apr/May 08
14. i) Write short note on series resonant inverter.
ii) Explain how inverter can be controlled using multiple and sine PWM techniques. Apr/May 08

UNIT V
APPLICATIONS

PART – A
1. Name the various configurations of UPS. Nov/Dec 06
2. State the merit merits of HVDC transmission Nov/Dec 06
3. What is principle role of FACTS? May/Jun 07
4. What is static VAR compensator? May/Jun 07
5. Mention the different types of HVDC link. Nov/Dec 07
6. List the parameters for controlling power in a transmission line. Nov/Dec 07
7. What is off-line UPS? Apr/May 08
8. Name any two types of FACTS devices. Apr/May 08

PART – B
1. What is an UPS? Describe the no-break static UPS configuration with block diagram. Nov/Dec 06, 07
2. Write technical notes on HVDC transmission. Nov/Dec 06
3. Write short notes on static VAR compensator. Nov/Dec 06, 08
4. With neat block diagrams explain the working principle of off – line and online UPS. May/Jun 07, 08
5. Draw the circuit diagram of UPS system in which a single circuit operates as a rectifier to change the battery when main supply is available and the same circuit act as inverter when main supply is not available. May/Jun 07
6. Write short notes on May/Jun 07, 08
i. Shunt static VAR compensator.
ii. Unified power flow controller (UPFC).

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