APEC PREVIOUS PAPERS(2010-2012)

                                                      APRIL 2012

           ANALYSIS OF POWER ELECTRONIC CONVERTERS

                 

1. What is the principle of operation of cyclo converters? What is the effect of load inductance on the performance of cyclo converter?

2. The load of an ac voltage controller is resistive, with R = 1.5Ω. The input voltage is 120V (rms), 60 Hz. Plot the PF against the delay angle for single phase half wave and full wave controllers.

3. Explain the operation of a three – phase, full converter with inductive load using necessary circuit diagram and wave forms.

4. Using neat circuit diagrams and necessary wave forms, explain the operation of Buck regulators. And also derive the necessary condition for continuous inductor current and capacitor voltage.

5.a) Explain the principle of operation of a single phase half bridge inverter with Resistive load.

b) The single phase, half - bridge inverter has a resistive load of R = 2.4 and the input voltage VΩ_s = 48V. Determine

i) RMS output voltage. ii) Output power

iii) Average and peak currents of each thyrister. iv) The THD

v) Distortion Factor.

6.a) Explain the operation of twelve pulse converter.

b) A three phase full converter is operated from a three – phase, 230V, 60Hz supply. The load is highly inductive and the average load current is I_a = 150A with negligible ripple. If the delay angle is α = 60⁰ Determine the ratings of thyristors.

7.a) Explain in detail the space vector Modulation.

b) What are the advantages of space vector Modulation?

8. Write a short notes on the following.

a) Sinusoidal PWM

b) Multi output boost converters

c) Delta Modulation.

                            April 2011 NR r09

           ANALYSIS OF POWER ELECTRONIC CONVERTERS

1. a) Explain the operation of 1-φ voltage controller with RL-load with neat circuit and

wave forms.

b) Discuss the concept of synchronous tap changes. [12]

2. A 3-phase, 3-wire AC regulator supplies a star connected resistive load of R=10.0

ohm and line to line input voltage is 230 V (rms), 50 Hz. The firing angle is 300.

Determine:

i) rms output voltage.

ii) Input power factor

iii) Expression for instantaneous output voltage of phase R. [12]

3. A single phase voltage controller feeds power to a resistive load of 3 Ω from

230V, 50 Hz source. Calculate:

i) The maximum values of average and rms thyristor currents for any firing

angle, ‘α ’.

ii) The minimum circuit turn-off time for any firing angle,α .

iii) The ratio of 3rd harmonic voltage to fundamental voltage for 3

α =π

iii) The angle, `α ’ at which the greatest forward or reverse voltage is applied

to either of the thyristors and magnitude of these voltages. [12]

4. Explain the operation of dual converter both circulating and non circulating

modes of operation. Mention its applications, advantages and disadvantages.

[12]

5. What is pulse width modulation control of converters and what are the

applications? A single phase full converter is connected to RLE load. The source

voltage is 230 V, 50 Hz. The average load current of 10A is continuous over the

working range. For R=0.4 Ω and L = 2mH, compute the firing angle delay for

E=120 V. [12]

6. A three-phase, half wave converter is operated from a 3-phase, Y-connected

440 V, 50 Hz supply and the load resistance is R = 20 Ω . If it is required to obtain

an average output voltage of 50% of the maximum possible output voltage,

calculate:

a) Firing angle, α .

b) rms and average output currents.

c) Rectification efficiency.

d) Input power factor. [12]

7. Discuss about switched mode regulators. Explain the operation of buck and boost  regulators. Mention the applications and advantages of these regulators. [12]

8. Write about:

i) Single phase bridge inverter.

ii) Harmonic reduction techniques.

                      APRIL  2011 NOVEBER  NR-R09

           ANALYSIS OF POWER ELECTRONIC CONVERTERS

 1. a) Explain the operation of 1-φ voltage controller with R-load with neat circuit and wave forms.

b) Explain two stage sequence control of voltage controller for R-load. [12]

2. A 3-phase, 3-wire AC regulator supplies a star connected resistive load of R=10.0 ohm, and line to line input voltage is 230 V (rms), 50 Hz. The firing angle is 300. Determine:

i) rms output voltage.

ii) Input power factor

iii) Expression for instantaneous output voltage of phase R. [12]

3. A single phase AC voltage regulator feeds a R-L load with the following parameters. Input voltage = 230V (rms), frequency = 50 Hz, resistance R=4 ohms and inductance L = 10 mH. Calculate:

i) The control range of firing angle,

ii) The maximum value of rms load current,

iii) The maximum power and power factor. [12]

4.a) What is a Cyclo converter? Explain the principle and operation of single phase cyclo converter with neat diagram and wave forms.

b) What are the applications of cyclo converter? What are the effects of load inductance on the performance of cyclo converters? [12]

5. A single phase fully controlled thyristor bridge converter supplies on inductive load. Assuming that the output current is virtually constant and is equal to Id, determine the following performance measures, if the supply voltage is 230 V and if the firing angle is maintained at 600.

a) Average output voltage,

b) Input rms current and input fundamental rms current,

c) Displacement factor and power factor,

d) Supply harmonics factor and voltage ripple factor. [12]

6. A 3-phase, fully controlled bridge converter is connected to a three phase AC supply of 400 V, 50 Hz and operates at a firing angle of 450. The load current is maintained constant at 10A and load voltage is 360 V. Compute

a) Source inductance

b) Load inductance

c) Overlap angle

d) If the source inductance is reduced to half, find the output voltage. [12]

7. Discuss about switched mode regulators. Explain the operation of buck and boost regulators. Mention the applications and advantages of these regulators. [12]

8. Explain the voltage control of single phase inverters with the help of waveforms.

                   

                                        APRIL 2010 NOVEBER

                       ANALYSIS OF POWER ELECTRONIC CONVERTERS

1. A synchronous tap changer is having primary voltage 240V(rms), 60Hz. The

secondary voltages are V1=120V andV2 =120V. If the load resistance is R = 0Ω and the rms load voltage is 180V. The delay angle is α = 49π/90 = 980. Determine the rms currents of T1, T2, T3, T4 thyristors.

2. With necessary waveforms explain the operation of a three phase star connected ac  voltage controller for a firing angle of α = 300.

3. (a) Analyze a three phase to three phase cycloconverter with midpoint configuration.

(b) What are the advantages of a cycloconverter?

4. A single-phase full converter with a highly inductive load so that the load current is continuous and ripple free is connected to a 120V, 60Hz supply. The turn’s ratio of

the transformer is unity.

(a) Express the input current in a Fourier series; determine the HF of the input

current, DF and input PF.

(b) If the delay angle is α = π/3, calculate Vdc, Vrms, HF, DF, PF.

5. Explain the operation of a Cuk regulator. Derive the expressions for critical values of  inductances and capacitances.

6. Explain about the phase displacement control and advanced harmonic injection

modulation of a single phase inverter.

7. With necessary waveforms explain the 1200 conduction of a three phase bridge

inverter.

8. (a) What are the different ways of combining two 6-pulse bridge converters to

produce an effective 12-pulse output?

(b) Explain the various parameters on which the quality of an inverter is normally

evaluated.

                                    APRIL 2010 APRIL

           ANALYSIS OF POWER ELECTRONIC CONVERTERS

1. a) Explain the operation of a single phase ac voltage controller with RL load by

drawing the necessary waveforms.

b) Also explain the operation when firing angle α is less than load phase angle

φ ( α<φ ).

2. With necessary waveforms explain the operation of a three phase star connected

ac voltage controller.

3. a) Explain the operation of a single phase step down cycloconverter.

b) What are the advantages, disadvantages and applications of a cycloconverter?

4. a) Explain the operation of a single phase dual converter.

b) Explain the techniques of extinction angle control and symmetrical angle control

for the improvement of power factor of phase controlled converters.

5. a) What are the different ways of combining two 6-pulse bridge converters to

produce an effective 12-pulse output?

b) The load current of a three phase full converter is continuous with a negligible

ripple content. Express the input current in Fourier series and determine the HF of

input current, the DF and the input pf .

6. a) Explain the operation of a Buck regulator. Derive the expressions for the critical

values of inductance and capacitance.

b) A Buck regulator has an input voltage of Vs=12 V. The required average output

voltage is Va=5 V at R=500Ω and the peak-to-peak output ripple voltage is 20mv.

The switching frequency is 25 KHz. If the peak-to-peak ripple current of inductor

is limited to 0.8A.

Determine a) The duty cycle K b) Fitter Inductance L

c) Filter capacitance C d) Critical values of L and C.

7. Explain the single PWM, multiple PWM, and sinusoidal PWM and modified

sinusoidal  PWM techniques of a single phase inverter.

8. With necessary waveforms explain the 1800 conduction of a three-phase bridge inverter.