Power Electronics Inverter MCQ

21. A PWM switching scheme is used with a three-phase inverter to

1. reduce low order harmonics and increase high order harmonics
2. increase the life of the batteries
3. minimize the load on the DC side
4. reduce the total harmonic distortion with modest filtering

22. In a PWM inverter, f_o and f are the frequencies in Hz for the carrier signal and reference signal respectively. Then the number of pulses per half cycle is

1. N = f/f_o
2. N = f/2f_o
3. N = f_o/2f
4. N = f_o/f

23. A constant current source inverter supplies 20 A to a load resistance of 1 Ω to a load resistance change to 5 Ω, then the load current

1. remains same at 20 A and the load voltage changes to 100 V
2. changes to 4 A from 20 A and the load voltage changes to 20 V
3. changes to 4 A from 20 A and the load voltage changes to 80 V
4. and load voltage stay at 20 A and 20 V respectively

24. In single pulse modulation of PWM inverters, the pulse width is 120°. For an input voltage of 220 V dc, what is the rms value at the fundamental component of the output voltage?

1. 89.81 V
2. 127 V
3. 254 V
4. 171.5 V

25. What is the effect of blanking time on output voltage in PWM inverter?

1. Distortion in instantaneous voltage at current zero crossing
2. low order space harmonics in output voltage
3. distribution in instantaneous voltage at voltage zero crossing
4. high order time harmonics in output voltage

26. For elimination of 5^th harmonics from the output of an inverter, what will be the position of pulse in a PWM inverter?

1. 90°
2. 60°
3. 36°
4. 72°

27. Consider the following statements, with respect to the power transistors used in inverters:

1. maximum collector-emitter voltage V_CEO
2. maximum power dissipation
3. maximum current gain at minimum load current
4. maximum current gain at maximum load current

Which of these statements is/are correct?

1. i only
2. i, ii, iii and v
3. ii and iii only
4. ii, iii and iv

28. Consider the following statements:

1. both voltage source inverter and current source inverter require feedback diodes.
2. only current source inverter requires feedback diodes.
3. GTOs can not be used in a current source inverter
4. only voltage source inverter requires feedback diodes

Which of these statements is/are correct?

1. i only
2. ii and iii
3. iii and iv
4. iv only

29. The pulse-width modulated inverter for the control of an ac motor is fed from which one of the following?

1. cycloconverter
2. ac regulator
3. uncontrolled rectifier
4. controlled rectifier

30. In a three-phase voltage source inverter operating in square wave mode, the output line voltage is free from

1. 13^th harmonic
2. 11^th harmonic
3. 7^th harmonic
4. 3^rd harmonic

31. A d.c. source is switched in steps to synthesize the three-phase output. The basic three-phase bridge inverter can be controlled. The angle through which each switch conducts, and at any instant, the number of switches conducting simultaneously is, respectively

1. 180° and 04
2. 180° and 02
3. 120° and 03
4. 120° and 02

32. The operation of an inverter fed induction motor can be shifted from motoring to regenerative braking by

1. increasing inverter frequency
2. decreasing inverter frequency
3. reducing inverter frequency
4. reversing inverter frequency

33. PWM switching is preferred in voltage source inverters for the purpose of

1. controlling output voltage, output harmonics and reducing filter size
2. reducing filter size
3. output harmonics
4. controlling output voltage

34. Modified McMurray full-bridge inverter works on

1. complementary commutation
2. load commutation
3. current commutation
4. voltage commutation

35. In a McMurray inverter, diodes are connected in inverse parallel to thyristors to

1. protect the thyristor
2. make the turn off of the thyristor successful
3. make the turn on of the thyristor successful
4. provide path to the reactive component of the load current

Which of the above statements are correct?

1. i and iii
2. i and iv
3. ii and iv
4. ii and iii