Power Electronics and Drives MCQs

1. What is the primary function of a rectifier in power electronics?
A. Voltage regulation
B. Current regulation
C. AC to DC conversion
D. DC to AC conversion
Answer: C

2. Which semiconductor device is commonly used as a switch in power electronic circuits?
A. Diode
B. Bipolar Junction Transistor (BJT)
C. Light Emitting Diode (LED)
D. Thyristor
Answer: B

3. In a buck converter, the output voltage is _____ than the input voltage.
A. Higher
B. Lower
C. Equal to
D. Unpredictable
Answer: B

4. A chopper circuit is used primarily for:
A. Stepping up DC voltage
B. Stepping down DC voltage
C. AC to DC conversion
D. DC to AC conversion
Answer: B

5. Which of the following is a unidirectional semiconductor device?
A. MOSFET
B. IGBT
C. Diode
D. BJT
Answer: C

6. In an H-bridge inverter circuit, how many switches are operated simultaneously to generate AC output?
A. 1
B. 2
C. 3
D. 4
Answer: D

7. The term ‘PWM’ in power electronics stands for:
A. Power Width Modulation
B. Pulse Width Modulation
C. Parallel Width Modulation
D. Period Width Modulation
Answer: B

8. Which of the following is not a type of electric drive?
A. DC drive
B. AC drive
C. Brushless DC drive
D. Mechanical drive
Answer: D

9. In a synchronous motor drive system, the speed of the motor is controlled by adjusting the:
A. Stator voltage
B. Rotor voltage
C. Frequency of the supply
D. Number of poles
Answer: C

10. A VFD (Variable Frequency Drive) is used for controlling the speed of:
A. DC motors only
B. AC motors only
C. Both DC and AC motors
D. None of the above
Answer: B

11. What is the function of a freewheeling diode in a thyristor-based circuit?
A. Prevents over-voltage
B. Prevents over-current
C. Allows reverse current
D. Allows forward current
Answer: D

12. The efficiency of a power electronic converter is highest when:
A. Operating at low load
B. Operating at full load
C. Operating at half load
D. Efficiency is independent of load
Answer: B

13. The term ‘IGBT’ stands for:
A. Insulated Gate Bipolar Transistor
B. Integrated Gate Bipolar Transistor
C. Isolated Gate Bipolar Transistor
D. Insulated Gate Basic Transistor
Answer: A

14. Which of the following is a disadvantage of using IGBTs compared to MOSFETs?
A. Higher switching losses
B. Higher gate drive power
C. Lower input impedance
D. Slower switching speed
Answer: D

15. The commutation process in a DC motor drive refers to:
A. Changing the direction of rotation
B. Switching off the motor
C. Transitioning from one pair of devices to another
D. Controlling the speed
Answer: C

16. A DC chopper is used for:
A. AC to DC conversion
B. DC to AC conversion
C. DC voltage control
D. AC voltage control
Answer: C

17. A cycloconverter is used for:
A. Stepping up voltage
B. Stepping down voltage
C. AC to DC conversion
D. AC voltage control
Answer: B

18. The function of a snubber circuit in power electronics is to:
A. Protect against over-voltage
B. Protect against over-current
C. Suppress voltage transients
D. Suppress current transients
Answer: C

19. Which of the following is a disadvantage of using a diode rectifier?
A. High rectification efficiency
B. High harmonic content in output
C. Low ripple factor
D. Low voltage drop
Answer: B

20. The term ‘IGCT’ stands for:
A. Integrated Gate Commutated Thyristor
B. Insulated Gate Controlled Thyristor
C. Insulated Gate Commutated Transistor
D. Integrated Gate Controlled Transistor
Answer: A

21. In a DC-DC boost converter, the output voltage is _____ than the input voltage.
A. Higher
B. Lower
C. Equal to
D. Variable
Answer: A

22. Which type of semiconductor switch is typically used in high-power applications due to its robustness and ability to handle high currents?
A. IGBT
B. MOSFET
C. SCR
D. TRIAC
Answer: A

23. Which of the following is NOT a component of a typical VFD system?
A. Rectifier
B. Inverter
C. Transformer
D. Controller
Answer: C

24. A regenerative braking system in electric drives is used to:
A. Increase speed
B. Decrease speed
C. Generate electricity
D. Store energy
Answer: C

25. The term ‘PWM’ in the context of motor drives refers to:
A. Power Width Modulation
B. Pulse Width Modulation
C. Parallel Width Modulation
D. Period Width Modulation
Answer: B

26. Which of the following is a disadvantage of using a PWM technique in motor control?
A. Reduced efficiency
B. Increased harmonic distortion
C. Limited speed control
D. Lower torque output
Answer: B

27. In a closed-loop speed control system of an electric drive, the speed feedback is typically obtained from:
A. Tachometer
B. Encoder
C. Potentiometer
D. Rheostat
Answer: B

28. Which type of motor drive is known for its high efficiency, quiet operation, and maintenance-free operation?
A. DC drive
B. Induction motor drive
C. Stepper motor drive
D. Synchronous motor drive
Answer: B

29. In a three-phase inverter, how many switches are operated simultaneously to generate a phase of AC output?
A. 1
B. 2
C. 3
D. 6
Answer: C

30. A DC motor drive using a four-quadrant chopper circuit allows:
A. Only forward motion
B. Only reverse motion
C. Both forward and reverse motion
D. Variable speed operation
Answer: C

31. Which of the following motor types requires an electronic drive for operation?
A. Universal motor
B. Synchronous motor
C. Series DC motor
D. Induction motor
Answer: B

32. A flyback diode is used across an inductive load in power electronics to:
A. Protect against over-voltage
B. Protect against over-current
C. Suppress voltage spikes
D. Suppress current spikes
Answer: C

33. The term ‘commutation’ in power electronics refers to:
A. Switching on a device
B. Switching off a device
C. Transferring conduction from one device to another
D. Controlling current flow
Answer: C

34. Which of the following is a characteristic of a soft starter used in motor control?
A. Provides step-up voltage
B. Provides step-down voltage
C. Reduces starting torque
D. Increases starting torque
Answer: C

35. The term ‘snubber circuit’ is used in power electronics to:
A. Limit the voltage
B. Limit the current
C. Limit the rate of change of voltage
D. Limit the rate of change of current
Answer: C

36. A buck-boost converter is used to:
A. Increase voltage
B. Decrease voltage
C. Increase or decrease voltage
D. Convert AC to DC
Answer: C

37. Which of the following is a characteristic of an ideal switch in power electronics?
A. High on-state voltage drop
B. High off-state leakage current
C. Low conduction losses
D. Low switching speed
Answer: C

38. A cycloconverter is typically used for:
A. Fixed frequency AC output
B. Variable frequency AC output
C. DC output
D. High voltage DC output
Answer: B

39. In a DC chopper circuit, the duty cycle of the chopper refers to:
A. Ratio of on-time to off-time
B. Ratio of off-time to on-time
C. Total time of operation
D. Peak voltage value
Answer: A

40. Which of the following devices is used for regenerative braking in an electric vehicle?
A. Battery
B. Capacitor
C. Flywheel
D. Motor generator
Answer: D

41. In a thyristor-based AC voltage controller, firing angle control allows adjustment of:
A. Frequency
B. Voltage magnitude
C. Current
D. Power factor
Answer: B

42. Which type of converter is used to provide isolation between the input and output in power electronic circuits?
A. Boost converter
B. Flyback converter
C. Buck-boost converter
D. Forward converter
Answer: B

43. The term ‘snubber circuit’ is typically used to reduce:
A. Voltage spikes
B. Current spikes
C. Both voltage and current spikes
D. Power dissipation
Answer: A

44. Which type of motor drive is known for its precise positioning capability and is commonly used in robotics?
A. DC drive
B. Induction motor drive
C. Stepper motor drive
D. Synchronous motor drive
Answer: C

45. The efficiency of a power electronic converter is typically highest when operating at:
A. Full load
B. Half load
C. No load
D. Overload
Answer: A

46. A soft starter is used in motor control to:
A. Provide step-up voltage
B. Provide step-down voltage
C. Reduce starting torque
D. Increase starting torque
Answer: C

47. The term ‘snubber circuit’ in power electronics is used to dampen:
A. Voltage oscillations
B. Current oscillations
C. Both voltage and current oscillations
D. Voltage and current harmonics
Answer: A

48. In a PWM-based inverter, the width of the PWM pulses determines the:
A. Amplitude of the output voltage
B. Frequency of the output voltage
C. Phase angle of the output voltage
D. Harmonic content of the output voltage
Answer: A

49. A DC chopper circuit is used primarily for:
A. AC to DC conversion
B. DC to AC conversion
C. DC voltage control
D. AC voltage control
Answer: C

50. Which type of semiconductor switch is characterized by bidirectional conduction capability?
A. IGBT
B. MOSFET
C. SCR
D. TRIAC
Answer: D

Power Electronics and Drives MCQs

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