Home › MCQs › Electronics Engineering › Question #11723
Back to Questions
Electronics Engineering QUESTION #11723
Question 1
A VFD drives an induction motor. What is the primary reason VFDs use PWM (Pulse Width Modulation) rather than direct AC voltage variation?
  • PWM reduces bearing wear by increasing output frequency
  • PWM creates a near-sinusoidal fundamental current through motor inductance while controlling average voltage efficiently✔️
  • PWM eliminates the need for an input rectifier stage
  • PWM reduces the DC bus capacitor size
Correct Answer Explanation
VFDs use PWM to switch the DC bus voltage at high frequency (typically 2–16 kHz) with varying pulse widths. The motor's inherent inductance integrates (filters) these pulses, producing a near-sinusoidal fundamental current at the desired output frequency. This achieves variable voltage and frequency with minimal harmonic distortion and high switching efficiency.