Red Seal Electrician Practice
Motor controlsQuestion 1278 of 1506

What does the pulse width modulated inverter in a variable speed drive do?

  1. It filters the line voltage into a pure and smooth DC level.
  2. It steps the line voltage up with a small built-in transformer.
  3. It removes the need to change frequency for speed control.
  4. It builds a sine wave by switching the output on and off.
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Correct answer: It builds a sine wave by switching the output on and off.

The on time of each pulse follows the instantaneous sine wave voltage.

Source: Lessons in Electric Circuits II: AC (Kuphaldt), 13.7: Tesla Polyphase Induction Motors

Practice motor controls

Questions last reviewed: 18 October 2026