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Audible noise from a PWM drive is reduced by

  • A.raising the switching frequency above the audible range
  • B.lowering the switching frequency towards a few hundred hertz
  • C.removing the dc link capacitor from the drive
  • D.increasing the dead time between switching transitions

Answer: A

Magnetostriction in the machine's iron at the switching frequency is what produces the whine, so moving it above about fifteen kilohertz removes it. The penalty is switching loss, and random or spread-spectrum modulation is the compromise where the loss cannot be afforded.

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