What parameter does a VFD vary to control the speed of an AC motor?

Master the Motor Controls Level 3 Test. Engage with flashcards and detailed multiple-choice questions, complete with hints and thorough explanations. Prepare effectively for your exam!

Multiple Choice

What parameter does a VFD vary to control the speed of an AC motor?

Explanation:
VFDs control motor speed by changing the output frequency. The rotor speed of an AC motor is tied to how fast the magnetic field rotates, which is set by the supply frequency (synchronous speed is proportional to frequency and inversely proportional to the number of poles). By increasing or decreasing the frequency, the drive directly sets the motor’s speed. To keep torque consistent, the VFD also adjusts voltage in proportion to frequency (the V/Hz relationship) so flux stays relatively constant. While torque and current relate to the motor’s ability to handle load, they are responses rather than the primary means of speed control in a VFD.

VFDs control motor speed by changing the output frequency. The rotor speed of an AC motor is tied to how fast the magnetic field rotates, which is set by the supply frequency (synchronous speed is proportional to frequency and inversely proportional to the number of poles). By increasing or decreasing the frequency, the drive directly sets the motor’s speed. To keep torque consistent, the VFD also adjusts voltage in proportion to frequency (the V/Hz relationship) so flux stays relatively constant. While torque and current relate to the motor’s ability to handle load, they are responses rather than the primary means of speed control in a VFD.

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