A VFD controls motor speed by changing what parameter?

A VFD controls motor speed by changing what parameter?

• A. Voltage only
• B. Frequency in hertz
• C. Temperature
• D. Direction

Answer: (B)

VFDs regulate motor speed by changing the frequency of the power delivered to the motor. For an AC induction motor, the speed is tied to the supply frequency (synchronous speed = 120 × f / number of poles). So increasing frequency raises speed, while decreasing frequency lowers it. The drive may also adjust voltage to maintain a constant V/Hz ratio to keep torque, but the actual speed setting comes from the frequency. Temperature is not used to set speed, and direction is controlled by the drive’s output configuration, not the speed parameter.

VFDs regulate motor speed by changing the frequency of the power delivered to the motor. For an AC induction motor, the speed is tied to the supply frequency (synchronous speed = 120 × f / number of poles). So increasing frequency raises speed, while decreasing frequency lowers it. The drive may also adjust voltage to maintain a constant V/Hz ratio to keep torque, but the actual speed setting comes from the frequency. Temperature is not used to set speed, and direction is controlled by the drive’s output configuration, not the speed parameter.