What does a Variable Frequency Drive (VFD) do?

What does a Variable Frequency Drive (VFD) do?

• A. Converts DC to DC
• B. Rectifies AC to DC
• C. Controls speed of AC motors by adjusting frequency
• D. Increases motor voltage for overload protection

Answer: (C)

A Variable Frequency Drive changes how fast an AC motor runs by adjusting the frequency of the power it supplies. The motor speed is tied to the supply frequency, so increasing frequency speeds the motor and decreasing frequency slows it. Inside, the VFD first converts incoming AC to DC and then inverts that DC back to AC at the desired frequency and voltage, keeping the voltage proportional to frequency to maintain torque. This means the device’s primary function is speed control through frequency adjustment, with voltage adjustments supporting smooth operation, not simply boosting voltage for overload protection.

A Variable Frequency Drive changes how fast an AC motor runs by adjusting the frequency of the power it supplies. The motor speed is tied to the supply frequency, so increasing frequency speeds the motor and decreasing frequency slows it. Inside, the VFD first converts incoming AC to DC and then inverts that DC back to AC at the desired frequency and voltage, keeping the voltage proportional to frequency to maintain torque. This means the device’s primary function is speed control through frequency adjustment, with voltage adjustments supporting smooth operation, not simply boosting voltage for overload protection.