What is the primary function of a Variable Frequency Drive (VFD) in electrical systems?

• A. To convert AC to DC.
• B. To regulate voltage for lights.
• C. To control motor speed.
• D. To measure electrical resistance.

Answer: (C)

The primary function of a Variable Frequency Drive is to control motor speed by varying the frequency (and corresponding voltage) supplied to an AC motor. By adjusting the output frequency, the motor’s rotational speed can be matched to the load, enabling smooth starts, precise speed control, and energy savings when running at lower speeds. Inside a VFD, the incoming AC is converted to DC, then inverted back to AC at the desired frequency and voltage to drive the motor.

Other options don’t fit as the main role. Converting AC to DC happens inside the device, but that’s a means to enable speed control, not the main purpose. Regulating voltage for lights is outside the typical use of a VFD, which is about motors. Measuring electrical resistance is the job of a meter, not a VFD.