What is a Variable Frequency Drive (VFD)?

• A. Variable Frequency Drive - Controls a motor's speed by varying voltage and frequency
• B. Voltage Frequency Device - Measures frequency of supply
• C. Very Fast Drive - Increases torque
• D. Vacuum Fluid Device - Pumps liquid

Answer: (A)

A Variable Frequency Drive is a device that controls an AC motor’s speed by changing the frequency of the electrical supply to the motor, and typically adjusting the voltage as well to keep the motor’s torque consistent. By increasing the frequency, the motor spins faster; lowering the frequency slows it down. Keeping the voltage proportional to the frequency (the V/Hz ratio) helps maintain usable torque across speeds and improves energy efficiency, soft-start, and precise speed control.

The other descriptions aren’t accurate: one defines something that would only measure or describe frequency rather than drive motor speed, another uses a nonstandard or misleading name, and the last describes something unrelated to motors altogether.