VFD

A Variable Frequency Drive (VFD), also known as an adjustable-frequency drive or inverter, is an electronic device used to control the speed and torque of an AC induction motor. It does this by varying the frequency and voltage supplied to the motor.

Unlike a direct-on-line starter that runs the motor at full speed (matching the fixed line frequency, e.g., 50/60 Hz), a VFD allows smooth, stepless speed adjustment from zero to above rated speed. It follows the principle that motor speed is proportional to input frequency.

A VFD typically has three sections: a rectifier (converts AC to DC), a DC bus (filters and stores energy), and an inverter (switches DC back to variable-frequency AC using IGBTs). The output is a pulse-width modulated (PWM) waveform that mimics a clean sine wave.

Benefits include significant energy savings (especially for pumps and fans), reduced mechanical stress, soft starting/stopping, and improved process control.

Common applications: HVAC fans and pumps, conveyors, machine tools, cranes, elevators, and industrial washing machines. Anywhere you need to match motor speed to a load requirement, a VFD improves efficiency and performance.