A 3-phase VFD (Variable Frequency Drive) works by converting fixed-frequency, fixed-voltage AC power into a variable-frequency, variable-voltage output to control the speed and torque of a 3-phase AC motor. In basic terms, it takes normal 3-phase supply power, processes it electronically inside the drive, and delivers controlled power to the motor — allowing it to run faster or slower as needed.
The operation happens in three main stages: Rectification, DC Bus, and Inversion. In the first stage, the incoming 3-phase AC power is converted to DC using a rectifier made of diodes or transistors. This produces a steady DC voltage, which is then filtered and stored in capacitors on the DC bus. This section smooths the power and prepares it for the next stage.
Next, the inverter section uses high-speed electronic switches called IGBTs (Insulated Gate Bipolar Transistors) to convert the DC power back into AC — but now with a variable frequency and voltage. By changing the switching pattern of these IGBTs, the VFD creates a Pulse Width Modulated (PWM) output that controls motor speed precisely. Higher frequency means higher speed; lower frequency means slower speed.
Finally, the 3-phase VFD maintains a proper voltage-to-frequency (V/F) ratio to ensure the motor develops the required torque at any speed. This technology allows soft starting, smooth acceleration, and efficient energy use while reducing mechanical stress and extending equipment life. In short, a 3-phase VFD works by electronically reshaping the incoming power to give full control over how a 3-phase motor runs — improving performance, safety, and efficiency in industrial applications.