Variable Frequency Drive Speed Control

Variable-frequency drives, also known as VFDs, are affordable, reliable controllers with the ability to adjust the speed of induction motors for optimal performance. VFDs are becoming standard equipment for powering small to large motors in fans, pumps, compressors, drills, and many other applications. Unlike fixed speed controllers, which instantly turn on a motor to full speed, VFDs can soft start a motor by gradually increasing speed to the desired level. Soft starts eliminate high starting torques and surge currents, reduce mechanical stresses, and increase equipment life and reliability. Furthermore, because loads torque and power vary with the square and cube of speed respectively, adjusting motor speed by even a small amount can save considerable energy. This video will demonstrate the configuration of a variable-frequency drive and its use in the control of a three-phase AC induction motor.

An AC induction motor has only two main parts, the stator and the rotor, and most commonly uses three-phase AC power. Three-phase current through the stator coils generates a stator magnetic field, which rotates with a angular velocity proportional to the AC frequency. This stator magneti