Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT. Variable frequency drives (VFDs) are a type of adjustable speed drive, which are becoming standard equipment to power most AC induction motors. VFDs are common in industrial and automation applications and typically provide robust control of the motor in speed, torque, or position modes. The VFDs tested and simulated in this experiment focus on speed and open-loop control with constant voltage to frequency ratio (V/f) control. The induction motor typically operates at a rated stator flux, and this flux is approximately proportional to the V/f ratio. To maintain constant stator flux, the voltage and frequency applied to the stator are maintained at a constant ratio, which is the V/f ratio. The VFD used in this experiment is a 1 hp Yaskawa V1000 drive, but the procedure applies to most commercially available general purpose drives.