Variable Frequency Drives and Power Factor

Variable frequency drives are being used in many applications which were previously fixed speed induction motor applications. The predominant ones are centrifugal pumps and fans where substantial energy savings can be realized with adjustable speed operation. The power factor of variable frequency drives when applied to centrifugal pumps and fans is discussed. The power factor characteristics of the three most commonly used controllers¿variable voltage input (VVI), current source input (CSI), and pulsewidth modulated (PWM)¿will be reviewed in detail. Also application guidelines on selection and installation of power factor correction capacitors will be reviewed.