Variable Frequency Drive

Variable Frequency Drive

How to Maintain a Variable Frequency Drive

By Dave Polka, Drives Training Instructor, ABB, Inc., New Berlin, WI

Do you know how to maintain Variable Frequency Drives (VFDs)? Doing so is easier than you might think. By integrating some simple, logical steps into your preventative maintenance program, you can ensure your drives provide many years of trouble-free service. Before looking at those steps, let’s quickly review what a VFD is and how it works. 


A VFD controls the speed, torque and direction of an AC Induction motor. It takes fixed voltage and frequency AC input and converts it to a variable voltage and frequency AC output. In very small VFDs, a single power-pack unit may contain the converter and inverter. Fairly involved control circuitry coordinates the switching of power devices, typically through a control board that dictates the firing of power components in the proper sequence. A microprocessor or Digital Signal Processor (DSP) meets all the internal logic and decision requirements.

From this description, you can see a VFD is basically a computer and power supply. And the same safety and equipment precautions you would apply to a computer and to a power supply apply here. VFD maintenance requirements fall into three basic categories: