VFD varies the revolving speed of an induction motor freely by changing the power supply frequency and the power supply voltage. A power transistor is used for the main circuit and IC, and a microcomputer is used for the control circuit of VFD.
Further advanced controlling technology has been applied due to improved semiconductor devices in recent years.
Moreover, generally, VFD is also called inverter control equipment or variable voltage variable frequency (VVVF) equipment.
The fundamental configuration is shown in Figure.
After changing an alternating power source into direct current in a converter part and making it smooth, transform the direct current inversely to variable frequency alternating current at an inverter part.