Direct torque control of induction motors using fuzzy variable switching sector

The direct torque control (DTC) scheme provides very quick torque response without the complex field-orientation block and inner current control loop. DTC is known as an appropriate scheme for high power induction motor drives because it can be used at lower switching frequency. There are two major drawbacks with the application of DTC schemes : flux drooping in low speed range and time varying inverter switching frequency. In this paper, a fuzzy variable switching sector scheme to prevent flux drooping, and a fuzzy switching frequency regulator for lowering the switching frequency are proposed and adopted in the DTC based induction motor drive system. An important contribution of this paper is the proposition of simple realization schemes of the fuzzy switching frequency regulator and the fuzzy variable switching sector.