Improved Direct Torque Control strategy for Wide Range Speed Control of Induction Motor Drives

Abstract

Induction Motor is popular option for most of the drives applications. It has simple construction but complex control. DC motor like decoupled control of induction motor drives similar to Field Oriented control is possible using Direct Torque Control (DTC) method which is very simple control strategy compared to vector control. The DTC strategy is very useful for automobile and traction applications using IM but due to use of hysteresis band controllers, DTC has problems of torque ripples, variable switching frequency and poor low speed performance. Because of these reasons, DTC is used in such applications for high speed range and not for the whole speed range. An improved DTC strategy suitable for wide range speed control is suggested in this paper which is based on a performance index calculated on the basis of what is the value of THD of stator current, value of operating speed and switching frequency. It uses new five level variable width torque hysteresis band controller and two level variable width hysteresis band flux controller along with new hybrid model for stator flux estimation. This improved strategy is designed to maintain simplicity of conventional DTC and give better performance than it. This new strategy is simulated using Matlab/Simulink