Adaptive direct torque control of induction motors

Abstract

In direct torque control (DTC), many induction motor parameters are needed, especially those that affect the values of current and flux required in the control algorithm. DTC of induction machines presents an acceptable tracking scheme for both electromagnetic torque and stator flux. This control scheme depends only on stator measurements. The measurement of the stator flux is very difficult to achieve and can be estimated by an observer. The electromagnetic torque and the stator flux (magnitude and angle) can be determined despite their direct dependence on the knowledge of the stator resistance. This resistance can change up to 180percent of its nominal value. The resistance changes with the operational conditions of the motor, such as temperature and frequency. Under these circumstances, a parameter identifier is developed to account for the resistance variations, hence establishing adaptive DTC (ADTC). Moreover, load torque represents the changing tasks required from the motor. In this article, the load torque variations are coupled with stator resistance changes, and the effectiveness of ADTC is investigated. More stable motor operations of polyphase induction motors are obtained under these uncertainties using ADTC.