Direct torque control of induction motor with extended Kalman filter

Induction motor speed control is an area of research that has been in prominence for some time now. Recent advances in this field have made it possible to replace the DC motor by induction machines, even in applications that demand a fast dynamic response. Many industrial applications demand high performance speed sensorless operation due to various reasons. Direct torque control (DTC) of induction motors is a popular method because of the resulting fast dynamic response of the motor, lower sensitivity to motor parameter variations and relatively low switching harmonics in the inverter. However, the present DTC approach is unsuitable for high-performance applications, especially at very low speeds, because of the need of a speed sensor for increased accuracy, system and measurement noises, and absence of any error decay mechanism. In this paper, an extended Kalman filter (EKF) is designed for stator flux and speed estimation. Estimated values along with other measured states are used for the closed loop speed sensorless control operation of the induction motor. At low speeds, where noise is predominant, performance is improved due to the filtering action of the EKF. Simulations are performed and the results discussed.