Original direct torque control strategy for speed-sensorless induction motors using extended Kalman filtering

In the framework of direct torque control (DTC) for induction machines, an original control strategy is developed to improve the drive performances. The latter is based on a two band hysteresis controller for the torque, and a one band hysteresis controller for the stator flux. This method provides additional degrees of freedom to adjust the inverter frequency and to control the torque ripple. Furthermore, a particular state observer based on the principle of extended Kalman filtering is developed. It is composed of a fast task to predict and filter the state variables, and a slow task to calculate the very complex covariance and gain matrix. Significant experimental results are discussed to demonstrate the good performances obtained with this particular observer in the sensorless DTC drive.