Application of estimation techniques in vector-controlled induction motor drives

The indirect method of vector control combines a slip calculation with a rotor position or speed measurement. The slip calculation requires a knowledge of the rotor time constant which may vary considerably over the operational range of the motor due to changes in rotor resistance with temperature. Therefore variations in motor parameters-particularly rotor resistance-should be tracked as they occur. One method of online tracking using parameter estimation techniques is described. The particular estimation techniques discussed employ a Kalman filter (KF) for rotor current (and hence rotor flux vector position) estimation and an extended Kalman filter (EKF) for rotor resistance estimation. The authors show how the estimation system is incorporated in a typical drive consisting of an inverter supplying a cage induction motor