Adaptation of the rotor time constant for variations in the rotor resistance of an induction motor

An induction motor with indirect field oriented control has a very good dynamic behaviour and as a consequence is well suited for high performance applications. But, the indirect field oriented controller is very sensitive to variations in the rotor time constant. Therefore, an adaptation algorithm has to be used to track the variations of the rotor time constant on-line. In this paper, the authors present a scheme for estimating the rotor time constant from the motor terminal measurements alone. The technique is based on estimation of the magnitude of the actual rotor flux space phasor when the motor drive torque is constant. This in turn is used for rotor time constant adaptation. A novel point in this approach is that the rotor time constant adaptation can be performed even at zero rotor speed and also at low loads. Further, the adaptation algorithm involves no derivative terms. The entire system has been simulated and the results presented validate the concept