Tracking the rotor time constant of an induction motor traction drive for HEVs

Field-oriented control methodology requires knowledge of the machine parameters, and in particular the rotor time constant. The interest here is in tracking the value of T_R as it changes due to ohmic heating so that an accurate value is available to estimate the rotor flux for a field oriented controller. The approach presented here is a nonlinear least-squares method that uses only measurements of the stator currents and voltages along with the rotor speed. The nature of this technique lends itself directly to an online implementation and therefore can be used to track the rotor time constant. Experimental results are presented to demonstrate the validity of the approach.