PI AND FUZZY ESTIMATORS FOR TUNING THE STATOR RESISTANCE IN DIRECT TORQUE CONTROL OF INDUCTION MACHINES

Direct torque control (DTC) of induction machines uses the stator resi stance of the machine for estimation of the stator flux. Variations of stator resistance due to changes in temperature or frequency make the operation of DTC difficult at low speeds. A method for the estimation of changes in stator resistance during the operation of the machine i s presented. The estimation method is implemented using proportional-i ntegral (PI) control and fuzzy logic control schemes. The estimators o bserve the machine stator current vector to detect the changes in stat or resistance. The performance of the two methods are compared using s imulation and experimental results. Results obtained have shown improv ement in DTC at low speeds.