Direct torque control of an induction motor using fuzzy logic

Direct torque control (DTC) system is currently one of the favourable control schemes for AC motor drives since it has the important advantage that system performance is not dependent on the motor parameters-except the stator resistance. However, if the stator resistance varies, the performance of the system will suffer, as the stator resistance value used in calculating the stator flux does not match the actual situation. Compensation for the effect of the variation of stator resistance then becomes necessary. This paper describes a fuzzy observer, which can estimate the stator resistance online, according to the actual stator current motor speed and operating time. The proposed fuzzy observer for stator resistance in this paper is applicable not only in the DTC system of induction motors but also in other types of motor drive systems.