FUZZY CONTROLLER FOR INVERTER-FED INDUCTION MACHINES

An induction machine operated with a direct self controller (DSC) show s a sluggish response during startup and under changes of torque comma nd. Fuzzy logic is used in conjunction with direct self control to min imize these problems. A fuzzy logic controller chooses the switching s tates based on a set of fuzzy variables. Flux position, error in flux magnitude and error in torque are used as fuzzy state variables. Fuzzy rules are determined by observing the-vector diagram of flux and curr ents. The operation of the direct self controller becomes difficult at low speeds due to the effect of change in stator resistance on the fl ux measurements. To improve the system performance at low speeds a fuz zy resistance estimator is proposed to eliminate the error due to the change in stator resistance. At constant flux and torque commands any change in stator resistance of the induction machines causes an error in stator current. This error is utilized by the fuzzy resistance esti mator to correct the stator resistance used by the controller to match the machine resistance. Both fuzzy controller and fuzzy resistance es timator are simulated for a 3 hp induction motor. The simulation resul ts demonstrate a good performance.