Two different methods for direct torque control (DTC) of induction motor are analyzed. The first one is conventional DTC strategy. In this method, stator voltage vectors are selected according to the differences between the reference and estimated actual torque and stator flux linkage. Torque and flux errors are compared in hysteresis comparators. Depending on the comparators a voltage vector is selected from the inverter optimal switching table. The other DTC method, proposed in the paper, is based on fuzzy logic concept, where fast torque response with low ripple in the torque of induction motor can be achieved. In this technique, the hysteresis comparators and the switching table used in basic DTC are replaced by a fuzzy logic switcher. Torque error, flux error and stator flux angle are given as input variables to fuzzy controller and output variable obtained from the fuzzy controller is switching state of the inverter. To approximate nonlinear functions Takagi - Sugeno fuzzy algorithm is used. Simulation results show the efficiency of the fuzzy logic switcher.
Keywords: direct torque control, Takagi – Sugeno fuzzy algorithm, fuzzy logic switcher