Precision torque control in inverter-fed induction machines using fuzzy logic

In direct torque control of induction machines, none of the switching states is able to generate the exact voltage vector to produce the desired changes in torque and flux in most of the switching instances. This causes a high ripple in torque. This ripple can be reduced by applying a selected inverter switching state for a portion of switching period (defined as duty ratio /spl delta/) and the zero switching state for the rest of the period. The duty ratio during each switching state is a nonlinear function of torque error, flux error and flux position therefore fuzzy logic control is used to determine the duty ratio during each switching state. The simulation results indicate the ripple is reduced to less than 1/3 of the conventional DTC using the duty ratio control. Under duty ratio control the torque depends upon the changes in torque and flux during the zero switching state. These changes are minimized by using the stator flux optimization.<>