Study on fuzzy control of induction machine with direct torque control approach

Direct torque control (DTC) is a new method of induction motor control. The key issue of the DTC is the strategy of selecting proper stator voltage vectors to force stator flux and developed torque within a prescribed band. Due to the nature of hysteresis control adopted in DTC there is no difference in control action between a larger torque error and a small one. It is better to divide the torque error into different intervals and give different control voltages. A fuzzy controller has been introduced to deal with this issue. However there arises the problem that the number of rules is too high. This will affect the speed of fuzzy reasoning both in simulation and hardware implementation. In this paper a stator flux angle mapping method is proposed to reduce the rule numbers while keeping the performance of the system satisfactory. To test the fuzzy control strategy a simulation platform using SIMULINK was built which includes induction motor d-q model, inverter model, fuzzy controller and the stator flux and torque estimator. The simulation results verified the new control strategy.