Research On Direct Torque Control Of Asynchronous Motor For Electric Vehicle

A systematic and comprehensive research on the Direct Torque Control System of asynchronous motor for Electric Vehicle is introduced in this thesis. The basic mathematical formula of DTC is deduced based on space vector. On the basis of the analysis, an optimization control strategy is introduced and the simulation results show the method is feasible.In recent years, because of environment problem and energy crisis, low pollution and high efficiency vehicles have put more and more eyes on. Electric Vehicles are propelled by electric motors with advantages of no emission, low noise and good efficiency, which have been focused on and stepped into markets. A high efficiency and fast response electric drive system is demanded for EV, and the DTC appears a good future with rapid development of control technology.This thesis describes the construct and the basic working principle of traditional DTC and presents a simulation method for asynchronous motor control system based on MATLAB/SIMULINK. Its simulation program is simple, visual and accurate. Using this program, the performance effect of the Direct Torque Control System is studied in detail. DTC has some drawbacks, e.g. the large torque ripple and flux aberrations are generated, in particular, in a low speed range because of the stator resistance voltage drop of an asynchronous motor.A method, named band width optimization, is introduced to improve the magnetic flux circle when the motor runs at low speed, at the same time, the method can improve the start characteristic of DTC control. The method is simple to be implemented and robust to the variation of the motor parameter. To demonstrate the validity of the method, some experiments with SIMULINK of MATLAB are given, and complex control methods are realized by user-defined S-FUNCTION. The results of computer simulations reveal that the introduced method is feasible and more suitable for EV drive system.