Fuzzy Control Research And Application Of Direct Torque Control System

The Direct Torque Control(DTC) is a high performance Alternating Current(AC)speed regulating technology following the vector control. It arouse wide concern because of its straight control thought, simple system structure, convenient for digitalization, as well as excellent static and dynamic performance when it was proposed. Its basic idea is changing the angle between stator flux and rotor flux by adjusting the rotating speed of stator flux while the amplitude of stator flux is constant, then the electromagnetic torque and rotor speed are controlled. Compared with vector control, no need to complex coordinate transformation and direct control of motor flux and torque are main advantages of DTC. DTC is applied successfully in some fields. The technology has been successfully applied in some areas, but as a new approach in theory and practical application, there are many shortcomings to be further improved.The paper entirely summarizes the actuality and development of Direct Torque control(DTC)of the induction motors, deduces transformation matrix the three-phase voltage and current which the three-phase coordinate system transform to the two-phase coordinate system, introduces the concept of the space voltage vector and its effect on the flux and torque, analyses the U-I model,I-N model and U-N model for the three kinds calculation model of the flux and its comparative advantages and disadvantages, and detailedly introduces the basic theory and principles of DTC. The basic principle of speed adjustment of motor is control of torque. The paper analyses the mathematical model and shows that the key of DTC is to select the right stator voltage vectors due to the stator flux and torque.The same space voltage vector is chosen by Bang-Bang control in the traditional Direct Torque Control (DTC) system in the case of both big and small error. To solve the problem, Fuzzy logic is introduced. The errors on the torque and the stator flux linkage are fuzzy classified and the space voltage vector can be reasonable obtained according to the errors. A design method of the fuzzy controller is presented particularly, it is proposed that the hysteresis and voltage vector table are replaced by a fuzzy controller, so as to increased torque dynamic response speed and reduce the flux and torque ripple.It is built a simulation model of direct torque control system and fuzzy direct torque control system under Matlab/simulink simulation environment and give them a comparative simulation study. The results of simulation indicated that the response of the fuzzy DTC system is quicker when the motor start or the rotate speed breaks, torque and flux ripple is smaller, the dynamic and static performance is improved. There are good results in the occasions that require fast dynamic torque response.Hardware and software design is given with the STM32F103R8as master chip after the feasibility of fuzzy direct torque control system control is verified through simulation.