Research On Direct Torque Control System Of PMSM Based On Fuzzy Sliding Mode Control

With the fast development of permanent magnet material recent years, Permanent magnet synchronous motor (PMSM) has been widely applied in control system for its high-performance, high rate of torque and inertia, and high-energy density. As a dynamic and static high-performance control mode, direct torque control (DTC) takes torque as the object controlled, and adopts bang-bang control to gain fast torque response. It is with novel control idea, simple control structure, small amount of calculation, and reduces the impact on system performance produced by the change of electrical mechanical parameter. But for its inherent characteristics, the system existes big flux linkage and torque ripple, which partly restricts its application and development. This thesis deeply researches the ripple problem of PMSM-DTC, and proposes the method of DTC based on fuzzy sliding mode coontrol.The main contents are as follows:Firstly, this thesis researches the traditional DTC system. The system existes the problem of big flux linkage and torque ripple, no-constant switching frequency and so on, because it uses hrsteresis regulator. Secondly, for the defect of the structure existing in traditional DTC, this thesis proposes the method of DTC based on space voltage modulation for the problem. This method uses the voltage component on the stator flux linkage coordinate to control flux linkage and torque of eletrical machine. Then we can obtain the needed voltage vector conbining the technology of space vector pulse width modulation. Finally, for the detect of PI regulator, this thesis improves the speed regulator by using fuzzy sliding mode controller instead of PI regulator. It uses fuzzy control to identify the rotation difference online and adjust the paramenters of the exponent approaching of sliding mode cintrol to constitute the fuzzy sliding mode controller. When the disturbance and torque mutation are appearing, we adjust the convergence speed of system state to the sliding surface based on the difference of actual rotor speed and given rotor speed. It can prevent large buffeting and draw a stable system, and can improve the problem of ripple of the single sliding mode controller.Fom the simulation results, the control method of this thesis is effective,and the PMSM-DTC system based on fuzzy sliding mode control not only reduces the ripple of flux linkage and torque in tradintional DTC system, but also improves the dynamic and static performance of the system.