Research On Direct Torque Control Of Permanent Magnet Synchronous Motor Based On Sliding Mode Variable Structure

Modern motor control technology is a core technology of high-performance servo drive, which has a direct relation to the development of advanced manufacturing technology. Permanent magnet synchronous motor with simple structure, high air-gap density and efficiency have become an indispensable basic unit, as a speed control system of servo drive in modern industry, daily life and national defense.Direct torque control as a high-performance control strategy has a good speed performance, which had been applied to permanent magnet synchronous motor control system. However, there are also some shortcomings, such as torque and flux pulse rippling, especially, poor performance in low speed run. Sliding mode control as a nonlinear control strategy has many advantages, such as a property insensitive to parameter variations and external disturbances, fast response, strong robustness, and easy to be implemented and so on. If it can be applied to direct torque control system of permanent magnet synchronous motor, it will greatly improve the performance of speed control system.In this thesis, the structure characteristics of permanent magnet synchronous motor and magnetic circuits were analyzed. A mathematical model in the three-phase and two-phase coordinate system was developed. Based the results a permanent magnet synchronous motor's direct torque control system was established. The control system was simulated by Matlab/simulink, and the pulsation problem from the simulation results was studied and analyzed. In order to solve the problem in the permanent magnet synchronous motor's direct torque control system, the research was deep developed in sliding mode control. With the buffeting issue brought from sliding mode control in the permanent magnet synchronous motor's direct torque control system, the methods of norm sliding mode,integral sliding surface and reaching law were applied and the effect in reducing uffeting was also simulated respectively. The main idea was that the resigned torque and flux sliding mode controller replaced the hysteresis comparator in the convention direct torque control system so as to resolve the pulsation and inconstant switch issues. The simulation results showed that the control scheme had the strong robustness to system parameters'uncertainty, external disturbances and noise, and the dynamic and static quality was signally improved. The buffeting issue brought from sliding mode control in the permanent magnet synchronous motor's direct torque control system resigned with composite reaching law was restrained well and a high-performance speed control system was obtained.