Research On Control System Of Permanent Magnet Linear Synchronous Motor

Permanent magnet linear synchronous motor(PMLSM)combines the high efficiency and energy saving of the permanent magnet synchronous motor with the simple structure and rapid response of the linear motor.PMLSM has been widely used in the linear feed system of high-grade CNC machine tools and magnetic levitation train in transportation industry.PMLSM without intermediate transmission mechanism makes parameter changes and external disturbances directly affect the motor drive system,which requires more stringent control strategy.This paper focuses on the direct force control(DFC)system of PMLSM to improve the control performance of thrust and speed.Firstly,the control strategies of PMLSM are classified,and the direct thrust control is the basis of the control strategies in this paper.The mathematical expressions of PMLSM in several different coordinate systems are established.The application of direct thrust control in PMLSM is analyzed theoretically and realized.The simulation model of PMLSM direct thrust control system is built in MATLAB/Simulink.Secondly,aiming at the problem of thrust and flux ripple in PMLSM direct thrust control system,the hysteresis controller of thrust and flux is eliminated,and SVPWM is used instead of the voltage vector switch state selection module to solve the problem of thrust ripple caused by discontinuous switching of space vector.The simulation results of PMLSM in different states such as loading,load shedding and speed changing show that the thrust fluctuation of PMLSM SVPWM-DFC system is reduced by about 71.4% compared with the traditional PMLSM DFC system,and the flux linkage fluctuation is also suppressed.and the flux ripple is also restrained to some extent.Aiming at the problem of overshoot of speed response in simulation results,the active disturbances rejection controler technology is introduced to redesign the speed loop controller,and a better control effect is obtained.Thirdly,aiming at the problems of relative lag of speed response time and weak anti-interference ability in PMLSM SVPWM-DFC system,an improved sliding mode control algorithm is proposed for speed loop control.The weighted integral gain reaching law was combined with the constant speed reaching law.The negative weighting value in the new hybrid reaching law can effectively avoid the increase of switching gain when the system is not in the sliding mode phase.The chattering of sliding mode structure is eliminated.The simulation results show that the improved algorithm greatly reduces the response time of speed and enhances the anti-interference ability of speed control,and the speed response has zero overshoot while maintaining the dynamic performance of the thrust.Fourth,implementing high performance PMLSM DFC system requires acquiring key information such as system speed and flux linkage.The speed sensorless control of PMLSM DFC system is studied by using model reference adaptive algorithm.By identifying the initial position estimates,a flux observer is proposed,which is observed in parallel through two different flux linkage calculation methods.The deviation is injected into the voltage vector as compensation,which weakens the influence of the variation of motor parameters and the accumulated integral error on the flux linkage.The simulation model of PMLSM SVPWM-DFC based on model reference adaptive system is established,and the feasibility of the control strategy is verified.