Research On Control Algorithm For Thrust Fluctuation Suppression Of PMLSM

Permanent Magnet Linear Synchronous Motor(PMLSM)has the characteristics of high speed,high precision and large thrust,which is widely used in precision machining fields such as IC core making and high-grade CNC machine tools.However,due to the defects of motor design and the nonlinear characteristics of the inverter,the electromagnetic thrust of PMLSM fluctuates greatly,which limits its application in high-precision applications.Therefore,it is of great engineering significance to study the control algorithm to reduce the thrust fluctuation of PMLSM and increase the thrust smoothness.Based on the introduction of the basic structure of PMLSM,mathematical model,vector coordinate transformation and space vector pulse width modulation control principle,this thesis analyzes the characteristics of harmonics generated by the inverter dead time and nonlinearity of power devices.Aiming at the 5th and 7th harmonics with high content in the current,a PMLSM harmonic mathematical model was established,and the relationship between thrust fluctuation and current harmonics was analyzed.In order to reduce the phase current harmonic content and the resulting motor thrust fluctuation,a dq voltage compensation algorithm based on the average value of harmonic currents is proposed.The algorithm can realize harmonic current extraction and harmonic voltage calculation.Compared with the traditional low-pass filter to extract harmonic DC components,the dynamic and steady-state performance of the system is better by harmonic current average method.Matlab/Simulink simulation results confirmed that the algorithm can effectively reduce the phase current harmonic content and motor thrust fluctuation.In order to comprehensively consider the non-linear change of inductance caused by the saturation of the magnetic field of the motor,and the influence of the tube voltage drop of the inverter on the control strategy,this thesis uses ANSYS finite element analysis software to establish a finite element model of the permanent magnet synchronous linear motor and build Simplorer-Simulink co-simulation system.The simulation of the simulation system confirmed that the proposed harmonic current average dq voltage compensation algorithm can effectively reduce the phase current 5th,7th harmonic content and 6th thrust harmonic content,and reduce the motor thrust fluctuation.In order to further improve the robustness of the control system and the ability to suppress external disturbances,this thesis designs a sliding mode variable structure control algorithm with a system disturbance observer based on exponential approach rate,and applies it to PMLSM control.The simulation results confirm that the algorithm can increase the thrust response speed when the load is suddenly applied and reduce the adjustment time;the disturbance thrust observer with the load thrust and speed as the observation can feedback the observation results to the speed loop,which further improves the robustness of the system.