Research On No-overshoot Positioning Strategy Of Permanent Magnet Synchronous Linear Motor Based On Active Disturbance Rejection Control

The traditional servo system adopts the driving mode of "roller screw + rotary motor" or "gear rack + rotary motor".The transmission accuracy is restricted by return error,mechanical deformation and other factors,which limit the control accuracy of the servo system.Because of its high speed,high dynamic response,high precision,long stroke and zero transmission,linear motor servo system is widely used in laser processing,additive manufacturing and high-grade computer numerical control(CNC)machine tools and other high-precision fields.The driving method of Permanent Magnet Synchronous Linear Motor(PMSLM)is under-damped direct drive.Load disturbance,friction disturbance and other unknown disturbances will directly affect the motor's mover,which seriously affect the control accuracy of the servo system.Therefore,in order to achieve high-precision positioning of linear motors,this paper proposes to use the active disturbance rejection control(ADRC)algorithm based on reduced-order state observer to suppress disturbances inside and outside the system and improve the control accuracy of the servo system.At the same time,as the core link of the control system,the current loop is the key loop for the linear motor servo system to achieve high precision control.However,due to the dead time effect,the nonlinearity of inverter,parameter mismatch and other factors,the current contains various harmonics,which make the linear motor generate thrust fluctuation,resulting in rough surface of machined parts and reduced accuracy.Therefore,for the linear servo system,it is necessary to not only meet the needs of positioning without overshoot,but also to suppress the current harmonics.The main structure of the paper includes the following aspects:1.The mathematical model of PMSLM in synchronous rotating coordinate system is established.PMSLM has the characteristics of strong coupling,non-linear and multi variable,which make it complicated to control.In order to simplify the control model,aiming at the three closed-loop control system of PMSLM,a PMSLM mathematical model based on the synchronous rotation coordinate system is established,and the relationship among the thrust,current,voltage and other variables of PMSLM is deduced.By discretizing the model and combining with the vector control mode with id = 0,the active disturbance rejection control model of PMSLM is derived.2.On the basis of linear ADRC,a second-order speed ADRC system based on reduced order state observer is constructed to realize the linear servo system without overshoot.The transformation conditions between linear and non-linear ADRC and the advantages of linear ADRC are analyzed.Based on this,in view of the permanent magnet synchronous linear motor in the process of achieving non-overshoot positioning,the internal and external disturbances of the system will seriously affect the accuracy of the servo control system.Linear ADRC is used to suppress the disturbances.At the same time,because the high-order ADRC controller has the disadvantage of phase lag,the order reduction of the extended state observer is used to overcome the phase lag and reduce the number of parameters,reduce the sensitivity of system parameters.Finally,the improved differential evolution algorithm is used to optimize the PI parameters of the position loop.Compared with the differential evolution algorithm,the improved differential evolution algorithm increases the screening stage,cancels the variation factor,reduces the number of artificial parameters,and has faster convergence speed and higher convergence accuracy.3.In order to reduce the current harmonic,steady-state error and realize the goal of no overshoot positioning,a double loop ADRC system with position-speed loop and current loop is designed.Because of the influence of the current harmonic,there is chattering in PMSLM servo control system.Therefore,in order to reduce the current harmonic content,a control algorithm based on reduced-order double-closed loop ADRC is proposed in this paper.First,a first-order nonlinear ADRC controller is designed for the current loop.Due to the filtering effect of the tracking differentiator,the filtering effect of the first-order nonlinear ADRC controller is better than that of the first-order linear ADRC controller.At the same time,a second-order linear ADRC is designed for the position-velocity loop.By reducing the order of the extended state observer,the adjustment range of the gain coefficient can be increased,and the system's anti-interference ability can be enhanced.At the same time,a second-order linear ADRC is designed for the position-velocity loop.By reducing the order of the extended state observer,the adjustment range of the gain coefficient can be increased,and the system's anti-interference ability can be enhanced.4.Based on the AD5435 simulation system,the PMSLM experimental control platform is built,and the experiments of linear motor positioning,harmonic suppression and thrust fluctuation under different disturbances are compared.Experimental results show that these methods have higher positioning accuracy,smaller steady-state error,and can effectively suppress current harmonics and reduce thrust fluctuation.