Research On Terminal Sliding Mode Control For PMSM Of Circumferential Scanning Rotary Table

With the development of image sensor and digital image processing technology,there requires a large field of view besides high resolution images in more and more occasions.The circumferential scanning imaging system(CSIS)has been widely used for search and surveillance tasks for it achieves 360°panoramic imaging by rotary ta-ble driven imaging equipments.High precision position and speed tracking control for the rotary table is one of the key technologies to ensure stable imaging of the CSIS.It is difficult to achieve high precision control for the system has strong coupling,high nonlinear and complex uncertainty disturbances.To improve the response speed,the tracking accuracy as well as the system's anti-disturbance performance of the tracking control for the circumferential scanning rotary table,the servo control algorithms for permanent magnet synchronous motor(PMSM)of the rotary table have been well stud-ied in this dessertation on the basis of the propotional integral(PI)control,the existing theories of terminal sliding mode(TSM)control and high-gain extended state observer(HGESO).Research results are shown as follows:1.The experimental platform of CSIS has been set up,and the PI based three-loop cascade vector control system has been designed for the rotary table and experiments have been carried out in an undisturbed environment.Experimental results show that the designed control system is effective to track ramp position signal and step speed signal at the same time,the position tracking error is less than 0.0010°and the speed tracking error is less than 0.50°/s.By calculation,the maximum value of image shifts of every single frame is less than 0.50 pixels and the maximum value of image shifts of the splicing part of adjacent frames is less than 0.26 pixels,which meets the basic design requirements of imaging definition of the CSIS.2.Aiming at problems of overshooting,oscillation,as well as poor anti-disturbance performance and low tracking precision in an uncertain disturbed environment caused by existing three-loop PI cascade vector control methods for PMSM,this dissertation proposes two kinds of nonsingular finite-time terminal sliding mode control algorithms:nonsingular fast terminal sliding mode(NFTSM)control and nonsingular global fast terminal sliding mode(NGFTSM)control.Firstly,NFTSM control is proposed by in-troducing the double-power function and the sign function to the switching control law of the existing nonsingular terminal sliding mode(NTSM)control,the stability of the controlled system is proved and the convergence time is estimated.Next,NGFTSM control is proposed by introducing a double power function into the switching control law as well as the NTSM variable,the stability of the controlled system is proved,and the convergence time is also estimated.Finally,the speed tracking controller and the position-speed tracking controller in the cascade vector control system are respectively designed for PMSM in CSIS.Simulation results show that compared with PI control,both NFTSM control and NGFTSM control can eliminate the overshooting and oscilla-tion caused by PI control,and significantly reduce the tracking deviations under abrupt disturbance as well as steady-state tracking errors under periodic disturbance;compared with FNTSM control,NFTSM control and NGFTSM control can significantly reduce the steady-state position error under the abrupt disturbance in position-speed tracking mode,and NGFTSM control can also significantly accelerate the tracking response speed of the system.3.In view of the problems such as uncontrollable speed in the position tracking mode,complex control structure,low overall stability of the PMSM cascade vector con-trol system and difficulty in realizing high-order control of the PMSM single cascade vector control system,an arbitrary order nonsingular fixed-time global terminal sliding mode(NFTGTSM)control algorithm has been proposed in this dessertation.Firstly,by the idea of global sliding mode control,a piecewise time dependent function is in-troduced into the traditional terminal sliding mode surface containing the double power function,so that the initial value of the new terminal sliding mode surface is zero,and the new terminal sliding mode surface can be converted into the traditional terminal sliding mode surface containing the double power function at a preset time.Next,a piecewise continuous equivalent control law is derived,and the switching control law is designed as a combination of a double power function and a sign function on the newly designed terminal sliding mode surface,so that the second-order NFTGTSM control is obtained.The terminal sliding mode surface and the control law thus designed consti-tute the second order NFTGTSM control.Then,9)-1 time dependent terminal sliding mode surfaces containing the double power function are constructed for the9)th-order system by applying the recursion method,and the switching control law is designed as the combination of the double power function and the sign function on the9)-1th time-dependent terminal sliding mode surface containing the double power function,thus the arbitrary order NFTGTSM control is proposed.Finally,The fixed-time stability and global nonsingularity of the second-order NFTGTSM control system and the arbi-trary order NFTGTSM control system are proved.In addition,the speed tracking single cascade vector control system and the position-speed tracking single cascade control system are respectively designed for the PMSM of CSIS.Simulation results show that compared with NFTSM control and NGFTSM control,NFTGTSM control can greatly shorten the adjustment time of the system,and further reduce the tracking deviations and recovery time under the abrupt disturbance,especially eliminate the position tracking error caused by NFTSM and NGFTSM under the abrupt disturbance in position-speed tracking mode;compared with the traditional nonsingular fixed-time terminal sliding mode(NFTTSM)control,NFTGTSM control has stronger fixed-time stability,higher utilization of torque current in speed tracking mode,smaller speed overshooting and better anti-abrupt disturbance performance in position-speed tracking mode.4.A series of composite control algorithms based on HGESO and TSM controls are proposed for the PMSM control system to solve the problems such as deterioration of the anti-disturbance performance deteriorates and decrease of the tracking accuracy under larger disturbances.Firstly,the stability theorem of arbitrary order HGESO un-der the relaxed conditions is proposed and proved,and the corresponding HGESOs are designed for the second-order or the higher order uncertain systems.Next,the dis-continuous switching function in the TSM controls are cancelled or transformed into continuous functions,and the disturbance function is added into the control law(the disturbance function is considered as known),thus the ideal feedback controllers based on the TSM controls are obtained.Then the observation values of system states and the extended state by HGESOs are used to replace the real system states and disturbance function in the ideal feedback control laws,thus the composite control laws are ob-tained.In the end,the composite NFTSM(CNFTSM)cascade vector control system,the composite NFTSM(CNGFTSM)cascade vector control system and the composite NFTGTSM(CNFTGTSM)single-cascade vector control system are designed for the PMSM of the CSIS.Simulation results show that in the speed tracking mode,the three kinds of composite TSM controls can further reduce the speed deviation value,recovery time under the abrupt disturbance and the velocity error under the periodic disturbance compared to the original TSM controls;in the position-speed tracking mode,the com-posite TSM controls improve the anti-disturbance performances of the original terminal sliding mode controls,and the CNFTGTSM control greatly improves the peak problem caused by the NFTGTSM control,which further improves the position-speed tracking control performance.