Research On Sliding Mode Control Of Magnetic Levitation System

Electromagnetic levitation trains are the development trend of rail transit in the future due to the advantages of green,comfortable,small turning radius and strong climbing ability.The control problem of its suspension system is a key problem restricting the development of electromagnetic levitation trains.Although the traditional control strategy can make the system run stably under certain conditions,in order to further improve the stability and anti-interference performance of the magnetic levitation system under different environmental conditions,scholars have tried many different control strategies such as self-disturbance rejection control,adaptive control,neural network control,etc.,while the sliding mode variable structure control strategy has the characteristics of insensitivity to external disturbance and internal parameter perturbation,mature theory,simple implementation,etc.,and has a wide range of applications in the magnetic levitation control neighborhood.Firstly,according to the physical properties of the magnetic levitation system,using the knowledge of electromagnetism,circuits,dynamics and other fields,the model characteristics of the electromagnetic levitation system are analyzed,and the mathematical model of the nonlinear electromagnetic levitation system is established,in order to meet the design requirements of the control system,the mathematical model of the electromagnetic levitation system is linearized to provide a basis for the design of the controller.Secondly,a double closed-loop control system is adopted,and the current inner loop adopts simple PI control,which improves the hysteresis of the electromagnetic suspension system due to the hysteresis of the coil inductance and simplifies the control structure.In order to improve the robustness and anti-interference of PID control of the position outer ring,the improved sliding mode control based on the linear expansion state observer is adopted,and in view of the problem of control jitter in the sliding mode variable structure,this paper introduces an improved sliding mode control method,slows down the jitter frequency,reduces the jitter amplitude value,and suppresses the instability caused by system jitter.Then,the total disturbance of the system is compensated to the sliding mode controller through the linear expansion state observer,which can not only alleviate the dependence of the sliding mode controller on the model,but also further improve the anti-interference and robustness of the system.The improved sliding mode control based on LESO reduces overshoot,accelerates response speed,and greatly enhances the anti-interference performance and robustness of the system,which has certain guiding significance for improving the operation stability of medium and low speed electromagnetic levitation trains under different working conditions.Finally,in order to further verify the feasibility of improved sliding mode control based on LESO,the F-rail electromagnetic levitation hardware platform is built,and according to the requirements of the experimental platform,the control chip,chopper,driver chip,sensor,etc.are selected,the signal conditioning circuit,minimum hardware system,etc.are designed,the algorithm interrupt subprogram is written through the CCS code editor,the main running program is configured.Through static performance experiments and dynamic performance experiments,the improved sliding mode control based on LESO is 17% faster than the PID control response time and the overshoot is reduced by 21%.When the same disturbance is loaded,the maximum gap amplitude fluctuation is reduced by 38% and the recovery time is reduced by 40%.It is concluded that the anti-interference performance,response time and overshoot of improved sliding mode control based on LESO are better than PID control.