Research On Control Method Of Electro-hydraulic Servo System

Electro-hydraulic servo system is a kind of electro-hydraulic integrated system which is widely applies in military industry and part of civil industry owing to its high efficiency,large output torque,fast response and other characteristics.Due to the condition of time-varying load and uncertain external disturbance,the research of electro-hydraulic servo system has been widely concerned.This thesis focuses on how to enhance the performance of electro-hydraulic servo system under the condition of time-varying load and uncertain disturbance.The main research contents are as follows:Firstly,the control mode of electro-hydraulic servo system is introduced and its system characteristics are analyzed.The reasons for the nonlinear problems and hysteresis of the system are summarized,and the unique advantages of the direct drive electro-hydraulic servo system are showed.Three common control modes of the direct drive electro-hydraulic servo system are compared and analyzed,and the speed control mode with double closed-loop structure adopted in this thesis is determined.Secondly,in order to improve the anti-interference ability of the electro-hydraulic servo system,the sliding mode controller is adopted in the speed loop.Aiming at the problem of high frequency shaking existing in the sliding mode variable structure and the time-varying characteristics of the system load,an improved reaching law sliding mode optimal control method is proposed.The advantages and disadvantages of four common reaching laws are analyzed,and the exponential reaching law is improved to obtain the sliding mode with rapid attenuation characteristics,so that the control performance is not affected by the sensitive parameters of the system,meanwhile,the high-frequency shaking is weakened;beyond that,the complex vector current controller is used in the current loop to improve the response ability of the system.The simulation results show that the high-frequency torque ripple of the optimal control is significantly reduced,the high-frequency jitter of the state variables is effectively weakened,the robustness and tracking performance of the system are improved,compared with the conventional sliding mode control(SMC).Finally,combined with the working conditions of the electro-hydraulic servo system,aiming at the problem of sudden speed drop caused by sudden load change in the electro-hydraulic servo system,a feed-forward compensation optimization control method based on improved load torque observer is proposed.The engineering design of the observer is improved,and the parameters of the improved observer are adjusted by combining with the engineering design method.The stability and effectiveness of the improved observer are analyzed.The simulation results show that the feed-forward control of the improved observer can suppress the sudden drop of speed when the load changes suddenly,and it has certain practicability and engineering feasibility.