Research On Nonlinear Modeling And Compensation Of Electro-Hydraulic Load Simulator

Due to significant advantages,electro-hydraulic load simulators are applicable for spacecraft simulations with large load torque,wide frequency band,and high precision.However,nonlinearity leads to large response deviations,start-up delays,low-speed ripples,and oscillation of the limit loop phenomena.This greatly restricts the control performance of the spacecraft.It is necessary to investigate compensation methods in order to eliminate the serious consequences caused by nonlinear factors.Modeling and identification of friction and gap nonlinearity of the electro-hydraulic load simulator are studied in this paper for the sake of increasing the control accuracy.Firstly,this paper adopts the equivalent physical model including two hydraulic cylinders to analyze the basic mathematical model of the electro-hydraulic load simulator.The physical model matches the actual structure of the rotary electro-hydraulic load simulator.Then,a nonlinear mathematical model with Stribeck friction and hysteresis clearance is established,and parameters of the friction model and the gap model are identified by experiments.According to the experimental data of torque angular and velocity,the friction parameters are identified by using the particle swarm algorithm,and the gap parameters are obtained by using amplitude identification method with small amplitude instruction signals.Finally,the friction of the system is compensated with the disturbance observer compensation method.An external loop robust controller is designed guaranteeing the norm of the closed-loop transfer function to be minimum.At the same time,an inverse gap model adaptive strategy is proposed.The inverse model parameters are adjusted according to the gap value in real time,and the hysteresis and tracking error are compensated.Experimental results show that,with proposed compensation method,the maximum angular position tracking error of the system is reduced from 0.726° to 0.185°,the maximum angular velocity tracking error is reduced from 2.623 rpm to 0.373 rpm.The identified friction and clearance parameters are matched with the rotary load simulator,which effectively compensates for hysteresis and deviation and improves the tracking accuracy of the rotary electro-hydraulic load simulator.The research shows that the proposed nonlinear compensation methods of the electro-hydraulic load simulator system are feasible.The research results of the dissertation have some reference for the future research and manufacture of the electro-hydraulic load simulator.