Research On Non-linear Control Methods For Electro-hydraulic Position Servo Systems

Electro-hydraulic servo systems are widely used in aviation,voyage,weapons control,vehicles and other engineering fields due to their compact structure,fast response,high precision,large work-to-weight ratio and high load resistance stiffness.However,multiple non-linearities are a common problem in electro-hydraulic servo systems,because of this,the systems are not accurately modelled and do not fully reflect the underlying mechanisms.In order to make up for the uncertainty and mismatch on the model,this thesis establishes a nonlinear model of valve-controlled asymmetric cylinder drive system in the form of state-space equation,and focuses on the control method,hoping that the control algorithm can make up for and optimize the uncertainty and non-matching problems established by the model.In order to make the results obtained by the control algorithm more convincing,this thesis also builds a co-simulation platform based on Amesim and C.The C program of the designed controller was written by Visual Studio software,and the drive mechanism of the electro-hydraulic position servo system was modelled by Amesim software.The effectiveness and accuracy of the control performance is verified by means of a joint simulation.Firstly,a nonlinear mathematical model of the symmetric valve-controlled asymmetric cylinder system is constructed by analyzing the correlation between the components of the electro-hydraulic servo system.Secondly,aiming at the nonlinear problem of the model,this thesis selects a nonlinear control method that is suitable for the model and practical to simulate the model and compare it with the traditional linear control algorithm PID.Aiming at the non-matching uncertainty problem of the model,this thesis adopts the backstep method to control the model.Aiming at the slow time variation and external interference of parameters,this thesis uses the sliding mode variable structure to control the model.Due to the limitations of each control algorithm,this thesis combines the backstep method and sliding mode.Then,C language and Amesim co-simulation are used to verify the reliability and practicability of control algorithms and strategies.Finally,taking the on-board pitching mechanism in engineering applications as an example,the model and simulation are carried out to verify the performance of the controller designed in this thesis when the load changes with the rotation angle.Simulation results show that the control effect of backstepping,sliding mode variable structure control and the control strategy combining backstepping and sliding mode variable structure is better than PID in terms of rapidity,accuracy and stability,and backstepping sliding mode control has higher control accuracy and better stability compared with single backstepping and sliding mode variable structure control.When there is a large disturbance,the control strategy combining sliding mode and backstepping has a certain resistance to disturbance,while the control performance of PID is more significantly affected by disturbance.