Research On Modeling And Control Strategy Of Nonlinear Valve Controlled Cylinder System

The valve controlled hydraulic cylinder system is a branch of hydraulic control system,which is widely used in national defense,aerospace and other industries.With the continuous development of society,higher requirements are put forward for the control accuracy of hydraulic servo system.Therefore,it is necessary to discuss the nonlinear part of the hydraulic control system in detail and design a more practical mathematical model and appropriate controller.In this thesis,taking the valve controlled hydraulic cylinder system as the research target and a new nonlinear mathematical model of valve controlled hydraulic cylinder system is established,which considering the actual working state of the servo valve,such as the nonlinear characteristics of the flow coefficient and pressure gain in the flow equation of the servo valve.At the same time,combining the advantages of sliding mode control and model predictive control,the sliding mode predictive controller is designed and applied to the electro-hydraulic position control system.Through MATLAB simulation and Simulink and AMESim co-simulation,the effect of sliding mode predictive control algorithm is analyzed.Finally,on the basis of simulation parameter adjustment,the mathematical model and position tracking control experiments are carried out by using the experimental device.The specific work can be summarized as follows:Firstly,the nonlinear mathematical model of the valve controlled hydraulic cylinder system is established.Based on the traditional flow equation of servo valve,combined with the content of fluid mechanics,the flow coefficient of each stage is rewritten according to Reynolds number.At the same time,the pressure gain is fitted by mathematical function,and a new flow equation of servo valve is established.Then,combining the flow continuity equation between the two chambers of the hydraulic cylinder and the load force balance equation between the hydraulic cylinder and the external load,and a new nonlinear mathematical model of the valve controlled hydraulic cylinder system is constructed.Secondly,the sliding mode predictive controller is designed by combining the sliding mode control algorithm with the model predictive control algorithm.By comparing the control laws obtained by choosing different reaching laws,it shows that the sliding mode predictive control algorithm has better performance.On this basis,the mathematical model of the valve controlled cylinder system is substituted into the sliding mode predictive control algorithm,and the control law expression of the valve controlled cylinder system position control is obtained,and the system stability is proved.In addition,the mathematical model of the valve controlled hydraulic cylinder system and the sliding mode predictive control method are simulated in the MATLAB /Simulink environment,and the simulation results are compared with the PID control method.At the same time,Simulink and AMESim co-simulation are carried out,and the simulation results show that the sliding mode predictive control method can make the position control of valve controlled hydraulic cylinder system achieve better effect.Finally,the servo valve test bench and valve controlled hydraulic cylinder system are built,and the mathematical model and control method are studied by experiments.The theoretical model is in good agreement with the experimental data,which verified the correctness of the flow model of servo valve and the applicability of sliding mode predictive control.