Electro-hydraulic Position Servo System, Robust Control,

This paper summarizes the current domestic and foreign research situation of electro-hydraulic servo control system. Thickness control system of hydraulic mill stand roll-gap is the test device, which is used in the study. For the non-linear flow characteristic of the Servo valve, Parameter changes and external interference is often found in the electro-hydraulic servo system. Using traditional control methods often fail to meet the control effect. Robust H_∞mixed sensitivity control method is applied to electro-hydraulic position servo system in the paper, and a lot of simulation research has been done through MATLAB software.First of all, the mathematical model of the electro-hydraulic position servo control system is established. The condition for the stability of the system, steady-state error and interference error is analyzed. Dynamic characteristics analysis of the system is carried out in frequency domain and time domain,as well as changes in system parameters on the system. The simulation results show that the conventional PID control system can effectively eliminate the steady-state error, but when parameters change in the system, PID control result is not satisfactory, and can not even make the system stable.Secondly introduced related to the mathematical theory of robust control and some basic robust control knowledge. Robust control theory is to design a controller whose structure and parameters are unchanged and can make the closed loop system maintain the stable performance with uncertainties. Robust H_∞mixed sensitivity control theory is one of the typical robust control theories; it can solve the tracking problem, anti-disturbance problem and robust stabilization problem at the same time. Therefore, H_∞mixed sensitivity control theory is applied to electro-hydraulic position servo control system.Finally, robust H_∞mixed sensitivity controller is designed by choosing appropriate weighting function. Simulation results show that when parameters change, un-modeled dynamics and external disturbances exist in the system. The robust controller is not very sensitive to the change of the system parameters, that is, the controller would be able to maintain the stability of the original and good dynamic characteristics. Therefore, robust H_∞mixed sensitivity control is superior to the PID control.