Nonlinear Control Of Electrohydraulic Servo System

According to an undercarriage loading system of an airplane, a linear model of an electrohydralic servo system was established and simulated. The linear model is feasible to the system that has relatively low frequency and small parameter variation and outer disturbs. But modern electrohydraulic servo systems have obvious nonlinear characteristics and often are required to have the ability to trace any curve function and endure relatively big outer disturb. So the working dot of the system changes greatly during the working process, which makes the linear model inapplicable. To solve the problem, a nonlinear model of the electrohydraulic servo system was established and linearized accurately under large scale with nonlinear control theory. Then a nonlinear controller was designed according to zero dynamics theory. Through searching a nonlinear state feedback, the method makes the nonlinear system to be transformed to a linear system which is completely controllable. Thus we can analyze the system using the mature theory of linear system. Through simulation, it was proved that the system controlled by the nonlinear controller had good dynamic performance and good robustness when the structure and parameters of the system changed.