The Study And Application Of Nonlinear Control In The Electro-hydraulic Position Servo System

Through dozens of development, the Classical Control Theory and Linear System Theory have formed a series of analysis and design ways of engineering application. But they have a basic requirement which has to accurately build a linear mathematical model of controlled object or process. However, most of actual controlled objects and processes appear the characteristic of nonlinear, so it is difficult or even impossible to build a accurate model of controlled object or process, furthermore, most of models have the characteristic of nonlinear. So is has the important significance of theory and the urgent actual demand to study the control method of the nonlinear system.The thesis takes an electro-hydraulic position servo system of Single Input Single Output (SISO) for example and builds the nonlinear model of the electro-hydraulic position servo system. Firstly, the thesis applies method of Taylor Series approximately linearization to linearize the model of electro-hydraulic position servo system, and then designs the controller and simulates the mathematical model with the method of linear system theory. It is possible that the linearization model is used in the system which has relatively low frequency and relative little variation of parameter and outer disturb. However, the modern electro-hydraulic position servo system is often required to have the ability to trace any curve function and endure relative big outer disturb, so the the dot of balance changes in a large range during the work, which makes the Taylor Series linearization model unsuccessful. So in the thesis the problem of the state feedback exact linearization of nonlinear system is studied by the theory of differential geometry. The method of state feedback exact linearization can process nonlinear system to be pseudo linear system, so we can apply the matured theory results of linear system to control the system. This method is obviously different from the method of Taylor Series approximately linearization. To a certain system, the method of Taylor Series approximately linearization loses the system informations, while the method of state feedback exact linearization completely retains all the system information.The thesis detailedly introduces the process of state feedback exact linearization of the electro-hydraulic position servo system, thus the nonlinear system is coverted into a linear system. The problem of the control system design based on exact linearization model is studied. The linear quadratic tracker design method is proposed to overcome the problem of output tracking control. Although the method of direct state feedback exact linearization has the simple structure and good performace of tracking, it has a obviously shortcoming which is the nonlinear of system can not be converted into linear completely when the system parameters vary, so the system will produce error. So the thesis also offers the method of grey prediction model combined with direct state feedback exact linearization, which can achieve the perfect controlling effect.Though simulation, it is made clear that under the controlling action of state feedback exact linearization, the system has good performance. While the method of grey prediction model combined with state feedback exact linearization has relatively strong robustness when the system parameters of the system vary.