Research On Uncertain Stochastic Nonlinear Systems Output Feedback

In the reality applied systems, due to the exists of all kinds of uncertainties, it is quite difficult to modify the systems precisely. Namely under most circumstances, we can only have a part of dynamic information of the precise systems of the object, but don’t get the overall informations. Since1950’, the control theory of uncertain nonlinear systems begun to formed slowly and has caused much attention of vast scholars. Where estimation and robust is widely applied to the controller and play a key role in dealing with the unknown and uncertain in systems. In recent years, many scholars pay attention to the research of output feedback of stochastic nonlinear systems and some significant results are obtained.According to the unknowns and uncertainties that exist in the systems, in this dissertation we studies the problems of stability analysis and output feedback stabilization of stochastic nonlinear systems which covers uncertainty or unknown control coefficient, with integral backstepping method and as the foundation, we adopt high-gain observer and reduced order observer respective, so as to make the equilibrium of the controlled systems is globally asymptotically in probability under the action of the controller.The main contents of this paper includes the following two aspects:(1)For a class of stochastic nonlinear minimal systems with uncertain disturbance, the state of closed-loop systems is disturbance rejection by the output feedback control law. In chapter3, due to the unmeasured stochastic nonlinear zero dynamics and uncertain disturbance noise are contained in the systems, at first we make a hypothesis that the established model is the stochastic input-to-state stable, and on the premise of this assumption, a undetermined high-gain observer was designed to construct a new equivalent systems, then by means of integral backstepping, we obtain the feedback control law of equivalent system, which guarantee the final controlled system is input state stable via select proper parameters of high gain. Finally, the simulation example is given to verify the effectiveness of control law. We relax the restriction of the system uncertainties, to make the closed loop system being disturbance rejection and asymptotical stable by output feedback in the more common case.(2)For a class of stochastic nonlinear system with unknown control coefficient and uncertain disturbance, we restrict the control coefficient to be bounder, due to the complexities and limits of practical control systems, we need to consider more flexible controller. In this chapter, first of all, we construct a observer for unmeasured but observable states, then under the action of control law, we can see that the closed-loop system has a unique solution. At last, we also use a simulation example to verify the effectiveness of the controller.