The Study Of Uncertain Nonlinear System Control

The paper is concerned with the problem of robust control of uncertain nonlinear systems and the application on the AC speed adjustable systems. Researching content includes: (l)Because there are drawbacks that nonlinear state feedback of affine nonlinear system depends on parameters, we use an adaptive control method on the basis of feedback linearization. In this scheme, parameters are estimated adaptively and used in nonlinear state feedback. Therefore, the robust feedback linearization control is obtained. (2)For affine nonlinear systems with parameter uncertainties, a novel nonlinear state observer is constructed. Under nonlinear feedback control based on observed state, the regulated system state is guaranteed to enter and remain in a enough small neighborhood of origin. (3)For a class of nonlinear systems, we point out a hybrid control of adaptive control and L₂ - gain less than or equal to γ . On the hand, the control strategies have overcome the complexities while only the adaptive control is used . On the other hand, the control strategies extend the scope of the H^∞ control. (4)A research on robust output practical tracking of uncertaion nonlinear systems is made. Based on feedback linearization, optimal control and Lyapunov method, a continuous, simple controller with good performance is proposed. The controller has some characteristices: the norm doesn't need to be computed in the course of controlling the systems, and the controller can be constructed concretely , and so on. (5) The robust H^∞ control problem for an affine nonlinear system with gain bounded uncertainty and exogenous disturbance is researched. It is shown that, for considered uncertain nonlinear systems, the robust H^∞ control problem is solved via state feedback or output feedback if an extended nonlinear system with no uncertainty has L₂ - gain less than or equal to y via state feedback or output feedback. The relationship between the controllers of uncertainty systems and those of extended nonlinear systems is given obviously. (6)As an example of nonlinear H^∞ control, the robust H^∞ controller for linear system with time-varying parameter uncertainty is investigated. The uncertainty under consideration is assumed to be unknown but bounded, and can exist in both the state and the input matrices. An approach is proposed for designing a state feedback control law which place closed-loop poles in a given circular region and guarantee a prespecified disturbance attenuation for all admissible uncertainties. (7)Considering the control objects of induction motors under adjustable coordinates and switched reluctance motors, we focuse on the application of nonlinear robust control strategies on AC drives. Computer simulation results show that , because of the use of nonlinear robust control strategies, the control systems of AC drives have good qualities.