Research On Practical Tracking Control By Output Feedback For Uncertain Nonlinear Systems

Based on backstepping technique, the thesis systematically investigates the practical tracking control problems by output feedback for two classes of uncertain nonlinear systems. First, we introduce the subject background and significance of the control for nonlinear systems and the research status of the tracking control for the nonlinear system. Then, the backstepping technique and some other basic tools for the research, including stability theory, vector norm and matrix norm, Young inequality and so on, are summarized, and a simple example is given to introduce the backstepping technique. Finally, we consider the practical tracking control problems by output feedback for the following two classes of uncertain nonlinear systems:(I) Global practical tracking by output feedback for a class of un-certain nonlinear systems with unknown control coefficientsIn this part, the problem of practical tracking control by output feedback is investigated for a class of uncertain nonlinear systems with unknown control coefficients. Only system output, not the reference signal, is required to be known. First, by using a state transformation, the original system is transformed into a new system; then, based on the new system, a high-gain observer with lower dimension and simple structure is introduced, and consequently the dimension of the closed-loop system is reduced efficiently; finally, by using the backstepping technique, we choose the appropriate Lyapunov functions, and design the virtual controllers step-by-step, and the desired tracking controller by output feedback is successfully designed. The main results show that if the design parameters are suitably chosen, the designed output feedback controller guarantees all the closed-loop states to be globally bounded, and the tracking error to converge to any prescribed small neighborhood of the origin after enough long time. Finally, a simulation example is given to illustrate the efficiency of the proposed control method.(II) Global practical tracking by output feedback for a class of non-linear parameterized systems with unknown control coefficientsIn this part, the problem of practical tracking control by output feedback is investigated for a class of nonlinear parameterized systems with unknown control coefficients. The system studied is more general than the related works. The control coefficients are unknown and contain the output-dependent polynomial nonlinearity, and the assumptions on the system are more general. In term of the design method of the former problem, we appropriately deal with the unknown control coefficients and the nonlinear terms, successfully construct a output feed-back controller for the class of nonlinear system by the backstepping technique, and consequently achieve the objective of output feedback practical tracking con-trol. The main results show that if the design parameters are suitably chosen, the designed controller guarantees all the closed-loop states to be globally bounded, and the tracking error to converge to the prescribed small neighborhood of the origin after enough long time. Finally, a simulation example is given to illustrate the efficiency of the proposed control method.