Fuzzy High-Gain Output Feedback Controller Design For Nonlinear Systems

Physical systems are nonlinear and highly uncertain in nature, and are often subject to uncertain nonlinear factors, such as external disturbance, uncertain dynamic input, delay and so on. Fuzzy logic systems are able to approximate a continuous function defined on a compact set to any given accuracy, which can effectively deal with nonlinear uncertainty. Some correlative issues in this area are studied in this thesis. For single-input single-output (SISO) strict-feedback uncertain nonlinear systems, multi-input multi-output (MIMO) strict-feedback uncertain nonlinear systems, and interconnected uncertain nonlinear large-scale systems, combined fuzzy adaptive control, backstepping design, dynamic surface control, command filtered design, small-gain theory and changing supply functions, the problems of stabilizing control, output tracking and disturbance attenuation are solved by output feedback, in cases of states being not available for feedback, and unmodeled dynamics and disturbance existing simultaneously. The main contents of this paper are stated as follows:1) The problem of output feedback control is addressed for a class of SISO strict-feedback uncertain nonlinear systems only with output measurements. A novel fuzzy high-gain observer is first developed for state estimation, combined fuzzy adaptive control with backstepping design, a fuzzy adaptive output feedback control is designed. Based on Lyapunov stability analysis, it is shown that the proposed fuzzy adaptive control method guarantees all the signals in the close-loop system to be uniformly bounded, and the observer error converges to a small neighborhood of the origin.2) The problem of output feedback almost disturbance decoupling is addressed for a class of SISO strict-feedback dynamic uncertain nonlinear systems with only output measurements. A fuzzy high-gain observer is designed to estimate the unmeasured states, and then, combined fuzzy adaptive backstepping design, small-gain theory and changing supply function, an output feedback robust controller is designed to achieve asymptotic stability of the closed-loop system in the sense of ISpS (input-to-state practically stable) respect to the disturbance input, while the effect of the disturbance on output is diminished to an arbitrary degree of accuracy.3) The problem of output feedback almost disturbance decoupling is investigated for a class of MIMO uncertain nonlinear systems. A fuzzy high-gain state observer is established to estimate the unmeasured states, and then, combined fuzzy adaptive backstepping control with dynamic surface control(DSC) technique, a novel fuzzy adaptive output feedback control scheme is constructed, DSC is adopted to implement physical constraints on the virtual control law, reduce the calculation of these derivatives. The proposed control scheme can not only achieve internal stability of the closed-loop system, but also diminish the effect of the disturbance on output. Furthermore, the above results are generalized to MIMO nonlinear systems in nested lower triangular form, a second-order command filter is different from DSC, and is introduced to cancel the restrictions of constructing a compact set in DSC.4) The problem of output feedback tracking control is investigated for a class of strict-feedback uncertain nonlinear large-scale systems. A fuzzy high-gain state observer is established to estimate the unmeasured states, and then, combined fuzzy adaptive control with sliding-mode-based filtered backstepping, A fuzzy adaptive decentralized output feedback controller is proposed, sliding-mode-based integral filter is adopted to implement physical constraints on the virtual control law, then the problem of "explosion of complexity" inherent in the traditional backstepping design method is canceled. It is proved that the proposed fuzzy adaptive control method guarantees all the signals in the close-loop system to be uniformly bounded, and the tracking error and observer error converge to a small neighborhood of the origin.5) The problem of output feedback tracking almost disturbance decoupling is investigated for a class of strict-feedback dynamic uncertain nonlinear large-scale systems. A fuzzy high-gain state observer is established to estimate the unmeasured states, and then, combined fuzzy adaptive control with backstepping design, a fuzzy adaptive decentralized output feedback controller is proposed. A nonquadratic Lyapunov function is used to analyze stability and turns out to be necessary. The proposed controller can not only achieve internal stability of the closed-loop system in the sense of ilSpS (integral input-to-state practically stable) respect to the disturbance input, but also diminish the effect of disturbance on output in the sense of Lp gain.6) For the proposed output feedback stabilizing control, practical tracking control and disturbance attenuation method, corresponding simulation examples are provided respectively, to illustrate the effectiveness and feasibility of the results.