Fuzzy-Approximation-Based Adaptive Control of Strict-Feedback Nonlinear Systems With Time Delays

This paper focuses on the problem of adaptive control for a class of nonlinear time-delay systems with unknown nonlinearities and strict-feedback structure. Based on the Lyapunov-Krasovskii functional approach, a state-feedback adaptive controller is constructed by backstepping. The proposed adaptive controller guarantees that the system output converges into a small neighborhood of the reference signal, and all the signals of the closed-loop system remain bounded. Compared with the results that exist, the main advantage of the proposed method is that the controller design is independent of the choice of the fuzzy-membership functions; therefore, a priori knowledge of fuzzy approximators is not necessary for control design, and the proposed approach requires only one adaptive law for an nth-order system. Two numerical examples are used to illustrate the effectiveness of the proposed approach.