Disturbance-Observer-Based Adaptive Fuzzy Control for Strict-Feedback Switched Nonlinear Systems With Input Delay

In this article, the problem of disturbance-observer-based adaptive fuzzy control is investigated for a class of strict-feedback switched nonlinear systems under arbitrary switching. Compared with existing results, a main contribution of this article is to design a piecewise switched nonlinear disturbance observer (NDO) for arbitrary switching systems to estimate unknown compound disturbances, which consist of external disturbances and approximate errors. Different from the common adaptive laws, the piecewise switched adaptive laws are designed, which reduces the conservativeness of controller design. In order to solve the difficulties caused by input delay and computational complexity, the Pade approximation and dynamic surface control technology are introduced, respectively. By utilizing the adaptive backstepping technique and the Lyapunov stability theorem, a novel controller based on the piecewise switched NDO is developed. It is proved that all the signals of the closed-loop systems are semiglobally uniformly ultimately bounded. The disturbance estimation errors and the tracking errors converge on a small neighborhood of the origin. Simulation results are provided to demonstrate the effectiveness of the proposed method.