Adaptive Control for Strict Feedback Systems With Actuator Aging and External Disturbance

Unknown actuator aging is inevitable in practice. However, reviewing the development of control theory, available results of handling actuator aging are still very limited. In this paper, we address such a problem by considering controlling a class of unknown nonlinear systems. In fact, unknown aging can be denoted as a nonlinear function of variable t with nonlinearly parameterized parameters which cannot be estimated by adaptive approach directly. To solve it, a new adaptive controller and update laws are proposed by linearizing aging function. Unlike the traditional approaches, a new Lyapunov function, including an integral term about estimation error of such parameter, is designed to analyze the stability of the closed-loop system. It is shown that the designed controller can ensure the stability and tracking performance of the closed-loop system.