Observer-Based Adaptive Fuzzy Fault-Tolerant Control for Nonlinear Systems Using Small-Gain Approach

This paper addresses the adaptive fault-tolerant control problem for a class of nonlinear systems with unmodeled dynamics, actuator faults and immeasurable states. Fuzzy logic systems are used to approximate the unknown nonlinear functions. A new input-driven filter is designed to cope with the problem caused by the immeasurable states, and the lower bound of the unknown function $$\vartheta _j({\bar{x}}_j)$$ϑj(x¯j) is contained in the filter. Based on backstepping technique, a recursive design process is designed for the considered nonlinear system. Combining input-to-state practically stable theory with small-gain approach, the designed adaptive fuzzy controller guarantees the semi-global uniform ultimate boundedness of all variables in the closed-loop system. The main contributions of this paper lie in that not only the nonlinear system under consideration is more general, but also an effective output-feedback control scheme is proposed for the investigated nonlinear system. Finally, simulation results are depicted to validate the efficiency of our presented control method.