Direct adaptive output-feedback fuzzy controller for a nonaffine nonlinear system

A direct adaptive output-feedback controller for highly nonlinear systems is proposed by considering uncertain or ill-defined nonaffine nonlinear systems and employing a static fuzzy logic system (FLS) with flexible structure, i.e. online variation of the number of fuzzy rules. A linear error observer whose dynamic order is the same as that of the controlled system is employed and the FLS approximates and adaptively cancels an unknown plant nonlinearity using the observed state variables. A control law and adaptive laws for unknown fuzzy parameters and bounding constant are established so that the whole closed-loop system is stable in the sense of Lyapunov. The state observation error and tracking error are guaranteed to be uniformly ultimately bounded. No a priori knowledge of an upper bound on a lumped uncertainty is required.