Adaptive Fuzzy Control for Uncertain Strict-Feedback Nonlinear Systems With Full-State Constraints Using Disturbance Observer

Adaptive fuzzy control via disturbance observer (DOB) is proposed for uncertain strict-feedback nonlinear systems with unknown disturbances and full-state constraints. By constructing an integral barrier Lyapunov function, it is ensured that all states in the strict-feedback system will not exceed their preset constraints. Moreover, the fuzzy-logic system is adopted to approximate the uncertainty of nonlinear functions in this system. To efficiently estimate the approximation error and unknown disturbances, this work designs a new DOB and ensures that the estimation error of lumped disturbances converge to a smaller and bounded set. The proposed control based on the Lyapunov criterion ensures that all signals in the nonlinear system are semi-global uniformly and ultimately bounded. Two simulation examples illustrate the efficiency of the proposed control.