Stable adaptive fuzzy controller with time-varying dead-zone

This paper proposes an adaptive fuzzy control scheme for a class of continuous-time nonlinear dynamic systems for which explicit linear parameterizations of the uncertainties are either unknown or impossible. To improve robustness under the approximation errors and disturbances, the proposed scheme includes a dead-zone in adaptation laws which varies its size adaptively. The assumption of known bounds on the approximation errors and disturbances is not required since those are estimated using adaptation laws. The overall adaptive scheme is proven to guarantee global uniform ultimate boundedness in the Lyapunov sense.