Robust adaptive control for a class of uncertain strict-feedback nonlinear systems

In this paper, robust adaptive control is presented for a class of perturbed strict-feedback nonlinear systems with both completely unknown control coefficients and parametric uncertainties. The proposed design method does not require the a priori knowledge of the signs of the unknown control coefficients. For the first time, the key technical Lemma is proven when the Nussbaum function is chosen by N (zeta) = zeta(2) cos(zeta), based on which the proposed robust adaptive scheme can guarantee the global uniform ultimate boundedness of the closed-loop system signals. Simulation results show the validity of the proposed scheme. Copyright (C) 2008 John Wiley & Sons, Ltd.