A robust modification of a new class of adaptive controllers

Recently, a new class of adaptive control schemes, motivated from nonlinear systems theory, has been proposed for minimum phase linear time invariant plants. Under certain assumptions on the plant transfer function, these schemes guarantee uniform signal boundedness and good transient and steady state response for the tracking error provided there are no disturbances and/or un-modeled dynamics. The purpose of this paper is to improve the robustness of this new class of adaptive controllers with respect to unmodeled dynamics and bounded disturbances. As in the case of the traditional adaptive controllers, robustness is guaranteed by modifying the adaptive controllers so that signal signal boundedness and “small” tracking errors are guaranteed in the presence of a general class of dynamic uncertainties and bounded disturbances. While the modification techniques are similar with those used in the more traditional adaptive controllers, the analysis is different due to the highly nonlinear nature of the new class of adaptive controller