ROBUST ADAPTIVE CONTROL.

Abstract

This paper considers the robust redesign of a direct adaptive controller applied to a linear time invariant plant with unmodeled stable dynamics. In order to achieve robustness the adaptive law is modified by retarding the updated parameters whenever they drift to large values and switching off retardation when their norm is less than an arbitrary upper bound. The modified adaptive law guarantees boundedness for any bounded initial conditions and convergence of the tracking error to a bounded residual set whose size depends on the bound for the reference input signal and the characteristics of the unmodeled dynamics. In the regulation case or in the absence of unmodeled dynamics the modified adaptive law guarantees zero tracking error as t yields infinity in addition to boundedness.