Performance improvement versus robust stability in model reference adaptive control

The mean square tracking error criterion and the L_∞ tracking error bound criterion are used to assess the performance of a standard robust model reference adaptive control schemes in ideal and nonideal situations. The controller performance is examined in an effort to establish a modified scheme that can have an arbitrarily improved nominal performance in the ideal case and in the presence of bounded disturbances. It is shown that for these cases the modified scheme can provide an arbitrarily improved transient performance and an arbitrary reduction in the size of possible bursts that may occur at steady state. As in the nonadaptive case the nominal performance has to be traded off with robust stability and therefore the improvement in performance achieved by the proposed scheme is limited by the size of the unmodeled dynamics