Enhancement of fixed controllers via adaptive-Q disturbance estimate feedback

Abstract

A direct adaptive control scheme is proposed, termed an Adaptive-Q scheme, which has the property that it can, if considered desirable, limit its searches to the space of all stabilizing linear proper controllers for a nominal linear plant. The adaptive controller feeds back disturbance estimates via a filter with operator Q. It augments any fixed linear stabilizing controller, viewed as a minimum variance disturbance decoupling controller, for the nominal plant. For a nominal plant, the adaptive-Q augmentations evanesce, but when the plant is other than the nominal one, the adaptive-Q scheme seeks to minimize the effect of disturbances and thus to improve the performance over that of the fixed controller. The proposed adaptive-Q disturbance estimate feedback (DEF) controllers can be simple to implement even for high order multivariable plants with high order fixed controllers, and have the significance that they seek to enhance performance of standard controller designs in the face of plant perturbations or uncertainties, rather than supplant or compete with them. Prior knowledge about the frequency band of plant uncertainty is readily incorporated into the adaptive design scheme.