AN OVERVIEW OF EXTREMAL PROPERTIES FOR ROBUST-CONTROL OF INTERVAL PLANTS

This paper provides an overview of recent results on the problem of ro bust stability and performance of feedback control systems in the pres ence of plant perturbations. The widely studied class of interval plan ts is considered, and an effort is made to cover different types of pl ant perturbations by incorporating, in addition to the interval plant description, unstructured norm bounded perturbations. Extremality resu lts for these classes of uncertain systems are provided in a unifying framework. Robust performance of control systems is addressed in the p aper and a number of extremal results are given for the computation of the structured singular value function for feedback systems with inte rval plants. Also, classical frequency response analysis for interval plant-controller families of open loop transfer functions is surveyed, with the aim of providing extremal results for the computation of spe cification parameters, such as phase or gain margins, and sensitivity and complementary sensitivity peaks.