FIXED-ORDER SCALED H-INFINITY SYNTHESIS

Given a stabilizing fixed-order controller, we propose two algorithms which improve its robust stability and robust performance in the frame work of the H-infinity, control problem with constant scaling. The ide a is to formulate the scaled H-infinity control problem as generalized eigenvalue minimization problems involving (non-linear) matrix inequa lities, and then to apply co-ordinate descent algorithms which split t he problem into successive (quasi)convex minimization problems. These methods can be considered an extension of the standard mu-synthesis me thod (the D-K iteration) for fixed-order controller design. Our method s are different from the standard D-K-type iterations in that the anal ytic centres are computed at each step instead of minimizing objective functions. The controllers obtained may not be globally optimal in ge neral, but are guaranteed to be better than the initial controller. He nce, our methods can be used to improve robustness/performance of a gi ven fixed-order stabilizing controller. Illustrative examples are give n for a benchmark problem. (C) 1997 John Wiley & Sons, Ltd.