On optimal robust disturbance attenuation

In this article, we give an explicit solution to the nonstandard H-infinity problem which includes the optimal robust disturbance attenuation problem and the two-disc problem. The solution depends on an operator which is analogous to the Sarason operator for the standard H-infinity problem, it allows to quantify the optimal performance of feedback systems and provides an explicit formula for the optimal controller. The nonstandard H-infinity problem is perhaps the simplest control problem which deals with significant plant uncertainty. Surprisingly, relatively little work has been done on it despite the large number of papers in the H-infinity control literature, (C) 2002 Elsevier Science B.V. All rights reserved.