Approximate recovery of H-infinity loop shapes using fixed-order dynamic compensation

Abstract

This paper presents a method for designing fixed-order dynamic compensators that approximate the Hm full state feedback, closed-loop transfer function properties from disturbance inputs to controlled outputs. This formulation uses an observer canonical form to represent the dynamic compensator which allows the design to be treated as a modified constant gain output feedback problem. The approximate recovery is accomplished through a unique selection of the quadratic performance index weighting matrices. This design procedure is demonstrated by two design examples. The first example is a simple fourth-order model used to demonstrate the procedure. The second example is a longitudinal flight controller for the F-18/HARV Supermaneuverable aircraft. This flight controller is compared to both a full- and reduced-order H^ compensator.