Stabilization of Uncertain Systems by Fixed Order Compensation

The problem of optimal output feedback is addressed in the context of controlling uncertain systems. The objective is to control a possibly high-order uncertain system with a compensator of low order. The compensator formulation precludes the use of direct feedback of the plant output and uses an observer canonical form to represent the compensator dynamics. Similarly to the case of observer design, a two-step design procedure is proposed. A robust design assuming full state feedback is performed, followed by compensator design using an approximate loop-transfer recovery method.