Compensator synthesis using (C,A,B)-pairs

This paper gives a general framework (in the geometric style) for the design of compensators for linear multivariable systems. Basic is the notion of a "(C,A,B)-pair of subspaces." This concept is newly defined here, and we give its simplest application (to the problem of disturbance decoupling by observation feedback). We then formulate a general compensator synthesis principle and show how several well-known synthesis techniques can be derived from it. We also show that "almost all" compensators can be interpreted as observer-based compensators, and discuss the relation between the compensator problem and the stable cover problem.