Reliable decentralized stabilization of feedforward and feedbackinterconnected systems

The synthesis of decentralized controllers that are reliable in the presence of breakdowns in the interconnections is considered for plants obtained via feedforward and feedback type interconnection schemes. The main objective is to determine the precise conditions on the plant which assure such reliable synthesis. It is shown that the central property for reliable decentralized stabilization is always an appropriate parity interlacing property among the poles of the interconnection subplants and certain blocking zeros of the overall plant. The conditions under which the stabilization of a two-channel plant is affected by the stabilization of its diagonal subplants are also obtained. The results also find application in multiple controller reliable synthesis problems. The discussion is restricted to two-channel plants