Decentralized robust control of large-scale systems via sensitivity reduction to the interactions

The problem of achieving stability and certain H_∞ performance objective for a large-scale system by a decentralized feedback law is considered. It is shown in order to reduce the sensitivity to the interactions, the states of the other subsystems can be considered as external disturbances for each subsystem. An appropriate H_∞ controller is designed for each subsystem. Solving H_∞ problems for the subsystems, the sensitivity to the interactions is reduced and the performance problem which is formulated as the standard weighted mixed sensitivity H_∞ problem, is solved. Sufficient conditions are derived when satisfied to assure the overall stability