Simultaneous stabilization under stable additive or feedback perturbations

It is shown that a given plant and one obtained by a known stable additive (or feedback) perturbation of this plant can be simultaneously stabilised by a common controller in the standard linear, time-invariant, multi-input multi-output unity-feedback system. No small-gain restrictions are imposed on the known stable perturbations. A set of simultaneously stabilizing controllers is proposed. The results extend the standard single connected set of plants description in robust control design methods to two (possibly disjoint) sets of plants