Observer-controller configuration approach to controller robustification

This paper proposes a design framework for robust control system design. The approach is based on giving robustness to a previously existing controller instead of the design of a robust controller: therefore the consideration of the controller robustification problem. The approach is based on the addition of a robustification block to the control system in such a way that (i) the robustness properties of the initial controller are improved, and (ii) it is not necessary to modify the initial controller. The resulting approach is presented as a two-step design. The paper concentrates the second stage of the design on the condition for robust stability