The parameterization of all two-degree-of-freedom strongly stabilizing controllers

When a plant can be stabilized by using a stable controller, the controller is said to be a strongly stabilizing controller. The importance of strong stabilizations is to solve some problems occurred by using unstable stabilizing controllers, for example, feedback control systems become high sensitive for disturbances. Hoshikawa et al. clarified the class of strongly stabilizable plants and proposed the parameterization of all strongly stabilizing controllers for those plants. However, in this parameterization, we cannot specify the input-output characteristic and the feedback characteristic separately. One of the ways to specify these characteristics separately is to use two-degree-of-freedom control system. However, the parameterization of all two-degree-of-freedom strongly stabilizing controllers has not been examined. The purpose of this paper is to propose the parameterization of all two-degree-of-freedom strongly stabilizing controllers for strongly stabilizable plants.