On suboptimal H∞ controllers for unstable distributed plants

In this paper we solve the 2-block H^∞ suboptimal control problem for a class of (possibly) unstable and (possibly) infinite dimensional plants. A solution to the H^∞ suboptimal control problem for infinite dimensional stable plants was obtained in [5]. Also, in [11] and [12] the H^∞ optimal control problem was solved for unstable distributed plants. Our solution for the suboptimal control problem of unstable distributed plants is based on the techniques developed in [5, 11].