The Negative Margin of Algebraic Riccati Inequality and H_∞ Robust Sub-Optimal Control for Plants with Time Varying Perturbations

Abstract

In this paper the concept of the negative margin of an algebraic Riccati inequality is introduced and its properties are discussed. Using these properties, H_∞ robust sub-optimal control problems are investigated for the plant with time varying structural uncertainties. Such a sufficient condition is given that a nominal H_∞ sub-optimal system has robust sub-optimality for structural uncertainties of the plant. When nominal parameters of the plant are given, a necessary and sufficient condition for existence of H_∞ robust sub-optimal controller by state feedback is derived and a design method is given.