抄録
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.
