All fixed-order H/sub /spl infin controllers: observer-based structure and covariance bounds

This note obtains a parameterization of the set of all stabilizing controllers of order less than or equal to the plant, which yields for the closed-loop transfer matrix a specified H/sub /spl infin norm bound. The algebraic results of covariance control are applied to the H/sub /spl infin control problem to yield a parameterization in terms of the Lyapunov matrix, which carries many system properties (such as H/sub 2/ performance, covariance bounds, system entropy at infinity, etc.). All low-order H/sub /spl infin controllers are shown to have observer-based structure for "reduced-order models" of the plant and are characterized by two Riccati equations with a coupling condition.<
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