Reduced-order H∞ controller design and separation principle

Properties and structure of the bounded real Riccati inequality are explored in this paper to establish the separation principle, in the H^∞ norm sense, between state feedback design and reduced-order observer design and provide a design procedure for reduced-order H^∞ controller design. The design essentially involves two uncoupled Riccati equations that are solved sequentially. Design flexibilities associated with the approach are identified and utilized to reduce conservativeness. The design approach is interpreted in terms of the separation structure of state feedback design and observer design.