Observer-based compensators for fixed-order H∞ control

This paper presents a two-Riccati inequality approach for the design of fixed-order H_∞ suboptimal controllers with an observer-based structure. The two Riccati inequalities are only one-way coupled and can be solved consecutively. The fixed-order controller has the structure of a fixed-order estimator of the state feedback control law in the presence of the worst case disturbances. It retains the observer-based compensator structure of the full-order central controller of the standard H_∞ design, but adds a fixed-order dynamic and mappings between the full-order and the fixed-order state spaces. In the full-order special case, this controller recovers to the minimal entropy central controller of the standard H_∞ design