Performance Preserving Controller Reduction via Additive Perturbation of the Closed-Loop Transfer Function

In this note, a new H-infinity performance preserving controller order reduction method is proposed, Here performance preservation indicates that the H-infinity norm bound of the closed loop transfer function with reduced-order controller is not greater than the H-infinity norm bound of the closed loop transfer function with full order controller, We assume additive perturbations to the closed-loop transfer function and obtain a sufficient condition for performance preservation. Two kinds of useful weightings are derived, and the controller reduction problem is solved via a frequency weighted model reduction problem.