Performance preserving controller reduction via additive perturbation of closed loop transfer function

An H_∞ performance preserving controller order reduction method is proposed. Here performance preservation indicates that the H_∞ norm of the closed loop transfer function with reduced order controller is not greater than that of the closed loop transfer function with full order controller. We adopt the additive perturbation of closed loop transfer function and obtain a sufficient condition for the performance preservation. Then two kinds of useful weightings are derived and the controller reduction problem is solved via frequency weighted model reduction problem