A 2DOF H_∞ robust tracking design for a special type of observed state feedback controllers

A control configuration for the design of robust controllers in the general context of LTI systems (SISO, MIMO, stable, unstable) is presented. It consists of a two-degree-of-freedom control architecture constituted by a particular observed state feedback controller arising from a right coprime factorization of the plant together with a prefilter block. Before detailing the general design methodology involving the available two degrees of freedom, the feedback part of the scheme is first analyzed by its own in order to establish connections with respect to a conventional state feedback controller with full state observer. A prefilter block is added afterwards and an optimization based design procedure for the resulting two-degree-of-freedom control scheme is suggested. The feedback part is designed in regulator mode to guarantee robust stability and some performance in terms of disturbance rejection whereas the prefilter controller deals with the servo specifications given in terms of a reference model.