Input-output approach to the control of time-delayed systems

An equivalence is established between the sufficient conditions obtained for stability, and consequently for H_infin-type performance, of linear retarded systems and the conditions that are achieved for stability and performance of systems without delay but with norm-bounded uncertainties. In the past, such an equivalence has been found for conditions that were derived for retarded systems using various model transformations. It is shown in this paper that such an equivalence also exists when the more recent and the more efficient descriptor model transformation is used to derive the corresponding sufficient conditions. The new input-output approach is applied also to the case of ´non-small´ delay (delay in a segment that starts from a positive value) and to state-feedback sampled-data control