Equivalence and reduction of delay-differential systems

A new direct method is presented which reduces a given high-order representation of a control system with delays to a firstorder form that is encountered in the study of neutral delay-differential systems. Using the polynomial system description (PMD) setting due to Rosenbrock, it is shown that the transformation connecting the original PMD with the first-order form is Fuhrmann’s strict system equivalence. This type of system equivalence leaves the transfer function and other relevant structural properties of the original system invariant.