Using the diophantine equation in the design of a digital perfect tracking compensator

Referring to a two-degree-of-freedom digital control system, the design of a feedforward unit that provides almost perfect tracking also in the nonminimum-phase case by using preview and preaction, is considered. The approach presented herein is only based on the Diophantine equation, without any reference to state-space modelling. Simplicity and efficiency of the proposed solution are pointed out with two numerical examples, and methods for evaluating and improving its performance are described.