A FEEDFORWARD CONTROLLER-DESIGN FOR PERIODIC SIGNALS IN NONMINIMUM-PHASE PROCESSES

A novel feedforward controller is derived in this paper for asymptotic decoupling of measurable periodic disturbances and asymptotic trackin g of periodic setpoints, when the process is non-minimum phase. The re sulting controller, which provides necessary amplitude phase precompen sation, is a finite impulse response (FIR) filter and hence the proble m of non-minimum phase zero cancellation is avoided. The controller ca n be designed by solving a diophantine identity, in which the parametr ic model of the process and the model of the periodic signal are invol ved. However, in the presence of process model uncertainties, the cont roller can instead be designed by using only the frequency response of the process al the frequencies defined by the periodic signals. The p roposed controller can be useful in a two-degree of freedom controller design, to avoid the introduction of the internal model of the period ic signal in the feedback loop which may give rise to stability robust ness problems.