A feedforward controller design for periodic signals in non-minimum phase processes

Abstract

A novel feedforward controller is derived in this paper for asymptotic decoupling of measurable conf disturbances and asymptotic tracking of conf setpoints, when the process is non-minimum phase. The resulting controller, which provides necessary amplitude phase precompensation, is a finite impulse response (FIR) filter and hence the problem of non-minimum phase zero cancellation is avoided. The controller can be designed by solving a diophantine identity, in which the parametric model of the process and the model of the conf signal are involved. However, in the presence of process model uncertainties, the controller can instead be designed by using only the frequency response of the process at the frequencies defined by the conf signals. The proposed controller can be useful in a two-degree of freedom controller design, to avoid the introduction of the internal model of the conf signal in the feedback loop which may give rise to stability robustness problems.