Reduced Order Internal Models in the Frequency Domain

TL;DR

This paper demonstrates that the internal model in control systems can be reduced in order when the class of perturbations is limited, using frequency domain methods and a two-stage design process.

Contribution

It introduces a method to reduce the internal model order in controllers for robust regulation under certain perturbation restrictions.

Findings

Reduced internal model order is achievable with frequency domain techniques.

A two-stage design process effectively implements the reduced internal model.

Experimental validation on a five tank process confirms the approach's practicality.

Abstract

The internal model principle states that all robustly regulating controllers must contain a suitably reduplicated internal model of the signal to be regulated. Using frequency domain methods, we show that the number of the copies may be reduced if the class of perturbations in the problem is restricted. We present a two stage design procedure for a simple controller containing a reduced order internal model achieving robust regulation. The results are illustrated with an example of a five tank laboratory process where a restricted class of perturbations arises naturally.