Relay feedback of multivariable systems and its use for auto-tuning of multi-loop PI controllers

Abstract

This paper presents an auto-tuning method for designing multi-loop PI controllers for a class of multivariable plants based on their behaviour under closed loop relay feedback. Unlike relay feedback in single loop plants, multi-loop relay feedback may exhibit a number of different behaviours depending on the strength of interactions, Loh and Vasnani [10]. Hence, different design strategies catering to all the possible scenarios will be proposed. The proposed technique uses ratios of some ultimate quantities to tune the required PI controllers, much like single loop plants, Astrom and Hagglund [5]. Simulation results are presented to illustrate the design methodology.