Multivariable control by ‘individual channel design’

Abstract

A new approach—individual channel design (ICD)—to an enduring problem— multivariable feedback control—is presented. The approach is applications-oriented: it starts from the engineering premise that feedback control design is interactive; it involves an interplay between customer specification, uncertain plant characteristics, and the multivariable feedback design process itself. It is shown that individual signal transmission channels arise naturally from customer specification on selected plant outputs with no loss of structural (loop interaction) information. By invoking customer performance specification on different channels, highly successful single-input single-output classical (Nyquist-Bode) design is made possible. ICD is not a design method per se per se; rather it is a global structural framework wherein the possibilities and limitations for local-loop-shaping design (e.g. Bode or Nichols) of a particular plant are made apparent from the outset. Also, the conditions are established whereby channel gain and phase margins are robust measures of stability. In this way, a transparent, flexible and supportive design methodology is developed which directly aims to meet the users’ control requirements and is well-suited to the engineering context. An automotive gas turbine control case study illustrates the salient features of the processs of ICD.