Multivariable Nyquist self-tuning: a general approach

The paper attempts to develop the framework that applies to the general case. In particular, consideration is given to fractional representations for the branches of the characteristic transfer functions, and algorithms are developed for both the computation of these representations and their implementation within a self-tuning configuration. Consideration is also given to issues of stability. The results of the paper are illustrated by means of numerical examples and it is concluded by a design study based on the open-loop unstable chemical reactor.