DESIGN OF MULTILOOP SISO CONTROLLERS IN MULTIVARIABLE PROCESSES.

A practical design procedure is proposed for determining the structure, variable pairing, and tuning of multiloop SISO controllers in a multivariable-process environment. The selection of controlled variables relies primarily on engineering judgment. The choice of manipulated variables is based on M. Morari's Resiliency Index (minimum singular value of the process transfer function matrix). Variable pairing is decided by first eliminating those pairings that give negative RGA's or negative A. Niederlinksi or Morari Indexes of integral controllability. The final variable-pairing selection is based on the B. D. Tyreus load rejection criterion. The simple BLT controller tuning method, recently proposed by W. L. Luyben, is used to give consistent, logical comparisons of alternatives. The method is illustrated by applying it to a multivariable ternary distillation column example.