McAvoy (1999) present a method in which the control objective is divided into two categories: variables that must be controlled and product flow and quality. His approach is
to find the set of input that will minimize valve movements, where only as many valves as
controlled variables are allowed to be used. This is first solved for the “must” variables,
then for product rate and quality. The optimization problem is simplified by using a linear
stable steady state model. He gives no guidance into how to find which variables that must
be controlled.
Hierarchical decomposition based on time scales
Buckley (1964) proposed to design the quality control system as high-pass filters for disturbancesand to design the mass balance control system as low pass filters. If the resonancefrequency of the quality control system is designed to be an order of magnitude higher thanthe break frequency of the mass balance system then the two loops will be non-interacting.
McAvoy and Ye (1994) divide their method into four stages: