Studies on plantwide control

Most (if not all) available control theories assume that a control structure is given at the outset. They therefore fail to answer some basic questions that a control engineer regularly meets in practice (Foss 1973): “Which vari-ables should be controlled, which variables should be measured, which inputs should be manipulated, and which links should be made between them? ” These are the question that plantwide control tries to answer. There are two main approaches to the problem, a mathematically oriented approach (control structure design) and a process oriented approach. Both approaches are reviewed in the paper. Emphasis is put on the selection of controlled variables, and it is shown that the idea of “self-optimizing control ” provides a link between steady-state optimization and control. We also provide some definitions of terms used within the area of plantwide control. This paper is an unpublished internal report which was written as part of the European Union CAPE.NE