Plantwide control – A review and a new design procedure

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 variables should be controlled, which variables should be measured, which inputs should be manipulated, and which links should be made between them? ” These are the questions 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 (“outputs”), 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