Economic Plantwide Control

Abstract

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 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and control.We also provide some definitions of terms used within the area of plantwide control.This paper is an unpublished internal report which was written as part of the European Union CAPE.NET project (working group 5). We welcome any comments you may have.

Simple Rules for Economic Plantwide Control

“…The definitions and terms presented here are based on terminology used in (Larsson and Skogestad, 2000) and (Skogestad, 2012), unless otherwise noted. A typical hierarchical decomposition of the plantwide control structure is depicted in Figure 1a.…”

“…A limiting factor for the updating frequency is the requirement that the plant has to settle, before the re-optimization problem can be solved. For more details we refer the reader to (Skogestad, 2012) Table 1: Economic Plantwide Control design procedure.…”

Plant-Wide Control of a Reactive Distillation Column on Biodiesel Production

“…The control design is based on a Skogestad approach, which has been reduced in seven simple steps [11].…”

Plantwide control: a review and proposal of an augmented hierarchical plantwide control design technique.

“…Although the problem itself is not perfectly defined, the following summary presents a concise idea of it: In a mathematical sense, the plantwide control problem is a formidable and almost hopeless combinatorial problem involving a large number of discrete decision variables. In addition, the problem has been poorly defined in terms of its objectives (Skogestad, 2012), (Gernaey, et al, 2012). Generally, it involves the following tasks (Foss, 1973), (Skogestad & Postlethwaite, 1996):…”

“…The major advances since the beginning of its formal studies are described, with the highlighting of the most noticeable contributions. Classically, plantwide control design is the selection of controlled variables (CVs), selection of manipulated variables (MVs), selection of extra measurements, selection of control configuration and selection of controller type (Skogestad, 2012). In other words, it typically includes all structural decisions of the control systems, but not the actual design of the system.…”