SELECTION OF PROCESS-CONTROL STRUCTURE-BASED ON LINEAR DYNAMIC ECONOMICS

It is recognized widely that the choice of measured and manipulated variables employed in a control system (the control structure) can have a strong effect on the performance of the process control system. This paper outlines a systematic method that can be used to select the economically optimal control structure of a process without designing the process controller, while maintaining good controllability characteristics. This requires examination of the effects of process dynamics on process economics and how changes in the control structure alter these economics. The scope of the problem is limited to selecting economically optimal square regulatory feedback control structures for processes whose operation is dominated by steady-state aspects. As the problem is combinatorial in nature, the method addresses systematic generation and efficient search of the space of potential structures through the use of integer programming techniques. Application of this approach to two case studies demonstrates that the technique leads to an improved understanding of the effects of the control structure on process economics and process controller performance.