Control structure design: New developments and future directions

Control structure design (CSD) deals with the following fundamental question: Given the process flowsheet, where should the controllers be placed, or more specifically, what variables should be measured (sensors) and manipulated (valves) and how should the two sets be interconnected for safe and economic operation? These choices are not obvious for most systems encountered in practice. The problem of CSD is also complicated by the increasing mass, energy and information integration among the different process units, which necessitates consideration of the whole plant together. In comparison with the vast amount of the literature available on controller design, CSD has received only limited attention. Despite the advances made, a systematic method is still lacking, which can be mainly attributed to the lack of proper mathematical formulation of the problem. Process control lore includes tales of multi-million dollar plants that never operated due to lack of sufficient theory for CSD (Luyben et al., 1998).