Design of plantwide control systems

Plantwide control refers to the control of an entire plant, consisting of many interconnected unit operations. The design of a plantwide control system is an open-ended problem, complicated by the large number of choices available for control structure, controller type and so on. A systematic method is thus needed to decompose this large-scale problem into more manageable sub-problems. It is the goal of this thesis to develop such methods. We have developed a hierarchical procedure for synthesizing a plantwide control system. The thrust of the procedure is to design a plantwide control system that ensures optimal operation in the presence of unmeasured disturbances and model uncertainty. The procedure decomposes the plantwide control problem into six levels of decisions. As one proceeds down the hierarchy, more modeling, not structural details, are added. Alternatives are generated at each level and evaluated based on profitability. Both steady-state economics and dynamic controllability are important criteria in the selection of an optimal control strategy. Several practical issues arise in the application of the procedure to typical industrial problems. Short-cut methods and new tools have been proposed to deal with these issues more effectively and efficiently