A multilevel, control-theoretic framework for integration of planning, scheduling, and rescheduling

In this paper, an integrated multilevel, control-theoretic framework has been proposed for effectively handling integration of planning, scheduling, and rescheduling. A general resource-constrained, multistage, multiproduct plant operating as a hybrid flowshop facility has been considered. The proposed approach is based on the inherent hierarchical decomposition of the overall decision-making process that is a typical characteristic of large enterprises. The overall problem is segregated into three levels with different horizons, wherein planning over multiperiods is at the top level followed by scheduling for a single period at the middle level and a detailed inventory management schedule for the operator at the lower level. In the hierarchical decomposition, the upper levels are equipped with abstractions of the lower levels and proactiveness for reactive scheduling. The integration of reactive scheduling is motivated by some of the process control principles like cascade control and the concepts of receding horizon. Using the philosophy of decentralized decision-making, it is demonstrated that the lower levels with accurate models have the flexibility and amenability for rescheduling without upsetting the global performance. As an illustrative case study, cyclic scheduling of a simple refinery flow sheet involving continuous lube production in a resource constrained hybrid flowshop is presented to demonstrate the proposed methodology.