(751c) Top-Down Approach for Scheduling and Control Under Time-Varying Electricity Prices
AIChE Annual Meeting
Friday, November 15, 2019 - 8:36am to 8:54am
Following the classification proposed by Baldea and Harjunkoski (2014), there are mainly two approaches for integrating scheduling and control: (i) top-down approach, which incorporates control elements into the scheduling framework and includes the sub-categories of control-defined transition times, dynamic optimization-based scheduling and bridging models; and (ii) bottom-up approach, which incorporates economic considerations into the control framework, e.g. Economic MPC. For the top-down approach, more specifically using control-defined transition times, recent studies have shown the benefits of integration. Mahadevan et al. (2002) presented a first study on how the control layer affects the scheduling of grade transitions in polymerization reactors, in which the authors screen the more difficult transitions before solving a simplified scheduling problem. Chu and You (2012) simplified the optimal control task by generating a set of candidate PI controller parameter values offline and selecting the optimal candidate in the integrated problem online. Subsequently, the same authors made several contributions extending the methodology for batch processes and different formulation and solution strategies (Chu and You, 2015). In these studies, the problem is originally cast as a mixed-integer dynamic optimization (MIDO), which requires a decomposition approach to be implemented online.
More recently, Tong et al. (2017) analyzed the integration with varying electricity prices and proposed a decomposition solution method and online implementation based on a receding horizon approach which address both optimal controller tuning and scheduling decisions. In the present work, the model proposed by Tong et al. (2017) is expanded to include important features such as start and end times for the scheduling task, and different criteria for the optimal tuning of the regulatory control parameters. A comparison is made between different solution strategies for the scheduling task, and the benefits and drawbacks of using the mathematical optimization formulation are highlighted. The impact of parameter uncertainty in the problem size and the choice of the solution method is also evaluated. Finally, the decomposition-based solution strategy originally proposed is adjusted to accommodate the more flexible scheduling model, and the results are evaluated from a Demand Response viewpoint. The methodology is applied to a simple case-study employing an energy intensive process unit.
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