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A Geometric Approach to Aggregate Flexibility Modeling of Thermostatically Controlled Loads

Journal Article · · IEEE Transactions on Power Systems

Coordinated aggregation of a large population of thermostatically controlled loads (TCLs) presents a great potential to provide various ancillary services to the grid. One of the key challenges in coordination and control of TCLs is developing a simple and portable model to accurately extract their aggregate flexibility. In this paper, we propose a novel geometric approach to model the aggregate flexibility of TCLs. We show that the set of admissible power profiles of an individual TCL is a polytope, and their aggregate flexibility is the Minkowski sum of the individual polytopes. In order to represent their aggregate flexibility in an intuitive way and achieve a tractable approximation, we develop optimization-based algorithms to approximate the polytopes by the homothets of a given convex set. As a special application, this set is chosen as a virtual battery model and the corresponding optimal approximation problems are solved efficiently by equivalent linear programs. Numerical results show that our algorithms yield significant improvement in characterizing the aggregate flexibility over existing modeling methods. Finally, we also conduct case studies to demonstrate the efficacy of our approaches by coordinating TCLs to track a frequency regulation signal from the Pennsylvania-New Jersey-Maryland (PJM) Interconnection.

Research Organization:
Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
Sponsoring Organization:
USDOE; National Science Foundation (NSF)
Grant/Contract Number:
AC05-76RL01830
OSTI ID:
2458240
Report Number(s):
PNNL-SA--120065
Journal Information:
IEEE Transactions on Power Systems, Journal Name: IEEE Transactions on Power Systems Journal Issue: 6 Vol. 32; ISSN 0885-8950
Publisher:
IEEECopyright Statement
Country of Publication:
United States
Language:
English

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