A Convex Cycle-based Degradation Model for Battery Energy Storage Planning and Operation
For battery energy storage operators, this provides a convex degradation model that can be integrated into optimization to improve profit and lifetime.
The paper proves that rainflow cycle-based battery degradation cost is convex, enabling its inclusion in optimization problems. A case study on PJM regulation market shows the model maximizes operating profits and extends battery lifetime.
A vital aspect in energy storage planning and operation is to accurately model its operational cost, which mainly comes from the battery cell degradation. Battery degradation can be viewed as a complex material fatigue process that based on stress cycles. Rainflow algorithm is a popular way for cycle identification in material fatigue process, and has been extensively used in battery degradation assessment. However, the rainflow algorithm does not have a closed form, which makes the major difficulty to include it in optimization. In this paper, we prove the rainflow cycle-based cost is convex. Convexity enables the proposed degradation model to be incorporated in different battery optimization problems and guarantees the solution quality. We provide a subgradient algorithm to solve the problem. A case study on PJM regulation market demonstrates the effectiveness of the proposed degradation model in maximizing the battery operating profits as well as extending its lifetime.