Design and Management of Battery-Supercapacitor Hybrid Electrical Energy Storage Systems for Regulation Services

Regulation services (RS) play an important role in maintaining the stability of electric grids by correcting for short-term mismatches between electricity generation and demand. RS providers dynamically supply electricity to the grid or consume electricity from it, in response to regulation signals, in return for economic compensation. This capability is commonly realized through large-scale electrical energy storage (EES) systems based on batteries. However, the highly transient nature of the regulation signals implies that the batteries used for RS are subject to frequent charge and discharge cycles, leading to shortened battery life and thereby impacting the profitability of RS. In this work, we explore the use of hybrid EES (HEES) systems, which combine batteries and supercapacitors, to improve the profitability of RS. HEES systems have the potential to reduce the cost of providing RS by utilizing supercapacitors to respond to the high-frequency components of the regulation signal, prolonging battery life. However, realizing this potential presents several challenges. First, the benefits of HEES systems have a profound dependence on the type of hybrid topology (i.e., active or passive), which results in a tradeoff between the implementation cost and the utilization of the supercapacitor capacity. Second, the allocation of energy storage capacity to batteries and supercapacitors should be carefully determined in the design phase because the reduction in battery replacement cost due to the use of supercapacitors must be balanced against the increased upfront cost for supercapacitors. Third, active HEES systems involve the problem of managing the power flows to batteries and supercapacitors so as to realize maximum cost benefits. To address these challenges, we present a framework for the design and management of a HEES system, so as to maximize the profit from the perspective of an RS provider. This framework consists of i) a design-time capacity optimization phase that determines the best allocation of capacity to batteries and supercapacitors and ii) a run-time management scheme that selects how the different storage devices are orchestrated considering their characteristics and the incoming regulation signal. Our experiments show that, with the proposed capacity optimization and management framework, the use of a passive or an active HEES system can improve the profit of RS providers by 1.16 x or 5.44 x, respectively.