A Comparison of Strategies for Managing Energy Constraints of Energy Storage Providing Frequency Regulation

Abstract

CAISO and PJM operate the majority of grid-connected batteries in the U.S. The two markets manage the energy constraints of batteries providing frequency regulation differently. PJM, which has a fast (RegD) and a slow (RegA) regulation signal, uses RegA to conditionally maintain energy neutrality of the RegD signal over short durations. CAISO offsets net energy produced/consumed for frequency regulation with energy from the real-time energy market. This paper presents a comparison of these strategies with the goal of assessing the advantages and disadvantages of each approach. Specifically, we compare the approaches in terms of regulation signal-following performance and additional system control effort. Case study results suggest that both strategies can reliably keep a battery away from its state of charge limits but that PJM's strategy requires larger energy deviation from base operations.