Optimal Coordinated Control of Multiple Battery Energy Storage Systems for Primary Frequency Regulation

In this paper, we consider a battery aggregator that coordinates a number of distributed battery energy storage systems (BESSs) to provide primary frequency control service in the ancillary service market. In particular, we propose a profit-maximizing BESS coordination strategy that is concerned with two operational phases, namely a frequency regulation phase and a state-of-charge (SoC) recovery phase. Regarding the frequency regulation phase, we minimize the regulation failure penalty by optimally coordinating the operation of multiple BESSs in response to local frequency deviations. The proposed coordination algorithm is "online optimal" in the sense that it does not require any knowledge of the future information, and yet achieves exactly the same optimal performance as if the entire future information is known. On the other hand, during idle periods, the BESSs shall recover their SoCs to a proper range to avoid regulation failure in the next frequency excursion event. We propose a SoC recovery strategy that is not only optimal, but also state invariant and separable in the sense that the target SoC range of each BESS neither varies with its own SoC nor depends on the operation of other BESSs. As such, the target SoC ranges can be calculated once and for all, resulting in extremely low run-time complexity. Numerical results based on real power system frequency measurement data show that the proposed algorithm significantly outperforms a number of benchmark algorithms.