A Framework for Optimizing Multilevel AC Battery Energy Storage Systems

Battery energy storage systems (BESS) play an essential role in modern grids by supporting renewable power systems, improving grid power quality through voltage and frequency regulation, and supporting electric vehicle (EV) charging stations. At the same time, and with the rapid growth of EVs, an enormous number of EV batteries will be retired soon. These second-use EV batteries still have approximately 80% capacity and can be utilized in stationary applications like grid-connected BESSs to reduce the emissions from producing new batteries for energy storage systems. Directly producing multilevel AC from batteries reduces cost by eliminating the need for an explicit conventional inverter. In this paper, a framework is presented for optimizing the multilevel integration of power processing in BESSs, which is particularly applicable to BESSs with heterogeneous second-use batteries.