AC Battery: Modular Layout with Cell-level Degradation Control

This paper proposes a three-phase AC battery based on the modular multilevel converter (M2C). The AC battery concept allows plug-and-play combinatorial integration of diverse battery cells with different characteristics such as nominal voltage, state of charge (SoC), and degradation levels. The resulting modular and reconfigurable battery pack can cost-effectively cover various applications, from electrified vehicles to stationary storage. To this end, in each sub-module (SM) of the M2C, battery cells (or battery modules composed of one or more battery cells) are connected to a single capacitor, thus enabling a cell-to-cell battery integration and control. In this scenario, the traditional battery management system (BMS) can be replaced by control schemes at the converter level, aiming to equalise critical parameters associated with battery cells (or battery modules). In this context, the degradation level of battery cells integrated by the proposed AC battery is a critical parameter to be considered. Indeed, it is likely that the integrated battery cells by the AC battery have different degradation levels. Therefore, methods for managing their degradation state are required to equalise the lifespan of battery cells within the AC battery. Based on that, this paper proposes a consensus-based distributed control scheme to manage the degradation process of battery cells (or battery modules composed of one or more battery cells) within the AC battery. Simulation results corroborate the effectiveness of the proposal.