A hierarchical active balancing architecture for Li-ion batteries

This paper proposes a hierarchical battery balancing architecture for the series connected lithium-ion batteries. The battery cells are grouped into different packs and the bottom layer is the Adjacent Cell-to-Cell structure consisting of the packs. The top layer is connected to different packs and can deliver the energy from one pack to any other pack bi-directionally, leading to high flexibility. A multi-directional multi-port converter is proposed to serve as the top layer. With the hierarchical architecture, the balanced energy transfer of the cells in different packs can be decoupled, which avoid the repeated charging and discharging during the balancing process. This is beneficial for lengthening the battery lifetime and increasing the State-of-Health (SOH). Moreover, the proposed architecture can lower the current rating of the balancing circuits, which helps decrease the required cost and improve the system efficiency. The experimental results verified the benefits of the proposed architecture.