Hierarchical Partial Power Processing for Second-Life Battery-Integrated Grid-Connected Multilevel Inverters

With the growing number of retired electric vehicle batteries, the second-life battery energy storage system (2-BESS) for power grid has attracted much research attention due to its cost-effectiveness and environmental benefits. This paper proposes a battery-integrated cascaded H-bridge (BI-CHB) 2-BESS architecture equipped by a hierarchical partial power processing (HiPPP) network, effectively addressing the challenges posed by second-life battery (SLB) heterogeneity. The proposed HiPPP network is based on a new statistical design framework integrating multivariate distribution flattening and mixed-integer linear programming. An active state of charge (SOC) balancing control using the HiPPP network is also proposed for high battery energy utilization. The study reveals a new trade-off frontier between power capability and energy utilization of 2-BESS for grids. The HiPPP network significantly improves the power-energy trade-off frontier and demonstrates robust reactive power injection capabilities. Validated by the Monte Carlo simulations, the HiPPP network effectively suppresses the propagation of SLB heterogeneity to the output power, enhancing reliability and reducing the uncertainty of 2-BESSs. Hardware-in-the-loop experiments verify the effectiveness of the proposed active SOC balancing control scheme and the compliance of the SLB power capability limit.