Efficiency Optimized Power-Sharing Algorithm for Modular Battery Energy Storage Systems

Modular battery energy storage systems (MBESSs) enable the use of lower-rated voltage converters and battery modules, and simpler battery management systems. They also improve the system's reliability and allow flexible power sharing among different modules. This article proposes a power-sharing algorithm that maximizes the energy conversion efficiency of this battery energy storage system, considering state of charge (SoC) balancing and battery lifespan. Real-time optimum power sharing is undertaken based on a simple lookup table, whose data were generated via offline genetic algorithm optimization considering the converter's efficiency map. To demonstrate the effectiveness of the proposed algorithm, a six-module prototype system was constructed, each comprising a half-bridge converter and a 10 Ah, 12.8 V, LiFePo4 battery. System testing occurred at different battery power levels in both charging and discharging modes, using the proposed efficiency-optimized power-sharing and the conventional SoC-based power-sharing methods. The results obtained show that the proposed power-sharing control significantly improves the light load efficiency compared to the conventional and equal power-sharing methods. At high loads, the proposed method gives a higher efficiency than the SoC-based method and an equivalent efficiency to the equal power-sharing method.