A Local-Distributed and Global-Decentralized SoC Balancing Method for Hybrid Series-Parallel Energy Storage System

Hybrid series-parallel structure provides an effective mean for large-scale energy storage system (ESS) integrating low voltage level energy storage units (ESUs). In ESS, the state of charge (SoC) balancing control plays an essential role. In this article, a local-distributed and global-decentralized SoC balancing control strategy is proposed for hybrid series-parallel ESS. Under the proposed scheme, the SoC of ESUs in each local string converge to the same value driven in a distributed manner and the SoC balance among different strings and power sharing of the ESS under both the charging and discharging modes are realized in a decentralized manner. Because there are no communication links between dispersed ESU strings, the scalability of the ESS is improved. Small signal stability analysis is carried out, which provides a guide for parameter design. Simulation results verify the effectiveness and correctness of the proposed method.