Hierarchical State-of-Charge Balancing and Second-Harmonic Current Suppressing Control With a Scalable DC Reconfigurable Battery Pack

This paper presents a hierarchical balancing architecture for the DC reconfigurable battery pack (RBP) with a modular design. The battery cells in the RBP are divided into several modules, and each module is equipped with a slave controller that is only responsible for a subset of cells. The system controller performs the closed-loop control and allocates the desired voltage steps into battery modules. The proposed architecture can significantly reduce communication and computation requirements for large-scale applications. Moreover, considering the second-harmonic current (SHC) widely existing in a single-phase DC/AC system, which may induce the aging of battery cells, the DC RBP is used to suppress the SHC for the first time without an additional central DC/DC converter. Due to the high output voltage quality and low-frequency operation of the DC RBP, the filter size can be significantly reduced. Experimental validation of the proposed control scheme is demonstrated through the utilization of a DC RBP comprising 48 3-Ah 18650 lithium-ion cells. The experimental results demonstrate that the proposed method achieves effective battery cell balancing and SHC suppression.