A balancing system for liquid metal batteries using the Floyd-Warshall algorithm

Abstract

Liquid metal battery(LMB) based on liquid metal electrodes and inorganic molten salt electrolyte has the advantages of low-cost, long-lifespan and high-safety, and has great application prospect in the field of large-scale power storage. The state of charge (SOC) balancing plays a vital role in ensuring efficient operation of the battery system. However, developing a balancing scheme for LMBs remains a significant challenge due to the relatively low and flat open-circuit-voltage versus SOC curve of LMBs. In this paper, a two-level bidirectional balancing architecture is implemented for series-connected LMBs to provide flexible energy transfer pathways. And the switches on the circuit are controlled by synchronous rectification to reduce the voltage drop across the circuit caused by the switches, which is particularly important for LMBs. In order to overcome the “energy transfer back and forth” problem, the Floyd-Warshall algorithm is proposed to optimize balancing pathways for series-connected LMBs. In the 16-series LMBs simulation, the result indicates that the energy transferring pathway can be effectively optimized, the equalization time of the proposed balancing methodology is 195 s and 200 s in the static and dynamic state, respectively. Compared to the most value equalization algorithm, this proposed scheme can equalize the SOC values of LMB strings efficiently with a faster speed.