Study on SOC equalization control of series-connected liquid metal battery packs

To address the problem of inconsistency in the state-of-charge (SOC) of series-connected battery packs that leads to the reduction of the efficiency and lifetime of the battery packs, this paper proposes an active equalization topology based on a buck-boost converter, which controls the state of the inductors through the on/off of switches. The proposed circuit has flexible equalization paths that allow different equalization processes to be performed simultaneously, improving the equalization time efficiency. In this paper, a two-stage equalization control strategy with "variable step" equalization current is proposed, and the range of SOC is used as the equalization object of the battery pack. MATLAB/Simulink software was used to build the model and equalization system for liquid metal batteries (LMBs), and the LMBs were simulated and analyzed in the static state, constant current discharge condition and DST dynamic discharge condition, respectively. The analysis of the simulation results shows that the equalization control system has high equalization efficiency and equalization accuracy, and can effectively improve the consistency of the SOC of LMB packs.