A double-layer ring-structured equalizer for series-connected lithium-ion battery pack based on model predictive control

The inconsistency of lithium-ion batteries will seriously affect the performance and safety of the battery pack in series, resulting in a decrease in the available capacity and shortening of the life span of the series battery pack. To alleviate this inconsistency, a double-layer ring-structured equalization topology is proposed, which has the advantages of flexible equalization path and fast equalization speed. In order to further improve the equalization speed and reduce the equalization loss, this paper proposes an equalization strategy based on model predictive control (MPC). By establishing a prediction model and solving the composite optimization objective function, the optimal control strategy is obtained. To verify the feasibility of the proposed equalizer, the simulation study has been carried out in Matlab-Simulink. The simulation results in static operating condition show that, compared with the single-layer Buck-Boost equalizer based on the mean-difference algorithm, the equalization time of the proposed equalizer based on MPC is reduced by 38.15 % and the energy transfer efficiency is increased by 27.25 %. The rationality of the proposed equalizer and equalization strategy is further verified in constant current (CC) charging and New York Bus Cycle (NYBC) discharging operating conditions.