Model predictive control based balancing strategy for series-connected lithium-ion battery packs

For reducing the inconsistent state of charges (SOCs) of lithium-ion battery cells and making the full use of battery packs, effective battery balancing technology should be in place for battery management systems. Since aged battery packs usually suffer from not only non-uniform cell SOCs and voltages but also non-uniform cell capacities, it is more challenging to balance an aged battery pack than a new one. This paper proposes a model predictive control (MPC) based balancing strategy to fully charge battery packs under such inconsistent conditions, especially for aged battery packs. The algorithm of the proposed strategy for computing the required average balancing current and the predicted balancing current for each cell is presented, followed by employing a minimum cost function value between these two currents to control the operation model of the equalizer for each cell. The simulation results verify the effectiveness of the proposed approach. Compared with the conventional average SOC strategy, the proposed MPC based strategy can effectively avoid over-equalization during the balancing process, thus reducing balancing energy consumption.