Research on balance control strategy of lithium-ion battery energy storage system

Lithium-ion batteries are widely used in grid energy storage, electric vehicles and other occasions because of their excellent performance. Passive equalization is widely used because of its high performance, but traditional passive equalization control strategies do not perform well. This paper proposes a new control strategy, which divides the battery pack into three state of charge (SOC) ranges according to the different SOC of the battery pack and different performance requirements. When the SOC of the battery pack is high, the maximum rechargeable capacity needs to be considered and the battery balancing should be realized in advance; and when the SOC of the battery is low, the maximum discharge capacity needs to be considered, the battery balancing should be delayed and, in other areas, it is the same as the traditional balancing control strategy. Moreover, the balance control strategy proposed in this paper keeps the high-performance battery at a lower voltage and the low-performance battery at a higher voltage; the low-performance battery works with more favorable conditions, so that the battery pack is in a more balanced state. The experimental results show that the battery pack consisting of four cells in series can be almost fully charged and the battery pack voltage is similar to 16.788 V; during the discharge process, the equalization system hardly operates to ensure its maximum discharge capacity. The strategy proposed in this paper is simple and easy to implement and has better performance.