Research on a balanced circuit and control strategy

For reducing the inconsistent state of charges (SOC) of lithium-ion battery cells and making the full use of battery packs, effective battery balancing technology should be used. In order to achieve the goal of balancing any single cell in the battery pack expediently and considering the cost and the balance efficiency, a balanced circuit is proposed. By changing the action state of single-pole double-throw relay connected to each of the single cell battery, the balanced single-cell battery is in a state of non-load power supply, at this point, the balanced battery is in `charging’ state compared with other batteries in the battery pack, thus achieving the balance target of the battery pack. On this basis, this paper also proposes a new balancing control strategy; it is different from the traditional control strategy to balance the SOC of the single cell to the SOC average of the battery pack, considering the different SOC change rates of the cells with different capacity in the battery pack. The balanced control strategy proposed in this paper allows the set condition of the single cell to end the equilibrium process in advance so as to reduce the unnecessary balance time and then improve the equilibrium speed. In order to verify the feasibility of the proposed circuit and control strategy, 18 650 batteries with different initial SOC in series are experimentally verified. The experimental results show that the balanced circuit proposed in this paper can well balance the cell of each single cell and make the battery pack reach a balanced state.