A lithium-ion battery active equalisation optimisation method

Battery Equalisation systems are necessary as cell imbalance can lead to poor performance and safety hazards. The equalisation circuit can be regarded as a DC-DC converter capable of transferring energy between its input and output with a certain efficiency and speed. The input and output of the converter can be a single cell or a entire battery pack. The topological structure of a single cell to a battery pack as input and output respectively has the advantages of short equilibration time and low energy loss. This kind of structure can only balance one battery at one time. In this case, the battery might reach the equilibrium threshold and waits for the balance. The battery health will be further deteriorated during the waiting process. In order to solve this problem, this paper proposes a balanced control strategy to set the action threshold, pre-action threshold and end threshold. The proposed strategy calculates the offset and relative rate of change of each battery's State-Of-Charge (SOC), then predicts the SOC of each cell for a period of time in the future, an appropriate single cell is selected for equalisation to achieve an optimal control of the equaliser. This paper use MATLAB/SIMULINK software to simulate a corresponding circuit controlled by the proposed strategy. Simulation results show that compared with the traditional control strategy in a same circuit, the proposed equalisation control strategy can solve the problem of equalisation time overlap without changing the equalisation circuit and increasing the equalisation current. This result confirms the feasibility of this balanced control strategy.