Lithium battery external circuit

　　Connection mode In the large-scale energy storage system, the batteries will be combined in series and parallel, so there will be many connection circuits and control elements between the batteries and modules. Due to the different performance and aging speed of each structural member or component, as well as the inconsistent energy consumption at each connection point, different components have different impacts on the battery, resulting in inconsistent battery pack systems. Inconsistent attenuation rate of battery in parallel circuit will accelerate deterioration of system.

　　The impedance of the connecting piece will also affect the inconsistency of the battery pack. The resistance of the connecting piece is different, and the resistance of the pole to each single battery branch is different. The battery far from the pole has a large resistance due to the long connecting piece, while the current is small. The connecting piece will make the single battery connected to the pole reach the cut-off voltage first, which will reduce the energy utilization rate and affect the battery performance, Moreover, the premature aging of the single battery will lead to overcharge of the battery connected to it, causing potential safety hazards.

　　As the number of battery cycles increases, the ohmic internal resistance will increase, the capacity will decline, and the ratio of ohmic internal resistance to connector resistance will change. In order to ensure the system security, the influence of connector resistance must be considered.

　　The BMS input circuit battery management system (BMS) is the guarantee for the normal operation of the battery pack, but the BMS input circuit will adversely affect the battery consistency. The battery voltage monitoring methods include precision resistance voltage sharing, integrated chip sampling, etc. Because of the existence of resistance and circuit board path, these methods cannot avoid the external load leakage current of the sampling line. The battery management system voltage sampling input impedance will increase the battery state of charge (SOC) uniformity, affecting the performance of the battery pack.

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