Li-ion battery equalization system can solve the problem of inconsistent voltage of single cell in battery pack. Usually, due to technical and production reasons, there are certain differences in the single cell of Li-ion battery, which makes the utilization rate, service life and safety of Li-ion battery pack after PACK far inferior to the performance of single cell. In order to solve this industry problem, the use of battery management system with efficient balance management function can significantly improve the overall performance of the power lithium battery pack, and extend the service life of the lithium battery pack. Reduce the use and maintenance cost of the whole vehicle. To provide a strong technical guarantee for the promotion of electric vehicles.
The consistency of Li-ion battery pack refers to the difference in capacity, internal resistance and SOC (voltage) between series-connected cells in the battery pack, which directly determines the performance of the whole battery pack and thus affects the power and range of the EV. The reason for the inconsistency of Li-ion battery formation is mainly the initial difference of single cell and the difference caused by the structure, usage conditions and environment of the battery after formation.
We can optimize the manufacturing process of Li-ion battery to reduce the initial difference of the battery to alleviate the performance degradation and life reduction of Li-ion battery after grouping; for example, screening before grouping and packaging the Li-cell combination with less inconsistency; fully considering the influence of connection method and structure on inconsistency in the battery structure; and reasonable battery management in the process of use, effective equalization as well as thermal management to reduce the inconsistency of single cells caused by different usage conditions or environmental factors.
Riding Electronics elaborates on the causes of inconsistency of lithium battery pack
① single lithium battery manufacturing process, the process and material selection led to the imbalance, resulting in the nuances of the inconsistency of the lithium battery parameters.
② lithium battery genuine loading use, due to the lithium battery pack of each single cell electrolyte density, temperature and ventilation conditions, the degree of self-discharge and the charge and discharge process of it over the impact of differences in the accumulation of small differences in each charge and discharge resulting in the imbalance.
What are the equalization techniques for lithium batteries?
1、Passive equalization method: The passive equalization method is to discharge the single cell with high voltage by connecting it to a load resistor through a circuit, and to determine whether its voltage is the same as that of other single cells through a comparison circuit, and to stop discharging if it is the same, the disadvantage of the passive equalization method is that it consumes the energy of the single cell, generates heat, and takes a long time to equalize.
2、Active equalization method: Active equalization method means that the energy of the higher voltage battery is not consumed through the resistance during charging and discharging, but its energy is transferred to the lower voltage battery, so as to achieve the balanced charging and discharging of the lithium battery pack; the active equalization circuit is complicated, and cannot equalize all the batteries at the same time, and the reliability needs to be improved.
3、Internal equalization method: The internal equalization method is to use the BMS in the process of charging the series-connected batteries to make the individual battery charge in the battery pack reach the basic consistency by adjusting the charging current and controlling the topological algorithm of the charging voltage. The internal equalization technology is characterized by simple algorithm, no energy loss, no additional charging and discharging process, no impact on battery life, and no additional hardware equipment, but it takes longer time to equalize the batteries if their charge levels are very different.
From the perspective of battery management system, the single battery parameters are detected during the use of the battery pack, especially the voltage distribution under dynamic and static conditions, so as to master the development law of the single battery inconsistency in the battery pack and make timely adjustment or replacement of the battery with extreme parameters, so as to ensure that the inconsistency of the battery pack parameters increases with use time. Meanwhile, from the management and strategy of energy, practical battery pack energy management and equalization system is introduced to develop reasonable battery equalization strategy to actively intervene and reduce the inconsistency of battery.
The battery inconsistency comes from the battery internal resistance, capacity and SOC, and the traditional consistency evaluation methods and equalization approaches with external voltage consistency as the control target do not effectively improve the available capacity of the battery pack, so they also cannot improve the adverse effects of the battery pack consistency problem on the use of the battery in groups.
Since DC internal resistance, polarization voltage and maximum available capacity are specific parameters of the battery, which basically do not change during one or several consecutive charging and discharging processes, the equalization of the battery pack is mainly achieved by adjusting the SOC of each individual cell. After the study, the SOC is used as the reference object for equalization, and the equalization object is relatively fixed to make full use of the equalization time and improve the equalization utilization to reduce the equalization current capacity.
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