502030 battery.Analysis of balancing technology of series lithium-ion batteries in power-based energy storage frequency modulation power stations

　　Foreword: In the balancing management process of megawatt-level energy storage frequency modulation power stations, the balancing current is required to be large, and the balancing process will produce large losses. Soft switching can reduce switching losses, improve balancing efficiency, avoid electromagnetic interference, and reduce volume. It is Development trends in balanced topology. However, with the development of large-capacity batteries in the future, improving the consistency of the battery body is the primary direction to extend the service life of energy storage power stations.

　　Research background: Lithium-ion batteries have developed rapidly in the field of frequency modulation of energy storage power stations in recent years due to their advantages such as high energy density, fast response speed, and long cycle life. In order to meet the voltage and power requirements of frequency modulation power stations, a large number of battery cells need to be connected in series. The resulting inconsistency in series connection of the battery packs, as well as the inconsistency aggravated by high rates and frequent switching of charge and discharge states during the frequency modulation process, seriously affect the battery. The service life and safety performance of the group. Among the measures to mitigate inconsistency, the battery manufacturing process and battery sorting only improve the consistency of the initial state of the frequency modulated battery pack. Battery aging maintenance management only targets frequency modulation modules in non-working states, and the use environment and usage condition management only It can slow down the deterioration of inconsistency in battery packs during frequency modulation applications. Therefore, under the limitations of the existing manufacturing process level, more effective balance management technology should be used to actively control the battery pack to improve the inconsistency of the series lithium-ion battery pack based on power frequency regulation in the resting state and in use. Sexual issues.

　　Key content introduction: At present, lithium-ion series battery pack balancing management technology is mainly used in application scenarios such as small-capacity storage battery packs, electric vehicle power batteries, and energy storage power stations. There is relatively little research on the balancing management of energy storage frequency modulation batteries. Therefore, this article focuses on current The lithium-ion series battery pack balancing management technology is studied in combination with the characteristics of power frequency regulation, and the applicability of the lithium-ion series battery pack balancing management technology based on power frequency regulation is reviewed and analyzed.

　　Among them, the energy transfer equilibrium topology between any monomers has the advantage of high equilibrium efficiency, but the equilibrium speed is low. Using multiple arbitrary inter-cell energy transfer topologies for hierarchical control can increase the number of target batteries in a balancing process, but the cost will be greatly increased and the control will be more complex. It is used for series-connected lithium-ion battery packs in large-scale energy storage power stations. Balanced management lacks economy. The energy transfer balancing topology between the cell and the battery pack can realize the energy transfer between one battery and the entire battery pack in one balancing process. It has the advantage of fast balancing speed and is suitable for large-scale energy storage frequency modulation power station applications. Advantages of fast equalization. However, in this type of topology, there is a phenomenon of reverse balancing of some battery cells during the balancing process. That is, when the single battery with the highest power transfers power to the entire battery pack, some of the battery cells with higher power in the battery pack were originally It should release power but increases its own power, resulting in a reverse equilibrium phenomenon, so it needs to be gradually improved. The energy transfer balancing topology between battery packs transfers the power of some batteries with higher power to some batteries with lower power in the battery pack. It has the advantages of fast balancing speed and high balancing efficiency. It is an ideal balance for large-scale energy storage frequency modulation power stations. Regarding the future development trend of management, the current main problems are that there are a large number of switches and complex control methods, and related research is still in its infancy. This article believes that the energy transfer balancing structure of any number of batteries between battery packs can solve the problem of reverse balancing while taking into account the balancing speed. This topology has important research value and will play an important role in balancing lithium-ion batteries in series for large-scale energy storage in the future. Management is of great importance.

　　Conclusion: This article classifies and reviews the different balancing topologies and control strategies of series lithium-ion battery packs from the perspective of energy flow and balancing control objectives. It also combines the high-rate shallow charging and shallow discharging of energy storage batteries based on frequency modulation and the frequent switching of charging and discharging states. Characteristics, the applicability of battery pack balancing in energy storage frequency modulation power stations is analyzed. The following suggestions are made for the development trend of balancing technology of series-connected lithium-ion battery packs in megawatt-level large-scale energy storage frequency modulation power stations:

　　(1) At present, the balancing efficiency of the two-way energy transfer balancing topology between the cell and the battery pack can reach 72%~93%, which is the most widely used. The balancing efficiency of the energy transferring topology between adjacent two cells between the battery packs is as high as 75%. ~99%. In the balancing process, increasing the number of cells of the balancing target battery in one balancing process and the selectivity of any balancing target battery can alleviate the reverse phenomenon and improve the balancing efficiency and speed. In the future, especially any multi-cell energy transfer balancing topology between battery packs will have important research value, and is of great significance to the balancing management of megawatt-level large-scale energy storage frequency modulation power stations.

　　(2) In terms of balancing strategies, since the parameters of the battery pack are coupled to each other and have complex relationships, they should be closely integrated with actual applications, and appropriate parameters should be selected as the balancing consistency evaluation criteria for different application scenarios. The balancing strategy that selects multiple parameters as the balancing target can effectively avoid the failure of the balancing target. Compared with the balancing strategy that uses a single parameter as the balancing target, it is more reliable and can be better suitable for power frequency modulation energy storage battery balancing, but its control process It is complex, has higher technical requirements and needs further research.

　　(3) The balanced topology should minimize the number of electrical components and switches used, reduce costs and control complexity, reduce the probability of component accidents, and reduce the impact of the balanced topology itself on the life of the energy storage power station. In addition, in the balancing management process of megawatt-level energy storage frequency modulation power stations, the balancing current is required to be large, and the balancing process will produce large losses. Soft switching can reduce switching losses, improve balancing efficiency, avoid electromagnetic interference, and reduce volume. It is Development trends in balanced topology. However, with the development of large-capacity batteries in the future, improving the consistency of the battery body is the primary direction to extend the service life of energy storage power stations.

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