Balanced charging of lithium battery packs effectively improves battery consistency issues. Power lithium batteries are used in groups. Each lithium battery requires protection from charging overvoltage, discharge undervoltage, overcurrent, and short circuit. During the charging process, the issue of balanced charging of the entire group of batteries must be achieved. Experiments have proven that the lithium battery pack balanced charging management circuit can effectively improve the consistency of battery pack charging, improve the working performance of the lithium battery pack, and extend the service life.

　　Balanced charging of lithium battery packs effectively improves battery consistency issues

　　As a new power technology, lithium battery packs must be connected in series to meet the voltage requirements. The uneven performance of individual cells is not entirely due to technical issues in battery production. Even if each battery leaves the factory with exactly the same voltage and internal resistance , differences will also occur after being used for a period of time, which makes solving the technical problem of power battery charging an urgent technical issue that needs to be solved.

　　In order to solve the consistency problem in the use of power lithium battery packs, this article proposes an implementation plan for a balanced charging management circuit. First, the characteristics of a single lithium battery are analyzed; then, based on comparing various balanced charging theories, the partial shunt method is selected as the design idea and the specific circuit design is carried out. Multiple lithium battery pack charging and discharging experiments have shown that this balanced charge management circuit can effectively improve the charging consistency of the lithium battery pack, improve the battery pack's working performance, and extend its service life.

　　Due to the problem of inconsistent battery performance, the performance of battery packs in terms of utilization, service life, safety, etc. is far inferior to that of single batteries. The lithium battery management system with efficient balancing management function can greatly improve the overall performance of the power battery pack, effectively extend the service life of the lithium battery pack, and greatly reduce the use and maintenance costs of the entire vehicle. Provide technical support for the promotion of safe, efficient and practical electric vehicles.

　　At present, lithium battery management systems have made certain progress in battery online monitoring, status assessment, charging management, data communication, control strategies, etc.

　　Lithium battery pack charging characteristics

　　In the power battery pack, there are inconsistencies between individual cells. The differences caused by continuous charge and discharge cycles will accelerate the capacity decay of some single cells. The capacity of the series battery pack is determined by the minimum capacity of the single cell, so these differences will shorten the service life of the battery pack. The main reasons for this imbalance are:

　　●During the battery manufacturing process, due to process and other reasons, there are differences in capacity, internal resistance, etc. of batteries in the same batch;

　　●Differences in battery self-discharge rates, accumulated over a long period of time, result in differences in battery capacity;

　　●During battery use, differences in usage environment such as temperature and circuit boards lead to imbalance in battery capacity.

　　Lithium battery pack equalizing charging solution

　　In order to reduce the impact of imbalance on the lithium battery pack, a balancing circuit must be used during the charging process.

　　Currently, there are two main solutions for balancing management of lithium battery packs, energy consumption type and feedback type. The energy consumption type refers to providing parallel branches for each single battery, and transferring the electric energy of the single battery with excessive voltage through shunting to achieve the purpose of balancing. The feedback type refers to feeding the deviation energy between cells back to the battery pack or certain cells in the battery pack through the energy converter.

　　Theoretically, when the conversion efficiency is ignored, feedback does not consume energy and dynamic equilibrium can be achieved. However, due to the complex control method of feedback design and high manufacturing cost, this charger adopts energy consumption design.

　　Since the DC internal resistance, polarization voltage, and maximum available capacity are specific parameters of the battery and basically do not change during one or several consecutive charge and discharge processes, the balance of the lithium battery pack is mainly achieved by adjusting the SOC of each single cell. accomplish. After research, SOC is used as the reference object for balancing. The balancing object is relatively fixed. Make full use of the balancing time and improve the balancing utilization rate to reduce the balancing current capacity.

　　Taking the SOC of the battery as the control object, the difference in SOC between batteries is reduced by charging and discharging the single battery. First, the balancing target needs to be determined. Usually in order to improve the efficiency of balancing and give full play to the advantages of charge and discharge balancing, the target is set as the average state of charge (SOC) of the lithium battery pack. The balance control band (dSOC) is also set to prevent balance fluctuations. For cells with high SOC, discharge balance is performed, and vice versa, charge balance is performed.

　　Commonly used lithium battery pack balancing charging technologies include constant shunt resistance balancing charging, on-off shunt resistor balancing charging, average battery voltage balancing charging, switched capacitor balancing charging, buck converter balancing charging, inductor balancing charging, etc. When charging a group of lithium batteries in series, each battery should be charged evenly, otherwise the performance and life of the entire battery group will be affected during use.

　　Summary: A single-cell lithium battery protection chip is used to design and implement a battery pack protection board for multiple lithium batteries connected in series. In addition to completing the necessary over-voltage, under-voltage, over-current and short-circuit protection functions, it can also achieve a balanced charging function. It is another important breakthrough in battery technology.

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