3.2v 280ah lifepo4 battery cell.Introduction to solutions for active balancing of lithium battery packs

　　When individual lithium-ion batteries are combined into a battery pack, they will encounter problems of power imbalance when shelved and when charging. The passive balancing solution is obtained by placing weak batteries (less current absorbed) during the charging process. Compared with strong batteries (which can absorb more current), the excess current is shunted to the resistor to balance the charging process of the lithium battery pack. However, "passive balancing" cannot solve the balance of each small battery during the discharge process. This requires a new solution - active balancing - to solve. Active balancing abandons the passive balancing method of consuming current and changes it to a method of transmitting current. The device responsible for charge transfer is a power converter, which allows the small batteries in the battery pack to transfer charge whether they are charging, discharging or idle, so that dynamic balance can be maintained between small batteries. Because the charge transfer efficiency of the active balancing method is extremely high, it can provide higher balancing current, which means that this method has better balancing ability when the lithium battery is charging, discharging and idle. 1. Strong fast charging capability: The active balancing function can make each small battery in the battery pack reach balance faster. Therefore, fast charging is safer and is suitable for high-rate charging with larger current. 2. When idle: Even if each small battery has reached the equilibrium state during charging, due to different temperature gradients, the internal temperature of some small batteries is higher and the internal temperature of some small batteries is lower, which will also cause the internal temperature of each small battery to The leakage speed is different. Test data shows that the leakage rate doubles every time the battery rises by 10°C. The active balancing function can ensure that the small batteries in the idle lithium battery pack "constantly" regain balance, which is beneficial to storage in the battery pack. The power can be fully utilized, so that when the battery pack ends, the remaining power of a single small lithium battery is minimal. 3. When discharging: There is no lithium battery pack with a discharge capacity of 100%. This is because the end of the working capacity of a group of lithium batteries is determined by a certain small lithium battery that is discharged first, and there is no guarantee that all small lithium batteries will be discharged. Lithium batteries can be fully discharged at the same time. Instead, there are individual small lithium batteries that retain unused residual energy. Through the active balancing method, when the lithium battery pack is discharging, the internal large-capacity lithium battery will distribute electric energy to the small-capacity lithium battery. Therefore, the small-capacity lithium battery can also be fully discharged, and there will be no residual electric energy in the battery pack. However, the battery pack with active balancing function has a larger actual storage capacity (that is, it can release electric energy closer to the nominal capacity). As a final note, system performance with active balancing methods depends on the ratio between balancing current and battery charge/discharge efficiency. The higher the imbalance rate of a set of lithium batteries, or the greater the charge/discharge rate of the battery pack, the higher the balancing current required. Of course, this current consumption used for balancing is quite cost-effective compared to the extra current obtained due to internal balancing. Moreover, this active balancing is also conducive to extending the life of the lithium battery pack.

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