However, "passive balancing" cannot solve the balance of each small battery during the discharge process, which requires a new solution—active balancing.
Active balancing abandons the current-consuming method of passive balancing and instead uses a current-transferring method. The device responsible for charge transfer is a power converter, which enables the small batteries in the battery pack to transfer charge whether they are charging, discharging, or idle, thus allowing the small batteries to maintain a dynamic balance at all times.
Because the active balancing method has extremely high charge transfer efficiency, it can provide a higher balancing current, which means that this method has a stronger balancing ability when lithium batteries are charging, discharging and idle.
1. Strong fast charging capability: The active balancing function can make the small batteries in the battery pack reach balance more quickly, so fast charging is safer and suitable for high-rate charging with larger current.
2. When idle: Even if each small battery has reached the equilibrium state it was in when charging, due to different temperature gradients, some small batteries have higher internal temperatures and some have lower internal temperatures, which will cause the leakage rate of each small battery to be different. Test data shows that for every 10°C increase in battery temperature, the leakage rate doubles. The active balancing function can ensure that the small batteries in the idle lithium battery pack can "constantly" regain balance. This is conducive to the full utilization of the energy stored in the battery pack, so that when the battery pack is no longer in operation, the residual energy of each small lithium battery is minimized.
3. During discharge: No lithium battery pack can discharge to 100% capacity. This is because the end of a lithium battery pack's operation is determined by the first small lithium battery to discharge completely, and it cannot be guaranteed that all small lithium batteries will reach full discharge simultaneously. On the contrary, some small lithium batteries will retain unused residual energy. Through active balancing, during discharge, the larger capacity lithium batteries in the lithium battery pack will distribute energy to the smaller capacity lithium batteries. Therefore, the smaller capacity lithium batteries can also be fully discharged, and no residual energy will remain in the battery pack. Battery packs with active balancing have a larger actual storage capacity (i.e., they can release energy closer to their nominal capacity).
Finally, it's worth noting that the system performance of the active balancing method depends on the ratio between the balancing current and the battery's charge/discharge efficiency. The higher the imbalance rate of a lithium battery pack, or the greater the charge/discharge rate of the battery pack, the higher the required balancing current. Of course, this current consumption for balancing is quite worthwhile compared to the additional current gained through internal balancing; moreover, this active balancing also contributes to extending the lifespan of the lithium battery pack.
