The balancing schemes of lithium-ion battery pack

When a series of lithium-ion batteries are assembled into a battery pack, there will be problems that power may be out-of-balance and power may be unbalance during charging. Passive balancing schemes is a way to balance during charging process via shunting extra current to voltage. Because in the process of charging, weak battery (absorption current smaller) will get extra current than the strong battery (to absorb more current). However, "passive balance" cannot solve balance problem to every single small battery during discharging, which requires a new scheme - active balance - to solve.

Active balancing abandoned passive consumption balance current method, the method of transmitting current changed. Responsible for the charge transfer equipment is a kind of power converter, the device makes small batteries inside the battery pack in both charging and discharging and idle state can transfer charge, so that can often keep the dynamic balance between small batteries.

Due to the active balance method of charge transfer efficiency is extremely high, therefore, can provide higher balance current, this means that, in this way the lithium battery Charge and discharge, and idle balance ability is stronger.

1, quick charging capability: active balancing function can make each small battery in the battery pack to reach equilibrium faster, so the safety of quick charge higher, more suitable for the current high rate of charging ways.

2, was idle: even if the small battery charging has reached a state of balance, but due to the temperature gradient is different, some small battery internal temperature is high, some small inside the battery low, also can make each small battery internal leakage rate, the test data shows that the battery every 10 ℃, the leakage rate is rising, active balancing function can ensure spare lithium battery pack, a small battery to regain balance "constantly", this is advantageous to the battery pack storage battery can be make full use of, make the battery pack at the end of the ability to work, a single small minimum residual power lithium batteries.

3, discharge: no discharge capacity of 100% of the lithium battery pack, this is because, a set of lithium batteries work ability is one by the end of the first to put the small electric lithium battery, there is no guarantee that all the small lithium battery can achieve after power at the same time. On the contrary, there will be individual small with unused residual power lithium batteries. Through active balancing method, lithium battery during discharge, internal the large capacity lithium battery Electricity will be assigned to a small capacity lithium battery, therefore, the small capacity lithium battery can also be fully discharge, and the residual power battery pack there won't be leaving, have active balancing function of battery pack has a larger practical capacity (i.e., can release closer to the nominal capacity of electricity).

Finally, to explain, the system performance of active balance method depends on the ratio of between balance current and battery charge/discharge efficiency. The higher imbalance rate of a set of lithium-ion battery, the higher the battery charge/discharge rate, the greater balance current it needs. Of course, this is quite a bargain that the current consumption relative to the additional current for internal balance, besides, the active balancing is conducive to the extension of lithium-ion battery life.

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