The meaning of lithium-ion battery pack balance is to use power electronic technology to keep the voltage deviation of the lithium-ion battery pack or the voltage of the lithium-power lithium-ion battery pack within the expected range, so as to ensure that each single lithium-power lithium battery at the same state in normal use to prevent the occurrence of overcharge and over-discharge. If the balance control is not carried out, with the increase of charge and discharge cycles, the voltage of each single lithium power lithium battery will gradually differentiate, and the service life will be greatly reduced.
During the use of the assembled lithium ion battery pack, the monomer inconsistency will also appear due to the degree of self-discharge and the temperature of the part. The inconsistency of the lithium-ion battery pack affects the charging and discharging characteristics of the lithium-powered lithium battery pack. PLS Battery, which is a lithium ion battery factory, finds that a 20% difference in the capacity of lithium-powered lithium battery cells will bring about 40% of the capacity loss of lithium-powered lithium battery packs.
The inconsistency of lithium-ion battery packs will worsen over time under the influence of random factors such as temperature. In general, when the operating environment temperature of the lithium power lithium battery is 10°C higher than its optimal temperature, the life of the lithium power lithium battery will be reduced by half. Due to the large number of series-connected lithium-powered lithium battery systems for vehicles, generally between 88 and 100 series, and their capacity is generally 20-60kWh, each string of lithium-powered lithium batteries is loaded at different locations and temperatures differences will occur.
Even in the same power lithium battery box, there will be a temperature difference due to the location and heating of the lithium power lithium battery, and this temperature difference will have a major negative impact on the life of the lithium power lithium battery, causing the lithium power of lithium pack to appear unbalanced. This reduces the cruising range and shortens the cycle life. It is precise because of these problems that the capacity of the entire battery system cannot be fully used, causing battery system losses, and mitigating such system losses will also greatly extend the service life of the battery system.
The consistency between lithium-ion battery packs has the most direct and most important influence on the capacity of lithium-ion batteries because the lithium-ion battery capacity is a parameter that cannot be directly measured in a short time. However, there is a one-to-one correspondence between the capacity of a lithium-ion battery pack and its open-circuit voltage. The voltage of a lithium-power lithium battery cell can be measured online in real-time, which makes it a favourable condition for measuring the consistency level of a lithium-power lithium battery cell. In the management strategy of the battery management system, there are discharge termination conditions, charging termination conditions, etc., where the voltage value of the lithium power lithium battery cell is used as the trigger condition.
For a parameter in this position, the voltage consistency of the lithium-ion battery pack is too large, which directly limits the charge and discharge power of the lithium battery pack. Based on this, the use of lithium-ion battery pack equalization methods to solve the problem of excessive voltage difference of lithium power lithium battery packs that are already in operation is an effective measure to increase the capacity of the lithium battery pack and prolong the service life of the lithium battery.