During the entire rechargeable battery manufacturing process, due to factors such as production technology, rechargeable batteries manufactured in the same batch may differ in terms of volume, internal resistance, and other aspects.
The lifespan and speed of rechargeable lithium-ion batteries differ, which, over a long period, results in varying battery capacities.
Throughout the application of rechargeable batteries, differences in the operating environment, such as temperature and circuit boards, can lead to an imbalance in battery charge levels.
Lithium-ion battery rechargeable battery balancing method.
To reduce the damage caused by imbalance to lithium-ion battery packs, a power balancing circuit should be used when charging the battery.
There are currently two main methods for balancing lithium-ion batteries: energy-consuming and energy-returning. The energy-consuming method involves creating a series loop for each individual battery, allowing batteries with excessively high voltage to dissipate energy and achieve balance. The energy-returning method refers to transferring the imbalance energy between individual batteries to the lithium-ion battery pack or some of the individual batteries within the pack via an energy converter.
Theoretically, ignoring the need for high-efficiency switching, feedback does not consume kinetic energy and can achieve a stable balance. However, due to the complexity of control measures and high manufacturing costs associated with feedback-based design methods, this charging head adopts an energy-consuming design approach.
Since internal resistance, polarization voltage, and maximum usable capacity are crucial parameters of rechargeable batteries, and the State of Charge (SOC) of a battery largely remains unchanged during one or several charging cycles, balancing the lithium-ion battery pack is essential. This is achieved by adjusting the SOC of each individual battery. Research has identified SOC as a balancing reference point, a relatively fixed balancing target, which allows for efficient use of balancing time, improves balancing efficiency, and reduces balancing volume.
By using the SOC of the rechargeable battery as the control target and implementing a battery charging method for individual rechargeable batteries, the difference between the SOC and the battery is reduced. Firstly, a clear overall balance target is defined, set as the average concentration polarization state (SOC) value of the lithium-ion battery pack, to improve balancing efficiency and fully utilize the advantages of battery charging balance. Secondly, a balance control band (dSOC) is set, performing charge-discharge balance for individual batteries with higher SOCs and charging balance for those with lower SOCs.
Key balancing charging techniques for typical lithium-ion battery packs include stable disconnect resistors, short-circuit disconnect resistors, equal voltage balancing charging, capacitor-based balancing charging, voltage-reducing SPWM balancing charging, and inductor-based balancing charging. When charging integrated lithium-ion batteries in series, it is crucial to ensure that all batteries are charged evenly; otherwise, the performance and lifespan of the entire battery pack will be affected during use.
