Introduction:
Power-related chips have always been a category of products that have received much attention. Battery protection chips are a type of power-related chips used to detect various fault conditions in single-cell and multi-cell batteries. In today's battery systems, the characteristics of lithium-ion batteries are very suitable for portable electronic systems, but lithium-ion batteries need to work within the rated limits, focusing on performance and safety. Therefore, the protection of lithium-ion battery packs is necessary and critical. The application of various battery protection functions is to avoid the occurrence of fault conditions such as discharge overcurrent OCD and overheating OT, and to enhance the safety of battery packs.
Battery management introduces balancing technology
First, let’s talk about the most common problem of battery packs, consistency. After the single cells form a battery pack, thermal runaway and various fault conditions may occur. This is the problem caused by the inconsistency of the battery pack. The single cells that make up the battery pack are inconsistent in capacity, charging, and discharging parameters, and the "barrel effect" causes the single cells with worse properties to affect the overall performance of the entire battery pack.
Battery balancing technology is recognized as the best way to solve the consistency of battery packs. Balancing is to adjust the real-time voltage of batteries of different capacities by adjusting the balancing current. The stronger the balancing ability, the stronger the ability to suppress the expansion of voltage difference and prevent thermal runaway, and the better the adaptability to the battery pack.
This is different from the simplest hardware-based protector. The battery protector can be a basic overvoltage protector or an advanced protector that can respond to undervoltage, temperature fault or current fault. Generally speaking, the battery management IC at the level of battery monitor and fuel gauge can provide battery balancing function. The battery monitor provides battery balancing function and also includes IC protection function with high configurability. The fuel gauge has a higher degree of integration, including the function of the battery monitor, and integrates advanced monitoring algorithms on its basis.
However, some battery protection ICs now also incorporate battery balancing functions through integrated FETs, which can automatically discharge high-voltage fully charged batteries during charging and keep low-voltage batteries in series charged, thereby balancing the battery pack. In addition to implementing a full set of voltage, current and temperature protection functions, battery protection ICs are also beginning to introduce balancing functions to meet the protection needs of multiple batteries.
From primary protection to secondary protection
From primary protection to secondary protection
The most basic protection is overvoltage protection. All battery protection ICs provide overvoltage protection according to different protection levels. On this basis, some provide overvoltage plus discharge overcurrent protection, and some provide overvoltage plus discharge overcurrent plus overheating protection. For some high-cell battery packs, this protection is no longer sufficient to meet the needs of the battery pack. At this time, a battery protection IC with battery autonomous balancing function is required.
This protection IC belongs to primary protection, which controls the charge and discharge FETs to respond to different types of fault protection. This balancing may solve the problem of thermal runaway of the battery pack very well. Excessive heat accumulation in a single battery will cause damage to the battery pack balance switch and resistors. Battery balancing allows each non-defective battery in the battery pack to be balanced to the same relative capacity as other defective batteries, reducing the risk of thermal runaway.
At present, there are two ways to achieve battery balancing: active balancing and passive balancing. Active balancing is to transfer energy or charge from high-voltage/high-SOC batteries to low-SOC batteries. Passive balancing is to use resistors to consume the energy of high-voltage or high-charge batteries to achieve the purpose of reducing the gap between different batteries. Passive balancing has high energy loss and thermal risk. In comparison, active balancing is more effective, but the control algorithm is very difficult.
From primary protection to secondary protection, the battery system needs to be equipped with a battery monitor or a fuel gauge to achieve secondary protection. Although primary protection can implement intelligent battery balancing algorithms without MCU control, secondary protection needs to transmit battery voltage and current to the MCU for system-level decision-making. Battery monitors or fuel gauges basically have battery balancing functions.
Conclusion
Aside from battery monitors or fuel gauges that provide battery balancing functions, protection ICs that provide primary protection are no longer limited to basic protection such as overvoltage. With the increasing application of multi-cell lithium batteries, large-capacity battery packs will have higher and higher requirements for protection ICs, and the introduction of balancing functions is very necessary.
Balancing is more like a kind of maintenance. Each charge and discharge will have a small amount of balancing compensation to balance the differences between batteries. However, if the battery cell or battery pack itself has quality defects, protection and balancing cannot improve the quality of the battery pack, and are not a universal key.
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Post time: Oct-21-2024