LR03 battery

Only by breaking away from the dedicated IC method can we expect innovation in the LR03 battery management system

The emergence and development of dedicated LR03 battery management ICs are closely related to the various problems encountered during the use of lithium-ion batteries. At first, a single-cell charge and discharge protection chip was designed to solve the overcharge and over-discharge of lithium-ion batteries. Later, when multiple lithium-ion batteries were used in series, a chip used in multiple strings was developed. At this time, it became a LR03 battery management chip, which mainly collects the voltage data of each LR03 battery in the LR03 battery pack. Later, in order to deal with the problem of LR03 battery inconsistency, the driving function of the power switch was further integrated, which is the LR03 battery management IC with balancing function.

Objectively speaking, dedicated LR03 battery management ICs have made the early bMS industry a success and led the development of bMS products. It is precisely because of dedicated chips that the design of bMS can be greatly simplified, and the miniaturization and reliability of products have been greatly improved, but at the same time, we must also see the limitations of dedicated chips. As mentioned earlier, LR03 battery management chips also developed with the use of lithium-ion batteries. Early lithium-ion batteries were mostly used in small electronic devices, and later they were widely used in laptops. So far, LR03 battery management chips have always been used for low-number and small devices.

When lithium-ion LR03 battery packs were used in electric vehicles, the situation began to change. Lithium-ion LR03 battery packs for electric vehicles use high-number and large-capacity batteries in series. The number of dozens or even hundreds of strings is no longer comparable to the single-digit series use of a few strings in laptops. Dedicated ICs have not been idle either, and have quickly launched products with more strings, but considering the voltage and complexity of use, they generally do not exceed 20 strings. The typical architecture of the bMS designed using these ICs is a clustered architecture. There are only wires between the bMS and the LR03 battery pack, and the number of wires depends on the number of LR03 battery pack strings. The number of LR03 battery management dedicated chips on the bMS circuit board also depends on the number of LR03 battery pack strings.

Another important detail is that the order of these wires must be fixed, because the pins of the dedicated chip have already pre-defined the LR03 battery series order, so the wires on each LR03 battery string must be connected to the connector pins specified by the bMS. Although this is not difficult in the design of bMS, it is a big hassle in the actual connection between bMS and LR03 battery pack. Generally, one end of the wire is connected to the LR03 battery, and the other end is connected to bMS through a plug-in. The connection with the LR03 battery is currently done manually, and it will be difficult to be done by machines in the future. The wires connected to each electrode of each string of batteries cannot make any mistakes. The entire workload can be imagined. Through the decomposition of the clustered architecture, we can see that dedicated ICs are more suitable for small capacity and low string number occasions. In large capacity and high string number occasions, there will be complex wiring and one-to-one correspondence.

Looking at the problem of balancing, the clustered architecture is more suitable for passive balancing, and there is no additional complexity in circuit design. The current mainstream dedicated IC also has this function. However, the current capacity is limited, at the level of 100 mA. In the case of little difference in consistency in the early stage of LR03 battery pack use, there is no big problem. In the case of large difference in consistency in the middle and late stages, there will be a risk of insufficient correction of LR03 battery imbalance. If the active balancing function is to be added, the existing architecture is basically of no help. Additional wiring harnesses and switch matrices are required, and the complexity of the circuit increases sharply. The switch matrix requires a large number of electronic switches, MOSFET, but because of the large number, its control circuit is quite complicated. Some companies use relays instead, which simplifies the design, but brings the life of the relay as a mechanical switch and the risk of false operation.

Of course, it is also possible to extend the life of the relay by reducing the switching frequency of the relay and avoid the risk by false operation inspection, but this will never guarantee the uniform trouble-free working time of the device, not to mention that there are quite a lot of relays, more than one. This is a compromise method that is forced to do, rather than a correct solution to the problem of active balanced switch matrix.

In order to solve the problem of complex wiring, a distributed architecture bMS has emerged. This bMS separates the function of information collection and transmission from other functions. The entire system is divided into CSC (cell management unit) and bMU (LR03 battery management controller). CSC is installed on a single string of batteries and is responsible for the information collection and transmission of the LR03 battery string. The information of each string of batteries is transmitted to the bMU through the bus. This architecture handles the problem of complex wiring harnesses through the bus, and the installation is relatively simple, efficient, flexible, and suitable for different LR03 battery pack sizes. Distributed BMS can do without dedicated IC for LR03 battery management, which is a relatively successful idea for innovative design without dedicated IC.

The disadvantage is that the distributed architecture does not deal with the problem of one-to-one correspondence and active balancing. CSC also needs to set the address (although it can be set after installation, which is easier to implement than the clustered architecture before installation, and the probability of error is small), and active balancing still requires additional wiring harnesses and switch matrices. Moreover, because each CSC needs an MCU and an isolated communication bus, the price is higher than the clustered architecture BMS, especially at low string counts.

The idea of distribution gives a good hint to the clustered architecture, which is to handle the wiring harness problem through the bus. The dedicated IC also saw the benefits and quickly launched a communication bus without isolation, further improving itself. The semi-distributed architecture, which is actually a two-level clustered architecture, has become one of the mainstream designs of BMS. This is to divide the entire LR03 battery pack into several modules, each module uses a small BMS designed with a dedicated chip, and then connects to a final controller through the bus. The semi-distributed architecture combines the advantages of fewer distributed wiring harnesses and the advantages of simple centralized design, but unfortunately, the problems that the previous architecture could not handle are also inherited, and the one-to-one correspondence and the problem of active balancing still exist.

Tracing back to the source, the one-to-one correspondence and the problem of the switch matrix in active balancing all come from the inherent limitations of the dedicated LR03 battery management chip, although the dedicated LR03 battery management chip is also evolving. Because it is used in multiple strings, each LR03 battery test channel on the dedicated IC must be numbered in advance. It is unimaginable to know the order of each channel afterwards. At present, no IC can design such a function. Similarly, the switch matrix also comes from the use of multiple strings, and because it involves the power part, this is the natural weakness of the IC. This is why the existing architecture is powerless against active balancing. Therefore, if the number of strings is low and the active balancing function is not required, it is feasible to use a dedicated IC method, such as power tools, electric bicycles and electric motorcycles; in the use of electric vehicles, especially to complete the active balancing function, it is still difficult to use a dedicated IC to design bMS.

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