The emergence and development of battery management ICs are closely related to the problems encountered in the application of lithium batteries. At the earliest, in order to solve the overcharge and overdischarge of lithium batteries, a single-cell battery charge and discharge protection chip was designed. Later, in the multi-section series application of lithium battery, it was developed into a multi-string chip. At this time, it became a battery management. The chip mainly collects the voltage data of each battery in the battery pack. In order to cope with the problem of battery inconsistency, the power switch function is further integrated. This is the battery management IC with equalization function.
Objectively speaking, the battery management IC has made the early BMS industry and led the development of BMS products. It is because of the special chip that the design of the BMS can be greatly simplified, and the miniaturization and reliability of the product are greatly improved, but at the same time, we must also see the limitations of the dedicated chip. As mentioned above, the battery management chip is also developed along with the application of lithium batteries. The early lithium batteries were mostly used in small electronic devices, and later widely used in notebook computers. At this point, battery management chips have always been low strings. Number, small equipment services.
When the lithium battery pack was applied to an electric car, the situation began to change. The lithium battery pack for electric vehicles is a series of high-serial and large-capacity batteries. The number of dozens of strings or even hundreds of strings is not comparable to the serial use of several serial numbers in a notebook computer. Dedicated ICs are not idle, and have rapidly introduced more products for serial applications, but generally do not exceed 20 strings in terms of voltage and application complexity. The typical architecture of a BMS designed with these ICs is a centralized architecture. There is only a connection between the BMS and the battery pack. The number of connections depends on the number of battery strings. The number of dedicated battery management chips on the BMS board depends on the number of battery strings.
As can be seen from the schematic diagram, the advantages of the centralized BMS product are simple structure and low cost. When the number of battery strings is low, for example, 10 strings, the connection is not too complicated, and in the case of a small battery pack capacity, the BMS installation position can be close to the entire battery pack, shortening the connection distance, the battery pack - ---BMS, the entire energy system is relatively compact, suitable for electric bicycles and electric motorcycles. However, when applied to an electric vehicle lithium battery pack, because the battery capacity is large, the physical size after grouping is relatively large, the connection length is long, and the length is different, and the number of strings is large, and the number of connections is also large. The arrangement of dozens or even hundreds of lines is very troublesome.
Another important detail is that the order of these connections needs to be fixed, because the pins of the dedicated chip have previously defined the battery serial sequence, so the connection on each string of batteries should be connected to the connector pin specified by the BMS. . Although there is no difficulty in the design of the BMS, it is a big trouble in the actual connection between the BMS and the battery pack. The general line is connected to the battery at one end and the BMS through the plug-in at the other end. The connection with the battery is now done manually, and it is difficult to be completed by the machine in the future. The wires connected to each electrode of each string of batteries are There can be no mistakes, and the whole workload can be imagined. Through the analysis of the centralized architecture, we can see that the dedicated IC is more suitable for small-capacity and low-string number occasions. In the case of large-capacity and high-serial number, there will be complicated wiring and need one-to-one correspondence.
Looking at the problem of equalization, the centralized architecture is more suitable for passive equalization, and the circuit design does not add complexity. Now mainstream mainstream ICs also have this function. However, the current capability is limited, and the level of 100 milliamperes is not significant in the case of a small difference in the initial consistency of the battery pack. In the case of a large difference in consistency between the middle and the latter, there is a risk that the battery imbalance is not corrected. . If you want to join the active equalization function, the existing architecture is basically not helpful, requires additional wiring harnesses and switch matrices, and the circuit complexity rises sharply. The switch matrix requires a large number of electronic switches, MOSFETs, but because of the large number, its control circuit is quite complicated, and companies use relays instead, simplifying the design, but bringing the life of the relay as a mechanical switch and the risk of malfunction.
Of course, it is also possible to extend the life of the relay by reducing the switching frequency of the relay, and avoiding the risk by checking the malfunction, but this always fails to ensure the average trouble-free working time of the device, not to mention the number of relays is quite large, more than one. This is a last resort compromise solution, not a positive solution to the problem of active equalization switch matrix.
In order to solve the complicated problem of connection, a distributed architecture BMS emerged. This BMS separates the function of information collection and transmission from other functions. The whole system is divided into CSC (single management unit) and BMU (battery management controller). The CSC is installed on a single string battery and is responsible for the collection of battery information. And pass, the information of each string of batteries is passed to the BMU through the bus. This kind of architecture solves the complicated problem of the wire harness through the bus, and the installation is relatively simple, high efficiency, good flexibility, and is suitable for different battery pack sizes. The distributed BMS can be used without a battery management dedicated IC, which is a relatively successful idea of â€‹â€‹abandoning a dedicated IC for innovative design.
Wenzhou Korlen Electric Appliances Co., Ltd. , https://www.zjmannualmotorstarter.com