lithium 3400mah 3.7v 18650 battery Management System (BMS)

　　I have introduced NTC in temperature sampling before. In fact, there is something about the temperature sampling circuit design that I have not mentioned. I plan to find another opportunity to write it. The second article will change the topic, otherwise it will be boring. I plan to introduce the whole picture of BMS, first the overall situation and then Partially, first understand the whole, and then break it down function by function. I think that in this process of summarizing and decomposing, there will be many new thoughts and gains.

　　I won’t go into details about the basic functions and functions of BMS. I searched a lot on the Internet, but I may not write more comprehensively than others. BMS is probably like a nanny for lithium-ion batteries. Without it, the lithium-ion batteries will become troublesome. Out of control; so I always thought that BMS was just a temporary job. When the lithium-ion lithium 3400mah 3.7v 18650 battery matures and grows up, BMS will no longer be needed, and I will be unemployed. Well, after I lost my job, I went to write novels. I don’t know if there is any People watch.

　　First, correct the definition of BMS. It is described as follows in the national standard QC/T897-2011:

　　The standard defines BMS as including a controller and a collector, which is an electronic component; the controller is called BCU, and the collector is called BE. Although the latter's name is relatively awkward, it is orthodox in blood.

　　However, in reality, the names are different. The controllers are called BCU, BMU, BMC, BECU, etc., and the collectors are called BMU, BIC, CMU, CMC, etc.; the name is not important, as long as the unified language is good.

　　Then we still can’t avoid looking at the location of the BMS in the lithium 3400mah 3.7v 18650 battery pack, as shown in the following diagram:

　　The BMS is usually placed inside the lithium 3400mah 3.7v 18650 battery pack, and the controller is also taken out and placed outside. Speaking of this, popular solutions are now packaged combinations, such as three-in-one, four-in-one, and various combinations of OBCDDCMCUVCU and so on. It is proposed to take out the controller in BMS and combine it with VCU and so on.

　　Taking the controller alone, the basic functional requirements and implementation solutions have not changed much compared to before, but a functional safety requirement has been added. Functional safety is a system project that ultimately falls on the controller hardware, which requires us to choose chips with functional safety certification when selecting complex chips (such as microcontrollers, power chips, etc.). Moreover, the concept of functional safety must be integrated into the solution design from the beginning. This puts forward higher requirements for hardware engineers and needs to be considered from a system perspective. To further understand the operating scenarios of the entire vehicle, it is a task for hardware engineers. Good thing. Functional safety mainly solves safety issues, but it is not the same thing as product reliability. It may not necessarily improve product reliability, but may even reduce product reliability; and cost compromise is also a difficult problem.

　　The collector must be placed inside the lithium 3400mah 3.7v 18650 battery pack, but they are all internal. Some are integrated inside the module, some are placed on the module, and there are also centralized solutions that are connected to the lithium 3400mah 3.7v 18650 battery through a long wire harness.

　　The technical solution of the collector was to use discrete components to overlap the sampling circuit at first (although there are still a few of them), and later it was gradually replaced by the current integrated AFE; the topology method is a variety of coexistence, distributed and centralized (recently I have seen many Centralized requirements), or a combination of the two; communication topologies also include CAN, daisy chain solutions, etc.

　　The key chip AFE in the collector is basically monopolized by large foreign manufacturers, and it started late in China; especially American semiconductor manufacturers: Maxim, ADI, TI, and other countries including Panasonic, ST, NXP, etc., which can be said There are quite a lot of things, I will write them later.

　　BMS design has been criticized by others because it does not use a few key indicators to prove its competitiveness like power circuits; for BMS, others will say that sampling is implemented using AFE, which is a good job done by semiconductor manufacturers and hardware design. The accuracy of SOX calculations is too difficult to prove, which creates an embarrassing situation: it is difficult to prove excellence in hardware and it is difficult to prove excellence in software, which makes people feel that there is no technical content.

　　This is because the entry threshold for BMS is low. Like the guitar among musical instruments, you can play it 53231323 times after taking one lesson. It seems very powerful, but in fact it is not a good start; many people can master BMS in just one hour. The implementation plan is almost understood, but in fact there is still a long way to go. It is also possible that BMS basically belongs to the category of digital circuits and lacks the mystery of power circuits.

　　Without going into the scope of knowledge involved in BMS, the number of signals processed by BMS is enough, and the processing object is still the most complex lithium 3400mah 3.7v 18650 battery cell, and it must adapt to different types of lithium 3400mah 3.7v 18650 battery cells. The signals processed by BMS are also rich enough: lithium 3400mah 3.7v 18650 battery cell, collision, CAN, charging, water pump, high voltage, insulation, etc., each of which will involve a series of knowledge points.

　　Summarize

　　If you want to do a good job in BMS, you need to know and master many things. The most basic device production process, device selection, and device failure modes require us to spend a lot of time learning, and there are many types of devices involved; then there are various standards, including test standards, design standards, etc.; then we get to the circuit The specific design, derating design, PCB design, etc.; and then to the verification and rectification of functions and performance; BMS does not omit any steps because it looks simple. On the contrary, because BMS is closest to the lithium 3400mah 3.7v 18650 battery, it is often more impacted. It is strong and gives it many unique features in design.

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