Let’s briefly talk about the potential equalization inside the battery system
Latest update time：2019-10-28
Reads：
I would like to find some actual BMSs from other manufacturers to analyze. I will only look at the advantages and not comment on anything else.
If you have a way to get some prototypes, you can contact me.
Especially BMSs from domestic manufacturers, you can now learn about them through the Internet. They are basically products from foreign manufacturers. On the contrary, domestic BMS product information is more closed. I don’t know why.
In fact, I personally feel that I have never thought about the problem of product grounding. It is like a gray rhinoceros. It will bring you unpredictable troubles unexpectedly.
In standard
18384.3
, the concept of potential equalization is mentioned. Simply put, it means that
the resistance between
exposed conductive
shells should be less than 0.1Ω.
In the "
Electric Vehicle Safety Guidelines
" it is stipulated that:
In another standard
LV123
, the impedance value requirements for potential equalization are also clearly specified.
The potential equalization between the leakage conductive shells is achieved through grounding. The main purpose is to prevent the voltage difference between the two leakage conductive shells from endangering personal safety.
The figure below is a simplified block diagram of a battery system, with the grounding of the major components marked.
In the picture, the ground of the metal tray of the battery pack and the ground of the car body are connected through a ground iron, so the ground of the battery tray and the ground of the car body are on the same network.
The body ground and pallet ground (GND) referred to here are actually suspended from the earth, and the potential difference between them and the earth is uncertain;
so the grounding in this article refers to the body ground, for example, the entire battery in the picture below The exposed metal portion of the pallet.
Battery cell grounding
To be precise, it is the grounding of the module shell after the battery core is formed into a module.
For example, a common square battery core is fixed to the chassis with screws through the four corner mounting holes of the module, as shown in the picture below:
Of course, there are also many cases where there is no grounding or poor grounding (as shown below).
Therefore, regarding the grounding of the module shell, it currently seems that if the module shell is non-insulated, it is more likely to be grounded to prevent the risk of electric shock.
BMS grounding
The BMS's own low-voltage power supply is the ground of the vehicle. It also needs to sample the high-voltage battery. The approximate block diagram is as follows. In order to prevent the high-voltage sampling line from leaking to the shell, the BMS shell needs to be externally grounded.
Some BMS have metal casings, some have plastic casings, and some do not even have casings;
and the metal casings are divided into two types: external painting and bare.
In fact, there are no unified standards and regulations for what material to choose for the shell of BMS, but most of the controller shells are made of metal.
It is the exposed metal shell that needs potential equalization grounding treatment, such as the following grounding treatment:
Summarize
:
This time I will briefly introduce the content of the grounding in the battery pack and the source standards. Later, I will separately introduce the problems that may be caused by poor grounding and illustrate it through some actual cases.
All of the above are for reference only.
京公网安备 11010802033920号