The battery management system of electric vehicles is called BMS, which manages the charge and discharge of the battery to keep the battery in an optimal state.
To charge an electric car at a charging pile, you first need to communicate with the car to understand the car’s battery needs and battery status,
and only then can you charge according to the car’s needs.
Why do we need management?
Because the battery cell is an electrochemical process, multiple cells form a battery. Due to the characteristics of each cell,
no matter how precise the manufacturing is, there will be errors and inconsistencies in each cell depending on the use time and environment.
Therefore, the battery management system uses limited parameters to evaluate the current status of the battery.
It is a bit like traditional Chinese medicine. It uses symptoms to determine what disease you have. It is not Western medicine, which requires some physical and chemical analysis.
The physical and chemical analysis of the human body is like the electrochemical characteristics of the battery. It can be measured through large-scale test instruments,
but it is difficult for embedded systems to evaluate some electrochemical indicators,
so BMS can be regarded as an old Chinese doctor who specializes in treating batteries.
There are many uses for BMS.
For large-scale battery systems, there are roughly two categories. One is for automobiles, and the other is for energy storage.
Cars are divided into FULL-EV, HEV, PHEV, etc. according to different battery capacities and charging methods.
Energy storage is used to store energy from the grid, which is equivalent to finding other outlets for used batteries in electric vehicles.
There are many battery data stored in BMS, such as:
1. Materials. There are many categories of battery materials. Common battery categories include lead-acid batteries,
nickel metal hydride batteries, lithium iron phosphate batteries, lithium manganese oxide batteries, and lithium cobalt oxide batteries.
ternary material batteries, polymer lithium-ion batteries, lithium titanate batteries, etc.
2. Capacity, AH is the capacity, that is, how much current is used to discharge for how long, for example, 200AH, using a current of 200A, can be discharged for one hour.
3. The voltage of the battery core. The voltage of a single battery core has a floating range. The voltage of the battery core is different depending on the SOC.
The voltage of the ternary battery is about 2.75V-4.2V, but for the sake of safety, no one will use so many.
The topology structure of BMS is divided into master-slave and integrated.
The one used in electric vehicles is basically the master-slave type. The master-slave power supply method is:
the main board is powered by a 12V low-voltage network; the slave board is powered by a 12V low-voltage network;
the sampling chip is powered by a high-voltage battery. The communication method is CAN communication between the master and slave boards; daisy chain communication between the slave boards.
BMS functions can be divided into three levels.
The first one is the boss in the battery system and the younger brother in the entire vehicle system. It controls the entire vehicle and does whatever it asks you to do.
The second one accepts vehicle control unit information and does not need to listen to the instructions of some control units.
There are multiple sections within the system, each responsible for its own functions so that the battery system can operate normally.