Nowadays, electric car models are changing with each passing day. How to stand out in many models? A powerful electric car must have a set of high-quality battery management system inside, and want to create high-quality BMS, isolated power supply and isolated CAN transceiver options to Critical, so how do you choose to isolate the power supply and isolate the CAN transceiver in the BM S solution?
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First, electric vehicle BMS introduction
BATTERY MANAGEMENT SYSTEM (BMS) is an important link between vehicle power battery and electric vehicle. Its main functions include: real-time monitoring of battery physical parameters, battery status evaluation, online diagnosis and alarm, and equalization control. Why is the electric vehicle BMS going to rise?
The power and energy storage batteries of electric vehicles are in the form of battery packs. However, based on the existing manufacturing level, the performance of the single cells cannot be achieved completely. The high-power, large-capacity power batteries are formed by series-parallel connection. After the group, the harsh conditions of use are also likely to induce local deviations, which leads to safety problems. BMS performance is critical for proper and effective management of the battery pack.
Figure 1 BMS product picture
Second, the working principle of BMS
The BMS is closely integrated with the power battery of the electric vehicle. How does the BMS ensure reasonable and effective management and control of the battery pack? Its specific work is as follows.
l Monitor the overall condition of the battery, and measure the voltage, current and temperature of the battery in real time through the sensor;
l Manage the working state of the battery, perform leakage detection, thermal management, battery balance management, alarm reminder, calculate residual capacity (SOC), discharge power, and report battery degradation degree (SOH) and remaining capacity (SOC) status;
l Battery state estimation, using the algorithm to control the maximum output power according to the voltage, current and temperature of the battery to obtain the maximum driving range, and using the algorithm to control the charger to charge the optimal current.
And this series of information transmission is through the CAN bus interface and the vehicle master controller, motor controller, energy control system, vehicle display system, etc. for real-time communication, and finally ensure reasonable and effective management and control of the battery pack, the specific structure block diagram as shown in picture 2.
Figure 2 BMS architecture block diagram
Third, the three elements that BMS should have
So how do you ensure that the BMS works properly? Let's start with the BMS working environment inside the car.
First, the mutual interference between the BMS modules should be avoided, and the isolated DC-DC power supply is used at the power input front end. There are many BMS modules in a car, and each module concentrates on taking power from the battery. The internal block diagram of the specific electric car is shown in Figure 3. In order to ensure that each module does not cross each other and ensure the independence of the BMS single module, it is necessary to use an isolated DC-DC power supply at the front end of the BMS's power input, and the input voltage range should be wide.
Figure 3 BMS block diagram of electric vehicle internal
Secondly, it should be ensured that the BMS can communicate with the electric vehicle in real time, and the communication front end does CAN isolation processing. The communication environment inside the car is relatively harsh, and there are interference signals such as surges and pulses. To ensure normal communication, and also based on the consideration of low coupling between systems and power supply safety regulations, the CAN terminal also needs to be isolated and protected. And the transmission rate requirements are higher.
Finally, the driver's personal safety should be guaranteed and a higher level of power isolation protection is required. Since a plurality of batteries are connected in series, the voltage of the battery pack is very high, generally up to about 500 VDC, which is a voltage that poses a safety threat to the human body. To ensure the safety of the low voltage side of the battery, the isolated DC-DC is generally used to separate the high voltage and Low pressure side.
Fourth, BMS power and signal isolation recommended solution
Due to the security considerations of the BMS, power and signal isolation are required between the systems, and the BMS motherboard is powered by the battery pack. It is generally 12V (also 24V), and more is a 2W/3W isolated DC-DC power supply module. 6W isolated DC-DC power modules are also used for some power requirements. For high EMI requirements, a π-type filter circuit can be added to the input of the isolated DC-DC power supply module.
Considering the security of BMS, CAN communication is often used, and it is necessary to spend a lot of thoughts on anti-interference and isolation.
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