What are the basic protection and core functions of lithium-ion battery BMS

(1) Determine the overcurrent and discharge conditions. In the smart battery charging and discharging state, when the current is detected to be greater than 3A, after a delay of 0.2s, if the current is still greater than 3A, it is judged as overcurrent. At this time, the protection execution circuit disconnects the discharge protection switch. The protection condition is to connect the charger. When the charger is switched on, the overcurrent protection will be removed. Otherwise, the smart battery will be in a protected state. (2) Determine the overcharge and discharge conditions. During the charging process, if the battery voltage exceeds 4.2v or the total voltage exceeds 16.8v, it is judged that the battery is in an overcharge state. At this time, the protection execution circuit disconnects the charging protection switch. The discharge state of overcharge is that the voltage of all batteries is less than 4V. (3) Determine that the overcharge protection fails. During the charging process, if the battery voltage exceeds 4.4v, the charging protection function is judged to be abnormal, and the secondary protection circuit is activated to blow the three-terminal fuse. (4) Determine the over-discharge, under-voltage and discharge conditions. During the discharge process, when the voltage of a battery is lower than 2.5v, it is judged that the battery is in the over-discharged state, and the protection execution circuit cuts off the discharge switch to stop the discharge. Release conditions for all battery voltages greater than 3V. (5) Determine over-temperature protection and release conditions. When the battery voltage temperature exceeds 55°C, it is judged that the battery is in an over-temperature state. At this time, the protection execution circuit disconnects the charge and discharge protection switch. Release conditions: The battery temperature is below 50°C. The core functions of BMS 1) Cell monitoring technology 1. Single battery voltage collection; 2. Single battery temperature collection; 3. Battery pack current detection; accurate temperature measurement is also very important for battery pack working status, including single battery Temperature measurement and temperature monitoring of the cooling liquid of the battery pack. It is necessary to reasonably set the position and number of temperature sensors to be used, and form a good cooperation with the BMS control module. The monitoring of the temperature of the cooling liquid of the battery pack focuses on the temperature of the fluid at the inlet and outlet, and the selection of monitoring accuracy is similar to that of a single battery. 2) SOC (State of Charge) technology: Simply put, how much electricity is left in the battery SOC is the most important parameter in BMS, because everything else is based on SOC, so its accuracy and robustness (also Called error correction capability) is extremely important. If there is no precise SOC, no amount of protection functions can make the BMS work normally, because the battery will often be in a protected state, and it will not be able to extend the life of the battery. The higher the accuracy of the estimation of SOC, the higher the range of the electric vehicle for the battery of the same capacity. High-precision SOC estimation can maximize the efficiency of the battery pack. 3) Equalization technology Passive equalization generally uses resistance heat to release the excess power of high-capacity batteries, so as to achieve the purpose of equalization. The circuit is simple and reliable, and the cost is low, but the battery efficiency is also low. During active equalization, the excess power is transferred to high-capacity cells, and during discharging, the excess power is transferred to low-capacity cells, which can improve the use efficiency, but the cost is higher, the circuit is complex, and the reliability is low. In the future, with the improvement of battery cell consistency, the demand for passive balance may decrease. Disclaimer: Some pictures and content of the articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous article: Why does USB take too long to charge the mobile phone lithium-ion battery?