The principle of balanced charging for BMS of lithium ion battery pack

The number of protection chips for a single lithium-ion battery is determined according to the number of lithium-ion batteries, and is used in series to protect the charging and discharging, over-current and short-circuit states of the corresponding single lithium-ion battery. At the same time of charging protection, the system realizes balance charging by controlling the on-off of shunt discharge branch switch devices by the protection chip. This method is different from the traditional method of balance charging at the charger end, and reduces the design and application cost of lithium-ion battery charger.

Power lithium-ion batteries are used in groups, and each lithium-ion battery requires the protection of charging overvoltage, discharging undervoltage, over-current and short-circuit. In order to realize the balance charging of the whole group of batteries during the charging process, a battery pack protection board with balance charging function is adopted, which uses a single lithium-ion battery protection chip to protect any number of groups of lithium-ion batteries in series Design method. The simulation results and industrial application show that the protection board has perfect protection function, stable operation, high cost performance, and the equalization charging error is less than 50 mV.

The commonly used balance charging technologies include constant shunt resistance balance charging, on-off shunt resistance balance charging, average battery voltage balance charging, switched capacitor blank charging, buck converter balance charging, inductance balance charging, etc. When a group of lithium-ion batteries are charged in series, the balance charge of each battery should be ensured, otherwise the performance and life of the whole set of batteries will be affected in the use process. However, the existing single lithium-ion battery protection chips do not contain the balance charging control function, and the balance charging control function of multiple lithium-ion battery protection chips needs external CPU; it is realized through serial communication with the protection chip (such as I2C bus), which increases the complexity and design difficulty of the protection circuit, reduces the efficiency and reliability of the system, and adds new power consumption.