Parallel equalization charging method for lithium battery packs.lithium golf cart batteries

　　Common equalization charging technologies include constant shunt resistor equalization charging, on off shunt resistor equalization charging, average battery voltage equalization charging, switch capacitor equalization charging, buck converter equalization charging, inductor equalization charging, etc. When charging lithium batteries in series, it is necessary to ensure that each battery is evenly charged, otherwise the performance and lifespan of the entire battery group will be affected during use. However, the existing single lithium battery protection chips do not include equalization charging control function, and the equalization charging control function of multiple lithium battery protection chips requires an external CPU; By implementing serial communication with the protection chip (such as I2C bus), the complexity and design difficulty of the protection circuit are increased, the efficiency and reliability of the system are reduced, and power consumption is increased.

　　This article focuses on the use of power lithium batteries in groups, and each lithium battery requires protection against charging overvoltage, discharging undervoltage, overcurrent, and short circuit. During the charging process, it is necessary to achieve balanced charging of the entire group of batteries. It introduces a design scheme of a battery protection board with balanced charging function that uses a single lithium battery protection chip to protect any number of series connected lithium batteries. The simulation results and industrial production applications have proven that the protection board has complete protection functions, stable operation, high cost-effectiveness, and balanced charging error less than 50mV.

　　Principle and Structure of Balanced Charging for Lithium Battery Pack Protection Board

　　1 is a single lithium-ion battery; 2 is the resistance of the charging overvoltage shunt discharge branch; 3 is a switching device for controlling the shunt discharge branch; 4 is the overcurrent detection protection resistance; 5 is the omitted lithium battery protection chip and circuit connection part; 6 is a single lithium battery protection chip (generally including charging control pin CO, discharge control pin DO, discharge overcurrent and short circuit detection pin VM, battery positive terminal VDD, battery negative terminal VSS, etc.); 7. The charging overvoltage protection signal is isolated by the optocoupler and forms a parallel relationship to drive the MOS gate for charging control in the main circuit; 8 is the MOS gate used for discharge control in the main circuit driven by a series relationship formed by the isolation of discharge undervoltage, overcurrent, and short circuit protection signals through optocoupler isolation; 9 is a charging control switch device; 10 is a discharge control switch device; 11 is the control circuit; 12 main circuit; 13 is a shunt discharge branch. The number of single lithium battery protection chips is determined based on the number of lithium battery packs, which are used in series to protect the charging and discharging, overcurrent, and short circuit states of the corresponding single lithium battery. This system not only provides charging protection, but also achieves balanced charging by controlling the on-off of the shunt discharge branch switch device through the protection chip. This scheme is different from the traditional approach of achieving balanced charging at the charger end and reduces the cost of designing and applying lithium battery chargers.

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