A balanced charging method for lithium battery pack -Lithium - Ion Battery Equipment
Abstract: In view of the use of power lithium-ion batteries in groups, each lithium-ion battery requires protection against charging overvoltage, discharge undervoltage, overcurrent and short circuit, and the problem of equalizing the charging of the whole group of batteries during the charging process, this paper analyzes the design method of a battery pack protection board with equalizing charging function that uses a single lithium-ion battery protection chip to protect any group of lithium-ion batteries in series. The simulation results and industrial processing use prove that the protection function of the protection board is perfect, the work is stable, and the performance price ratio is high.(Lithium - Ion Battery Equipment)
introduction
Common equalization charging technologies include constant shunt resistance equalization charging, on/off shunt resistance equalization charging, uniform battery voltage equalization charging, switch capacitor equalization charging, step-down converter equalization charging, inductance equalization charging, etc. When charging a group of lithium-ion batteries in series, ensure that each battery is evenly charged, otherwise the performance and life of the whole group of batteries will be affected during use. However, the existing single lithium-ion battery protection chip does not contain the equalizing charge control function, and the equalizing charge control function of multiple lithium-ion battery protection chips should be connected to an external CpU; It is realized by 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 power consumption.
In view of the use of power lithium-ion batteries in groups, each lithium-ion battery requires the protection of charging overvoltage, discharge undervoltage, overcurrent and short circuit. During the charging process, it is necessary to realize the balanced charging of the whole group of batteries. This paper analyzes the design method of a battery pack protection board with balanced charging function that uses a single lithium-ion battery protection chip to protect any group of lithium-ion batteries in series. The simulation results and industrial processing use prove that the protection board has perfect protection function, stable operation, high cost performance, and the equalizing charging error is less than 50mV
1. Principle and structure of equalizing charging for protection board of lithium ion battery pack
The structure block diagram of the protection board of the lithium-ion battery pack with equalizing charging capability designed with a single lithium-ion battery protection chip is shown in Figure 1 below.
Figure 1 Structural block diagram of lithium ion battery pack protection board, wherein: 1 is a single lithium ion battery; 2 is the resistance of charging overvoltage shunt discharge branch; 3 is a switching device used for shunt discharge branch control; 4 is the overcurrent test protection resistance; 5 is the omitted lithium ion battery protection chip and circuit connection part; 6 is a single lithium-ion battery protection chip (generally including charge control pin CO, discharge control pin DO, discharge overcurrent and short circuit test pin VM, positive battery VDD, negative battery VSS, etc.); 7 is the MOS tube grid used for charging control in the main circuit driven by the parallel connection formed by the optocoupler isolation of the charging overvoltage protection signal; 8 refers to MOS tube grid used for discharge control in main circuit driven by series connection after optocoupler isolation of discharge undervoltage, overcurrent and short circuit protection signals; 9 is the charging control switch device; 10 is a discharge control switching device; 11 is the control circuit; 12 Main circuit; 13 is a shunt discharge branch. The number of protection chips for a single lithium-ion battery is determined according to the number of lithium-ion battery packs. They are used in series to protect the charge discharge, over-current and short circuit status of the corresponding single lithium-ion battery. At the same time of charging protection, the system realizes balanced charging by controlling the on-off of shunt discharge branch switch devices through the protection chip. This method is different from the traditional method of achieving balanced charging at the charger end, and reduces the cost of designing and using the lithium ion battery pack charger.
introduction
Common equalization charging technologies include constant shunt resistance equalization charging, on/off shunt resistance equalization charging, uniform battery voltage equalization charging, switch capacitor equalization charging, step-down converter equalization charging, inductance equalization charging, etc. When charging a group of lithium-ion batteries in series, ensure that each battery is evenly charged, otherwise the performance and life of the whole group of batteries will be affected during use. However, the existing single lithium-ion battery protection chip does not contain the equalizing charge control function, and the equalizing charge control function of multiple lithium-ion battery protection chips should be connected to an external CpU; It is realized by 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 power consumption.
In view of the use of power lithium-ion batteries in groups, each lithium-ion battery requires the protection of charging overvoltage, discharge undervoltage, overcurrent and short circuit. During the charging process, it is necessary to realize the balanced charging of the whole group of batteries. This paper analyzes the design method of a battery pack protection board with balanced charging function that uses a single lithium-ion battery protection chip to protect any group of lithium-ion batteries in series. The simulation results and industrial processing use prove that the protection board has perfect protection function, stable operation, high cost performance, and the equalizing charging error is less than 50mV
1. Principle and structure of equalizing charging for protection board of lithium ion battery pack
The structure block diagram of the protection board of the lithium-ion battery pack with equalizing charging capability designed with a single lithium-ion battery protection chip is shown in Figure 1 below.
Figure 1 Structural block diagram of lithium ion battery pack protection board, wherein: 1 is a single lithium ion battery; 2 is the resistance of charging overvoltage shunt discharge branch; 3 is a switching device used for shunt discharge branch control; 4 is the overcurrent test protection resistance; 5 is the omitted lithium ion battery protection chip and circuit connection part; 6 is a single lithium-ion battery protection chip (generally including charge control pin CO, discharge control pin DO, discharge overcurrent and short circuit test pin VM, positive battery VDD, negative battery VSS, etc.); 7 is the MOS tube grid used for charging control in the main circuit driven by the parallel connection formed by the optocoupler isolation of the charging overvoltage protection signal; 8 refers to MOS tube grid used for discharge control in main circuit driven by series connection after optocoupler isolation of discharge undervoltage, overcurrent and short circuit protection signals; 9 is the charging control switch device; 10 is a discharge control switching device; 11 is the control circuit; 12 Main circuit; 13 is a shunt discharge branch. The number of protection chips for a single lithium-ion battery is determined according to the number of lithium-ion battery packs. They are used in series to protect the charge discharge, over-current and short circuit status of the corresponding single lithium-ion battery. At the same time of charging protection, the system realizes balanced charging by controlling the on-off of shunt discharge branch switch devices through the protection chip. This method is different from the traditional method of achieving balanced charging at the charger end, and reduces the cost of designing and using the lithium ion battery pack charger.
