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Balanced charging method for lithium ion battery pack

Balanced charging method for lithium ion battery pack


Common equalization charging techniques include constant shunt resistor equalization charging, on-off shunt resistor equalization charging, average battery voltage equalization charging, switching capacitor equalization charging, step-down converter equalization charging, inductance equalization charging, etc. When groups of lithium ion batteries are charged in series, each battery should be charged in a balanced way, otherwise the performance and life of the whole battery will be affected in the process of use. However, the existing single lithium-ion battery protection chip does not contain the function of balanced charging control, and the balanced charging control function of multi-lithium-ion battery protection chip needs to be connected to the CPU. Through the 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 the power consumption is increased.

For power lithium-ion batteries used in groups, each lithium-ion battery requires protection of overvoltage, undervoltage, overcurrent and short circuit, and balanced charging of the whole group of batteries should be realized in the charging process. This paper introduces a design method of a battery pack protection plate with balanced charging function which uses a single lithium-ion battery protection chip to protect any series number of lithium-ion batteries. The simulation results and industrial application show that the protection plate has perfect protection function, stable operation, high cost performance, and the balance charging error is less than 50mV.

1. A parallel equalization circuit is attached to each single battery of the lithium ion battery pack to achieve the purpose of shunting. In this mode, when a battery is first fully charged, the equalizer stops it from overcharging and converts the excess energy into heat to continue charging the undercharged battery. This method is simple, but it will cause energy loss, so it is not suitable for fast charging system.

2. Before charging, discharge each monomer one by one through the same load to the same level, and then carry out constant current charging, so as to ensure a more accurate equilibrium state between each monomer. However, due to the physical differences among individuals, it is difficult for each cell to achieve the same ideal effect after deep discharge. Even if the same effect is achieved after discharge, new disequilibrium phenomena will appear in the charging process.

3. Detect and charge the single battery in the lithium-ion battery pack on time, in order and separately. When the lithium ion battery pack is charged, it can ensure that each lithium ion battery in the battery pack will not be overcharged or overdischarged, so it ensures that each battery in the lithium ion battery pack is in the normal working state.

4, the use of time-sharing principle, through the control and switching of switch components, so that the extra current into the battery with a relatively low voltage to achieve the purpose of balanced charging. The method is efficient, but the control is complicated.

5. Take the voltage parameters of each battery as the equilibrium object, so that the voltage of each battery can be restored to the same. In equalizing charging, the capacitor is connected alternately to two adjacent cells through a control switch, receiving the charge from the high-voltage cell and discharging the low-voltage cell until the voltage of the two cells converges. This balancing method can solve the problem of voltage imbalance of lithium-ion battery pack well, but it is important to use in the occasion of less battery number.

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