Lithium-ion battery pack equalization charging method
When lithium-ion battery packs are manufactured and stored for an extended period, the voltage of each cell in the pack becomes inconsistent due to differences in static power consumption across the protection board and varying self-discharge rates among individual cells. Balancing mechanisms in lithium-ion battery packs balance the voltage, enabling full charging and discharging of the battery pack and maximizing its efficiency.
Commonly used lithium-ion battery pack equalization charging technologies include constant shunt resistor equalization charging, on-off shunt resistor equalization charging, average battery voltage equalization charging, switched capacitor equalization charging, buck converter equalization charging, and inductor equalization charging. When charging lithium-ion batteries in series, it is essential to ensure that each cell is charged evenly; otherwise, the performance and lifespan of the entire battery pack will be affected during use.
1. A parallel balancing circuit is added to each individual cell in the lithium-ion battery pack to achieve current distribution. In this mode, when a battery reaches full charge first, the balancing device can prevent it from overcharging and convert the excess energy into heat to continue charging the batteries that are not fully charged. This method is simple, but it results in energy loss and is not suitable for fast charging systems.
2. Before charging, each individual cell is discharged to the same level through the same load, and then constant current charging is performed to ensure a relatively accurate balance between the individual cells. However, for battery packs, due to the physical differences between individual cells, it is difficult to achieve a completely consistent ideal effect after deep discharge. Even if the same effect is achieved after discharge, new imbalances will appear during the charging process.
3. Perform timely, sequential, and individual testing and uniform charging of each individual cell in the lithium-ion battery pack. This ensures that no lithium-ion cell in the pack is overcharged or over-discharged during charging, thus guaranteeing that each cell is in normal working condition.
4. Utilizing the time-sharing principle, additional current flows into the battery with a relatively low voltage through the control and switching of switching components to achieve balanced charging. This method is relatively efficient, but the control is more complex.
5. Using the voltage parameters of each battery as the balancing object, the voltage of each battery is restored to be consistent. During equalization charging, the capacitor is alternately connected to two adjacent batteries through a control switch, receiving charging from the higher-voltage battery and then discharging to the lower-voltage battery until the voltages of the two batteries tend to be consistent. This balancing method effectively solves the problem of voltage imbalance in the battery pack, but it is mainly used in situations with a small number of batteries.
6. The entire system is controlled by a microcontroller, with each individual battery having its own independent module. The module manages the charging of each individual battery according to a pre-programmed sequence, automatically disconnecting the circuit upon completion of charging. This method is relatively simple, but it significantly increases costs when dealing with a large number of individual batteries and hinders the reduction of system size.
Lithium-ion battery pack charging equalization principle
The number of protection chips for a single lithium-ion battery is determined by the number of batteries in the lithium-ion battery pack. They are connected in series to protect the corresponding single lithium-ion battery from charging, discharging, overcurrent, and short-circuit conditions. While providing charging protection, the system also achieves balanced charging by controlling the switching devices of the shunt discharge branch through the protection chips. This method differs from the traditional approach of achieving balanced charging at the charger end, reducing the design and application cost of lithium-ion battery pack chargers.
A lithium-ion battery pack consists of multiple individual lithium-ion batteries connected in series. Due to the differences between the individual cells, the voltage rise during series charging is inconsistent, leading to some cells being overcharged and others undercharged. During equalization charging, all batteries are connected in parallel, while during regular charging and power consumption, they are connected in series. During equalization charging, all batteries connected in parallel have equal voltages, achieving forced balancing of the individual cells.
