1. Energy dissipation-type equalization is achieved by discharging individual cells in the battery pack through parallel shunt resistors connected across each cell. The shunt resistor discharge equalization circuit is the most direct equalization technique. This technique discharges the cells with higher capacity through shunt resistors until all cells have the same capacity.
2. Compared with energy dissipative balancing, energy non-dissipative balancing circuits consume less energy but have a more complex circuit structure.
① The Flying Capacitor Generator connects a capacitor in parallel with each battery cell. By switching on and off, this capacitor can be connected in parallel to the same battery cell or to an adjacent battery cell. When the voltage of a battery cell is too high, the capacitor is first connected in parallel with the battery cell, so that the capacitor voltage matches that of the battery cell. Then, the capacitor is switched to an adjacent battery cell, and the capacitor discharges into the battery cell, thus achieving energy transfer.
② Switched Capacitor Balancing: For a power lithium battery pack composed of n individual cells connected in series, the switched capacitor balancing circuit requires n-1 capacitor elements and 2n switching devices. Taking the inconsistent terminal voltages of individual cells B1 and B2 as an example, there are two states during the control process. The disadvantage of this circuit is that it can only be used for balancing the terminal voltages between individual cells, and it can only realize energy flow between adjacent individual cells. Therefore, when the number of cells connected in series is large, the balancing time is relatively long.
③ The double-layer capacitor equalization circuit is also a derivation and transformation of the switched capacitor circuit. The difference lies in the fact that this circuit uses two layers of switched capacitors to achieve energy transfer between batteries. Compared with the switched capacitor equalization circuit, the advantage of this circuit is that by using the newly added outer switched capacitor, a single battery can not only perform voltage equalization with adjacent single batteries, but also with non-adjacent single batteries, thus improving the equalization speed.
A parallel balancing circuit is added to each individual cell in the battery pack to achieve current distribution. In this mode, when a cell reaches full charge first, the balancing device prevents it from overcharging and converts the excess energy into heat to continue charging the cells that are not fully charged. This method is simple, but it results in energy loss and is not suitable for fast charging systems.
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 among the 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.
The individual batteries in the battery pack are tested and charged evenly on a regular, sequential basis. This ensures that no battery in the battery pack is overcharged or over-discharged during charging, thus guaranteeing that each battery is in normal working condition.
By employing the time-sharing principle, additional current flows into the battery with a relatively low voltage through the control and switching of switching components, thereby achieving balanced charging. This method is relatively efficient, but its control is quite complex.
The equalization method uses the voltage parameters of each battery as the balancing target to restore the voltage of each battery to a uniform level. During equalization charging, the capacitor is alternately connected to two adjacent batteries via 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 the same. This equalization method effectively solves the problem of voltage imbalance in battery packs, but it is mainly used in situations with a small number of batteries.
The entire system is controlled by a microcontroller, with each individual battery having its own independent module. The module manages the charging of each 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.
