Manufacturers analyze the commonly used lithium battery series use of voltage equalization circuit
Because of the special characteristics of lithium batteries, lithium battery pack is usually equipped with protection circuits used together, with the development of the lithium battery industry, the energy density of lithium batteries is getting higher and higher, power lithium batteries tend to use high energy density lithium batteries, in the series use of power lithium batteries must use the voltage equalization circuit. Lithium battery manufacturer and share with you, often use several battery equalization circuit, I hope it will help you.
A load consumption equalization method
That is, a resistor is connected in parallel to each cell, and a switch is connected in series for control. When the voltage of a string of cells is too high, the switch is passively opened and the charging current is shunted through the resistor. In this way, the charging current of the high-voltage battery is smaller, while the charging current of the low-voltage battery is larger. In this way, the balance of the voltage of the power battery pack can be achieved. However, this method is only applicable to low-capacity batteries. The higher the capacity, the more current needs to be balanced, and the balancing in this way will be more strenuous.
Load consumption balancing principle diagram
Second, the oscillation capacitor method
Each cell is connected in parallel with a capacitor, which can be connected in parallel with a switch. When the voltage of a string of cells is too high, the capacitor is first connected in parallel with the battery, and the capacitor voltage is the same as the battery voltage. Then the capacitor is switched to the neighboring battery and the capacitor discharges the battery. The transfer of energy is achieved. Since the capacitor does not consume energy, it can achieve a lossless energy transfer. If this is the way, many switches are needed to control it.
The working schematic of Fido's capacitor method is to draw the equalization schematic of two adjacent batteries
The first equalization is the charging of the power battery pack. 80AH battery capacity is connected in parallel with two groups, the equalization current requirement is 10A. the principle of the original equalization is theoretically insufficient, such a large current is equivalent to a small module, and finally it is really using n series of small modules, each battery is connected to a small module in parallel, if the single battery voltage is lower than the set value, the corresponding module is started in parallel and starts to give low voltage If the voltage of a single cell falls below a set value, the corresponding module is activated in parallel and starts charging the low voltage cell, replenishing the energy and increasing the voltage to achieve balance.
The DC-DC input bus can be either the battery voltage or the DC input provided by other modules, which can be flexibly configured as needed.
The active equalization method can use the transformer multiplexing method mentioned earlier.
I have used this balancing method to balance 1000AH, 7 series batteries and 300AH, 80 series batteries. After balancing is completed, the voltage of all individual cells can be achieved within 5mV.
Multi-winding transformer method structure diagram
Active balancing can also take the form of energy transfer. The so-called energy transfer can either take energy from the whole group voltage to supplement the low voltage part, or take energy from the over-voltage battery to feed back the whole group voltage.
The second method of battery equalization is implemented in the communication power supply system. The circuit schematic is as follows:
So what we have done is to balance 16 lithium batteries and divide them into two groups of 8 cells each, here we have drawn only 6 describing how they work.
During the experiment, the two groups are balanced. When there is a deviation between the two groups, bi-directional DC-DC can be used for energy conversion, using fewer modules and a more convenient design.
Here, bidirectional DC-DC is not used, but simply energy consumption is used to balance the battery between the two groups. From the final test results, the balance of the batteries is relatively good.
If the battery B5 voltage is too high, control Q5 to work in PWM mode. When Q5 is on, the inductor L5 can store energy. When Q5 is off, the energy stored in the inductor charges batteries B1-B4 through D5, reducing the voltage of battery B5 and increasing the voltage of the remaining batteries. The same principle can be used to analyze the working process of the remaining battery pack when the voltage is too high.
The process of balancing, if it is felt that there is no need to give each battery to provide all the charging modules, so that the energy consumption does not meet the technical requirements, but also the need for active balancing, then the above-mentioned transformer multi-output method, may be more suitable, the use of a suitable transformer as the original side feedback current-limited multi-output flyback power supply can be.
With the development of power lithium battery applications, not only the balance of the battery, overcharge and overdischarge protection needs to be appropriate, but also indicates that the application of pole plate protection will become more and more widespread.
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