Electric quantity equalizing method and system of battery pack

Abstract

The invention provides an electric quantity equalizing method of a battery pack. The electric quantity equalizing method comprises the steps of detecting the voltage of each cell of the battery pack;forbidding the cell from performing equalization discharge based on the condition that the voltage of each cell of the battery pack exceeds an equalization discharge threshold; and when the voltages of one or more cells exceed the equalization discharge threshold, and the voltage of the at least one cell does not exceed the equalization discharge threshold, performing equalization discharge on thecell of which the voltage exceeds the equalization discharge threshold. The efficiency of the electric quantity equalizing function of the battery pack electric quantity equalizing system is improved, the meaningless electric quantity consumption is avoided, and the power supply time of the battery to the application system is prolonged. The equalization discharge threshold also can be freely setaccording to the requirements on cell characteristics and charger output voltage within a wide voltage range that is higher than the discharge overvoltage protection threshold and lower than the charge overvoltage protection threshold.

Description

technical field [0001] The present invention relates to the technical field of battery management, in particular to a method and system for balancing electric quantity of a battery pack. Background technique [0002] In a multi-cell lithium battery, there is a difference in the capacity of each battery cell that makes up the cell string, and the difference tends to increase with the aging degree. As a result, as the number of charge and discharge increases, the voltage difference between the cells becomes larger and larger. For safety reasons, the battery protection system uses the battery cell with the lowest voltage below the discharge overvoltage protection threshold as the standard for prohibiting discharge, and the battery cell with the highest voltage higher than the charging overvoltage protection threshold as the standard for prohibiting charging. It can be seen that the greater the voltage difference between the cells, the less power the battery pack can effectivel...

AI Technical Summary

Problems solved by technology

[0003] There are defects in the above method: 1) If all cells in the battery pack exceed VBL, then all cells will be discharged in a "balanced" manner. At this time, since each cell is performing the same balanced discharge, this When the balance discharge current has lost the meaning of balancing the power of the battery cells, it will instead become an additional power loss of the battery pack. The effect will make the battery pack fully charged, and the power stored in the battery cells in the VBL to VOC range will be consumed in vain by the balance discharge. drop, resulting in a decrease in the effective capacity of the battery

2) On the basis of the original balanced discharge method, in order to reduce this "waste" interval, it is necessary to increase the VBL voltage setting to reduce the difference between VBL and VOC, but this will encounter contradictions on the other hand, that is, battery protection The set VOC is the upper limit of battery charging, that is to say, for a battery pack composed of N cells connected in series, the highest charging voltage is N times the VOC, and the charger produced for the battery pack is often out of safety considerations , its output charging voltage will be limited to be lower than N times VOC, once VBL is set too high or the upper limit of charging voltage output by the charger is too low, so that N times VBL exceeds the output upper limit of the charger, in this case In this case, the total voltage cannot be charged to be higher than N times VBL, and the balance function can hardly be triggered, which is useless

VBL setting range is very limited

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