Device and method of battery pack balance and protection

Abstract

The invention relates to a device and method of battery pack balance and protection. The device comprises a main system control unit, an upper computer unit, a programmable high voltage charging unit,a low voltage constant voltage charging unit, a lower computer, a cell detection unit, a hardware protection circuit, a cell unit, a relay and the like. The main system control unit is in charge of receiving an external operation, displaying the current state, controlling the working state of the upper computer unit, receiving information returned by the upper computer unit and conducting corresponding disposal according to the returned information; after receiving control of the main system control unit, the upper computer unit automatically detects other units and uploads detection and processing results to the main system control unit; under cooperative control of the unit, it is ensured that the charging and discharging circulation frequencies and the depths of all cells are generallyconsistent, safety accidents caused in the charging and discharging process of the battery pack are avoided, so that the reliability of the battery pack is improved by a large margin, and the circulation life of the battery pack is prolonged by a large margin.

Description

technical field [0001] The invention relates to the technical field of battery charging, in particular to a device and method for equalizing and protecting a battery pack. Background technique [0002] Most of the current battery packs are used in series, because there are more or less differences in the internal resistance of the cells, although the battery packs have been strictly paired before leaving the factory, after the battery has been used for a period of time, various factors will lead to The internal resistance of the battery changes. If no corresponding measures are taken, the battery cell with large internal resistance and small capacity will obtain a high charging voltage during series charging, and it is easy to overcharge, resulting in premature damage to the battery cell; small internal resistance 1. The charging voltage obtained on the battery cell with large capacity is low, so that the battery cell cannot be fully charged; when discharging, the battery wi...

AI Technical Summary

Problems solved by technology

The disadvantages of the above method are also significant. Due to the use of a large number of switching power supplies, the circuit is complex and the failure rate is high, and when balancing large-capacity batteries, it will be restricted by the following conditions: When charging, if you want to charge the battery with high voltage The electric energy on the cell is quickly transferred to other low-voltage cells, and it is necessary to draw a large current from the high-voltage cell and couple it to other low-voltage cells through a transformer. However, since the voltage of a single cell is only Around 4V or even below, as well as the limitations of various factors such as transformer capacity and transformer multiplexing, this makes the transformer and its components unable to draw too much current, so it takes a long time to equalize. If the battery core is used for a long time , the difference will become larger and larger, and the equalization time will be longer. If a capacitor is used to transfer energy, the speed will be slower

When discharging, the energy transfer switching power supply is used to transfer the electric energy on the high-voltage cell to the low-voltage cell. However, since the voltage of a single cell is only about 4V or below, and there are many kinds of transformer capacity and transformer multiplexing, etc. factors, which will also cause the transformer and its components to not provide too much current, and will also cause the equalization time to be too long

And this trend will become more and more serious, often unable to meet the needs of high-current discharge, and sometimes even a drop in the bucket. For example, in pure electric vehicles that have been used for a period of time, the speed of energy transfer often cannot keep up with the speed of battery discharge. As a result, sometimes the electric vehicle has to stop for energy transfer, and the internal resistance of the battery cell whose power drops rapidly must be relatively large, which means that the capacity of the battery cell is also small. The more frequent charging and discharging, it will inevitably lead to a rapid acceleration of its capacity decay, thus affecting the service life of the entire battery pack

[0005] 3. There is another method, such as the method proposed in the patent (Patent No.: 201310619867.0 and Patent No. 201110008944.X). This method seems to solve the charging balance problem of the battery when the battery pack is still relatively new, but There is also the following problem: when the battery cell is charged to the set charging voltage, the battery cell is cut out of the battery pack. At this time, the charging voltage must be reduced to match the battery pack with a reduced number of cells. Provide a suitable charging voltage, After a period of time has elapsed for a cell that has been fully charged and cut out from the charging circuit, and the voltage of the cell drops to a preset voltage value, the cell will be cut into the charging circuit again, and the charging voltage will be appropriately increased to match the A battery pack with an increased number of cells provides the proper charging voltage, so that the charging voltage varies repeatedly, extending the charging time

From the charging curve of a single cell, it can be seen that after the constant current charging mode ends, it will switch to the constant voltage charging mode. If charging is stopped when switching to the constant voltage mode, the battery is only charged to 70%-80% of the full capacity. % or so, this will cause a lot of waste

Since the cells have been strictly paired before leaving the factory, in the initial stage of battery pack use, the charging capacity of each cell caused by the above-mentioned constant current and constant voltage charging method is not much different. The difference in internal resistance, if no measures are taken, this difference will form a rapid vicious circle, resulting in high charging voltage applied to the battery cell with large internal resistance, and low charging voltage applied to the battery cell with small internal resistance. As far as the battery is concerned, because the voltage applied to the battery is relatively high, the time for constant voltage charging is shortened, and even there is no constant voltage charging process, resulting in shallow charging of the battery and deep discharge, especially during charging. In the later stage, because it is impossible to set a reasonable charging current for the battery cell according to the current voltage applied to the battery cell, the battery cell works under relatively poor conditions, thereby shortening the cycle life of the battery cell rapidly

Ultimately resulting in a shortened lifespan of the battery pack

Secondly, when the entire battery pack is fully charged, only a few battery cells or even one battery cell are being charged at this time, and the output voltage of the charging power supply is only a few volts at this time. In terms of tens of volts or even hundreds of volts output by the current charging unit, the efficiency is still very low, and the voltage stability is difficult to guarantee. Not only is it easy to damage the battery cells being charged, but the charging power itself is also prone to failure.

In the same way, the above-mentioned patent still cannot achieve effective discharge equalization during discharge. For example, when a cell with a large internal resistance in the battery pack drops to the lowest voltage value, the cell will be cut out of the battery pack. At that time, the cell was already in a state of deep discharge. As we all know, the number of charge-discharge cycles and the depth of charge-discharge cycles have a significant impact on the life of the cell. The phenomenon of the rapid shortening of the life of the cell with high internal resistance has not been effectively controlled. In addition, due to the use of the charging and discharging mechanism of cutting in and out of the battery cell, this will cause the instantaneous power failure of the battery pack during discharge, which is unacceptable in many occasions, although it can be solved by connecting the battery pack in parallel. This problem, but the cost and complexity of the related control circuit will increase exponentially, thereby reducing the reliability and operability of the related control circuit

In addition, if one or more cells need to be activated in a battery pack with a large number of cells connected in series, it will cause the entire battery pack to wait for the cells to be activated before charging the entire battery pack. The charging efficiency is further reduced

[0006] More importantly, for the above several schemes, for a battery pack with many batteries, the number of lower computers (electronic switches or energy transfer switching power supplies) is also very large, and the lower computers (electronic switches or energy transfer switching power supplies) And the failure rate of related circuits and batteries will inevitably rise sharply. No matter in the process of charging or discharging, if there is no effective comparison verification, automatic detection and perfect protection mechanism, once the battery opens, the lower computer (electronic switch) or energy transfer switching power supply) and related circuits and relay failures, or the lower computer (electronic switch or energy transfer switching power supply) and related circuits and relay failures caused by the open circuit of the battery cell, the system will be difficult to deal with, which will directly lead to accidents. even threaten the life safety of users

[0007] As we all know, among the multiple factors that affect the service life of the entire battery pack, the number of charge and discharge cycles, the depth of discharge, and the interval between charge and discharge cycles are very critical factors. However, in the above three solutions, whether it is charge equalization or discharge equalization , to a certain extent, solves the short board phenomenon of the battery cell, but at the expense of the number of cycles of the cell, the charge-discharge cycle interval, and the charging time, its safety is also very low, and some methods will also cause the battery to fail. The instantaneous power failure caused by switching batteries during the operation of the battery pack greatly limits the application occasions of the battery pack.

Images