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High-voltage lithium-ion battery pack charging method

2006-12-9 23:53:33 Category:Professional News

Lithium-ion battery as a result of high voltage, small size, light weight, no memory effect, no pollution, low self-discharge, long cycle life, is an ideal power source. In actual use, in order to obtain higher discharge voltage, typically at least two in series cell lithium-ion batteries use lithium-ion battery pack. Currently, lithium-ion battery pack has been widely used in notebook computers, electric bicycles and backup power and other areas.

Therefore, how to charge lithium-ion battery pack when it is particularly good use of the key, now commonly used in lithium-ion battery charging method and I think some of the most suitable charging method Shishu as follows:

An ordinary series charging

Currently charging lithium-ion battery pack charge is generally used in series, mainly because the series charging method is simple, low cost, relatively easy to implement. However, between the single lithium-ion battery capacity, impedance, attenuation characteristics, self-discharge performance difference in the series of lithium-ion battery charging, the battery capacity of the smallest bird in the single-cell Li-ion battery will The first is full of power, but this time, no other battery is fully charged, if the series continues to charge, already fully charged cell lithium-ion batteries may be overcharged.

The rechargeable lithium-ion battery battery performance will be seriously damaged and may even cause an explosion causing damage, so in order to prevent cell lithium-ion rechargeable battery, lithium-ion battery pack when used with a battery management system, general (Battery ManagementSystem, referred to as BMS), through the battery management system for each single-cell Li-ion battery only been charging protection. Series charging, if there is a single lithium-ion battery voltage reaches the overcharge protection voltage, the battery management system will cut off the charging circuit in series, stop charging, to prevent over charging the battery is only monomer, and this will cause other Lithium-ion battery is not fully charged.

After years of development, lithium iron phosphate batteries because of high security, good cycle performance and other advantages, electric cars have basically been able to meet the particular requirements of electric cars, technology also has a large-scale production of basic conditions. However, the performance of lithium iron phosphate lithium-ion batteries and other there are some differences, in particular, the voltage characteristics of lithium manganese batteries, lithium cobalt oxide and so different. The following is a lithium iron phosphate with two kinds of lithium rechargeable lithium-ion battery lithium ion deintercalation curves and comparison of correspondence:

Figure 1, lithium iron phosphate rechargeable lithium ion deintercalation curve with the corresponding relations


From the above curve is not difficult to see that in the fast lithium iron phosphate batteries fully charged, the lithium ion deintercalation almost entirely from the cathode to the anode, the battery terminal voltage will quickly rise, the charging curve of upturned phenomenon, this will cause the battery to be easy to achieve over charge protection voltage. Therefore, lithium iron phosphate battery charging some group dissatisfied with the relative power of the phenomenon in terms of manganese lithium batteries will be more apparent.

In addition, although some battery management system with a balance of features, but because of cost, heat dissipation, reliability, and many other considerations, the balance of current battery management system generally charge much less than the current series, so the effect is not obvious balance will appears less certain single battery charge power, and this requires high current for a rechargeable lithium ion battery pack, such as electric vehicles using lithium-ion batteries in terms of the more apparent.

For example, the discharge capacity is 100 to 100Ah lithium-ion batteries in series to form battery packs, but if the former of which 99 groups of single lithium-ion battery charged 80Ah, also a single lithium-ion battery charged 100Ah, will
 The battery charging in series, in which the dog charged 100Ah single lithium-ion batteries will be fully charged to achieve the overcharge protection voltage, in order to prevent the only cell lithium-ion battery is over charging, battery management system will cut off the charging circuit in series, it makes the other 99 can not be fully charged battery to the battery discharge capacity, it was only 80Ah.

Battery manufacturers typically test the capacity of the factory when the single constant current charging the battery first and then constant voltage charging, constant current discharge and then to measure the discharge capacity. General discharge capacity equivalent to capacity with constant voltage and constant current charging capacity.
 The actual process of charging the battery packs in series in terms of single cells generally do not have constant voltage charging process, so there will not be constant charge capacity, battery capacity will be less than the single battery capacity. The general charge current smaller, the smaller the constant ratio of charge capacity, the smaller battery capacity loss, it has developed a battery management system and coordination charger series charging mode.

2 battery management system and coordination charger charging series

Battery management system is state of the battery's performance and the most comprehensive understanding of the equipment, so the battery management system and establish contact between the charger, you can make the battery charger to understand the information in real time, so as to more effectively solve the battery charging have some problems, the schematic diagram below.

Figure 2: power lithium battery systems integration

Figure 3 power lithium battery systems integration


Figure 4 based system for lithium-ion battery system

Figure 4: BMS and charger charging series Diagrammatic illustration of coordination

Figure 5 BMS and charger charging series Diagrammatic illustration of coordination

Battery management system and charger charging mode coordination principle is: the battery management system through the battery's current state (such as temperature, single battery voltage, battery current, consistency and temperature, etc.) to monitor, and use these
 parameters on the current battery charge current to estimate the maximum allowable; charging process, through the communication line and the battery charger management system linked to data sharing. The total voltage of battery management system, the highest single battery voltage, maximum temperature, temperature rise, the maximum allowable charge voltage, the maximum allowable single battery charge voltage and current parameters such as maximum allowable transmitted in real time to the charger, battery charger can be based on management system provides information to change their charging policies and output current.

When the battery management system provides the maximum allowable charging current than the charger designed for high current capacity, the maximum charger output current according to the design charging; when the battery voltage, temperature gauge, the battery management system can detect and notify in real time change the charger current output; when the charge current is greater than the maximum allowable charge current, the charger started to follow the maximum allowable charge current, so that effectively prevent the battery charging, to extend the battery life of purpose. The event of a failure during charging, the battery management system can be set to 0, the maximum allowable charge current to force the charger shut down to avoid accidents, protect the safety of charge.

In the charging mode, the battery management system not only improve the management and control functions, it also enabled the state depending on the battery charger, the output current changes in real time, to prevent the battery charging all the batteries and optimize charging occurred purpose The actual discharge capacity of the battery pack should charge more than the ordinary method of series, but this method is still not solve the battery charging less for some battery power, especially when the number of multi-string battery pack, battery consistency is poor, the charge current large.

3 parallel charging

To address some of the battery pack and charger single battery charge less electricity problem, but also developed a parallel approach to charging, the schematic diagram below.

Figure 6 Diagrammatic illustration of parallel charge Figure 6 Diagrammatic illustration of parallel charge

But the parallel charging method requires use of multiple low voltage, high current power supply for each charge only single battery charge, charging power supply there is high cost, low reliability and low charge efficiency, connectivity and other defects in thick wire, so there is no large the scope of use of this charging method.

4 series high-current charge plus a small current parallel charging

Because of the three charging methods have problems, I developed one of the most suitable for high-voltage battery pack, especially the electric vehicle battery charging method, which uses battery management system and coordination of charger-current charge plus constant series pressure limit of the parallel mode of small current charge, schematic below.
Figure 7, the battery management system and charger plus coordination of parallel charging in series Diagrammatic illustration of chargeThis charging method has the following characteristics:(1) BMS as this system has the function of preventing overcharge in order to ensure the battery will not overcharge issue. Of course, if BMS can not communicate with the parallel charging power and control, due to the constant value of charging power supply in parallel with the lithium-ion battery pack generally in the single-cell Li-ion battery is fully charged voltage of the same value, so it will not overcharge issue .(2) can be parallel charging because you do not need low reliability and relatively high cost of a balanced circuit, and the charge is better than a balanced circuit in series with only charging method, and its maintenance is also easy.(4) charge in series and parallel charging charging order and the number of parallel charging power supply to have flexibility, you can simultaneously charge; can be charged in series after the end of the parallel charge; also can use a parallel in the charging power supply voltage according to battery the situation to turn the battery voltage minimum charge.(5) With the technology development, parallel to a non-contact charging power supply charging power supply (wireless charging power supply) or the solar battery power, so that the parallel charging easier.(6) When the lithium-ion battery pack in a larger number of single-cell Li-ion battery, the lithium-ion battery pack can be divided into a number of lithium-ion battery modules, each module uses lithium-ion battery pack and charger BMS coordination of a large series Constant current charging with a small current-limiting charging the parallel combination of the charge.Its main aim is to reduce the number of battery cells in series is higher, the relative consistency between the single cells even worse, resulting in coordination of BMS and charger charging charging method shortcomings of poor results in order to play the BMS and charger coordination with the maximum effect of charging mode.This method is particularly suitable for high-voltage battery pack can be quickly replaced by a low voltage (eg 48V) battery module system consisting of battery system, so that you can recharge the battery replacement stations or parallel charging station or repair (usually the average user charge can not parallel charging), according to the actual situation by hand sorting and re-distribution group.In short, this battery-management system and coordination charger series constant-current charge plus a small current-limiting charging the parallel charging method can effectively solve the lithium-ion rechargeable battery packs in series prone to over-charge, charge less electricity and other issues and avoid the parallel charging of the charging power supply and high cost, low reliability, charging efficiency is low, thick wire connection and so on, is the most suitable for high-voltage battery pack, especially the electric vehicle battery charging method.