Design of lithium battery charging management -Lithium - Ion Battery Equipment

Design of lithium battery charging management power supply -Lithium - Ion Battery Equipment

With the soaring price of international crude oil, research on various new energy sources has become the focus of public attention. As a power source, electric energy has been widely used in various vehicles. Lithium ion battery has become the first choice of power electric energy for its advantages of high energy mass ratio and energy volume ratio, no memory effect, more rechargeable times, and long service life.

As a new power technology, lithium-ion batteries must be connected in series to meet the demand for service voltage in use. The uneven performance of individual batteries is not all due to the battery processing technology. Even if the voltage and internal resistance of each battery are completely the same when it leaves the factory, there will be differences after a period of use, which makes it an urgent technical problem to deal with the charging technology of power lithium-ion batteries. On the basis of fully considering the industrial cost control and stability requirements, this design adopts the energy consumption partial diversion method to conduct balanced management of power lithium ion battery charging, which improves the imbalance of battery pack charging and improves the working performance.(Lithium - Ion Battery Equipment)

Selection of charging method for lithium-ion battery pack

1. Charging requirements for single lithium-ion battery

The charging requirements for a single lithium-ion battery (Gb/T18287-2000) are first constant current charging, that is, the current is certain, and the battery voltage gradually increases with the charging process. When the battery terminal voltage reaches 4.2V (4.1V), the constant current charging is changed to constant voltage charging, that is, the voltage is certain. The current gradually decreases with the continuous charging process according to the saturation degree of the cell. When it decreases to 10mA, the charging is considered to be terminated. The charging curve is shown in Figure 1.

2. Charging characteristics of lithium ion battery pack

In the power lithium-ion battery pack, there is inconsistency between individual batteries. The difference caused by the continuous charging and discharging cycle will accelerate the capacity decline of some single batteries. The capacity of the series battery pack is determined by the minimum capacity of the single battery, so these differences will shorten the service life of the battery pack. The critical reasons for this imbalance are:

● During battery production, due to process and other reasons, the capacity and internal resistance of the same batch of batteries are different;

● The difference of battery capacity is caused by the difference of battery self discharge rate after long-term accumulation;

● During the use of the battery, the difference of the use environment, such as temperature and circuit board, leads to the imbalance of the battery capacity.

3. Charging method selection

In order to reduce the impact of imbalance on the lithium-ion battery pack, an equalization circuit should be used during the charging process.

At present, there are two important methods for balanced management of lithium-ion battery packs, energy consumption type and feedback type. Energy consumption type refers to supplying parallel branches to each single battery, and balancing the single battery with excessive voltage by shunting and transferring electric energy. The feedback type refers to feeding the deviation energy between cells back to the battery pack or some cells in the battery pack through the energy converter.

Theoretically, when the conversion efficiency is ignored, the feedback does not consume energy and can achieve dynamic equalization. However, due to the complexity of the feedback design control method and the high manufacturing cost, this charger adopts the energy consumption design

Energy consumption type can be divided into cutoff and diversion according to the energy circuit solution. Current cutoff refers to the disconnection of the charging circuit of the single battery when certain conditions are met on the basis of monitoring the voltage change of the single battery, and the charging current completely passes through the bypass resistance. Through the switch matrix composed of mechanical contacts or power electronic components, the connection structure between cells in the battery pack is dynamically changed. Instead of shunting and disconnecting the working circuit, a bypass resistance is added to each battery. When a single battery is higher than other batteries in the group, all or part of the charging current is introduced into the bypass resistance. So as to realize the balanced charging of each single battery. Due to the high power of the power lithium-ion battery pack, after comprehensive consideration of charging efficiency, thermal management and other factors, we use the partial shunt method to design the charger.



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