Balanced charging of lithium battery packs effectively improves battery
consistency issues. Power lithium batteries are used in groups. Each lithium
battery requires protection from charging overvoltage, discharge undervoltage,
overcurrent, and short circuit. During the charging process, the issue of
balanced charging of the entire group of batteries must be achieved. Experiments
have proven that the lithium battery pack balanced charging management circuit
can effectively improve the consistency of battery pack charging, improve the
working performance of the lithium battery pack, and extend the service
life.
Balanced charging of lithium battery packs effectively improves battery
consistency issues
As a new power technology, lithium battery packs must be connected in
series to meet the voltage requirements. The uneven performance of individual
cells is not entirely due to technical issues in battery production. Even if
each battery leaves the factory with exactly the same voltage and internal
resistance , differences will also occur after being used for a period of time,
which makes solving the technical problem of power battery charging an urgent
technical issue that needs to be solved.
In order to solve the consistency problem in the use of power lithium
battery packs, this article proposes an implementation plan for a balanced
charging management circuit. First, the characteristics of a single lithium
battery are analyzed; then, based on comparing various balanced charging
theories, the partial shunt method is selected as the design idea and the
specific circuit design is carried out. Multiple lithium battery pack charging
and discharging experiments have shown that this balanced charge management
circuit can effectively improve the charging consistency of the lithium battery
pack, improve the battery pack's working performance, and extend its service
life.
Due to the problem of inconsistent battery performance, the performance of
battery packs in terms of utilization, service life, safety, etc. is far
inferior to that of single batteries. The lithium battery management system with
efficient balancing management function can greatly improve the overall
performance of the power battery pack, effectively extend the service life of
the lithium battery pack, and greatly reduce the use and maintenance costs of
the entire vehicle. Provide technical support for the promotion of safe,
efficient and practical electric vehicles.
At present, lithium battery management systems have made certain progress
in battery online monitoring, status assessment, charging management, data
communication, control strategies, etc.
Lithium battery pack charging characteristics
In the power battery pack, there are inconsistencies between individual
cells. The differences caused by continuous charge and discharge cycles will
accelerate the capacity decay of some single cells. The capacity of the series
battery pack is determined by the minimum capacity of the single cell, so these
differences will shorten the service life of the battery pack. The main reasons
for this imbalance are:
●During the battery manufacturing process, due to process and other
reasons, there are differences in capacity, internal resistance, etc. of
batteries in the same batch;
●Differences in battery self-discharge rates, accumulated over a long
period of time, result in differences in battery capacity;
●During battery use, differences in usage environment such as temperature
and circuit boards lead to imbalance in battery capacity.
Lithium battery pack equalizing charging solution
In order to reduce the impact of imbalance on the lithium battery pack, a
balancing circuit must be used during the charging process.
Currently, there are two main solutions for balancing management of lithium
battery packs, energy consumption type and feedback type. The energy consumption
type refers to providing parallel branches for each single battery, and
transferring the electric energy of the single battery with excessive voltage
through shunting to achieve the purpose of balancing. The feedback type refers
to feeding the deviation energy between cells back to the battery pack or
certain cells in the battery pack through the energy converter.
Theoretically, when the conversion efficiency is ignored, feedback does not
consume energy and dynamic equilibrium can be achieved. However, due to the
complex control method of feedback design and high manufacturing cost, this
charger adopts energy consumption design.
Since the DC internal resistance, polarization voltage, and maximum
available capacity are specific parameters of the battery and basically do not
change during one or several consecutive charge and discharge processes, the
balance of the lithium battery pack is mainly achieved by adjusting the SOC of
each single cell. accomplish. After research, SOC is used as the reference
object for balancing. The balancing object is relatively fixed. Make full use of
the balancing time and improve the balancing utilization rate to reduce the
balancing current capacity.
Taking the SOC of the battery as the control object, the difference in SOC
between batteries is reduced by charging and discharging the single battery.
First, the balancing target needs to be determined. Usually in order to improve
the efficiency of balancing and give full play to the advantages of charge and
discharge balancing, the target is set as the average state of charge (SOC) of
the lithium battery pack. The balance control band (dSOC) is also set to prevent
balance fluctuations. For cells with high SOC, discharge balance is performed,
and vice versa, charge balance is performed.
Commonly used lithium battery pack balancing charging technologies include
constant shunt resistance balancing charging, on-off shunt resistor balancing
charging, average battery voltage balancing charging, switched capacitor
balancing charging, buck converter balancing charging, inductor balancing
charging, etc. When charging a group of lithium batteries in series, each
battery should be charged evenly, otherwise the performance and life of the
entire battery group will be affected during use.
Summary: A single-cell lithium battery protection chip is used to design
and implement a battery pack protection board for multiple lithium batteries
connected in series. In addition to completing the necessary over-voltage,
under-voltage, over-current and short-circuit protection functions, it can also
achieve a balanced charging function. It is another important breakthrough in
battery technology.
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