BYD lithium iron phosphate battery management system BMS design and
functionality. Lithium iron phosphate batteries have better lifespan and safety,
and are more suitable for plug-in hybrid vehicles. BYD's new energy vehicles
will appear more and more in our lives. When using new energy vehicles, everyone
is generally concerned about battery issues. It is understood that "Qin"'s
charging modes mainly include scheduled charging and instant charging. It can
charge the vehicle regularly according to the charging time set by the customer,
and can also charge the vehicle directly at random.
BYD lithium iron phosphate battery management system BMS function
BYD's lithium iron phosphate battery BMS management system is not as
dispensable as some battery manufacturers say, but a must-have, and it must be
used throughout the application of lithium battery packs. There have been many
studies on the BMS lithium battery management system at home and abroad, and it
has begun to be applied in many fields. It has been able to meet the needs of
some markets. The application of lithium power batteries has put forward higher
requirements for the battery management system to ensure the use of power
battery packs. Safety is the top priority of the lithium power battery
management system.
The power BMS lithium battery management system can effectively monitor,
protect, energy balance and fault alarm the lithium battery pack, thereby
improving the working efficiency and service life of the entire power battery
pack. Lithium iron phosphate batteries are widely used in various precision
equipment due to their many advantages such as high operating voltage, small
size, light weight, high energy density, no memory effect, no pollution, small
self-discharge, and long cycle life.
Although lithium iron phosphate batteries have more advantages than other
types of batteries, there is a risk of explosion when the lithium battery is
severely overcharged, causing damage to the lithium battery pack and posing a
threat to the user's life safety. Therefore, the lithium battery pack must be
equipped with a targeted lithium battery management system BMS to effectively
monitor, protect, energy balance and fault alarm the battery pack, thereby
improving the efficiency and service life of the entire lithium battery.
The lithium battery BMS management system has the following
characteristics
●The lithium battery management system consists of a management host (CPU),
voltage and temperature acquisition module, current acquisition module and
communication interface module.
●Can detect and display the total voltage, total current, and reserve
capacity of the lithium battery pack; the voltage of any single cell and the
temperature of the battery box; the highest and lowest single cell voltage and
battery number, the highest and lowest temperature, and the temperature of the
battery pack Charge and discharge capacity.
●The UPS battery host also provides alarm and control output interfaces to
provide alarm and control output for extreme conditions such as overvoltage,
undervoltage, high temperature, low temperature, overcurrent, and short
circuit.
●Provides RS232 and CAN bus interfaces, which can directly read all
information on the lithium iron phosphate battery management system on the
computer.
BYD Lithium Iron Phosphate Battery Management System BMS Design
Analysis
First, let’s talk about the batteries of BYD Tang and Qin. The models
should be the same, but Qin’s lithium battery pack has fewer cells and a
capacity of 13 kilowatt hours, while Tang’s has more cells, 18 kilowatt hours.
Each cell is a lithium iron phosphate battery manufactured by BYD itself, with a
rated voltage of 3.2V and a capacity of 26AH. Why not the recently popular
ternary lithium battery? The reason is as follows:
Lithium iron phosphate batteries have better lifespan and safety, and are
more suitable for plug-in hybrid vehicles. The battery cell platform looks like
this, but this one should be on the bus, because the power reserve is as high as
120AH, and ours is only 26AH, but they are roughly the same, they are all
rectangular.
Tang's BMS battery pack is located in the middle of the chassis and is
relatively large in size and weight. The advantage of placing it on the chassis
is that it lowers the center of gravity of the vehicle without affecting the
trunk space. The disadvantage is that the requirements for water release and
bump prevention are relatively high. In daily use, be careful not to soak this
area in water or bump it. Qin's BMS lithium battery pack is located behind the
back seat and in front of the trunk. Advantages: The water discharge and
bump-proof performance are very good. Disadvantages: The center of gravity is
relatively high, which affects the trunk space. It is exactly opposite to
Tang~.
The connection method is series connection. To put it figuratively, it is
similar to the flashlight we have used before, with several batteries connected
end to end. In this connection method, each battery cell uses the same current
to discharge to the outside world when discharging, and the same current to
charge when charging. It is impossible to charge and discharge a single battery
cell without the help of a balancing system. Moreover, when a battery cell is
full, the charging of the entire BMS lithium battery pack must be stopped,
otherwise the battery cell will be overcharged and damaged. When a battery cell
is empty, the entire battery pack must stop discharging, otherwise the battery
cell will be overcharged and damaged. Will be damaged by overdischarge.
Balance module of BMS lithium iron phosphate battery management system.
Tang and Qin's balancing module uses a passive balancing method, that is to say,
the battery core with a higher voltage is discharged through a bypass resistor
so that it reaches the same voltage as other battery cells. That's it: each
battery cell has a resistor that is individually controlled by the lithium iron
phosphate battery management system. When needed, the circuit of this resistor
is connected to discharge the battery cell.
Because the battery packs of BYD Tang and Qin are unbalanced, most of them
have one or two cells with too low voltage, requiring a large number of other
cells to be discharged. When the battery is low, the remaining cells can be
correctly marked. When the battery is high, the system will only mark the
battery with the highest voltage when fully charged. You can imagine the
efficiency, which is almost negligible.
Why BYD insists on using lithium iron phosphate batteries
Lithium iron phosphate battery refers to a lithium-ion battery using
lithium iron phosphate as the positive electrode material. The cathode materials
of lithium-ion batteries mainly include lithium cobalt oxide, lithium manganate,
lithium nickel oxide, ternary materials, lithium iron phosphate, etc. Among
them, lithium cobalt oxide is the cathode material currently used in most
lithium-ion batteries. Lithium iron phosphate battery is a domestic lithium
battery completely independently developed by BYD with huge investment. It is
now a mature product and has been widely used in China. Although compared with
foreign lithium battery products, the characteristics of lithium iron phosphate
battery are not perfect yet. , but because of its existence, it broke the
foreign technology monopoly and created a path for us to follow our own lithium
battery research and development route, so we admire its spirit very much. In
addition, BYD insists on using lithium iron phosphate batteries that will not
explode.
In fact, Chinese companies have mastered the world's most advanced
technology and processes for lithium iron phosphate batteries. The absolute
advantages of lithium iron phosphate batteries over ternary lithium batteries in
terms of safety and cycle life are the key elements and development needs of
China's new energy vehicles. As long as its development status is clear and
investment is increased to solidify this advantage, China's new energy vehicles
will have the possibility of overtaking in corners.
The material formula of ternary lithium batteries, whether it is lithium
nickel cobalt manganate or lithium nickel cobalt aluminate, is inseparable from
two precious metals, namely cobalt and nickel. Both metals are scarce in China
and have limited global reserves. Lithium iron phosphate batteries, on the
contrary, do not contain any precious metals, and the main raw materials for
producing cathode materials, iron oxide and lithium carbonate, are very abundant
in China. If the demand in the downstream new energy vehicle market expands, the
cost of its upstream materials will plummet due to the scale effect. The decline
in the price of cathode materials, which accounts for more than 30% of the cost
of lithium iron phosphate batteries, will promote the rapid decline in the price
of lithium iron phosphate batteries. .
Lithium iron phosphate battery is the core component of BYD's new energy
vehicles, which provides driving power for the entire vehicle. It is mainly
wrapped in a metal shell to form the main body of the battery pack protection.
The battery core realizes the integration of the battery core through the
modular structure design, and includes the cooling hardware of the battery core.
The quality of the cooling system design is the prerequisite for BMS to achieve
excellent management.
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