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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