BMS (battery management system) is an indispensable and important component of electric vehicles. It is the hub for managing and monitoring power batteries. It manages, maintains and monitors each battery module. It is responsible for preventing battery overcharge and over discharge, extending battery life and helping the battery to operate normally.The battery management system (BMS) is an important link between the on-board battery and the electric vehicle. Its main functions include: real-time monitoring of battery physical parameters, battery status estimation, online diagnosis and early warning, charge and discharge and pre-charge control balance management, thermal management, etc. If any of the above functions is not implemented well, it will cause fatal harm to the battery.
What are the mainstream BMS supporting companies?
Let’s take a look at which manufacturers provide the BMS for the current mainstream domestic pure electric vehicles?BMS is an important link between battery packs, vehicle systems and motors. It is the core technology of power battery packs and the most important indicator for measuring the performance of a pure electric vehicle.The complexity of the BMS system itself determines that it has strong technical barriers and requires time for technical research and development. Its cost accounts for about 20% of the total cost of the battery pack.my country's BMS companies can be roughly divided into several types: self-operated by battery manufacturers, self-operated by vehicle manufacturers, and operated by third parties.1) For battery factories that operate their own businesses, the current first-tier domestic power battery companies include: CATL, CITIC Guoan Mengguli, Guoxuan High-tech, Microvast Power, etc. They have a complete set of core technology advantages and have strong market competitiveness.2) Self-operated companies by vehicle manufacturers, represented by BYD, BAIC New Energy, and Zhongtong Bus, not only have core technologies, but also have cost advantages over other companies.3) Representative companies provided by third parties include Dongguan Juwei Power, Huizhou Yineng Electronics, Shenzhen Kelie Technology and other companies.Let's take a look at the ranking of companies that are currently providing BMS for mainstream new energy vehicles (TOP20 BMS installed capacity for new energy vehicles in September 2019). Most of the BMS for domestically produced pure electric vehicles we purchase come from these companies. After reading this installed capacity data, I believe it will be of great help to you in purchasing pure electric vehicles.
How important is the functionality of a BMS?
BMS is the lifeblood of electric vehicles!BMS is the link between the battery and the vehicle. It processes a rich variety of signals, including: battery cells, collision, CAN, charging, water pumps, high voltage, insulation, etc. Over-discharging once will cause permanent damage to the battery. In extreme cases, overheating or overcharging of lithium batteries will lead to thermal runaway, battery rupture, or even explosion. Therefore, BMS must strictly control charging and discharging to avoid overcharging, over-discharging, and overheating.Batteries have different working performance at different temperatures. The best working temperature for lithium-ion batteries is 25-40 degrees. BMS improves inconsistency through balancing and improves the overall performance of lithium batteries.Electric vehicles use lithium batteries as their main power source, which is due to their high energy density and relatively stable performance. However, the quality of lithium batteries is difficult to control when they are mass-produced. There are slight differences in the power of the battery cells when they leave the factory. With the change of operating environment and other factors, the inconsistency between batteries will become more obvious, and the battery efficiency and life will also deteriorate. In addition, overcharging or over-discharging may cause safety problems such as fire in serious cases.BMS can accurately measure the battery pack usage status, protect the battery from over-charging and over-discharging, balance the power of each battery in the battery pack, analyze and calculate the battery pack power and convert it into understandable endurance information to ensure the safe operation of the power battery.
BMS battle: Tesla vs. Chevrolet Bolt
Without a good BMS, an electric car is a moving bomb!The main purpose of the battery management system is to ensure the design performance of the battery system, and to provide functions in three aspects: safety, durability, and power. In terms of safety, the BMS battery management system can protect the battery cells from damage and prevent safety accidents; in terms of durability, the BMS battery management system can make the battery work in a reliable and safe area and extend the battery life; in terms of power, the battery's working state is maintained to meet the vehicle's requirements.Tesla's battery management system is the most mature system today. Thanks to the full application of deep learning and artificial intelligence, Tesla's BMS can continuously obtain big data from actual driving, and then self-reinforce the algorithm, so that the battery life of Tesla's battery pack is relatively longer.Let's take Tesla Model 3 as an example and list the five major features of its BMS:1. 4416 small low-capacity batteries support the 75kWh system, and a large number of small cells make the battery system more stable.2. Although the batteries are purchased, Tesla has developed its own management system to manage the temperature of each battery cell.3. The two-stage method is used for cell balancing to achieve higher battery utilization efficiency and a relatively low attenuation rate.4. Tesla reduces the relative flammability of NCA batteries by using non-conductive materials and embedding thermometers.5. Tesla has accumulated experience data related to BMS: driving, charging, battery temperature, battery capacity changes, etc.The five major features of Tesla BMS bring many advantages:1. Most electric vehicles’ battery capacity drops below 80% within 4-8 years, while most Teslas maintain over 90%.2. Tesla's BMS has a high risk tolerance and makes maximum use of big data to maintain and manage a large number of battery cells.3. The Tesla system can use the same battery to power a sedan, truck, sports car, SUV or other type of car.In addition to the obvious advantages, the weaknesses of Tesla's battery pack are also obvious:1. The safety of the battery cells is relatively poor: Model S and Model X have experienced multiple fire accidents. All the battery cells of the new Model 3 are fixed with flame-retardant materials, which are relatively difficult to burn.2. High cost of module replacement: Damaged cells will not affect the overall performance of the battery pack, but damaged modules will cost more to replace.3. Risk of momentary loss of control: Once a short power outage occurs, the power control system cannot be activated in time, which will render the safety protection and temperature control functions ineffective.In the US new energy vehicle sales list, besides Tesla, the Chevrolet Bolt is the next in line. Compared with Tesla's BMS, Chevrolet Bolt's BMS has the following features:1. The chip that monitors voltage and temperature in Bolt BMS is not developed by itself, but designed by LG Chemical and produced by ST Microelectronics.2. Bolt has 25 BMS MCUs, Model 3 has 18.3. Bolt only has single-stage cell balancing. If the battery capacity is increased, the cell balancing accuracy will be unbalanced, resulting in faster decay.In summary, we can draw the conclusion that Tesla's BMS is indeed excellent.
Passive balancing : Passive balancing technology achieves voltage balance between cells by connecting a resistor to the cells with higher voltage in the battery pack to dissipate energy and reduce the SOC of the cells. The advantages of this method are simple circuit structure and low cost, but the disadvantages are low energy utilization, increased heat dissipation of the module, and can only be performed during the charging cycle. The current of passive balancing is usually limited to 0.25A, which is mainly suitable for battery packs with lower capacity.
Active balancing : Active balancing technology uses power electronics to transfer electrical energy from high-voltage cells to low-voltage cells to achieve energy redistribution. The advantages of active balancing include fast balancing speed, high energy utilization, and can be performed during charging or discharging, which helps to extend the operating time of the battery pack. The current of active balancing can be as high as 6A, supporting larger capacity battery cells. The topology of active balancing mainly includes methods based on capacitors, inductors and transformers.
Currently, active balancing technology is increasingly being adopted due to its advantages such as high current and fast balancing. For example, the MP264x series devices are highly integrated bidirectional buck-boost active balancers that can provide up to 3A of charge redistribution between two series-connected lithium-ion cells. In addition, the bidirectional buck-boost active balancer is considered the most effective of the three types of active balancers because of its simplicity and reliability.
In practical applications, the battery management system (BMS) will establish a battery model and a balancing algorithm model based on the characteristics of the battery and the principle of the balancing algorithm, and evaluate the balancing effect and performance through simulation. For example, the active balancing method based on the buck boost topology can be simulated and verified in Simulink.
Transformer-based active balancer : This approach uses a bidirectional flyback converter to allow bidirectional charge transfer. Each battery cell requires a converter and transformer, but this approach may require multiple transformers, resulting in a large and costly solution.
Switch Matrix + Transformer Active Balancer : This approach reduces the number of transformers by connecting one transformer to each cell through a switch array. It allows each cell to exchange energy with the battery pack or auxiliary power rail during charging or discharging, with the advantage of requiring only one transformer.
Bidirectional buck-boost active balancer : This solution uses buck-boost battery charger technology to move charge to directly adjacent cells. This solution is simple and reliable, can move charge throughout the battery pack, and is one of the current mainstream active balancing technologies.
Parallel balancing circuit method : Add a parallel circuit to each single battery for current distribution. When a battery is fully charged, the balancing device will prevent it from overcharging and convert the excess electrical energy into heat energy while continuing to supply power to other batteries that are not fully charged. This method is simple and easy to implement, but the energy loss is large.
Voltage parameter balancing method : The voltage of each battery is used as the balancing target, and the capacitor is connected to two adjacent batteries alternately by controlling the switch. After the capacitor receives power from the high-voltage battery, it discharges to the low-voltage battery until the voltages of the two batteries become consistent. This method effectively solves the problem of unbalanced battery pack voltage, but it is mainly suitable for scenarios with a small number of batteries.
Single chip control module method : The entire system is controlled by a single chip, and each single battery is equipped with an independent module. These modules manage the charging of each single battery according to the preset program and automatically disconnect after charging is completed. This method can achieve precise control of the single battery, but the cost is relatively high.
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