Recently, there have been a number of complaints on a complaint platform about the significant reduction of the mileage of new energy vehicles upgrading BMS (battery management system) and the slow charging speed. The owner of the car questioned the suspect of "locking the electricity" after the manufacturer upgraded the system.
Similar incidents have happened in Tesla, in 2019, some car owners sued Tesla, and after the vehicle upgraded the BMS through a manufacturer-led procedure, the battery capacity, mileage and charging power were significantly attenuated. So Tesla made a certain compensation to the owner of the lawsuit, and said that it was to protect the battery and extend the service life of the battery, which was implied to be good for you. Is this really the case?
As we all know, the power output of pure electric vehicles relies on batteries, and the battery management system BMS (Battery Management System) is the core of it, responsible for controlling the charging and discharging of batteries and achieving functions such as battery status estimation. If an electric car is likened to a human body, the battery system is his heart, and the BMS battery management system is the brain that governs the operation of his body.
BMS (Battery Management System) appliance architecture
Why have a BMS?
Since it is called a battery management system, the main job of the BMS is to deal with tasks related to the on-board battery. Although the current battery manufacturing process has narrowed the differences between the individual cells, there are still differences in internal resistance, capacity, voltage, etc. between single-cell lithium batteries, so in practical applications, the cells inside the battery pack are prone to uneven heat dissipation or overcharge and discharge. Over time, these batteries in poor working conditions are likely to be damaged in advance, and the overall life of the battery pack is greatly shortened.
Not only that, the battery is in a seriously overcharged state and there is a danger of explosion, causing damage to the battery pack and posing a threat to the user's life safety. Therefore, the power battery pack on the electric vehicle must be equipped with a targeted battery management system (BMS), so as to effectively monitor, protect, energy balance and fault alarm of the battery pack, thereby improving the efficiency and service life of the entire power battery pack.
What is the main role of BMS?
An electric car has hundreds of batteries, how is the BMS managed? If we have seen the analysis of the battery pack, we will see that there are hundreds of cells inside, how to manage these dense cell systems? The main work of the BMS system is divided into two major tasks - the detection of the battery and the guarantee of battery safety.
Among them, the battery detection is relatively simple, mainly through the sensor to collect the battery in the use of the parameter information such as: temperature, the voltage of each battery cell, current, battery pack voltage, current and so on. These data play a crucial role in the subsequent battery pack management, it can be said that without the data of these battery status as support, the system management of the battery can not be talked about.
If we regard the testing process of the battery as a "physical examination" of the battery, then this "physical examination" is online, continuous, and uninterrupted. In the process, when the data is found to be abnormal, the corresponding battery status can be queried in time and the battery in question can be selected, so as to maintain the reliability and efficiency of the operation of the entire group of batteries. When the "physical examination" of the battery is completed, it will enter the stage of analysis, diagnosis, and calculation, and then generate a "physical examination report", which can be understood as the evaluation of the state of the battery.
What is SOC?
If you've ever driven an electric car, you're sure to see the SOC logo on the dashboard, what does that mean? SOC, or State of Charge, is the abbreviation of the state of charge of the battery pack, and we are more accustomed to calling it battery remaining power. SOC is the basis for judging a series of faults such as battery overcharge and overdischarge, accurate estimation of SOC, can prevent battery overcharge and overdischarge, prolong the service life of the battery, thereby improving the utilization rate of the battery.
In fact, in addition to SOC estimation, there is also SOH (State of Health), SOP (State of Power), users can see these data through the instrument display on the car, so as to confirm the working and functional status of the battery. According to this, on the basis of protecting the battery, the potential is maximized, which greatly improves the driving experience.
For battery life, the accuracy of the SOC is very important
SOC's algorithm has always been one of the key technologies for the development and application of battery management system (BMS), and the accuracy of its calculation directly affects the difference between the apparent endurance and the actual endurance, if the calculation is not accurate enough, it will even lead to the situation that the battery is exhausted and the vehicle breaks down.
Estimating the state of the battery requires a series of complex calculations. That is, accurately estimate the remaining power of the battery, ensure that the SOC is maintained within a reasonable range, prevent damage to the battery due to overcharge or overdischarge, and predict at any time how much energy is left in the energy storage battery of the hybrid vehicle or the charging state of the energy storage battery. The SOC has high estimation accuracy and can have a higher range for the same amount of battery. Therefore, high-precision SOC estimation can effectively reduce the required battery cost.
At present, the technical threshold of vehicle-grade BMS chips is high, and the suppliers are mainly foreign enterprises. The rapid development of the new energy automobile industry has led to the continuous expansion of the overall market size of BMS, and the importance of BMS chips has become increasingly prominent. However, the technical threshold of BMS chips is relatively high, such as BMS MCU chips require a lot of proprietary technology (Know-how) experience accumulation, and a large number of mature solutions are currently mastered by manufacturers such as NXP; the main suppliers of BMS AFE are overseas companies such as Yardnold and Texas Instruments. Enterprises do not have long-term research and development accumulation and a large amount of data accumulation, and it is difficult to develop BMS chips that truly meet the needs of downstream applications.
Vehicle grade BMS chip certification is demanding and has a long certification cycle. With the continuous advancement of the national "carbon neutrality" strategy, China's new energy automobile industry will usher in a golden 5 years, providing a broad market blue ocean for the application of BMS chips. Before entering the supply chain system of automakers, automotive-grade semiconductor companies generally need to pass the quality management system IATF 16949 and the reliability standard AEC-Q series. After completing the certification and audit of the relevant vehicle specifications and standards, it is also necessary to undergo rigorous application test verification and long-term on-board verification before entering the automotive front-loading supply chain.
The patron saint of battery and personnel safety
Another core function of BMS is to provide security for battery packs and personnel. As we all know, the battery overcharge and over-discharge will bring local overheating, affecting the battery life, not to mention, it will threaten the safety of the battery pack when it is serious, and then cause personal safety hazards. At this time, the BMS's "charge and discharge management" module opens the protection function, on the one hand, it communicates with the whole vehicle and the charger, and on the other hand, it provides the battery status in real time, which is convenient for timely command control and effectively prevents the occurrence of high charge and low discharge.
In the module of battery protection, equalization is also an important part, which is a necessary means to protect and improve battery life. In addition, the protection of the battery also includes protection against overvoltage, undervoltage, overtemperature, overcurrent, etc. To put it simply, when the actual parameters are higher or lower than a certain agreed value, the system will automatically make a judgment and take disconnection, pre-charging and other ways to protect the battery safety.
In terms of personal safety, BMS is protected by means of high-pressure control. Battery high voltage up to 300-500V, far more than the human safety voltage of 36V, the risk is extremely hidden, must do a good job of high voltage control, the most common is relays, high voltage interlock, insulation protection. Comprehensive high-pressure protection control can effectively protect the personal safety of drivers, passengers and maintenance personnel.
How to understand the safety level of the battery
Many domestic battery companies use the internationally accepted ISO 26262 evaluation standard. The ISO 26262 standard is divided into Automotive Safety Integrity Level (ASIL) from A to D according to the degree of security risk, of which D level is the highest level and requires the most demanding security requirements. The higher the level, the higher the security requirements for the system, and the higher the cost to achieve security, which means that the higher the diagnostic coverage of the hardware, the more stringent the development process, the corresponding development costs increase, the development cycle is extended, and the more stringent the technical requirements.
The ASILD rating, with a failure rate of 10^-8/h, means that a vehicle assumes 4 hours of operation per day and takes 70,000 years to experience a functional failure caused by a BMS. And such a low probability of failure efficiency is comparable to the requirements of aircraft operation. Generally speaking, the automotive industry requires parts and components to be grade B or C.
Vehicle grade BMS chips mainly rely on imports
The main chips used in BMS are AFE, MCU, ADC, digital isolator, etc. The main suppliers who can provide complete solutions for automotive-grade BMS chips are ADI (AFE products mainly from the acquisition of MAXIM and Linear product lines), TI, Infineon, NXP, Renesas (AFE products mainly from the acquisition of Intersil's product lines), ST and ON Semiconductor.
Among them, the BMS AFE chip (analog front-end chip) is responsible for collecting the battery voltage and converting it to a digital value through an analog-to-digital converter (ADC) and feeding it into the MCU to calculate the state of charge.
In terms of vehicle-grade MCUs, according to incomplete statistics, in recent years, domestic manufacturers including Jiefa Technology, Quanzhi Technology, Gigabit Innovation, Chipwang Micro, Sai Teng Micro, Xiaohua Semiconductor, Chipways, Core Sea Technology, Yuntu Semiconductor, And Chipwang Microelectronics have successively passed the automotive-grade AEC-Q100 certification.
In terms of BMS AFE chips, the chip has the highest technical difficulty and the highest added value, and there are fewer manufacturers involved in the product in China. From the public information, BYD Semiconductor has launched a car-grade AFE chip that meets the AEC-Q100 standard; Chipways' vehicle-grade BMS AFE (meets ASIL-C level) chip has also been successfully mass-produced.
In addition, Silicon Jie already has BMS AFE chip products, but mainly used in the industrial field, Core Sea Technology, Saiwei, Huatai Semiconductor has also said that it will develop multi-section BMS chips.
In 2021, the number of BMS supporting units exceeded 3 million sets, of which the top ten BMS companies accounted for 74% of the market share.
Source: NE Times
Industry insiders pointed out that the vehicle specification grade BMS AFE chip products alone will reach 1.5 to 2 years in the verification cycle, from product definition to molding at least 4 years, for the harsh automotive application environment, in addition to the reliability needs to meet the AEC Q100 Grade1 quality standards, ISO 26262 automotive safety integrity level ASIL-D level certification, or will become a restriction on domestic chip manufacturers to force BMS chips in the way.
Why "lock the electricity", the car company said does not count?
Last year, new energy vehicles had a number of spontaneous combustion and explosion accidents, and in December 2021 alone, a domestic brand car had 3 spontaneous combustion accidents in succession. A domestic car company R & D engineer said that although the fast charging speed is fast, but the battery in the power battery can not be guaranteed to be completely consistent, high current fast charging will lead to inconsistent cell voltage, which in turn affects the discharge capacity of the entire battery pack; in addition, some cells are full, some cells are not full, the BMS system may judge that the battery pack is not full, and then continue to charge, resulting in some cells overcharge. Earlier, some car companies had spontaneous combustion accidents due to battery overcharge. In order to solve this problem, some car companies will use small current charging when the power battery is about to be full, so that the battery voltage is as consistent as possible, and the problem is that the charging time increases and the user experience becomes worse. The "locked power" can ensure a fast charging speed while limiting the charging power and reducing the situation of overcharge. Overcharge and overdischarge may cause the power battery to "analyze lithium", and the resulting "dendrites" may puncture the diaphragm and cause a short circuit of the positive and negative poles, causing thermal runaway and spontaneous combustion. The purpose of "locking the power" is to prevent the occurrence of this situation, but some related OTA upgrades or offline upgrades, car companies have not clearly informed the owner of the impact and effect of locking the power, the regulatory authorities should introduce relevant regulations, requiring car companies to clearly inform the owner of the upgrade content and impact.
The matter of "locking electricity" is no longer an accidental behavior of a car company, and it has almost become an industry phenomenon. A technical expert who once worked for a large car company said that "locking the power" is not the decision of the car company, and the decision-making basis is more from the battery supplier. The "locked power" ratio is also a protection threshold set by the battery supplier according to the use time and the cumulative state to a certain state. The primary consideration of "locking electricity" is the probability of fire. In other words, the "power lock" is to reduce the probability of the battery catching fire after a fixed service life.
Relevant technical experts pointed out that considering the reaction characteristics of chemical batteries, SOC valuation needs to leave a buffer zone to ensure that the battery is always working in a safe area. Therefore, for the actual use scenario, each car has a real power range, for example, it can be set to 5%-95%, releasing 88% or 90% of the power.
Taking European car companies as an example, they will generally give two data and directly identify the use range, such as the earliest version of the BMW i3, and the ratio of available energy to total energy is between 82% and 90%.
In the United States, car companies are setting the highest power or the highest SOC to alleviate security problems, or set the highest SOC in the BMS, or set the recommended SOC range in the central control screen system.
According to insiders, "locking the electricity" is not the car company's decision, as for the responsibility, that is, the car company and the battery supplier are responsible. However, as for how to define the responsibilities of both parties, and how the service life and status affect the proportion of "locking electricity", the other party failed to inform on the grounds that it involved a confidentiality agreement. In recent years, spontaneous combustion accidents of new energy vehicles have occurred frequently, and car companies have limited charging rates and charging amounts, which may be related to spontaneous combustion of cars, but this has not been confirmed by car companies, it is just speculation.
The "power lock" controversy has sparked a deeper discussion on how to protect the owner's right to know and choose while OTAs bring more and more intelligent experiences to smart car owners, and whether car companies and suppliers can infringe on the owner's ownership of the battery through OTAs.
On November 25, 2020, the General Office of the State Administration for Market Regulation issued the Notice on Further Strengthening the Supervision of Remote Upgrade (OTA) Technology Recalls in Vehicles (hereinafter referred to as the Notice), which regulates the application of OTA technology. As mentioned in the Notice, consumers, parts manufacturers, software and system or data service providers who are aware that the producer uses OTA to conceal vehicle defects and avoid recall liability can directly report to the Quality Development Bureau of the State Administration for Market Regulation. The Notice also mentions that the Quality Development Bureau of the State Administration for Market Regulation will organize relevant units to strengthen research on automotive OTA safety supervision technology, explore the establishment of an OTA regulatory data platform, organize OTA safety technology assessment, and strengthen relevant recall supervision.
"Locking electricity" can only cure the symptoms, not the root causes. In order to solve the problem of spontaneous combustion of automobiles, we should fundamentally strengthen the research on battery materials, manufacturing processes and heat treatment to improve the quality of battery systems. The owner should also maintain it in time, replace the battery if necessary, observe the condition of the car before charging, and avoid prolonged exposure to the sun. Auto safety requires the joint efforts of car companies and car owners to consider the performance and safety of the car. Industry insiders said.
Source: Sina Technology, Sohu Auto, Jiwei Network, NE Times and other network content synthesis