From battery charging, battery life to car safety, BMS has more new missions

Battery, motor, and Electronic control technology are important components of an electric vehicle, and the three determine the performance and quality of an electric vehicle. The core of electronic control technology is the BMS system, which directly affects the cruising range and charging time of electric vehicles. It is responsible for the safe monitoring and effective management of the power battery of electric vehicles, so that the power battery can work in the best state, improve the efficiency and reliability of the power battery and prolong its service life. Therefore, the BMS is seen as the “link” connecting the battery pack, the vehicle system and the motor.

As the global electric vehicle sales continue to increase, the market size of BMS also expands. According to data from authoritative institutions, the global BMS output value in 2018 was 5.31 billion US dollars, and the global BMS output value in 2019 exceeded 6 billion US dollars. It is expected that the global BMS output value will reach 11.17 billion US dollars in 2025. According to the data of the Electric Vehicle Research Institute (GGII) of the High-tech Industrial Research Institute, in 2018, the installed capacity of China’s new energy vehicle power lithium battery BMS products reached 1.22 million sets, with an output value of 5.5 billion yuan. It can be seen that BMS is playing an increasingly important role in electric vehicles.

“Pain reliever” for BMS electric car battery life

Although electric vehicles are accepted by more and more users, power batteries still face the pain points of short cruising range and long charging time. “On the premise of ensuring battery safety, BMS can maximize the use of battery energy and improve energy recovery efficiency, and maximize the charging current to increase the charging speed.” STMicroelectronics Greater China and South Asia Automotive Electronics Market and Application Department Jiang Jiongdi, senior manager of the New Energy Vehicle Technology Innovation Center, analyzed, “During the charging and discharging process, the BMS monitors the battery’s external characteristic parameters (such as voltage, current, temperature, etc.) in real time, and then uses appropriate software algorithms to realize the internal control of the battery. State (SoC, SoH) detection and control, and then through thermal management, battery balance management and charge and discharge management to make the battery in the best working state, will not achieve over-discharge or over-charge, while maximizing the charging current.”

In response to battery life and charging issues, Peng Yongjun, founder and general manager of Anhui Youdan Technology Co., Ltd., said in an interview with Yufei.com, “Increasing the cruising range requires improvement in three aspects: first, improve the balance efficiency of the battery. A battery The system consists of many battery-saving cells and follows the barrel effect, that is, the performance of the battery system depends largely on the worst-performing battery cell. Improving the battery balancing efficiency and improving the consistency of the battery cells can effectively prolong the vehicle’s battery life. Second, improve the energy recovery efficiency during braking or vehicle downhill. A good energy feedback control algorithm needs to give full play to the battery charging performance under the premise of ensuring battery application safety. The real-time calculation of power and continuous charging power yields the most efficient current feedback power strategy; third, improve the estimation accuracy of SOC. This can also be understood as improving the cruising range from another dimension, that is, the more accurate the user’s grasp of the real power, the The more confident you can use a wider SOC range.”

As a leading supplier of automotive electronic solutions, Zhang Wei, technical marketing manager of Renesas Electronics China Automotive Solutions Division, analyzed the four core technologies of the BMS system from a technical point of view: First, the battery state estimation technology can be based on the accurate construction of the battery. Mode and parameter monitoring. Through big data analysis and advanced algorithms, accurate estimation of battery states such as SOC, SOH, SOP, etc., provides a reliable basis for battery management; second, balanced management technology, the inconsistency of single cells in lithium battery packs of electric vehicles The performance of the battery pack will greatly affect the usable capacity of the battery pack, which requires the use of balanced management techniques (usually including passive balance and active balance technology) to improve the consistency of the single cells and improve the service life of the battery pack; third, BMS The distributed architecture of the system, the distributed BMS system integrates the battery module and the battery acquisition unit, which makes the battery pack more modular, standardized and intelligent, and has stronger scalability. It can also simplify the assembly process and facilitate the realization of battery integration. Echelon utilization; fourth, the integration of BMS technology and vehicle controller (VCU) functions, this technology can be used by VCU to adopt more reasonable and efficient control strategies based on vehicle information and battery information, which can improve real-time, safety and security. Sex and reliability are also helpful.

Extend battery life to do “right”

Battery life has always been an important issue for electric vehicles, and BMS technology acts as the “brain” behind the battery pack to provide important protection against damage to the battery. “A battery pack consists of multiple independent battery cells that work together seamlessly to provide the maximum power output for the car,” said Wang Xingwei, senior manager of ADI’s China automotive technology market. “If the cells are out of balance, they will be subject to stress and cause charging. Premature termination, in turn, shortens the overall life of the battery. Analog Devices offers both a complete portfolio of battery management system BMS devices for lithium and hydrogen fuel cells, and a novel architecture for wireless battery management system BMSs using wireless network crossover technology. “

Zhu Yuping, senior manager of automotive analog device product market at NXP Greater China, believes, “From the perspective of BMS, it is necessary to accurately measure and monitor the battery status, and use advanced algorithms to model the battery, so as to ensure that the battery works as safely as possible. These measures include: battery thermal management control to ensure that the battery is in a suitable temperature range under various operating conditions, usually the operating temperature of the battery is between -25~55℃, and the optimal operating temperature of the battery is 25~35℃ between; battery charge-discharge rate and discharge depth control, high discharge rate leads to serious polarization of the battery, increased internal resistance, and increased heat generation. Excessive charge and discharge will lead to the destruction of the crystal structure of the electrode material. Balance these parameters to Extending battery life is very important; the traditional measurement method of calculating battery power and real-time internal resistance according to battery current, voltage and time through Kalman-like filtering and ampere-hour method has certain errors and delays. The method that can directly detect the internal resistance of the battery in real time can improve the accuracy of monitoring the battery status, so as to control the working condition of the battery more accurately.”

Car safety do a good job of safety isolation

The safety of electric vehicles has always been concerned by users. Due to the limitations of chemical and physical characteristics, the current parameters such as voltage, current and temperature of electric vehicle batteries need real-time, strict and accurate monitoring to effectively avoid battery spontaneous combustion accidents. Due to parameters such as temperature The detection of the battery has a time delay, and the parameters of the battery model will change with the use time. Zhu Yuping pointed out, “The traditional BMS generally ensures that the battery is in a safe working area by leaving enough margin for the system. More advanced BMS can expand the safe working area of ​​the battery by improving the measurement accuracy and algorithm, thus ensuring the safety of the battery. On the premise of increasing the cruising range, speeding up the charging time, and extending the service life.”

Lin Qifeng, assistant manager of the second group of vehicle-mounted FAE department of South China FAE Department of ROHM semiconductor Technology Center, said that BMS is not only responsible for preventing abnormal voltage, abnormal current, abnormal temperature, etc. (Load) also plays an important role, in the battery periphery of xEV etc., mechanical relays are used to turn off the power. The mechanical relay has the problem of failure caused by the wear and tear of the mechanical part. Therefore, it is expected that the popularity of semiconductor relays will be driven by SiC power components in the future. Using semiconductor relays not only avoids wear failures, but also quickly shuts down the power supply in the event of an overcurrent, enabling safer battery use.

In the interview, Peng Yongjun emphasized to the reporter from Yufei.com, “Highly reliable and high-precision signal sampling and software and hardware stability are the basis of battery system safety, and battery models and algorithms are the core of battery system safety. Three aspects should be considered. To protect:

First, temperature protection. BMS has a clear working temperature threshold setting, and there are the highest and lowest temperature limits for charging and discharging. If the set limit is exceeded, the system must not be turned on or must run with reduced power; second, voltage protection. For the risk of overcharge and overdischarge, the BMS is set with the highest and lowest charging and discharging voltage thresholds to ensure that the system automatically stops running when the thresholds are reached; third, current protection. Accurately estimate the battery state through high-precision battery models and algorithms, calculate safe and efficient available power, monitor the current of the battery, and prevent risks such as battery deterioration and dendrites caused by overcurrent.

Summarize

The evolution of BMS technology is highly related to the development of battery technology and changes in electric vehicle architecture. At present, BMS mainly includes master-slave, integrated, and semi-centralized. At present, there are three major development trends of BMS: First, from discrete ECU control to domain control, centralized control is conducive to the online upgrade of automotive software and the development of intelligent driving. The BMU, the main control part of the BMS, may be handed over to the power domain controller in the future; second, the communication mode of the analog sampling front-end AFE is developed from wired to wireless, which is conducive to simplifying and intelligentizing the production, assembly, maintenance, and maintenance of battery packs. Recycling and other links; third, simplify the design of the BMS sampling plate. With the increasing requirements of the market for the energy density of battery packs, the space left for BMS in the battery pack is getting smaller and smaller. How to simplify the design, use fewer devices, take up less space, and achieve the same function may be an industry issue. The direction and trend of efforts.

In the future, on the vehicle architecture, some functions of BMS will be simplified to other modules, such as high-voltage measurement, control and diagnosis of high-voltage relays, and thermal management, so that the functions of BMS will be more concentrated on the measurement functions of single cells (voltage, current, temperature, etc.) and protection above.

For more related articles on BMS, please refer to:

From electric vehicle endurance pain points to safety challenges, SiC power components are expected to achieve “double solutions”

Nearly half of the world’s electric vehicles will be electrified in 2030, and it is the key for chip manufacturers to ensure the durability of the vehicle

Breaking the shackles of traditional BMS, iBMS conducts beneficial exploration based on big data

“Power chip + high reliability MCU” join forces to solve the “urgent need” of BMS

The role of BMS as a “link” is self-evident, and chip manufacturers face challenges to meet opportunities

BMS technology improves battery monitoring accuracy and increases the residual value of electric vehicles

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