How to re-meaning electric vehicle battery management system
As the electrified power system becomes more and more complex, the functions to be performed by the BMS increase, and its burden is unprecedented.
Whether it is a simple charge controller or a complex control unit, the demand for battery management systems (BMS) is rising rapidly, especially in the field of electric vehicles. In addition to traditional charging status monitoring, BMS systems must also comply with increasingly stringent safety regulations, paying attention to control and standby functions, thermal management, and encryption algorithms used to protect OEM car manufacturers' batteries. In the future, even the components and parts of the vehicle control unit (VCU) will be associated with the BMS.
In the future, BMS will play an essential role in electric vehicles. However, the various sub-functions of BMS are often customized by OEM car manufacturers, and there will be significant differences due to different system configurations. Therefore, it is impossible to develop a complete list of BMS requirements applicable to every electric vehicle manufacturer. However, the fact that the scope of tasks handled by the battery management system continues to expand is beyond doubt. The most common requirements of BMS include security requirements, control and monitoring functions, standby functions, thermal management, encryption algorithms, and new functions reserved for expandable interfaces.
Safety requirements
Within the scope of the ISO26262 safety standard, specific electrical and electronic systems such as BMS will be classified as high safety categories from ASILC to ASILD. The corresponding fault detection rate is at least 97% to 99%. The most dangerous sources of faults in the battery system include high-voltage leakage on the chassis of the vehicle due to cable wear or accidents without being discovered; various causes of fire or explosion of high-voltage batteries: such as overcharging the battery (for example, in public power Online or due to power failure recovery), premature battery aging (such as explosive gas leakage), liquid entry and short circuit (such as caused by rain), abuse (such as improper maintenance), and thermal management errors (such as cooling failure).
The main switch (main relay) plays an essential role in preventing high-voltage-related accidents in terms of safety. It can ensure that the BMS electronic system can respond adequately to failures. When a fault occurs, the BMS module will open the switch within an appropriate fault response time (for example, within 10ms). The characteristics of non-critical fail-safe conditions are usually: if the BMS microcontroller (MCU) fails, even in the case of a complete failure of the controller logic, independent external safety components (such as window watchdog) can still ensure the reliability of the main switch relay Ground opens the two high voltage contacts of the inverter (positive/negative). Other safety functions are also integrated with the BMS system, including leakage current monitoring and central switch relay monitoring.
Control and monitoring functions:
Other BMS functions include monitoring, maintenance, and maintenance of expensive high-voltage batteries in electric vehicles. The BMS control and monitoring functions are derived from the electronic balance unit installed in the battery pack. Manage the balance of each battery pack and accurately sense the voltage of every single cell. The balance chip can usually manage groups of up to 12 single cells. After a corresponding number of battery groups are connected in series, a high intermediate circuit voltage of up to hundreds of volts can appear for inverter control, which is necessary for the inverter electric drive of electric vehicles. It is located in the main switch to measure the total current of all high-voltage batteries and the slave chip to accurately and synchronously monitor the voltage of each battery cell. BMS can use specific algorithms (for example, based on the battery chemistry Matlab Simulink model) to evaluate the state of charge, health, etc. Battery parameters. The BMS is usually not installed very close to the high-voltage battery. Still, it is generally connected to the electronic balance-driven component through a redundant galvanic decoupling bus system (such as CAN or other suitable differential buses). It is powered by the car voltage (12-volt battery), so it can be combined with the existing control unit group through the existing network architecture without further galvanic decoupling measures. Finally, it also improves safety because it allows the BMS to ensure that it functions safely and adequately disconnects the main switch in a high-voltage battery event of a mechanical or chemical defect.
With the increasing complexity of battery-specific chemical/electrical algorithms, it is expected that BMS will use microcontrollers (MCUs) such as AURIX with 2.5MB to 4MB of flash memory and a robust multi-core processor architecture. This combination can ensure enough memory to calibrate the parameters and fully provide computing power.
Standby function:
Electric vehicle manufacturers tend to regularly monitor the charging status of the battery pack and individual cells. Therefore, BMS must provide a dedicated low-power standby function, which requires only ¦ÌA-level MCU power consumption and can quickly wake up the system with the help of a timer, for example, record specific cell data through a balancing chip in BMS activation mode. To realize the cyclical wake-up of the BMS with the help of the wake-up timer, there are multiple models of AURIX microcontrollers that integrate an 8-bit monolithic standby MCU in an independent low-power domain (on the same chip).
Thermal management:
For design reasons, high-voltage battery modules usually include active thermal management, such as heaters for winter and cooling systems for summer. These can be achieved by air cooling or water cooling. In both cases, BMS is used to sense battery-related temperature data and actively execute and control radiators (for example, fan motors or water pumps). The AURIX microcontroller has a built-in ADC sampler and multiple timer functions, which can do this task.
Encryption Algorithm:
The original OEM battery of electric vehicles should be prevented from being repaired by unauthorized third parties. Replacing single cells in a battery group or assembling individual parts removed from used batteries can conceal safety-related failures and even signs of explosion or fire hazards. To ensure that the car factory confirms the normality of the battery warranty, Infineon's Origa chip and other appropriate protection modules should be directly installed in each battery group. At the same time, the logic protection of individual battery data constituted by the integration of a hardware security module (HSM) in the MCU can be used as a low-cost alternative method.
In this case, because the battery can control these parameters and store them in a secure data storage protected by HSM, the HSM in AURIX can effectively detect the various parameters of the storm. For example, in terms of service life, in this way, the status of every single battery is stored as an AES encrypted file, so that unauthorized replacement of every single storm can be detected based on this data. We can compare a typical battery group file to a fingerprint, and its uniqueness will help detect the presence of replacement groups. Another application area of the encryption algorithm is responsible for monitoring and comparing the charging capacity calculated by the external supplier with the charging capacity measured by the BMS. Future tasks:
According to the specific electronic topology of the electric vehicle selected by the manufacturer, there are currently inverter control units with high-end drive strategies and an independent vehicle control unit, namely VCU. At the same time, there is the entire torque control system. These systems also have other advanced functions, such as intelligent power management. The power processor (through the integrated navigation unit) covers the driving route planning and can optimize the entire power system according to the specific route, thus helping to increase the driving distance range of the battery.
Independent OEM manufacturers are now considering changing all the components of the previous VCU to the BMS and inverter control unit, thereby reducing the total electronic component cost of electric vehicles. In the final analysis, the prerequisites for removing VCU are determined by the specific parameters of the microcontroller that can be processed by the BMS, such as the number and performance of flash memory and SRAM, the independence of each control unit function in terms of real-time capabilities, and the shared, scalable microcontroller Seamlessly integrate safety-related software functions (from QM to ASILD) in the architecture. In response to this specific situation, Infineon has introduced a three-core processor-based AURIX multi-core architecture controller hardware that can integrate all the above-mentioned required functions in future BMS customer applications.
