18650 lithium-ion battery

　　How to redefine 18650 lithium-ion battery management systems

　　As electrified power systems become increasingly complex, BMS needs to perform more functions and bear an unprecedented burden.

　　Whether it is a simple charge controller or a complex control unit, the demand for battery management systems (BMS) is growing rapidly, especially in the field of electric vehicles. In addition to traditional state-of-charge monitoring, BMS systems must comply with increasingly stringent safety regulations, focusing on control and standby functions, thermal management and encryption algorithms used to protect OEM batteries. In the future, even the components and functions of the vehicle control unit (VCU) will be linked to the BMS.

　　In the future, BMS will play an important role in the field of electric vehicles. However, each sub-function of the BMS is often customized by the OEM car manufacturer, and will vary greatly depending on the system configuration. Therefore, it is impossible to develop a complete list of BMS requirements that applies to every electric vehicle manufacturer. However, there is no doubt about the fact that the range of tasks handled by battery management systems continues to expand. The most common requirements for BMS include security requirements, control and monitoring functions, standby functions, thermal management, encryption algorithms and reserved extensible interfaces to add new functions.

　　security requirements

　　Within the scope of the ISO26262 safety standard, specific electrical and electronic systems such as BMS will be classified into high safety categories from ASILC to ASILD. The corresponding fault detection rate is at least 97% to 99%. The most dangerous sources of failure in battery systems are: undetected high-voltage leaks in the vehicle chassis due to worn cables or accidents; various causes of high-voltage battery fires or explosions: such as overcharging the battery (e.g. on a utility power grid) online or caused by power outage recovery), premature battery aging (such as explosive gas leaks), liquid ingress and short circuits (such as caused by rain), abuse (such as improper maintenance) and thermal management errors (such as cooling failure).

　　In terms of safety, the main switch (main relay) plays an important role in avoiding high voltage-related accidents by ensuring that the BMS electronic system can respond adequately to faults. When a fault occurs, the BMS module will turn off the switch within the appropriate fault response time (for example, within 10ms). Non-critical fail-safe conditions are often characterized by: If the BMS microcontroller (MCU) fails, an independent external safety element (such as a window watchdog) ensures that the main switch relay is reliable even in the event of a complete failure of the controller logic Ground opens the two high voltage contacts of the inverter (positive/negative). Other safety functions are integrated into the BMS system, including leakage current monitoring and main switch relay monitoring.

　　Control and monitoring functions:

　　Other BMS functions include monitoring, care and maintenance of expensive high-voltage batteries in electric vehicles. The BMS control and monitoring functions come from the electronic balancing unit installed in the battery pack. Manage the balance within each battery pack (batteryslavepack) while accurately sensing the voltage of each single cell. Balancing chips typically manage groups of up to 12 single cells. A relevant number of battery groups connected in series can generate high intermediate circuit voltages of up to several hundred volts for inverter control, which is required for the inverter electric drive of electric vehicles. Located in the main switch, the total current of all high-voltage batteries is measured, and the slave chip accurately and synchronously monitors the voltage of each single cell. The BMS can use specific algorithms (for example, based on the battery chemistry Matlab Simulink model) to evaluate the state of charge and health, etc. battery parameters. The BMS is usually not installed very close to the high voltage battery, but is usually connected to the electronically balanced slave element via a redundant galvanically decoupled bus system (such as CAN or other suitable differential bus). It is powered by vehicle voltage (12-volt battery) and can therefore be used in conjunction with existing control unit groups via existing network architectures without further galvanic decoupling measures. Finally, it also improves safety, as it allows the BMS to ensure proper functionality and safely disconnect the main switch in the event of a mechanical or chemical defect in the high-voltage battery.

　　As battery-specific chemical/electrical algorithms become increasingly complex, BMS is expected to require the use of microcontrollers (MCUs) such as AURIX with 2.5MB to 4MB of flash memory and powerful multi-core processor architecture. This combination ensures sufficient memory for comprehensive calibration parameters and provides sufficient computing power.

　　Standby function:

　　Electric vehicle manufacturers tend to regularly monitor the state of charge of the battery pack and individual cells. Therefore, BMS must provide a dedicated low-power standby function that requires only μA-level MCU power consumption and can quickly wake up the system with the help of a timer. For example, in BMS activation mode, the balance chip records specific single-cell data. . In order to realize the cyclic wake-up of the BMS with the help of the wake-up timer, multiple models of AURIX microcontrollers integrate an 8-bit single-chip standby MCU in an independent low-power domain (on the same chip).

　　Thermal management:

　　For design reasons, high-voltage battery modules often 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, the BMS is used to sense battery-related temperature data and actively actuate and control the heat sink (e.g., fan motor or water pump). The AURIX microcontroller is up to the task with its built-in ADC sampler and multiple timer functions.

　　Encryption Algorithm:

　　Original OEM batteries for electric vehicles should be protected from unauthorized third-party repairs. Replacing individual cells in a battery group or assembling individual parts disassembled from used batteries can mask safety-related faults or even signs of explosion or fire hazards. In order to ensure that the car manufacturer confirms the normality of the battery warranty, appropriate protection modules such as Infineon's Origa chip should be directly installed in each single battery group. At the same time, the logical protection of individual battery data composed of a hardware security module (HSM) integrated in the MCU can be used as a low-cost alternative.

　　In this case, the HSM in AURIX can effectively detect the various parameters of the above-mentioned battery because the battery can control these parameters and store them in a secure data memory protected by the HSM. For example, in terms of service life, the status of individual cells is stored in this way as an AES-encrypted file, so that unauthorized replacement of individual cells can be detected based on this data. We can liken a typical battery group profile to a fingerprint whose uniqueness will facilitate detection of replaced groups. Another application area for encryption algorithms is the monitoring and comparison of the charge level calculated by an external supplier with the charge level actually measured by the BMS. Future tasks:

　　Depending on the specific electronic topology of the electric vehicle selected by the manufacturer, there are currently inverter control units for high-order drive strategies and independent vehicle control units, namely VCUs. There are also entire torque control systems with other advanced features such as intelligent power managers. The power processor (via the integrated navigation unit) includes driving route planning and optimizes the entire power system according to the specific route, thus helping to increase the range of the battery.

　　Independent OEMs are now considering retrofitting all parts of the previous VCU into the BMS and inverter control unit, thereby reducing the total electronic component cost of electric vehicles. The prerequisites for removing the VCU are ultimately determined by the specific parameters of the microcontroller that the BMS can handle, such as the amount and performance of flash memory and SRAM, the independence of the individual control unit functions in terms of real-time capabilities and the shared scalable microcontroller The architecture seamlessly integrates safety-related software functions (from QM to ASILD), etc. In response to this specific situation, Infineon has launched controller hardware based on the AURIX multi-core architecture of triple-core processors that can integrate all the above required functions in future BMS customer applications.

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