【Introduction】Battery management system (BMS) is quietly changing electric vehicles. At the beginning of this year, STMicroelectronics released the L9963E battery monitoring and protection chip, which aims to solve the battery management system design problems faced by the world, including China’s new energy vehicles. The new product adopts a unique architecture that can measure 4 to 14 battery cells in series without any delay in desynchronizing between sample signals. The test results prove that although 31 L9963Es can be daisy-chained, the entire chain delay is still less than 4 µs.
However, the L9963E is much more than a simple voltage measurer or typical coulomb counter, so we’ve also published a white paper that dives into the intricacies of BMS design. Additionally, to further help engineers and decision makers design BMSs, we would also like to discuss five things that must be considered when developing a battery management system.
Why use a battery management system?
The BMS measures the current and voltage of the battery cells, and sends the information to the state-of-charge SOC application system to determine the operating state of the battery. After a period of use, the actual maximum capacity of the battery will decrease. Measurements from the BMS can calculate the actual maximum capacity of the battery, help the system determine the battery’s state of health (SOH) and remaining useful life (RUL), estimate whether the battery is still working or needs to be replaced, and can enable additional battery optimization features . By determining the SOC and SOH conditions of each cell, the BMS can balance the charge and discharge operations of the cells to ensure uniform loss across all cells, resulting in longer battery life and higher performance. Now, the L9963E also plays a key role in ensuring the safe operation of the battery.
1. Pay attention to the accuracy and speed of measurement
Power battery packs in electric vehicles
Engineers have traditionally focused first on the measurement accuracy of a BMS. If the system measurement data is inaccurate and lacks valuable information, users will experience huge frustration. Therefore, when the BMS measures the status of each battery cell, the accuracy must be very high, and the speed must also be very fast, otherwise, when the chip has finished reading the last cell of the battery pack, the first cell’s reported measurement The value is no longer accurate, and the application system cannot provide a true reflection of the battery state of charge.
Maximum error ±2 mV
The L9963E’s voltage measurements are very accurate with a maximum error of ±2 mV, while also measuring current to see the actual capacity of each cell. In addition, the product’s architecture ensures that each battery cell has dedicated resources for processing the electrical data monitored by the chip, while similar products on the market usually share data processing resources among battery cells. By dedicating processing resources to each cell, we can provide synchronized readings and avoid the delays caused by desynchronization. Within a daisy-chained network structure, the L9963E can also communicate over a serial bus with a bandwidth of 2.66 Mbps, while most bandwidths in the industry hover around 1 Mbps. Therefore, it takes 4ms to 16ms to read and process 434 cells.
2. Battery management system: pay attention to safety, this is the top priority
Learn about security
BMS security is often overlooked by many designers. The measurement accuracy of the BMS system helps improve battery performance and can also determine if there is overvoltage and undervoltage on the battery, or if overheating or overcurrent is present. For example, in the event of a collision, an electric vehicle must be able to determine that the battery parameters are not within normal safe values, and immediately initiate a battery shutdown procedure, otherwise catastrophic losses will result.
These functions require the chip to be highly robust and work well even in harsh environments. It is also important to prevent erroneous readings, which can be very dangerous when the car is cruising at high speed and can cause the battery pack to shut down. The L9963E has a unique redundancy feature that cross-checks the analog-to-digital converters (ADCs) to ensure accurate conversion results. If the current ADC is abnormal, the L9963E can force the adjacent ADC to take over the abnormal ADC and troubleshoot.
3. Pay attention to cost performance
As electric vehicles become cheaper, cost constraints become more important. Chips that are powerful but too expensive lose much of their appeal. Uniquely, the L9963E offers rich features without increasing die size, continuing to be cost-effective. In addition, traditional BMS chips require that each battery cell must be connected in parallel with an external Zener diode. During assembly, the system has no way of knowing which cell touches the connector first, and this is always a random event, so a Zener diode on each cell protects the battery management chip. With the L9963E’s hot-swappable and robust architecture, engineers can eliminate these Zener diodes, simplifying printed circuit board layout and reducing overall cost.
4. Two evaluation boards with a powerful MCU can not only develop prototypes, but also expand the field of vision
Learn about the ecosystem
A successful battery management system starts with a simple proof of concept. ST provides two evaluation boards for the L9963E. The first evaluation board, the EVAL-L9963E-MCU, includes a microcontroller with graphical user interface software STSW-L9963E to help developers create applications faster. The second evaluation board, the EVAL-L9963E-NDS, plugs into the first board, allowing multiple L9963E evaluation boards to be daisy-chained.
L9963E for use with SPC58 Chorus
There are many customers who prefer to use the L9963E with the SPC58 Chorus MCU, because the application needs to save a large number of data points output by the BMS system, this microcontroller has 6 MB or more memory space, which can meet all the storage needs of the application, The multi-core architecture enables developers to dedicate one core to handle battery management tasks, dedicating other cores to other common applications. This MCU also has many peripheral interfaces, including six FlexCAN buses, making the entire design more flexible.
5. Battery management system: focus on the future, focus on the present
All engineers try to design their products with the future in mind, however, when it comes to battery management systems, the design must take into account not only the cars of tomorrow, but also all new products that are currently using BMS, such as e-bikes and scooters, or Portable medical equipment, etc. The L9963E has high application flexibility and is suitable for many other designs in addition to traditional electric vehicles. The ability to measure as little as four cells, the small 10mm x 10mm TQFP64EP package, and cost-effectiveness allow a company to easily develop various types of vehicles or applications using the same ST device, saving development costs.
The Links: VI-BTT-EU PM150RSA060 BEST-IGBT