E-Mobility Engineering 014 l InoBat Auto dossier l In Conversation: Brandon Fisher l Battery monitoring focus l Supercapacitor applications insight l Green-G ecarry digest l Lithium-sulphur batteries insight l Cell-to-pack batteries focus

and cost, but implementing the link in a hostile, high-voltage environment can be difficult. The varying, high- power electric fields make transmission difficult, but the relatively low data rate of the battery monitor chip leaves plenty of bandwidth for more complex protocols to minimise the interference and ensure that each packet of data is sent and received reliably. One protocol for this is similar to the well-established RS-485 used on wires but adds design mechanisms to attenuate high common-mode voltages caused by the noisy conditions typical in vehicle environments. Each byte transmits at 2 MHz with a 250 ns pulse, but the time between each byte depends on the UART baud rate, which is typically 1 Mbit/s in normal operation. However, this ‘byte time’ is always the same. This gives the deterministic delivery of the data via a star architecture to a central wireless receiver on the BMS. It also fits into the requirement to monitor up to 300 cells each second, or a time slot of 200 µs. Other battery monitoring chips are using new data management and connection techniques. One monitoring chip using these new techniques is built in a rugged 55 nm CMOS process to combine storage with an ARM Cortex-M3 microcontroller Focus | Battery monitoring Multiple devices can be connected in series, permitting simultaneous cell monitoring of long, high-voltage battery strings. Using an isolated serial port interface allows the monitoring chip to be connected in a daisy chain, with each segment reaching 20 m, all controlled by a single host processor connection. This daisy chain can be operated bidirectionally, ensuring comms integrity even in the event of a fault along the comms path by allowing comms in the other part of the loop. To ensure maximum range per charge, the vehicle’s power consumption must be managed not only during driving but when the vehicle is parked. BMS devices support multiple battery cell configurations that enable the battery to be monitored continuously, even when the vehicle is turned off to ensure safety under all conditions while maximising vehicle range. The monitor chips are designed with no desynchronisation delays between samples to ensure that the data from the cells, which may be more than 300 for 1200 V packs under development, is all captured in a timely fashion. The speed of the interconnect is important. A 2.66 Mbit/s isolated serial comms port with regenerative buffer with a dual access ring allows a latency of less than 4 µs between the start of conversion of the first and the 31st device in a chain. Less than 4 ms is required to convert and read 96 cells in a system, 8 ms to convert and read 210 cells or 16 ms to convert and read 434 cells. Wireless monitoring There is also a move to connecting the battery monitor chips wirelessly. This can eliminate the wiring for the bidirectional daisy chain to save weight Some suppliers of batterymonitoring systems Germany In ineon Technologies +49 800 9519 51951 www.in ineon.com Innovation Labs – www.innovationlabs.de TWAICE +49 89 997 324 58 www.twaice.com India ION Energy – www.ionenergy.co Japan Renesas Electronics +81 3 6453 3010 www.renesas.com Switzerland STMicroelectronics +41 22 929 29 29 www.st.com UK Dukosi +44 131 445 7772 www.dukosi.com Silver Power Systems +44 1793 784242 www.silverpowersystems.com USA Analog Devices +1 800 262 5643 www.analog.com Texas Instruments +1 855 226 3113 www.ti.com This stackable precision battery monitor supports up to 14 cells in series (Courtesy of Texas Instruments) 36 Summer 2022 | E-Mobility Engineering