E-Mobility Engineering | November/December 2023 31 Xerotech battery system | Dossier crashes. An onboard SD card logs data from that and the BMS’ components to monitor for abuse conditions relevant to warranty compliance. Lastly, a board for operating warning LEDs is installed and programmed for flashing short fault codes to operators, technicians and nearby workers, to avoid the need for reading complex diagnostics reports in the field. “That sounds rudimentary, but it’s a hugely undervalued thing to put into battery packs. It’s actually helped us a lot in field tests and operations,” Dr Flannery notes. Future prospects Standards for road EVs such as ISO 26262 have influenced the software and hardware development for the BMS, and upcoming regulations for offhighway vehicles will inform Xerotech if any further changes are needed for functional safety compliance, as will any changes in the years ahead, as safety requirements become clearer with more off-highway EVs being used. With almost all the major names in off-highway and mining now looking into electrification, and trialling bespoke battery designs in serial or pre-serial production, demand for battery packs is expected to ramp up in the years ahead. To meet that demand, Xerotech plans initially to keep scaling its site at Claregalway, effectively using it as a prototype factory for 400 MWh worth of Hibernium packs per year, as mentioned, after which a facility nearby is prospectively planned for outputting 2 GWh/year initially and up to 4 GWh/ year once fully scaled. “And after that, around 2026, we aim to have a location in the US, of a similar size and scale to the larger Ireland facility we’re planning,” Dr Flannery says. “Production will accelerate once we’re confident we’ve optimised our manufacturing and testing flows.” Come the first quarter of 2025, Xerotech also plans to have its nextgeneration packs designed and in volume production. While off-highway electrification will remain its primary market, those new packs will include units designed for lower-cost, onhighway integrations such as trucks and buses. “For redundancy, the slave BMS measures four temperature sensors per module, and that’s specifically at the discharge point, which is always either the hottest or coldest point, depending on whether you’re heating or cooling the pack,” Dr Flannery says. “Meanwhile, our high coolant flows ensure even temperatures across our modules, and the slave BMS chips communicate with each other over a daisy chain SPI interface. That has a ring architecture for bidirectional and hence redundant comms; if there’s a break on one side, the data signals can run and be read around the other way.” Over and undercurrent conditions are read by the master BMS, which tracks the shunts while communicating with the slave chips. The master’s gateway chip is a TI BQ79600, which in turn communicates with the BDU’s central microcontroller, a TI TMS570, one of Texas’ safety-critical transportation MCUs designed for ASIL ratings in system design. It is powered by a 160 MHz ARM Cortex R4F CPU, and comes with 2 Mbytes of flash memory and 160 kbytes of RAM, both with ECC. “Getting the hardware layer and the BSW to work was quite complicated,” Dr Flannery says. “The daisy chain bus for instance was challenging, we ran into quite a few edge cases but worked with TI to solve them. “We’ve designed our BMS for compliance with ASIL-C, and that drives a lot of the key design requirements inside. Both current shunts are isolated components rated at up to 1000 A each. We also have an isolation monitoring circuit continuously checking both the HV+ and HV- to ground, making sure there’s no leakage or other connection issues, and a pre-charge contactor and resistor for initial power-up.” Inside the BDU is also a triple-axis accelerometer and gyroscope for measuring shock and vibration during operations, principally to acquire data for understanding customer applications but also for detecting Xerotech’s battery disconnect unit contains each pack’s master BMS, its manual service disconnect system, a board for warning LEDs, and inertial sensors for usage and crash monitoring
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