30 November/December 2023 | E-Mobility Engineering of charge, to better understand how the SoC and SoH can degrade over time and temperature, along with other key information for BMS inputs and timely control outputs. “You’ll see all that in our data sheets. We give the full power map across different temperatures and C-rates and so on, because it’s fundamental for integrators looking to optimise their vehicle designs to know everything their battery can do,” Dr Flannery notes. “And it saves us a huge amount of time and questions when customers come in, to have publicly available documentation that exposes all our testing results to them and contains all the answers.” The machines for leak-testing Xerotherm ducts are designed and built on-site. Xerotech’s original leak-testing machines tested one duct at a time, but the present version tests eight at once automatically, incorporating repeatability and traceability gained through data over time. A leak-test engineer first installs eight ducts – a complete batch for a Hibernium module – into the test machine’s nozzles, and presses a button to start its testing profile. At that point they are cycled with water-glycol while being scanned for leaks and traced for QC; the test takes 3 minutes. Given the variety of tests and associated equipment, and the amount of data produced, Xerotech uses a range of COTS data acquisition systems from National Instruments and similar organisations; LabView is used to set up data acquisition programs. Once acquired, the data is typically logged and graphed in .CSV and other Excel spreadsheets. “Obviously, our CAE processes are more complicated than that,” Dr Flannery explains. “FEA and CFD simulations come with all sorts of Python-based workflows with pre- and post-processing of data to bring into our models, but the bulk of our data organisation rests on pretty simple tools, with quite a few back-ups for our cloud share points. “And while we’re focused for now on getting as much data as possible, we’ll be looking into things we can do with that data in the future for safety, transparency and keeping our BMS algorithms optimised. That will include machine learning [ML], adaptive algorithms and cloud-based BMSs. ML is being used for degradation analyses and other insights, and our battery data could interplay well with that.” Traceability is vital throughout both testing and manufacturing, with barcodes and QR codes used across materials, duct manifold assemblies and some battery cells to track parts and trace bottlenecks or faults throughout workflows. While Xerotech is ISO 9001-rated, at the time of writing it was aiming for the IATF 16949 automotive certification standard, meaning full traceability throughout production. Battery management Developing the BMS started with defining the system concept in terms of core functions and features, after which the circuit boards and physical layout could be designed. Validations of those designs followed, with tests for EMC, shock, vibration, overvoltage, undervoltage and temperature from -20 to +50 oC then being run. After verifying the hardware, software development began. It consisted primarily of writing lower-level base software (BSW) such as firmware drivers and application software for higher-level functions including all the customerfacing features. The BSW architecture has been designed to make it transferable between BMSs and abstracted away from the hardware layer. The BMS architecture consists of a centralised master BMS inside the BDU and distributed slave BMS units installed in each module, with CAN J1939 connections linking them to the master. The centralised battery management architecture serves the scalable, modular pack design architecture vital to Xerotech’s off-highway customer base. Each slave BMS mounted at the end of each module reads cell voltages and temperatures, using a Texas Instruments (TI) BQ79616 as a monitor chip, which comes designed for tracking up to 16 series of cells; it therefore works for both the 8S and 16S module configurations. It can also withstand temperatures from -10 to +125 oC, potentially enabling continued operation during thermal events. Once assembled and bolted together, packs go through non-destructive end-of-line tests
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