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

changes, which translate into changes of pressure that can be captured by foil sensors. This allows engineers to measure the state of charge directly, implement preload and cell-balancing measures and detect irregular behaviour. This can prevent over- charging and provides vital information on the state of health. Sensor foils in a 32 x 65 matrix can monitor the pressure distribution from 0.5 to 500 N/cm² as the cells swell, or can be used to measure the temperature with an accuracy of 0.1º. This approach requires electronics to recognise and inhibit crosstalk between the measurement coils, with a low- noise 12-bit ADC to provide digital data to the visualisation, storage and analysis software. The electronics uses several comms interfaces, including CAN bus, Ethernet, serial USB and wi-fi. The technology is being extended to combine temperature and pressure sensors in the same matrix, and the foil sensors can also be used to measure humidity. The matrices are also being extended to 96 x 96 arrays to provide better spatial resolution. These arrays are used for r&d and prototyping rather than volume production in vehicles, collecting data that is not possible with other techniques. Eight measurement points for each cell, 15 cells in a module and six modules in a pack, requires hundreds of measurement points, which presents a major challenge in fitting all the sensors into the pack. With the thin foil approach, all the sensors can be incorporated inside the pack, avoiding the need to have lines to the outside and avoiding the need for glands that can operate in a high- voltage environment. Such detailed, accurate data is used to create a model of the cell, also known as a digital twin. This can be used as the ‘golden reference’ for the performance of the cells in production systems via the BMS. Digital twins The more accurate measurement of the performance of battery packs during r&d also opens up the development of digital twins. These are cloud-based models that use the same initial model from r&d and add in the real-world data acquired from the vehicle. This can Cyber security and wireless monitoring Cyber security is a key issue for wireless battery monitoring systems. ISO/SAE 21434 is the new standard for cyber security risk management throughout the life cycle of the vehicle, from concept, product development and production, to operation, maintenance and decommissioning of electrical and electronic systems. It builds on the ISO 26262 safety-critical standard to cover the cyber security issues at every stage of the development process and in the ield, increasing a vehicle’s own cyber security defences and mitigating the risk of potential vulnerabilities for every component. There is a framework provided in the standard to help suppliers work together on cyber security challenges. ISO/SAE 21434 was developed by technical committee ISO/TC 22, Road vehicles, subcommittee SC 32, Electrical and electronic components and general system aspects, in collaboration with SAE International’s Vehicle Cybersecurity Systems Engineering Committee. The secretariat of ISO/TC 22/SC 32 is the JISC, the ISO’s member for Japan. ISO/SAE 21434 requires that manufacturers and developers perform a risk assessment to identify any component, application programming interface (API) or software function that could be vulnerable to attack. After the assessment, any vulnerabilities can be identi ied. This can be carried out using techniques such as fuzzing, which scans the system to ind potential vulnerabilities in the same way an attacker would scan a system. Di erent certi ication labs use di erent tools to test applications and components to a particular cyber security assurance level (CAL). The CAL is de ined from 1, the lowest, to 5, depending on the feasibility of the attack and the impact of a breach. If an attack requires a team of expert hackers and costly equipment, the risk will be lower compared to an attack that anyone can execute and lead to the same damage. These are similar to the ASIL levels de ined in ISO 26262, and are described in an annex of the standard. The standard does not prescribe a speci ic method of analysing the system and calculating risk values, but it does provide some guidance and examples. Depending on the target CAL, certain cyber security activities can be omitted or carried out with less rigour. The CAL 4 classi ication according to the ISO/SAE 21434 standard for the latest wireless battery management requires strong risk assessments to proactively identify any component, API or software function that could be vulnerable to a cyber attack. A component classi ied as CAL 4 indicates that it might be suitable to perform critical functions that require a high level of security assurance and protection of critical assets. Manufacturers and developers now have to identify any component, application programming interface or software function that could be vulnerable to cyber attack (Courtesy of Analog Devices) Summer 2022 | E-Mobility Engineering 39 Focus | Battery monitoring