E-Mobility Engineering 017 l ECE Doosan electric excavators dossier l In Conversation: Matt Faulks l Battery testing focus l Battery Show North America 2022 report l Ariel Hipercar digest l Cathode materials insight l Thermal management focus

6 kWh battery that can discharge at 100C – we’ve been building packs like that in Formula One for years – and combine them through a high-end DC- DC converter and some clever control systems. That gets you the 800 kW and ramp rates needed for sprinting with a hypercar, torque for a fully loaded HGV or take-off for an eSTOL aircraft. “Say we want to do a 200 mph sprint. We max-out our starting acceleration using just the battery’s 600 kW output as the fuel cell ramps up, and beyond 125 mph we add the latter’s energy on top of the former. “After that sprint, say we want to pull back to a 150 mph cruise: we can maintain that speed using just 175-180 kW from the fuel cell alone. And every time we slow down we’re regenerating a lot of energy for replenishing the battery, which again is easy to do because we have a very high C-rate pack.” The high regeneration rates of Viritech’s energy management approach bear some similarity to those of the Riversimple Rasa FCEV (featured in EME 10, Summer 2021). Faulks notes however that that car’s energy deployment topology is less flexible and sophisticated than that being proven in the Apricale, in which any combination of fuel cell and battery can be used for the power, torque and speed modes that are unique to each application. “While supercapacitors work great for the Rasa, they don’t fit our energy density requirements; our batteries pack a lot of energy into very small spaces,” he says. “Ultracapacitors give us megawatts per second, whereas conventional battery EV [BEV] packs give us kilowatts per hour. We needed something in between, at hundreds of kilowatts per minute.” The company has therefore developed its own proprietary DC- DC converter in-house using silicon carbide (SiC) technology to achieve the high switching speeds necessary for sending kilowatts per minute to its inverters using both battery and fuel cell simultaneously. “In functional terms, we use SiC in our DC-DC for the same reasons it’s used in e-machine inverters: it’s lighter, smaller and easier to mass-produce than silicon MOSFETs and IGBTs,” Faulks says. “All that, together with its power density and minimal cooling requirements, mean you’d be crazy not to go that route. “And the argument of it being too expensive doesn’t hold much water when we’re seeing so many BEV inverters using SiC. Granted, it’s more complicated, and the control system requirement is much higher, but the benefits make it worthwhile, especially in terms of lighter weight. Right now, a 60 kW DC-DC weighs 25-30 kg; we want something under 10 kg if we’re to make power electronics with the low weights and very high outputs and duty cycles necessary for commercial EV fleets in the future.” To develop the control architecture required for Viritech’s high-power, high-speed energy management, the company keeps all the necessary software programming and hardware design and manufacturing in-house. That includes making its own PCBs, and keeping abreast of automotive requirements such as ISO 26262 and ASIL-D. “Both the control board and the DC-DC board are modular,” Faulks adds. “We have a specified design for each, and we can daisy-chain them for ever-higher power requirements, so scaling our technology for bigger EVs is sensible and straightforward.” Rethinking hydrogen tanks As mentioned, energy management has been a major area of focus for Viritech’s r&d; the other has been how to pressurise hydrogen at 700 bar with minimal mechanical complexity, and hence improve the energy density of hydrogen gas (which is less than its very high specific energy). The company says that, typically, 5 kg of Graph-Pro tanks double as hydrogen vessels and structural membranes, as shown here in a render of Viritech’s Jovian HGV, to hold hydrogen at 700 bar without excess weight or ancillary parts 18 January/February 2023 | E-Mobility Engineering