ISSUE 012 Winter 2021 Sigma Powertrain EMAX transmission dossier l In conversation: David Hudson l 48 V systems focus l 2021 Battery Show North America and Cenex-LCV reports l Everrati Porsche 911 digest l Switching insight l Motor laminations focus

Researchers at the US National Renewable Energy Laboratory (NREL) have been working with heavy-duty equipment maker John Deere on a new thermal management system for SiC inverters (writes Nick Flaherty). Equipment such as trucks and construction machines account for 39% of greenhouse gas emissions in the transportation sector, so there has been a focus on electrifying these systems. The inverter is responsible for controlling the power flow between the DC and AC electrical networks in order to run vehicle systems, accessories and electric machines such as motors and generators. Using SiC transistors can provide a four times increase in power density over previous silicon- only inverters, but this is driving the need for more efficient thermal management. “The key to NREL’s design innovations for SiC thermal management is to improve the heat transfer coefficient, which allows this system to cool itself efficiently and continuously during operation with the engine coolant,” said Kevin Bennion, NREL senior researcher and a thermal management expert. The thermal management system helps to optimise system efficiency while regulating the operating temperatures of the SiC modules, which are directly cooled using 115 C water-ethylene glycol. A common strategy for the thermal management of EV inverters is to run a fluid coolant parallel to the component’s surface to transfer heat and cool the system quickly. However, the NREL system incorporates a perpendicular jet flow with mini-channel- and mini-manifold- based cooling systems to extract heat from the inverter and power module. This enables a heat transfer coefficient of up to 93,000 W/(m 2 K), more than four times higher than current commercial systems. The design uses an existing diesel engine’s cooling system for a simplified engine-coolant-capable architecture. Conventional heavy-duty inverters require a separate coolant system to operate successfully while ensuring the inverters’ durability. By eliminating the need for a separate cooling circuit, the NREL design achieves a power density of 43 kW/ litre, which the researchers say is a 378% improvement over baseline silicon systems. The smaller size of the cooling system and the inverter allows for a smaller and lighter system, with benefits to efficiency and operating costs. Cool SiC invertersmove THERMAL MANAGEMENT 3D-printed e-motorwinding design Maxxwell Motors has used additive manufacturing for a copper e-winding design for its axial flux electric motors (writes Nick Flaherty). Axial motors can be used in electric cars as well as a range of heavy- duty vehicles and industrial devices. Maxxwell worked with 3D printing company ExOne to use binder jet 3D printing to produce the high-efficiency copper e-winding design. Maxxwell holds nine US and global patents, and has launched two products – a 10 kW air-cooled motor/generator and a 150 kW liquid- cooled motor – that do not use rare earth magnets and so rely on more sophisticated winding designs. Optimising the design of the copper windings and rotors in electric motors is key for improving motor performance, but Maxxwell aims to 3D-print the winding assemblies as a single monolithic component. This eliminates the need for coil wrapping, bending, tooling and welding individual parts together. When produced with binder jet 3D printing, the final part would require fewer manufacturing steps and less energy use, as well as less material waste, resulting in components that are more efficient and deliver improved performance. MOTORS ;Oe Rey to tOerTal TanaNeTent in :iC in]erters is to iTpro]e tOe Oeat transfer coeɉcient 10 Winter 2021 | E-Mobility Engineering