Integrated Traction Drive Thermal Management

This is a section in the Fuel Cell Technologies Office's Annual Progress Report that summarizes the research to enable the mass market penetration of electric-drive vehicles and to meet consumer electric vehicle performance expectations, the US DRIVE 2017 Electrical and Electronics Technical Team Roadmap proposes aggressive research and development targets aimed at reducing cost and increasing electric traction drive system power density to 33 kW/L by 2025. The target includes high-voltage power electronics and a single traction-drive electric motor. Achieving this level of system power density would most likely require integration of the inverter and the electric motor into a single traction module. However, this approach will also require innovative thermal management solutions to provide adequate cooling to more densely packed electrical components and keep their operating temperatures within optimal range. This project reviews and evaluates motor-integrated power electronics topologies and thermal management solutions for electric traction drives using finite element analysis (FEA) thermal modeling. During current project year, initial modeling efforts were focused on building an FEA model of an electric traction drive (based on BMW’s i3 traction drive component geometries) with separate enclosures for electric motor and power electronics. Another area of focus for the project is a thermal characterization of direct cooling of temperature-sensitive components with driveline fluids. The current work is a continuation of NREL’s efforts in free-surface jet impingement heat transfer characterization for cooling of electric machines with automatic transmission fluid (ATF). During recent in-situ jet impingement experiments it was found that the target surface temperature significantly affects convective heat transfer coefficients (HTC). Namely, increasing surface temperature from 90°C to 120°C enhanced HTC values by up to 15%. In addition to experimental HTC measurements, CFD modeling was performed for fan-shaped and orifice jet impingement with ATF.