Comparative Design and Thermal Performance of Stator Cooling Strategies for a High-Speed Electrically-Excited Synchronous Machine (EESM)

The present work investigates and compares three stator cooling configurations for a high-speed, cost-effective Electrically Excited Synchronous Motor (EESM) for automotive application. Starting from a lumped thermal model in MotorCAD to retriever losses and heat distribution, three stator forced liquid cooling solutions were designed: (I) Housing Water-Jacket (WJ), (II) Direct-Slot with in-slot flow (DirectSlotV1), and (III) Direct-Slot with in-slot flow plus stator ducts (DirectSlotV2). The geometries were then defined in SolidWorks and SpaceClaim and solved numerically in Ansys Fluent considering a steadystate non isothermal flow. A 50/50 EGW coolant was used with an inlet temperature of 65°C and four different flow rates (6, 10, 15 and 18 l/min) were tested under the same thermal setup and conditions provided by MotorCAD. The performance of the solution was evaluated via channel pressure drop Δp, and the maximum reached stator temperature. All the three solutions meet the imposed temperature limit for continuous operation, but DirectSlotV2 provides the best trade-off between cooling performance, pressure drops, and cost-effectiveness. The study outlines the modeling assumptions and limitations, and provides a solid foundation for future studies.