Cooling System Analysis of an Enclosed Yokeless Stator for High-Power Axial Flux PM Motor With Distributed Winding

In this article, the stator cooling system of an axial-flux permanent-magnet (PM) motor with an integer-slot distributed winding (ISDW) for high-speed, high-power electric vehicle traction applications is discussed. The aim of this research is to quantitatively figure out the power/power density boundaries of this type of axial field PM motor with the adoption of the proposed oil-immersed cooling system consisting of multicooling channels. First, the structural-cooling design considerations are provided. Then, a comparative study of the stator thermal performance of the high-power axial field PM motor with various cooling methods is conducted with three-dimensional computational fluid dynamics analysis. The oil circuits inside the stator are further optimized to achieve a better cooling effect, with a focus on improving the oil circuit layout configuration. Finally, a full-scale oil-immersed cooling prototype motor with 120 kW output peak power and 15 000 r/min is manufactured and tested. The long-time stable operation at high speed verifies the reliability of the stator structural design. The thermal performance is verified with measured results of end-winding temperature rise under continuous conditions.