In-Core Cooling for Yokeless and Segmented Armature (YASA) Axial Flux Machines: Analysis and Experimental Validation

This paper presents a novel in-core cooling method for yokeless and segmented armature (YASA) axial flux machines to address the challenges posed by high temperatures in these machines, thereby unlocking their full potential. The proposed in-core cooling method involves forming cooling channels within each laminated stator core segment, through which a coolant is circulated to transfer heat from windings and core to the coolant. This solution increases thermal performance and reliability by effectively cooling the stator core and windings. Additively manufactured connectors are utilized to achieve continuous coolant path through the adjacent stator segments. In order to assess the performance of the proposed in-core cooling, this paper presents both CFD and analytical lumped-parameter thermal network models. As a case study, a 36-kW YASA motor is designed, and a performance comparison study is conducted with conventional stator jacket cooling. The results showed that the proposed in-core cooling can boost the current density up to 15.5 A<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub>/mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at the stator windings, resulting in 60% torque capability increase compared to the conventional methods. An experimental verification on a stator motorette also verifies the accuracy of the analysis tools and models used for the proposed in-core cooling of YASA motors.