Validation of a Thermal Model for Electromagnetic Co-Optimization of Electric Machines

Multi-physics optimization enables one to explore tradeoffs between machine mass (size), and loss, or an objective such as the temperature difference between slot conductors and coolant. To facilitate coupled thermal-electromagnetic design, a thermal equivalent circuit (TEC) model has been developed that aims to accurately predict temperatures within the stator while maintaining computational efficiency necessary for exhaustive design space exploration. This paper focuses on detailed validation and characterization of the TEC model, and in particular, its reduced-order stator core conduction model and winding-to-stator thermal interfacial resistances. An experimental facility is developed to support model validation and demonstration. The setup includes a prototype stator subsection (statorette) installed into a cooling flow loop that is used to control thermal boundary conditions. The prototype statorette is fabricated by adhesive bonding of multiple laser-cut lamination layers, forming the stator teeth and backiron. This process allows for laser-cutting of internal holes for temperature sensors, as well as internal cooling channels for precise control of the temperature boundary conditions needed for validation. To validate the TEC model, the temperatures measured in the test section are compared with the model predictions. The results demonstrate that the low-resolution conduction model representation of the stator core can provide accurate temperature predictions. Further, the instrumented statorette is demonstrated as a platform for characterization of the internal interface contact resistances under controlled boundary conditions.