EXTENDED LAYER APPROACH FOR THERMAL MODELING OF A TOOTH-COIL WINDING IN ELECTRICAL MACHINES

Designing small and high-power density machines requires a good knowledge of the thermal behaviour in an early stage of the design process. As the end windings have a comparable long thermal path to the cooling medium, it is most likely the hottest component in an electrical machine. Therefore, it is essential to have a thermal model of the end windings in order to estimate the temperature distribution in it. In this paper, we present an analytical lumped-circuit approach for the thermal modeling of the end windings. We have applied the extended layer approach, which homogenises the stator slot considering four directions in predefined layers, and extended it in axial direction. With the extension in axial direction, we can simulate the heat flow and can predict a temperature distribution along the wires. We have implemented the approach for a tooth-coil winding, simulated and validated it with a Finite Element Analysis (FEA). The innermost layers in the end windings show the hottest temperature due to the longest thermal path to the cooling medium. For a defined load step, which equals the rated operating point in the observed driving cycle, the maximum temperatures differ by a maximum of 12:1K compared to the FEA results. The average and minimum temperatures differ by a maximum of 4:4K and 8:8K. In thermal steady-state, the temperatures differ by 9:5K, 0:8K and 8:8K for the maximum, average and minimum temperatures. Along the windings in axial direction the temperature difference for the average temperatures is given by 4:6K and 2:5K for the analytical approach. The validation with FEA results shows a good accordance to the analytical approach, while the simulation time is about 400 times faster.