An upgraded hybrid subdomain method toward three-dimensional thermal performance of synchronous reluctance motor

This study addresses the lack of reliable 3D thermal analysis models for synchronous reluctance motors (SynRM) with complex rotor structures. It proposes an upgraded hybrid subdomain method (UHSDM) to enhance the efficiency and accuracy of thermal performance prediction. The UHSDM utilizes a two-part subdomain model, consisting of radial-angular (r-θ) and radial-axial (r-z) sub-models. In the first step, the r-θ sub-model employs an improved finite difference method (IFDM) integrated with a variable density method (VDM), which simplifies the modeling of intricate rotor structures while ensuring high accuracy. The remaining regions of the motor are modeled using the subdomain method (SDM), achieving high computational speed and precision. In the second step, the r-z sub-model applies SDM to analyze axial thermal characteristics, enhancing both calculation accuracy and efficiency. This r-z sub-model also accounts for the anisotropic thermal properties of the motor core by incorporating additional subdomains on both sides of the axial stacking zone, and improves accuracy further by iteratively calculating the resistance thermal characteristics. The results from the r-z sub-model are then embedded into the r-θ sub-model, facilitating rapid and accurate 3D steady thermal field analysis. Finally, a transient temperature rise model based on Neton's Cooling Law is established, significantly improving computational efficiency. The proposed method is validated through finite element method (FEM) and experimental tests. Results demonstrate that the memory usage is reduced by 98.3 % for steady-state calculations and by 99.7 % for transient calculations. These findings highlight the potential of UHSDM to serve as a highly efficient and accurate thermal analysis tool in the early stages of SynRM development, providing critical technical support for motor design and manufacturing.