Analytical Model for Predicting Rotor Eddy Current Loss of PMSMs Considering Magnetic Saturation and Diffusion Effect

Rotor eddy-current loss (RECL) in permanent-magnet synchronous machines (PMSMs) is strongly influenced by magnetic core saturation and diffusion effect (eddy-current reaction) in conducting parts. Many analytical models omit one of these, leading to errors at high load or under rich harmonics. This paper proposes a nonlinear hybrid analytical framework that couples a magnetostatic model (MSM) with a frequency-domain model (FDM) via an equivalent current-sheet (ECS) interface. The MSM computes the load-dependent magnetic field under nonlinear core permeability. Over one electrical period, the tangential field at the inner stator surface is sampled and decomposed by fast Fourier transform (FFT) into ECSs with explicit space-time orders. These ECSs are subsequently fed to the FDM, which solves the diffusion problem in conductive rotor regions, yielding per-harmonic RECL estimates. Compared with 2D finite-element analysis (FEA), the method maintains high accuracy across saturation levels and frequencies while requiring substantially lower computational effort. Experimental validation is carried out on a PMSM using a thermal-based method to infer rotor losses. The proposed model using a 3D correction shows good agreement with the test results. This model provides a transparent loss mechanism and is suitable for early-stage design studies where both saturation and diffusion are significant.