Comparison of Two Finite-Permeability Subdomain Models for Surface-Mounted Permanent-Magnet Machines

Subdomain models have been widely used to quickly model the fields and the torque of surface-mounted permanent-magnet machines (SMPMMs). Nevertheless, when magnetic saturation occurs, those models which assume the permeability of the iron parts to be infinite tend to be inaccurate. More recently, two types of models have been developed that take the finite magnetic permeability of the machines into account, but a comparison of those models is still lacking. This article compares two finite-permeability subdomain models of SMPMMs. In the stator teeth and slots of the first model, boundary conditions are used in both radial and tangential directions. In the second model, the permeability change as a function of the angle in the stator slot and teeth is modeled using the Fourier series and the Cauchy product to solve Maxwell’s equations. In this study, the calculation of two different SMPMMs shows that both models can handle machines with low and high numbers of teeth. This study shows that the error of the first model has a low sensitivity to iron permeability and parameter changes, while the accuracy of the second model heavily depends on the iron permeability and parameters. For a higher iron permeability, the second model is less accurate. Both models can achieve high prediction accuracy at a faster calculation speed than the finite element model. The first model needs only a few harmonics to have high accuracy.