Anisotropic model of nonlinear permanent magnets in finite element method software

Rare earth elements are associated with many challenges, and therefore, rare earth free options are being investigated as an alternative. The further improvement of the electrical machines with rare earth free permanent magnets requires an accurate and efficient finite element method (FEM) model to predict and overcome the issues related to a low magnetic flux density or partial demagnetization of permanent magnets. The main challenges of the permanent magnet model development are related to the nonlinearity of the hysteresis loop in the operating region and permanent magnet anisotropy. The model presented in this paper is a dynamic model of anisotropic nonlinear permanent magnet (PM) developed in COMSOL Multiphysics 6.2 software. The model can be used for modelling magnetic materials with a hysteresis loop. Measurement results of Alnico 8 LNGT40 nonlinear permanent magnet were used in this model. The model includes all four quadrants of hysteresis loops, recoil lines, and knee points of preferred or easy (EA) and transverse or hard (HA) magnetization directions. It allows correct modelling of not only generators but also motors and memory machines. The flowcharts of the permanent magnet modelling logic were presented for both directions. Partial demagnetization in the preferred (EA) direction and partial magnetization in the transverse (HA) direction can be observed in the simulation results after the short circuit. Partial remagnetization of the magnet in the preferred (EA) direction and partial demagnetization in the transverse (HA) can be observed after applying a current with the same amplitude but in the opposite direction. The top part of the magnet was mostly affected by the magnetic field of the stator. Simulation results differ from the previous version of the magnet model. The new version of the model has a higher accuracy and shows higher demagnetization in the preferred (EA) direction than the previous version.