Air-gap Flux Density Distortion and Iron Losses in Anisotropic Synchronous Motors

The anisotropy of the rotor of the synchronous reluctance motor (sometimes assisted by permanent magnets) causes a high content of flux density harmonics. These harmonics cause flux density fluctuations in the stator iron teeth, and thus iron losses. These losses increase with the motor speed and are independent of the main flux, that is, they exist even during the flux-weakening operations. An analytical model, validated by finite-element analysis, shows the dependence of flux density harmonic content on the rotor geometry. Therefore, this model is adopted to individuate the flux-barrier geometry so as to minimize the stator iron losses.