Iron Losses Reduction in Synchronous Motors with Anisotropic Rotor

In a synchronous reluctance motor (including the PM assisted and interior PM configurations), the anisotropy of the rotor causes high contents of flux density harmonics. These harmonics yield flux density fluctuation in the stator, especially in the teeth, and thus additional 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. In fact iron losses increase even under flux-weakening operations, due to that the speed increase is higher than the flux density decrease. An analytical model is developed, showing the dependence of flux density harmonic contents on the rotor geometry. Therefore, the results of this model allow to individuate the flux-barrier geometry so as to minimize the stator iron losses.