Analysis and Reduction of Magnet Eddy Current Losses in Surface Mounted Permanent Magnet Machines

Due to its high energy density, NdFeB permanent-magnets (PM) are very often used in the rotors of radial-flux PM machines. As the NdFeB-magnets are good electric conductive, electric currents are induced in the magnets when they are exposed to a varying magnetic field. This varying magnetic field has two causes: variation of the air-gap reluctance due to the effect of stator slots, and armature reaction due to the stator currents when the machine is supplied with invertor. The rise of temperature due to eddy current loss in the PM leads to serious deterioration of the PM, especially in high speed operation. This paper describes an original analysis of the eddy current loss in the PM of a surface-mounted PM synchronous machines (PMSM) for electric vehicles, and also harmonic analysis of eddy current loss is carried out to calculate PM eddy current loss due to carrier harmonics of the PWM inverter. And then segmentation of magnets was proposed to reduce magnet eddy current loss, and finally a new structure based on segmentation was proposed to optimize the eddy current loss.