Loss Investigation of Interior Permanent-Magnet Motors Considering Carrier Harmonics and Magnet Eddy Currents

In this paper, we investigate losses of interior permanent-magnet motors driven by pulsewidth-modulated inverters using 3-D finite-element analysis, which can estimate the eddy-current loss in the permanent magnet accurately. The calculated losses are compared with the measured results and the theoretical solution to verify the validity of the analysis. The variation of the magnet eddy-current loss due to the division of the magnet is also investigated. It is clarified that the eddy-current loss in the permanent magnet is mainly produced by the carrier harmonics of the inverter and that the axial length of the divided magnet should be smaller than the skin depth of the eddy currents produced by the major harmonics for the loss reduction.