Effect of Eddy Current Loss Reduction by Segmentation of Magnets in Synchronous Motors: Difference Between Interior and Surface Types

In this study, we investigate the effect of eddy current loss reduction by segmented rare-earth magnets that are used in synchronous motors driven by inverters. First, the difference in the loss-reduction effect due to the rotor shape is estimated by the 3-D finite-element analysis that considers the carrier harmonics of the inverter. The results are compared to the theoretical solution. Next, a basic experiment using magnet specimens is carried out in order to confirm the calculated results. It is clarified that most of the magnet eddy current losses in the analyzed motors are caused by the carrier harmonics of the inverter and that the loss-reduction effect of the segmented magnet in the case of the interior permanent magnet motor decreases when it is compared to that of the surface permanent magnet motor. This phenomenon is mainly caused by the increase in the reaction field by the high-frequency harmonic eddy currents.