Effect of circumferential segmentation of permanent magnets on rotor loss in fractional-slot concentrated-winding machines

Permanent-magnet (PM) segmentation is a plain and valid way for eddy current (EC) loss reduction in fractional-slot concentrated-winding (FSCW) machines and it has no passive effect on the machine itself. In this study, compared with PM asymmetrical segmentation, the authors prove that symmetrical segmentation adopted by most scholars, in general, is the optimal choice by using both analytical method (AM) and time-stepped transient finite-element method (FEM), when the skin effect is neglected. Furthermore, two surface-mounted PM machines with FSCW are proposed to investigate the effect of PM symmetrical segmentation on EC loss in rotor PMs. The actual effect of PM segmentation is to cut off the EC path and increase the resistance value in return circuit, thus decreasing EC density in PMs. In addition, some theoretical expressions evaluating the EC loss with consideration of magnet segmentation effect are derived step by step. Finally, Maxwell FEM software is used to verify the theoretical analysis, showing that the proposed AM is able to accurately predict the EC loss with different segmented numbers.