Harmonic Loss Calculation in Rotor Surface Permanent Magnets—New Analytic Approach

The paper introduces an analytic permanent-magnet eddy-current loss calculation method for rotor surface permanent magnets. The problem has been studied widely in the literature, yet many of the suggested methods are difficult to use. A straightforward analytic solution is needed to speed up the motor preliminary design as present day computational capabilities are not fast enough to be used for 3-D time-stepped finite element analysis (FEA) of permanent-magnet eddy-current losses in every day design problems. An analytic approach is suggested to calculate different-harmonics-caused eddy-current losses. The results are compared both with 3-D FEA and measurement results. A comparison between the theoretical and experimental results is reported for an axial-flux two-stator single-rotor machine with no rotor yoke. The method has, however, been used in evaluating permanent-magnet losses also in machines with narrow slot openings where the flux density dips do not penetrate through the whole magnet or in machines having a laminated rotor yoke.