Comparison of rotor eddy current losses in permanent magnet motor and generator

In this paper, the rotor eddy current loss of surface-mounted permanent magnet (SPM) machine is predicted using a simplified analytical model, which accounts for curvature, time and space mmf harmonics, and is applicable to calculate the eddy current loss in both permanent magnets and sleeve, but neglects the influence of stator slotting and eddy current redistribution effect. The analytical method is employed to research two identical prototype SPM machines when they are back-to-back connected mechanically and used as a motor and a generator, respectively. Finite element analysis (FEA) is employed to validate the model. Thermal fields are analyzed using analytical lumped-circuit method based on the obtained eddy current loss and the predicted temperature rises of machines are compared with the measured results. Good agreement between analysis and measurement is achieved. The analysis in this paper reveals that the time harmonics significantly influence the eddy current loss and temperature rises in magnets and sleeve of motor, which causes large difference in temperature rises of the motor and generator.