Investigation of the impact of magnet segmentation on high frequency eddy current losses in an interior permanent magnet motor

Interior permanent magnet motor (IPM) is the most common candidate in electric vehicle (EV) application. Although smaller in scale, magnet eddy current losses play a major role in rotor losses, which are usually difficult to remove unlike in the case of stator losses. A common solution for reducing magnet losses is to segment the magnets both axially and circumferentially, such that the total magnet loss becomes smaller. Various 2D and 3D analytical models have been developed to describe the magnet eddy current losses under the excitation due to slot harmonics and inverter harmonics. Both analytical and finite element analysis (FEA) confirm the effectiveness of magnet segmentation in loss reduction below a certain frequency, while the segmentation increases eddy current losses beyond that frequency. The cross-over frequencies between different segmentation levels depend on magnet material properties, dimensions, magnetic circuit and is useful in determining the overall benefits of segmentation. This paper first validates the predicted FEA model crossover frequency using calorimetric method. Two rotors are manufactured to demonstrate the differences in magnet losses due to segmentation. Their results will be analyzed and compared by experimental and FEA methods to validate the overall effects of segmentation.