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An interior permanent magnet (IPM) machine with ∇ + U shape rotor topology is proposed and its electromagnetic performance with typical V shape and ∇ shape for electric vehicle (EV) applications are compared. The pole-arc to pole-pitch ratios are optimized to maximize the fundamental air-gap flux density and minimize its total harmonic distortion (THD) of all the three IPM machines by the finite element (FE) method. It can be obtained that ∇ + U shape rotor topology has the lowest THD of the air-gap flux density. The back electromotive force and its THD orders, cogging torque, torque density, torque ripple, d- and q-axis inductances, saliency ratio, and iron loss of three machines are analyzed and compared. It is demonstrated that the ∇ shape IPM machines have the highest average torque, and the torque ripples of the V shape and ∇ shape machines are almost the same. The ∇ + U shape IPM machine has the lowest torque ripple and iron loss with only a little reduction of average torque. Finally, the ∇ + U shape IPM machine is prototyped to verify the results of the FE analysis.
Hu et al. (Tue,) studied this question.