In these days Permanent magnet synchronous motor (PMSM) with multi pole has been developed as the driving motor for hybrid electric vehicle (HEV). It should be designed to have sinusoidal back emf and low cogging torque for low torque ripple [1], and to have high winding fill factor and air-gap flux for high power density. Some design papers related to shape optimization are presented continuously [2]. However, the shape optimization of PM for sinusoidal air-gap flux and minimal volume usually gives negative effect on partial demagnetization of PM. In this paper, we designed the outer rotor PMSM for high power vehicle like bus, and optimized it towards pole arc ratio and pole shape. We simulated partial demagnetization distribution of PM at fault current condition and high temperature. We analyze the characteristic variation in terms of back emf, cogging torque, load angle distribution and torque ripple after partial demagnetization. Finally, the robust model of PMSM for HEV with high power density, low cogging torque and low torque ripple is presented.
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