A rotor design method of external rotor surface permanent magnet machine for in-wheel application

The rotor shape of external rotor surface permanent-magnet machine (SPM) substantially affects the induced voltage, the iron losses and the torque ripple, which are importance machine performances. This paper proposes a rotor design method to optimize these motor performances, by using rectangular magnet without complex shape. According to the rectangular magnet, a non-uniform air gap is obtained, which affects the air gap flux density harmonic spectrum. To validate the proposed method, the performances of an external rotor SPM optimized by the new rotor design method have been compared with an optimized motor using surface radial magnet, by finite element analysis (FEA) software.