Influences of Rotor Design on Air-Gap Field Modulation Effect in Spoke-Type Permanent Magnet Machine for Traction Applications

This paper investigates the influences of the rotor design on air-gap field modulation (AGFM) theory in spoketype permanent magnet (STPM) machines for traction applications. Due to flux-concentrated effect, STPM machines exhibit abundant air-gap field density harmonics and relatively high torque density. The Maxwell stress tensor (MST) method is adopted to identify and quantify the torque contributions of the various air-gap field harmonics in STPM machines. It reveals a fact that, except the main-order working harmonic is responsible for average torque generation, abundant modulated air-gap field harmonics contribute a non-negligible torque component. Besides, the influences of rotor open-slotting and PM arrangements on AGFM effects in STPM machines are evaluated and compared by finite element (FE) analysis, which identifies that the rotor open-slotting and PM arrangement designs show a more conspicuous effects on their torque components and AGFM effect.