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

This article investigates the influences of the rotor design on air-gap field modulation (AGFM) theory in spoke-type 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 slot and PM arrangements on AGFM effects in STPM machines are evaluated and compared by finite element (FE) analysis, which identifies that the rotor slot and PM arrangement designs show a more conspicuous effects on their torque components and AGFM effect. Finally, the experimental results on a STPM prototype with rotor closed slot design are carried out to validate the theoretical and FE analyses.