Investigation of Torque Improvement of Modular Stator Surface-Mounted Permanent Magnet Machines With Flux Gaps

Novel modular stator surface-mounted permanent magnet (SSPM) machines are investigated, which feature E-type stator modular units with surface-mounted permanent magnets (PMs) on central teeth, as well as the tangential flux gaps (FGs) sandwiched by the stator units. The symmetrical sinusoidal phase flux-linkage can be obtained in the machines with specific slot/pole number combinations, albeit with the unipolar coil flux-linkages. Based on the theoretical and finite element analyses, the influences of FGs on electromagnetic performances of 12-slot/11-pole and 12-slot/13-pole modular SSPM machines, including winding factors, back-EMFs, cogging torques, on-load torques, inductances, and losses, are comprehensively evaluated. It is revealed that the appropriate stator FGs not only enhance the manufacturability and phase independences of the two machines, but also improve the back-EMF and average torque by 21.6% and 7.1% respectively in the 12-slot/13-pole case. Moreover, the distinct working harmonics for torque generations in the two modular SSPM machines are identified. Finally, a 12-slot/13-pole modular SSPM prototype machine is fabricated and tested.