Analysis and Suppression of Core and PM Losses in Fractional-Slot Permanent Magnet Vernier Machine and PMSM for in-Wheel Application

In the article, the comparative study of core loss and permanent magnet (PM) loss in fractional-slot permanent magnet vernier machines (PMVMs) and permanent magnet synchronous machines (PMSMs) for in-wheel drive are investigated. Firstly, the definitions of “Family” and “Group” for armature magnomotive force harmonics in fractional-slot PM machines are proposed, and the relationship between PMVM and PMSM is illustrated, where the generalized PMSM concept is proposed. Secondly, the core and and PM losses are calculated and compared by the theoretical and finite-element analysis (FEA) methods. The contribution of each harmonic on the core and PM losses is extracted, where the sub-harmonic and slot-harmonic that not contributed to the torque are mostly responsible for core and PM losses. Thirdly, the influence of stator slot opening, flux barriers, and PWM control on the core loss, PM loss, and torque are all investigated. The losses of PMVM and PMSM under various conditions is calculated and exhibited, and the PM loss is much severer in PMVM. Finally, two prototypes of PMVM and PMSM are manufactured and tested, and the total losses and efficiencies are measured, where the experiments agree well with the FEA and theoretical analysis.