Investigation of Eccentric PM on High-Frequency Vibration in FSCW PM Machine Considering Force Modulation Effect

This study investigates the negative influence of an eccentric permanent-magnet (PM) design on high-frequency electromagnetic vibration in fractional-slot concentrated-winding (FSCW) PM machines. First, an analytical expression for the sideband current harmonics was derived using the double Fourier series expansion method. Then, the characteristics of the flux-density harmonics are studied from the perspective of the space-time distribution and initial phase relationship. The influence of the eccentric PM design on high-frequency electromagnetic and concentrated forces was studied based on the electromagnetic force modulation effect. Consequently, an eccentric PM design is not conducive to reducing the $2p^{\text{th}}$ -order high-frequency electromagnetic forces. Finally, two FSCW PM machines with conventional and eccentric PM designs are manufactured and tested to verify the theoretical analysis. The results show that the eccentric PM design worsens high-frequency vibrations.