Performance Trade-Off Design Based on Electromagnetic Noise Reduction of Fractional-Slot Permanent Magnet Synchronous Motors

The electromagnetic (EM) vibration noise of fractional-slot permanent magnet synchronous motors (PMSMs) has become increasingly prominent. This paper initiates by deriving the spatial and frequency characteristics of radial EM force density (REMFD) and presents a general expression linking the key parameters of the lowest nonzero order REMFD with the stator auxiliary slots. The effectiveness of the formulas and traceability analysis is verified using finite element analysis of prototypes with various pole-slot combinations and numbers of auxiliary slots. The addition of auxiliary slots typically reduces torque ripple, but also affects the average torque and the REMFD. Consequently, a comprehensive analysis and trade-off designs of the 10-pole 12-slot motors with a eccentric arc rotor and a three-arc-segment rotor, are conducted, covering the total harmonic distortion (THD) of the air-gap flux density, main REMFD harmonics, cogging torque, average torque, torque ripple and process. Finally, the EM noise are validated through multi-physics FEA models of multiple optimization schemes. Experimental tests on both the original cogging torque optimization prototype and newly proposed comprehensive process and performance optimization prototype substantiated the validity and precision of the previous analyses. Additionally, it is demonstrated that the lowest non-zero order REMFD significantly contributes to EM noise at even multiples of the frequency but lacks $6kf_{0}$ components. Tangential forces are identified as the primary contributors to $6kf_{0}$ EM noise.