Optimal Pole Number for Magnetic Noise Reduction in Variable-Speed Permanent Magnet Synchronous Machines With Fractional-Slot Concentrated Windings

Increasing the number of pole pairs leads to a lower electromagnetic yoke, and therefore, lower vibration and magnetic noise occur. In this paper, the influence of different numbers of pole pairs on the vibroacoustic design aspects of the machine is studied for the first time using a multislice subdomain method (MS-SDM) while considering the natural frequencies under a variable speed analysis. This paper aims to determine the optimal number of pole pairs for a low-speed, high-torque permanent magnet synchronous generator (PMSG) with double-layer, fractional-slot, nonoverlapping, concentrated windings (FSCWs) for wind turbine applications. First, all possible slots per pole per phase combinations, which offer the use of double-layer FSCW, are studied through a magnetomotive force (MMF) harmonic analysis. Second, the MS-SDM of the PMSG is studied to examine the vibroacoustic performance under a variable speed analysis. Finally, all affected major parameters are compared in order to find the optimal pole number of the PMSC. To verify the MS-SDM-based results, both 3-D finite element analysis and experimental investigations are employed.