Investigation of Air-Gap Magnetic Field Harmonics and Generated Torque in Low-Speed High-Power Density Spoke-Type FSCW PMSMs

This article investigates the magnetic flux-concentrated effect in spoke-type (ST-PMSMs) to examine the abundant air-gap magnetic field harmonics and its effect on the torque generation mechanism. A low-speed high-power density ST-PMSM (400kW) is analyzed in this study. First, ST-PMSM’s air-gap magnetic field harmonics are analyzed applying finite element analysis (FEA), and then the traditional PMSM torque generation mechanism and the magnetic gearing effect’s contributions to the average generated torque are separately investigated using FEA and analytical methods. Also, the effects of PM slot-opening on air-gap magnetic flux density harmonics, produced torque, and cogging torque, along with torque ripples, are examined. This study provides a detailed analysis of the air-gap field modulation theory and the mechanism of torque generation in high-power density, low-speed ST-PMSMs.