Detection Method of Static Eccentricity Using Third-order Harmonic Component of No-load Line-line Voltages on Three-group and Three-phase Permanent Magnet Synchronous Motors

Abstract

Since permanent magnet synchronous motors (PMSMs) have advantages of efficiency and energy density, they are now widely being used for many purposes. Based on such increased use, they require improved efficiency, lower acoustic noise, and fewer vibrations. However, such fabrication tolerances as eccentricity and roundness degradation generate a magnetic unbalance in the magnetic gap and cause low-order harmonics of electromagnetic force and cogging torque that create acoustic noise and vibrations. Since multi-three-phase PMSMs can individually control the phase current of each group, reducing the magnetic unbalance is possible in the magnetic gap. To control the phase current of each group, magnetic unbalance must be detected. In this study, we focus on static eccentricity as a representative fabrication tolerance and propose a method to detect it using the third-order harmonic component of no-load line-line voltages, which is easily measurable in practical production processes. We demonstrate our method that estimates the amount and direction of static eccentricity with a theoretical approach and confirm its detection by finite element analysis (FEA).