Influence of axial variation of magnetic saturation on magnetic noise in induction machines with dual skewed rotor

Lightly saturated induction machines can improve material utilization. However, the magnetic saturation effect and its axial variation due to skew may lead to high noise levels. In order to improve the calculation accuracy of the magnetic noise, this study proposes an analytical model of the magnetic saturation, which newly introduces the permeance difference to quantify the axial variation. Using the harmonic analysis, the magnetic flux density and electromagnetic force are extracted via Fast Fourier Transform (FFT). The saturation magnetic flux density is nearly sinusoidal at different axial positions of the skewed rotor. The influence of skewed angle on saturation harmonics is discussed based on comparison between two kinds of skewed-rotor motors. Compared with the single-skewed rotor, the dual-skewed rotor with inverted structure hinders the rapid change of saturation harmonics. The validity of saturation model with axial variation is verified through the coupled simulations and noise experiments. The proportion of saturation harmonic is raised with significantly reduced slot harmonics by the dual-skewed rotor. Compared with the regular skewing design, the optimized skewed distance of 0.9 slot pitch achieves the lower noise level in dual-skewed rotor induction machine.