Transfer Coefficients from Air-gap to Stator Bore Radius for Magnetic Force Wavenumbers - Application to Electrical Machines

Authors Raphaƫl Pile; Jean Le Besnerais; Guillaume Parent; Yvonnick Le Menach; Emile Devillers; Thomas Henneron; Jean-Philippe Lecointe
Status Pre-print
Keywords Maxwell Tensor, Magnetic pressure, Electrical machines, Magneto-mechanical, Vibration

Abstract

The Maxwell Stress Tensor (MST) method is commonly used to accurately compute the global efforts, such as electromagnetic torque ripple and unbalanced electromagnetic forces in electrical machines. The MST has been extended to the estimation of local magnetic surface force for the vibroacoustic design of electrical machines under electromagnetic excitation. In particular one common air-gap surface force method based on MST is to compute magnetic surface forces on a cylindrical shell in the air-gap. This air-gap surface force method is well-adapted to compute local magnetic surface forces from analytical air-gap field methods - such as methods based on permeance and magneto-motive force (PMMF) - because these air-gap field methods can only predict the magnetic field in the middle of the air-gap. However the air-gap surface force distribution depends on the radius of the cylindrical shell. This paper main contribution is to demonstrate an analytic transfer law of the air-gap surface force between the air-gap and the stator bore radius. It allows to quantify the error between the magnetic surface force calculated in the middle of the air-gap and the magnetic force computed on the stator teeth. This paper shows the strong influence of the transfer law on the computed tangential surface force distribution through numerical applications with induction and synchronous electrical machines. However the demonstrated transfer law keeps the global electromagnetic torque constant for any radius. At last the surface force density at stator bore radius is more accurately estimated when applying the new transfer law on the air-gap surface force.

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