Transient modeling of coupled magnetoelastic problems in electric machines

This paper investigates some aspects on noise and vibrations of electrical machinery based upon the coupling between the magnetic field and the mechanical deformation in the stator. This coupling is typically considered by using reluctance forces. Since the deformations occurring are small compared to the machine's dimensions, there is no feedback to the magnetic system in numerical models. However, stator deformations are caused not only by reluctance forces, but also by magnetostriction effect of the stator iron. Magnetostriction is One of the main causes of noise in electromagnetic systems particularly when the flux density is above 1.5 Teslas. Here, the authors develop numerical models that incorporate magnetostriction effects and all other possible electromechanical forces and related material interactions. Magnetostriction presents a problem at all levels of frequencies. At frequencies, particularly 2E, magnetostrictive forces are undesirable and can be large as well as generate acoustic noise, which can impede the system's performance. The magnetostrictive deformations can be calculated based upon the magnetic field. If the magnetostrictive deformations are slightly higher than the magnitude of the deformations caused by the reluctance forces, there will be a need for feedback to the magnetic system. In order to account for this effect, the magnetostriction characteristic of iron 1(H) is needed. The dependency of permeability on mechanical stress must be accounted for and be built into a strong coupling scheme. Implementation results on a 2-hp, permanent magnet motor indicate that magnetostrictive forces are significant and must be accounted for in the electromagnetic system's design stage.