Improved analytical calculation of axial AMB by means of fringing estimation

Active magnetic bearing (AMB) systems are designed to develop the force to compensate external forces acting on shaft alongside the support of the rotor system. The accurate analytical approach of attractive force calculation is demanded to avoid time-consuming finite element method (FEM) optimisation. According to the general theory of magnetic circuits, the model of iron is accurately modelled up to its saturation point. Lower accuracy is obtained for the air-gap permeance model. Fringing around the air-gap is usually neglected in the theory of linear magnetic circuit. In this paper fringing flux contribution to the air-gap permanence is studied. The fringing flux is modelled in FEM software for various geometry configurations focusing on the general solution without geometry dependencies. A new set of interlinking variables is presented in this paper. Tradition shape of thrust AMB is examined but the approach can be applied on similar geometries as well as to geometries beyond the scope of this paper. The result of the paper is a set of equations used to model fringing around air-gap.