Comparison of methods for computation of electromagnetic forces in the radial active magnetic bearing

Abstract

Rotor systems supported by the radial active magnetic bearings (AMBs) are considered in this paper. If dynamic characteristics of the rotor systems are examined numerically by the finite element method, it is necessary to determine forces in the bearings. Considering supporting by the AMBs, a shaft levitates in an air gap between the rotor and the stator part. Forces of magnetic levitation are caused by the electromagnetic field in the bearing. Electromagnetic forces in AMB are determined by two methods. One is based upon the principle of virtual work and the other one upon the Maxwell stress tensor. The forces computations are provided for three-dimensional and two-dimensional finite element models of the radial AMB. One-dimensional approximation of the magnetic circuit is provided as well. Rates of convergence, efficiencies and accuracies of the electromagnetic forces computations are evaluated from several points of view. These are compared also with used type of material model, methods of the forces calculation and size of AMB model meshes.