Improved design and analysis of a radial magnetic bearing with paired-pole or alternating-pole configurations

The magnetic saturation of iron-core will reduce the maximum output force, influence the linear force characteristic and control precision of the magnetic bearing. To avoid these problems, a modified iron-core design rule for the alternating-pole magnetic bearing is proposed. The thickness of both stator yoke and rotor journal should be designed as 3/4 of the stator pole width for the alternating-pole configuration, which is successfully verified by 3D finite element method and experiments. Based on the improved design, the structural sizes, rotor iron losses, and force coupling characteristics of the paired-pole configuration and the alternating-pole configuration are compared. The results show that the size of the alternating-pole bearing is smaller than that of the paired-pole bearing; the alternating-pole configuration generates slightly higher rotor iron loss than the paired-pole configuration; the coupling strength of the alternating-pole configuration is stronger than that of the paired-pole configuration irrespective of whether the magnetic force coupling is caused by rotor displacements or control currents. The presented method and results can provide a reference for the design and selection of the active magnetic bearings.