Comparison of Load Capacity and Inductance for Common Active Magnetic Bearings Designs

Active magnetic bearings have become more popular as an alternative to fluid-film or rolling element bearings in rotating machinery. They have also become a method for force excitation for rotordynamic experiments, including system identification experiments. The current work considers alternate active magnetic bearing designs for a fluid film bearing test rig. The three designs considered include a conventional 8-pole design with equal widths, a 12-pole bearing with e-core quadrants, and a 16-pole alternate with two exterior auxiliary poles and two interior main poles per quadrant. Several previous studies have considered equal pole widths in optimizing magnetic bearing stator geometry. While not an optimization study, this analysis presents a comparison of popular AMB geometries commonly used in industrial applications. The load capacity, magnetic field energy, and inductance were compared. The 16-pole bearing was shown to have the highest load capacity of the three designs. The inductive load also increased with increasing number of poles. The 12 and 16 pole designs, with reduced auxiliary pole width, also exhibited better containment of the magnetic flux within each active magnetic bearing quadrant, which simplifies the control problem. The results are of use for AMB designers and provide guidance for future stator optimization studies.