Analytical Asymmetric Air Gap Model for Active Magnetic Thrust Bearings of Mixed Materials Including Eddy Currents

The electrodynamics of magnetic thrust bearings are characterized by an above-average dependency on the used materials. Axially directed fields render laminated stators and rotors ineffective. High induced voltages inside the magnetic core evoke eddy currents and opposing fields, which are compensated by an additional magnetizing cur- rent causing a significant delay between the measurable coil current and the force-related magnetic flux. Although this effect, hampering control dynamics, can be reduced by the use of Soft Magnetic Composites for non-rotating parts, the thrust disk will be made of steel due to its superior tensile strength and saturation flux density. The analytical modeling of mixed-material magnetic thrust bearings reveals new challenges arising from asymmetries and low permeable magnetic core sections, which are both addressed in this paper.