Comparison of predicted and measured rotor losses in planar radial magnetic bearings

The rotor loss mechanisms associated with magnetic bearings have yet to be adequately characterized or quantified and thus pose a problem for the designer and user of magnetic bearings. Accurate calculations of losses associated with the operation of magnetic bearings is particularly important for high speed applications where the rotor losses are expected to be larger and for aerospace applications where low power consumption of components is critical. Rotor losses in magnetic bearings are due to both windage effects and iron losses. The iron losses are the result of three different mechanisms including the generation of eddy currents and the occurrence of both alternating and rational hysteresis effects in the magnetic material. While theoretical models for these losses exist for transformer and electric motor applications, they have not been adequately modified for magnetic bearings. This paper presents the results from a low speed experimental test rig and compares them to calculated values from a new modification of previous theory. Experimental data was taken over a range of 1.5 Hz (90 rpm) to 46.7 Hz (2800 rpm) for several bias currents, two different pole configurations, and for both a linear power amplifier and a switching power amplifier. With certain assumptions, agreement between measured and calculated power losses was within 10 percent for speed comparisons greater than 25 Hz and within 25 percent for the comparison at the 8.3 Hz speed. This body of work represents the foundation for upcoming extensive high speed tests on a larger scale.