Null-Flux Radial Electrodynamic Bearing

The design of a new electrodynamic bearing is often based on the intuition and experience of its inventor. This paper proposes general guidelines for the design of null-flux electrodynamic centering bearings based on the interaction between a short circuited winding and permanent magnets. These design guidelines are deduced from an analytical analysis of the magnetic flux, and forces in a bearing with a radial magnetic field and an arbitrary winding. Considering that the electromotive force (EMF) in the winding should cancel when the rotor is centered and should appear as the rotor is off-centered, inducing a current in the winding and therefore a centering force on it, the design guideline is to have $q = p \pm 1$ where $q$ and $p$ are the number of pole pairs of the winding and permanent magnets, respectively. This guideline is validated by finite element simulations and some additional comments are made on the phase shift between the induced EMF and current that maximizes the centering force on the bearing.