Null-Flux Radial Electrodynamic Bearing

Abstract

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 ± 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.

Linear State-Space Representation of Heteropolar Electrodynamic Bearings With Radial Magnetic Field

“…As stated in section I, the conductors of null-flux heteropolar EDBs are short-circuited windings. Following the conclusions of [4], the windings considered in this paper have q = p±1 pole pairs, with p the number of pole pairs of the PMs. The q = p + 1 condition should be preferred when the PMs are internal and vice-versa.…”

“…The conductor of the homopolar EDBs can be bulk or wound. However, the conductor of heteropolar EDBs should be wound to be null-flux [4]. This paper focuses on null-flux heteropolar EDBs.…”

“…This paper focuses on null-flux heteropolar EDBs. The design guidelines for such bearings are given in [4].…”

“…1) the number of pole pairs of the PMs p is even and the number of winding pole pairs is q = 1 while a wider range of null-flux EDBs could be considered by following the design guidelines from [4] which are less restrictive; 2) the number of winding phases is equal to 2 while it was shown that increasing the number of phases has a positive impact on the bearing stiffness [15] and reduces the parasitic eddy currents in the conductors [16]; 3) the PMs are attached to the stator which should be the case for homopolar EDBs but is not necessary for heteropolar EDBs; 4) the rotor off-centering does not impact the PMs magnetic field distribution, which prevents the use of ferromagnetic materials attached to the windings which could increase the bearing performance.…”

Evaluation of the electrodynamic forces in high-speed permanent magnet machines with rotor eccentricity

“…have a negative effect since their interaction yields the UMP (Chiba et al, 2005). On the other hand, the two pole pairs harmonic can be linked by a winding that also has two pole pairs, thereby inducing balancing currents which tend to restore the centered position of the rotor (Dumont et al, 2014). Similarly, in the case of a one pole pair PM motor, the parallel connection of each motor phase may allow for the existence of conducting paths with two pole pairs and passive centering forces.…”