A Solution for the Stabilization of Electrodynamic Bearings: Modeling and Experimental Validation

Abstract

Electrodynamic bearings are a kind of passive magnetic bearings based on eddy currents that develop between a rotating conductor and a static magnetic field. Relative to active magnetic bearings, their passive nature implies several advantages such as the reduced complexity, improved reliability, and smaller size and cost. Electrodynamic bearings have also drawbacks such as the difficulty in ensuring a stable levitation in a wide speed range. The most common solution to improve the stability is to add a nonrotating damping between the rotor and the stator. Although effective, this solution implies the installation of a dedicated magnet on the rotor. This increases the rotor weight and complexity and rises some concerns about the mechanical resistance. The aim of the present work is to experimentally validate the model of an electrodynamic bearing proposed by the same Authors in a previous paper and to investigate a new solution for the stabilization of electrodynamic bearings based on the introduction of compliant and dissipative elements between the statoric part of the bearing and the ground. The performances of the proposed solution are studied in the case of a simple Jeffcott rotor by means of root loci to investigate the stability of the system. The results show an improved stability relative to the test cases reported in the literature.

Unified modelling of passive homopolar and heteropolar electrodynamic bearings

“…It has been demonstrated both analytically [1,9,16,19] and experimentally [9] that the introduction of nonrotating damping directly between rotor and stator is a possible solution for this problem. Another possibility is the introduction of damping between two nonrotating parts, namely the stator of the electrodynamic bearing and the casing of the machine [20].…”

“…(20), it is possible to proceed with the analytical treatment of both homopolar and heteropolar electrodynamic bearing configurations in a unified way. Analysing one case or the other becomes a simple parametric problem.…”

“…Combining Eqs. (20) and (23), it is possible to obtain the final state equation describing the electromechanical interaction created by the electrodynamic bearing. Putting in evidence the mechanical inputs (q c , O) and outputs (F q ), the state and output equations become…”

“…The stability of a rotor running on EDBs has been studied using a Jeffcott rotor model. The present authors have studied various techniques for the stabilisation of rotors supported by EDBs [20]. An extensive collection of experimental results produced to validate the models was presented, and the sensitivity of the stability threshold to certain design parameters was investigated.…”

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

“…6a. At higher values of ω, the centering electrodynamic force increases and saturates above ω = 600 [rad/s], because the winding becomes inductive at high speed (Tonoli et al, 2011). The effect is significant, resulting in a reduction ofF to 40% of its value at zero spin speed.…”