Design, modelling and evaluation of a single-phase passively levitated self-bearing machine

Details

Supervisors

Dehez, Bruno ; Van Verdeghem, Joachim

Faculty

Ecole polytechnique de Louvain
Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil électromécanicien, à finalité spécialisée: énergie
Master [120] : ingénieur civil électromécanicien, à finalité spécialisée: mécatronique

Abstract

Magnetic levitation has become a top-tier alternative to classical guidance systems for applications which require high rotation speed, power density, long lifetime and high purity environment. Among the existing solutions, passively levitated self-bearing machines combine the bearing and drive functions within a single unit and rely on electrodynamic forces. This design overcomes the need for active control of at least one degree of freedom, as stated by Earnshaw's Theorem. They have been extensively investigated, particularly by Dr. Joachim Van Verdeghem and Pr. Bruno Dehez, to increase compactness, reliability, simplicity and to reduce the cost by removing the need for position sensors and electronics dedicated to the rotor suspension. However, all structures that have been studied so far are multi-phase powered machines. The increasing demand in single-phase machines is due to cost and space savings on power electronics circuitry and control electronics. Nevertheless, single-phase machines present two main challenges: a null-torque starting position issue and the pulsating nature of the magnetic field generated by the armature windings. In this context, this Master's thesis aims to develop a single-phase passively levitated self-bearing machine and evaluate its performances. Firstly, an introduction to magnetic levitation, and especially passively levitated self-bearing machines, is presented. Then, a review of the literature on single-phase permanent magnet synchronous machines, focusing on the self-starting capability and drive, is done. Thanks to it, a motor structure is proposed. Afterwards, a general electromechanical model describing the axial and spin dynamics is presented, also providing quasi-static analysis and parameters evaluation with Finite Element Analysis. Following on from this, an optimisation process based on the specifications of a fan is performed on the single-phase and three-phase equivalent machines, aiming at minimising Joule losses and maximising the axial electrodynamic stiffness. Results show that the single-phase machine outperforms the three-phase one for axial levitation. Finally, dynamic behaviour of the proposed solution for a fan application is investigated in a simulation environment. As a result, a further step in the field of passively levitated machines has been achieved through this Master's thesis, with the next one being the experimental investigations.