Design, modelling and prototyping of an electrodynamic thrust bearing

Magnetic bearings ensure contactless guiding of rotors through electromagnetic forces. In the absence of contact, there is no friction and thus mechanical wear, allowing to increase the lifetime of the bearings as well as largely diminishing the losses and the maintenance costs. Magnetic bearings are thus attractive and even more compelling in very high speed and vacuum applications, compared to conventional solutions such as ball or hydrostatic bearings. Electrodynamic magnetic bearings (EDBs) are based on forces arising from currents induced by the relative rotation between the permanent magnets and the conducting parts of the bearing. As these bearings do not need a control system, they are simpler, cheaper, more compact, more energy efficient and more reliable than active bearings. Radial EDBs, that ensure the radial guiding of rotors, have already focused much research efforts, allowing to highlight critical issues as their low stiffness, and, above all, their stability properties. By contrast, the interest for the electrodynamic thrust bearings (EDTBs) is much more newer. Contrary to the radial bearings, they present the primary advantage that they are stable in the usual spin speeds range without additional external damping. However, to date, almost all the research efforts are focused on the same thrust bearing topology. As a result, this master’s thesis aims at designing, modelling and prototyping a new topology of electrodynamic thrust bearing. First, a set of new bearing topologies that have not been explored yet is introduced. Following on from this, a global model allowing to predict the axial dynamics as well as the quasi-static behaviour of electrodynamic thrust bearings is derived. It consists in a set of eight parameters and four linear state-space equations, allowing for straightforward stability analyses. Compared to existing models, it requires neither assumptions on the rotor axial kinematics nor solving for the currents. It can be applied to study a wider range of bearings, including those with an arbitrary number of phases and ferromagnetic yokes. Various bearings can thus be objectively compared and it becomes easier to determine the most suitable solution for an application. In particular, this model could be exploited in a process of optimal design of an electrodynamic thrust bearing. The originality of the designing and modelling work has actively encouraged writing an article published in the journal "Transactions on Magnetics" of the IEEE. Third, the prototype of an eletrodynamic bearing and its test bench are developed. Through experimental measurements, the working principle of the new topology implemented in this prototype has been validated. The prototype being not fully functional, the model could not have been completely validated. However, the critical issues are highlighted and several ways to address them as well as to improve the test bench and the prototype performances are provided. As a result, a further step towards a fully passive magnetic suspension has been passed through this master’s thesis.