Dynamical electromechanical model of magnetic bearings subject to eddy currents

Eddy currents forces may play a significant role in magnetic bearings. They generate losses and induce forces, which may lead to a malfunction of the magnetic bearing. But eddy currents in magnetic bearings may also be used positively, to generate desired forces, like in electrodynamic bearings. This thesis proposes a phenomenological electromechanical model aimed to explain the physical consequences of the forces due to eddy currents in any type of rotating magnetic bearing. The developed model is able to predict, analyze or simulate the dynamical behavior of these magnetic bearings, or of more complex systems integrating these bearings. The model integrates the mechanical aspects linked to the rotor dynamics and the electrical aspects linked to the electromagnetic nature of the forces. By a rigorous approach, the electromagnetic forces are modeled by equivalent mechanical components, like springs and dampers. The impact of resistive and inductive effects of the conductors where the eddy currents take place are considered. The presence of the skin effect in the conductors is taken into account via phenomenological models presented in the work. It is explained how the parameters characterizing the proposed model can be identified on the basis of simple quasi-static finite elements simulations or experiments. This identification is applied to different study cases and shows that the forces predicted by the model fit well with those obtained from finite element simulations. Finally, the model is useful to better understand the influence of the model parameters and physical parameters on the bearing stability and on the stiffness induced by the eddy current forces. It also provides some guidelines for the design of magnetic bearings. This work shows the model ability to simulate the dynamical behavior of more complex systems such as a magnetic bearing with damping between the stator and the fixed frame.(FSA 3) -- UCL, 201

Comparison between models predicting the evolution of the electrical impedance with the frequency

This paper explains and compares different models describing the evolution of the impedance of complex shaped conductors with low and with high frequencies. Indeed, at low frequencies, the evolution of the impedance of conductors with the frequency is negligible whereas at high frequencies, it is quite significant and generally well-known. Parameterized models, based on the diffusion equation or on phenomenological approaches, are applied on complex shaped conductors, with a variable or not section. The parameters are found by identification with finite elements models. It is shown that simple phenomenological approaches gives accurate models with few parameters

Parameterized electromechanical model for magnetic bearings with induced currents

The purpose of this paper is to present a parameterized electromechanical model taking into account both the electromagnetic nature of the forces acting inside a magnetic bearing and the general rotating machinery aspects, as well as their interactions. This model specifically includes the effect of induced currents. These induced currents in the bearings are submitted to inductive and resistive effects, as well as skin effect, and the influence of these effects is considered. It is shown that the stability of a bearing may be analysed, based on this model. The parameters of the model are identified from experimental results for an existing semi-passive magnetic bearing, and it is shown that the forces predicted by the model are close to experimental measurements

Dynamical Electromechanical Model for Magnetic Bearings Subject to Eddy Currents

Eddy-current forces may play a significant role in magnetic bearings. They generate losses and unpredicted forces, which may lead to a malfunction of the bearing. But eddy currents in magnetic bearings may also be used positively, to generate desired forces, like in electrodynamic bearings. This paper presents a model able to predict, analyze, or simulate the dynamical behavior of any rotating magnetic bearing in which classical eddy-current forces arise. This model integrates the mechanical aspects linked to the rotor dynamics and the electrical aspects linked to the electromagnetic nature of the forces. This papers explains how the parameters of the model can be identified on the basis of quasi-static finite element method (FEM) or experiments. The validation of the model is done by comparison with FEM results on an electrodynamic radial bearing

Optimisation d'une génératrice électrique à aimants permanents intégrée au moteur d'un avion

L’Université catholique de Louvain pratique depuis plusieurs années une pédagogie active dans les premières années de formation des ingénieurs civils. Forts de cette expérience, certains enseignants tentent d’appliquer ce type de pédagogie à un stade plus avancé de la formation. Dans ce contexte, les enseignants des cours de convertisseurs électromécaniques ont proposé, dans le cadre d’un cours plus avancé dans ce domaine, un projet portant sur l’optimisation d’une génératrice à aimants permanents pour une application en aéronautique. Le présent article présente ce projet, la manière dont il a été organisé ainsi que les principaux résultats techniques et pédagogiques qui ont été atteints

Exact Expression of Corner Reluctances in a Magnetic Circuit of Rectangular Section

We provide an exact, simple and explicit analytical expression of corner reluctances for magnetic circuits of rectangular section. Obtained values are appreciably different from those obtained by making usual approximations. Besides, due to a decomposition of the solution in two terms which can be interpreted as an lengthening of the adjacent rectilinear legs, our expressions are very easy to use in order to compute reluctance of magnetic circuits, and thus also inductances and forces in magnetic devices, as well as magnetic losses. The present study applies also to electric and thermal resistances calculation. Although obtained expressions are rigorously exact only in the case of linear materials, this study allows also for flux and magnetic losses simplified calculation in the case of saturable materials. The accuracy of this simplified calculation is examined on a test structure by comparison with finite elements computation results

Computation of the forces acting on a Magnetic Bearing due to Eddy Currents

Forces due to induced current can play a significant role in the behavior of electromagnetic devices. In some case these forces produce a useful effect, like in induction motors, whereas in others they involve non-desired phenomena, like instabilities in magnetic bearings. This paper set out to compute theses forces, first in a simple case, and second on a semi-passive magnetic bearing. Through these two examples, we show the influence of the skin effect on the magnetic field distribution in a conducting part and on the way of modeling these elements by replacing volume currents by equivalent surface currents density in COMSOL software. Finally, modeling results are compared to experimental measurements

Experimental Investigations on Passively Levitated Electrodynamic Thrust Self-Bearing Motors

Recent researches have revealed that electrodynamic thrust bearings can gather, within one single armature winding, both the passive axial restoring force and the driving torque, thus yielding a new passively levitated electrodynamic thrust self-bearing (EDTSB) motor. Although their operation principle as well as the model describing their axial and spin dynamics have already been corroborated, experimental results still lack to properly characterise these machines. In this context, this paper is devoted to an in-depth experimental investigation of an EDTSB motor. Measurements performed on the prototype endorse the assumptions regarding the linearisation of the flux linkages as well as the negligible impact of the magnetic field harmonic content. They also disclose that suspension currents are induced even when the rotor is centred. Finally, the thrust bearing and self-bearing motor behaviours are studied in quasistatic and dynamic conditions, validating the dynamical model