Modèles analytiques électromagnétiques bi et tri dimensionnels en vue de l'optimisation des actionneurs disques : étude théorique et expérimentale des pertes magnétiques dans les matériaux granulaires

The axial flux actuators are potentially an attractive solution for demanding automotive applications such as hybrid vehicles. However, the design of these actuators for such applications encounters some difficulties: the specifications in terms of torque and speed are complex, conflicting criteria to minimize, such as mass and losses. One solution is to use systematic optimization algorithms. To use these algorithms, flexible models are needed, both accurate and fast. This thesis focuses on developing analytical models based on the formal resolution of Maxwell's equations, which allows a good compromise between computation time and accuracy, if some simplifying assumptions such as linearity of magnetic materials are accepted. The first part concerns the electromagnetic two-dimensional models, developing the axial flux structure at its mean radius. For these models, particular attention was paid to modeling of the salience as well as the rotor stator. It is especially shown that the approximation of the Carter coefficient can effectively determine the average torque of the machine with precision. However, if we want to determine the inductions into the iron parts so as to calculate the magnetic losses, a model of stator slotting is required. In a second step, three-dimensional analytical models were developed to calculate the no-load flux in the actuator, taking into account the edges effects and the curvature effect. It is shown that taking into account the edges effects is important in the modeling of the actuators. A study on the curvature effect of the machine shows that the development of the actuator to the mean radius, provided 3D models are used, is not so wrong. A second point concerns the study of magnetic losses in isotropic composite materials, composed of particles of pure iron insulated from each other, put in a binder, and then compressed. Indeed, these materials are very promising in electric machine design, allowing three-dimensional magnetic flux paths and a thermal isotropy, despite their relatively low magnetic permeability. Two materials of the Swedish company Hoganas (one dedicated to electric machines, the other to power electronics, with grains of smaller size) were characterized in terms of magnetic losses in a wide frequency range . A classical loss model was formulated, based on microscopic observations of samples of materials. With this estimate of the classical losses component, the procedure of loss separation can be carried out. The calculation of the excess loss component revealed some specific magnetization mechanisms in these granular materials, in which grains are independent of each other. Unlike laminated materials that have a number of active magnetic objects relatively low on their section at zero field, (eddy currents allow homogenization of the magnetic behavior when the frequency increases), the granular materials appear to exhibit a totally different behavior, with at least one active magnetic object at zero excess field. This changes the dependence of excess losses as a function of frequency (the excess losses are then proportional to the frequency f, while we remember that they are proportional to f ^ 0.5 in most laminated materials). Finally a pre-optimization has been carried out, with just two-dimensional electromagnetic models, and conventional laminated materials. Various studies, as the control law, or the residual induction of the magnets, have been done. This work finishes with an analysis of the influence of a power constraint on the geometry of the electrical machine.