Design and Analysis of Interior Permanent Magnet Synchronous Machines for Electric Vehicles

The adoption of permanent magnet (PM) on rotating electrical machines represents now a fashionable design option in all elds as transportation, industrial processing, power plants, domestic appliances, actuators and so on. The corresponding power ratings of such machines ranges now from fractions of Watts to some million of Watts, as in a wind generator. Actually, among the electrical machines, the PM synchronous machine is the more deeply studied from academia and industry. In particular, the PM synchronous machine combines several advantages as high effciency, high power factor, high torque density, high overload capability, robustness, reduced maintenance, compactness and low weight. These advantages are becoming crucial for those non-industrial application, as the electric vehicles. High performance and compactness are often the winning characteristics of such machines as respect to the induction machines. Referring to the automotive eld, variable speed drives as PM synchronous machine are adopted to improve the overall performance of the vehicles. The design exibility due to the absence of rotor winding excitation and the variety of PM sizes and characteristics allow to achieve several features, e.g. fault-tolerance and fux-weakening capability. Thanks to these features the PM machine is a suitable candidate for traction requirements. However the recent trend is to select those congurations that allow to minimize the PM utilization. It is also due to the issues related to PM temperature derating, mechanical stress, and PM reliability. The PM synchronous reluctance machine or interior PM machine is, among the others, a promising candidate to satisfy the traction requirements. Thanks to its anisotropy rotor structure is able to provide torque not only due to the PM ux. In addition the adoption of fractional-slot winding, as respect to the standard integral-slot winding, is imperative to achieve some of the appealing features. In this field, several topics are under study by the international community of researchers. However, the aim of the doctoral work is to deepen some aspects concerning the design of these machines. It is worth noticing that the complexity of the rotor structure of these machine involves several drawbacks, such as torque oscillations, additional iron losses, vibrations, and so on. Therefore, some aspects have been analyzed by means of analytical procedures, nite element simulations and experiential measurements on prototypes. The variety of topic treated is directly due to the complexity of the design: a tradeo between advantages and drawbacks is usually necessary rather than a perfect minimization of a single aspect. Therefore, an overview of the design options is required in order to design a suitable machine. In the contest of the analysis of the interior permanent magnet machines, the objectives can be summarized as: 1) To evaluate how the rotor geometry aects the torque ripple, and thus the solutions allowing to minimize it. 2) To evaluate how the rotor geometry aects the eddy current iron losses in the stator teeth, and thus the solutions allowing to minimize it (in particular referring to the fux-weakening operating conditions). 3) To deeply investigate the torque mechanism and complex magnetic phenomena, in particular adopting fractional-slot winding. 4) To investigate a particular conguration of fault-tolerant machine, the dual three-phase machine provided of a suitable anisotropic rotor. To the knowledge of the author, the remarkable contribution of this thesis for future researchers in this eld are: 1) An analytical model of the anisotropic synchronous machine that can be simply adopted to evaluate optimal solutions allowing to satisfy selected objectives. It has been applied to the issues of torque ripple minimization and stator tooth eddy current minimization. The model has been veried experimentally comparing the measured and predicted stator tooth flux density. 2) An extended analysis of the dual three-phase machine provided of an interior permanent magnet rotor, supported by experimental verication. A simple design rule to select the appropriate number of slots and poles in order to achieve a six- phase machine is proposed.