M. Gabsi

Homopolar and bipolar hybrid excitation synchronous machines

This paper presents a description and operating principle of different hybrid excitation synchronous machines. Four prototype machines of different power rating (3 kW and 15 kW) have been studied. These machines combine two flux sources: permanent magnets, located in the rotor, and field coils, located in the stator. Thanks to this particular configuration the air gap flux can be easily controlled, without any risk of magnets demagnetisation. Tests are performed on the prototype machines to asses their flux weakening capability. Three of prototype machines are modular and can be assembled to have a homopolar or a bipolar configuration. These two configurations are compared using experimental measurements. The advantages and drawbacks of each configuration are described

3-D Formal Resolution of Maxwell Equations for the Computation of the No-Load Flux in an Axial Flux Permanent-Magnet Synchronous Machine

This paper presents a 3-D analytical model of an axial flux permanent-magnet synchronous machine, based on formal resolution of Maxwell equations. This method requires much less computation time than conventional 3-D finite elements, and is therefore suitable for optimization purposes. In a first part, the mathematical procedure used to compute the machine no-load flux is described in detail. This method is 3-D, and then takes into account the radial edge effects of the machine, as well as the curvature effects by a resolution in cylindrical coordinates. Moreover, the originality of this method lies in the fact that it is totally analytical. The obtained results are verified using 3-D finite elements, and compared with simpler analytical models of axial flux machines, taken from the literature. This work puts in evidence the advantages of the proposed model. In particular, it is shown that the radial edge effects are important for a correct estimation of the no-load flux. On the contrary, the curvature effects are a second-order phenomenon.

Piezoelectric Actuator Design and Placement for Switched Reluctance Motors Active Damping

This paper describes the design and the placement of piezoelectric actuators on switched reluctance motors by means of a genetic algorithm (nondominated sorting genetic algorithm II) for the purpose of reducing stator vibrations. Two distinct approaches are presented: one energy-related and the other based on a minimization of the resultant displacement. These methods lead to design and placement strategy for the piezoelectric actuators. A number of optimal actuators obtained using these kinds of approaches is also compared with mechanical finite-element simulations. At last, a solution is achieved in order to validate optimal placement using positive position feedback active filtering.

Measured Performances of a New Hybrid Excitation Synchronous Machine

Abstract PM synchronous machines may operate over broad speed ranges at constant power rhanks to the introduction of control laws, that enables flux weakening. Generally, this control is accomplished by applying a strong demagnetizing current in the d-axis: yet, such an approach engenders the risk of an irreversible magnet demagnetization and a reduction in machine performance, In this paper will be presented an original layout for the hybrid-excitation synchronous machine: an excitation by both magnets and coils. This solution allows for effective flux weakening while reducing the risk of magnet demagnetization. Attention is focused on the study of maximum power limits of these machines.

Three-Dimensional Analytical Modeling of a Permanent-Magnet Linear Actuator With Circular Magnets

We describe a 3-D analytical model based on formal resolution of Maxwells equations of a permanent-magnet linear actuator, with circular-shaped magnets. We present all details of the 3-D analytical calculation for the no-load flux and then compare results obtained by this model to those obtained by 3-D finite-element analysis. The comparisons show a good agreement between the two models and so validate our analytical model. Unlike 3-D finite-element analyses, which are time consuming, the analytical models that we present in this paper are suitable for an optimization process of such a structure.

An Analytical Model for the Computation of No-Load Eddy-Current Losses in the Rotor of a Permanent Magnet Synchronous Machine

This paper describes an analytical model for computing the rotor eddy-current losses in the case of permanent magnet synchronous machines, based on a formal resolution of Maxwells equations. We focus on the computation of the eddy currents in the machine magnets, in which the diffusion equation is analytically solved, using an accurate electromagnetic model of the stator slotting. The model originality lies in its capacity of taking into account both the diffusion phenomenon and the magnets finite length over the pole pitch, imposing that the total current over the magnets surface should be zero at each instant. This important problem is studied by solving a Fredholm integral equation. A validation using a 2-D time-stepping finite-element model is also performed, and the obtained losses are shown to be in good agreement with those given by the analytical method, for a shorter computation time.

3D magnetic equivalent circuit model for homopolar hybrid excitation synchronous machines

A 3D magnetic equivalent circuit model is developed to predict the total excitation flux of an homopolar hybrid excitation synchronous machines. It is established using the main flux path and a part of the magnets leakage fluxs path. This model takes into account the lamination effect and ferromagnetic parts reluctances. Results from the model are compared with finite-element predictions and the obtained results are similar.

Extended frequency analysis of magnetic losses under rotating induction in soft magnetic composites

We present novel results on magnetic losses in soft magnetic composites (SMCs) excited with rotating field. Soft composites are very promising in electrical engineering applications, where new topologies of electrical machines with two- and three-dimensional induction loci are increasingly found. An experimental characterization of industrial SMC products has, therefore, been carried out, up to the kilohertz range, under alternating and circular flux loci, making use of a specifically designed and optimized loss measuring setup. The obtained results have been analyzed for all kinds of excitation, according to the loss separation concept, with the emphasis being placed on the relationship between the rotational and the alternating loss components. In particular, it is found that the ratio between the rotational and the alternating losses is, for any given peak induction, independent of frequency.

Computation of the Losses in a Laminated Ferromagnetic Material Under Bidirectional Induction Excitation

In this paper, an analytical method for the calculation of power losses in FeSi laminations, taking into account skin effect and the ferromagnetic material nonlinearity, is used to compute iron losses. The electromagnetic field is assumed to be bidimensional, as it is the case in many applications in electrical engineering. The results of the analytical method used to solve the nonlinear diffusion equation are used as a starting point for the losses computation in the ferromagnetic material, using a losses separation model. The computation assumptions are detailed, and the results are discussed.

Design of a synchronous machine with concentric stator windings and permanent magnets in focusing configuration

A permanent magnets synchronous machine electromagnetic design is presented in this paper. The machine is characterised by a concentrated windings stator and focusing principle ferrite permanent magnets rotor. First, an analytic study is lead to determine the main influent parameters. A finite element analysis is then achieved in order to study more precisely the geometric parameters impact on the magnetic performances.