Smail Mezani

A New Analytical Torque Formula for Axial Field Permanent Magnets Coupling

In this paper, we present a simple and accurate analytical expression to compute the torque of axial-field magnetic couplings. The torque expression is obtained by solving the three-dimensional (3-D) Maxwell equations by the method of separation of variables. Here, we adopt the assumption of linearization at the mean radius, the problem is then solved in 3-D Cartesian coordinate (we neglect the curvature effects). To show the accuracy of the torque formula, the results are compared with those obtained from 3-D finite-element simulations and from experimental tests. As the proposed formula needs very low computational time and depends directly on the geometrical parameters, it is used for a design optimization using multiobjective genetic algorithms.

Original article: Analytical calculation of the flux density distribution in a superconducting reluctance machine with HTS bulks rotor

This paper deals with the analytical computation of the magnetic field distribution in a wholly superconducting reluctance motor. The rotor is made with high temperature superconductor bulks which nearly present a diamagnetic behavior under zero-field cooling. The stator consists of superconducting armature windings fed by AC currents of high amplitude. The superconducting stator winding can generate a high rotating magnetic field without the need of ferromagnetic material in the rotor. The electromagnetic torque is obtained by the interaction between the rotating magnetic field created by the superconducting stator windings and the variable reluctance due to the superconducting bulks. The proposed analytical method is based on the resolution of Laplaces equation (by the separation of variables method) for each sub-domain, i.e. rotor shaft, holes between superconducting bulks and air-gap. The global solution is obtained using boundary and continuity conditions. Magnetic field distribution and electromagnetic torque obtained by the analytical method are compared with those obtained from finite element analyses.

A New Topology for Induction Heating System With PM Excitation: Electromagnetic Model and Experimental Validations

This paper presents a new structure of an induction heater for aluminum parallelepiped workpiece. The studied device uses a magnetic field created by a permanent magnet inductor (Halbach inductor), in which the conducting workpiece is subjected to a linear oscillatory motion with an alternating velocity. An analytical electromagnetic model is developed to find the induced heating power in the workpiece. To consider the transverse edge effect, an analytical corrected model is also presented. The most important results obtained by these models are verified experimentally on a prototype.

Computation of Wound Rotor Induction Machines Based on Coupled Finite Elements and Circuit Equation Under a First Space Harmonic Approximation

This paper presents a fast method to compute wound rotor induction machines in steady state. Coupled time-harmonic finite-element (FE) circuit equation is used under a first space harmonic approximation for the air-gap magnetic field. It is shown that only four magnetostatic FE computations are necessary to determine the machine performances for any slip value. The performance comparison with a conventional complex magnetodynamic and time-stepping FE analyses show the effectiveness of the proposed approach.

Magnetically Geared Induction Machines

A wound-rotor induction machine is artfully coupled to a magnetic gear to achieve a high-torque-density drive system called magnetically geared induction machine (MaGIM). The high-speed rotor of MaGIM is common to both the machine and gear sides. A rotating diode rectifier electrically links the machines wound rotor and a dc boost winding on the gear side to increase the torque-transmission capabilities of the overall system. The first investigations on a 100 kW-120 r/min MaGIM are promising, since an increase in torque of ~15% could be obtained by inserting the diode rectifier. For fixed speed applications, this induction-machine-based system can be directly supplied from the mains.

A Fast Analytical Method to Compute the Radial Flux Density Distribution in the Airgap of a Superconducting Inductor

An original topology of superconducting rotating machine propose to use the diamagnetism of high temperature superconducting (HTS) bulk. Here, YBCO bulks allow to shield the magnetic field created by two solenoids supplied by dc currents in contra-directions. The obtained airgap field is multipolar as in conventional ac machines. A quick analytical method is developed here to compute the magnetic field distribution. It is based on the determination of the modulating function associated with the radial flux density distribution resulting from the introduction of the superconducting bulks. A first step allows the calculation of the modulating function by a 2D analytical method (using the resolution of Laplaces and Poissons equations by the separation of variables technique). The later is used in a second step together with the field produced by the two solenoids to calculate the radial flux density distribution in the airgap of the considered inductor. Comparisons to experiments and to 3D FE results show the validity of the proposed approach with the benefit of low computation time.

Modeling and analysis of eddy current losses in permanent magnet machines with multi-stranded bundle conductors

This paper investigates the influence of eddy current losses in multi-stranded bundle conductors employed in out-runner permanent magnet machines, by adopting an analytical model. The analytical model is based on a sub-domain field model that solves the two-dimensional magnetostatic problem using the separation of variables technique for each of the non-magnetically permeable machine sub-domains: PM, airgap and slots. The validity and accuracy of the proposed model is verified using finite element analysis and then used to investigate the eddy current losses. The machine considered for the analysis has 36 slots and 42-poles previously designed for aircraft taxiing. The influence of the number of turns and the conductor cross-sectional area are investigated. It is shown that efficiency can be improved considerably by the choice of multi-stranded bundle conductors.

Study of HTS Magnetic Coupler Using Analytical and Numerical Computations

In this paper, we propose a method to calculate the magnetic field in flux concentration superconducting magnetic coupling (FCSMC) with rectangular permanent magnets (PMs). The inner rotor is composed of rectangular PMs, and the external rotor is made of high-temperature superconducting coils supplied by dc current. First, an exact 2-D analytical computation is developed in polar coordinates for calculating the magnetic field distribution in FCSMC with sector PMs having the same volume as the rectangular PMs. The model is validated by finite-element computations. The analytical model is then used to predict the performances of FCSMC. The electric loadability of the FCSMC is determined by considering the dependence of the critical current versus the flux density distribution. A parametric study showed that the analytical model can predict the torque with reasonable precision. Therefore, this model can be used for optimization purposes where reductions in computation time are needed.

Comparison of transient performances for synchronous and eddy-current torque couplers

In this paper, we compare the transient performances of synchronous and eddy-current magnetic couplings. Based on a two-dimensional approximation for the magnetic field distribution, closed-form expressions for the transmitted torque are first presented. The torque formulas are then used to study the transient responses during a start-up and for a sudden application of a load torque. Simulation results are compared with those obtained from tests. It is shown that overload torque condition leads to the loss of synchronism for the synchronous coupling. A discussion about the benefits and the disadvantages of each topology in terms of transient responses is given.

Thin-Layer Insulation of HTS: Analytical Study

The aim of this paper is to take into account the thin layer of insulation of a superconducting tape or a superconducting coil to calculate heat transfer during a quench. The main problem is that this thin layer is very difficult to mesh in finite-element method. In this paper, we propose a modified factor of the convection coefficient obtained due to an analytical solution of the heat equation. The aim of this modification is to take into account the thickness of the resin, which bands a thin coil, or a superconducting tape immersed in cryogenic bath. Introducing this modified factor leads to a significant simplification of the 3-D thermal study because the diffusion in the resin is taken into account due to the modifying factor.