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 (3D) 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 3D Cartesian coordinate (we neglect the curvature effects). To show the accuracy of the torque formula, the results are compared with those obtained with 3D finite-element simulations, and 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.

High Temperature Superconducting (HTS) electrical machines have high torque density with a very high efficiency. Torque tubes are usually used to transmit the torque from the cold to the warm environment which results in thermal losses and mechanical problems. To overcome these difficulties, we propose to transmit the torque of the HTS machine through an integrated HTS magnetic coupling. A prototype has been constructed and tested showing the effectiveness of the proposed solution. The machine and the coupling share the same HTS rotor while the torque produced by the machine is transmitted to the load via a permanent magnets rotor. This solution allows the reduction of the thermal losses and a natural protection against overload during fault. The electromagnetic design is carried out using 3D finite elements. The HTS material electrical behavior is described using a power law so it was possible to determine the operating current of the HTS coils of the device. Many test results such as curves of the HTS coils, static torques, back-EMF and on-load characteristics are presented and checked by the FE computations.

Abstract-In this paper, we propose an analytical method for modeling a permanent magnets axial field magnetic coupling. The three-dimensional model takes into account the radial fringing effects of the coupler. The analytical solution requires resolving the Laplace equation in low permeability subdomains. The magnetic field calculation allows the determination of global quantities like axial force and torque. 3D finite element computations as well as measurements validate the proposed model.