Abstract Body

This article presents the superconducting machine demonstrator developed as part of the FROST (Flux-barrier Rotating Superconducting Topology) project, which began in 2020. The demonstrator is a 250 kW partially superconducting machine featuring three key components:

• A rotor made of HTS bulk material (Figure 2).
• An HTS static coil, powered by DC current, generating a strong magnetic field within the machine (Figure 3).
• A three-phase armature constructed with Litz copper wire, positioned on both sides of the rotor (Figure 4).

The static part of the inductor, comprising a superconducting coil, produces an axial magnetizing field. The rotating component consists of superconducting bulks placed inside the bore of the superconducting coil. These bulks shield the magnetic flux, resulting in flux density modulation low near a pellet and high elsewhere, so between O and B_maximum. This system produces a homopolar component of the modulated magnetic flux. The armature uses traditional three-phase windings made of copper, without iron teeth, to enhance performance.

This topology is brushless, as only the HTS bulks rotate, yet it allows for excitation control via the current in the static coil. Additionally, the large magnetic field generated by the HTS enables the machine to be entirely iron-free.

This design has been studied for several decades, with small prototypes primarily in the radial-flux configuration [1]. More recently, the RESUM project (Realization of a Superconducting Motor) resulted in a 40 kW prototype using BiSrCaCuO tapes for the coil and multi-seeded YBaCuO bulks for the rotor [2], completed in 2019. Since 2020, a second prototype has been under development within the FROST project, aiming to achieve 250 kW. Recent efforts have focused on modeling [3] and designing the demonstrator, which was assembled in the summer of 2024. The goal of the FROST project is to scale up from the 40 kW machine of the RESUM project to 250 kW without a significant increase in mass.

To achieve this, we replaced the BSCCO tape in the static coil with a RE_BaCuO tape. Additionally, we modified the shape of the superconducting screen from a round to a trapezoidal form, closely matching the armature coils. Finally, we introduced liquid cooling for the armature.

We will also conduct preliminary magnetization of the superconducting pellets using the static coil. This approach will combine flux modulation with magnetization, eliminating the homopolar component of the magnetic field and allowing it to oscillate between plus and minus B_maximum, thereby doubling the machine's potential power.

References

[1] E. H. Ailam, D. Netter, J. Leveque, B. Douine, P. J. Masson, and A. Rezzoug, “Design and Testing of a Superconducting Rotating Machine,” IEEE Transactions on Applied Superconductivity, vol. 17, no. 1, Art. no. 1, Mar. 2007, doi: 10.1109/TASC.2006.887544.

[2] A. Colle, T. Lubin, S. Ayat, O. Gosselin, and J. Leveque, “Test of a Flux Modulation Superconducting Machine for Aircraft,” J. Phys.: Conf. Ser., vol. 1590, p. 012052, Jul. 2020, doi: 10.1088/1742-6596/1590/1/012052.

[3] R. Dorget, T. Lubin, S. Ayat, and J. Lévêque, “3-D Semi-Analytical Model of a Superconducting Axial Flux Modulation Machine,” IEEE Transactions on Magnetics, vol. 57, no. 11, Art. no. 11, Nov. 2021, doi: 10.1109/TMAG.2021.3108632. Example reference – replace or delete

Acknowledgment

The authors would like to thank the Direction Générale de l’Armement (DGA), the Agence de l’Innovation de Défense (AID), and the Agence Nationale de la Recherche (ANR).

Figure 1. Representation of the active components of a flux modulation machine in its axial flux form.

Figure 2. Picture of the assembled rotor

Figure 3. Picture of the HTS coil

Figure 4. Picture of an assembled cooling carter of the armature

Figure 5. Picture of the assembled machine (without the armature)

Keywords: Axial Field Machine, High Temperature Superconductors, Superconducting Motor, Synchronous Machine