Development of a methodology for design and optimization of flux pumps to efficiently excite electrical machines with high temperature superconductors

• Applicants: Professor Dr.-Ing. Christian Kreischer; Professor Dr. Marcus Stiemer
• Subject Area: Electrical Energy Systems, Power Management, Power Electronics, Electrical Machines and Drives
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 562957642

This research proposal aims at providing the technological base for the design of scalable, efficient synchronous generators with a controllable DC-winding for magnetization, which consists of high-temperature superconducting (HTS) material excited by a travelling wave flux pump in a contactless way. Non-contacting magnetization reduces cooling efforts for the HTS windings while increasing its efficiency compared to other methods. A technology to provide a sufficient number of low-loss electrical machines of sufficient size for wind energy harvesting without resorting to permanent magnets and a high amount rare-earth elements is crucial for a transition to a sustainable energy supply. To reach the project’s aim, the simulation of HTS materials and their contactless excitation via traveling wave flux pumps are integrated into the usual simulation-based CAD-process. To this end, efficient and precise numerical methods for the magneto-quasistatic approximation to Maxwell’s equations with a constitutive material law for HTS materials are developed and utilized for optimizing flux pump designs to fulfil given requirements. Such requirements are defined in terms of the desired magnetic field, geometric restrictions, demands on the controllability of the HTS electromagnets, and minimization of AC losses. The new simulation method will be implemented as a module into commercially available CAD-systems for electrical machines to enable the industrial design of a suitable low-loss HTS coil and a corresponding flux pump for an electrical machine to be developed. After establishing suitable measurement methods, a micro-physically motivated phenomenological material law for type II HTS conductors will be identified, validated and utilized for the numerical simulation. To capture the flux pumping effect correctly in the simulation, efficient use of the available numerical resources is mandatory (to resolve the thin gab between HTS conductor and flux pump and to resolve the spatial variation of the conductivity in the feeding area). Hence, numerical methods for error estimation and adaptive finite element techniques will be employed. The simulation framework shall be validated by systematically conducted experiments with different flux pumps. Particularly, the current excited in the HTS conductor under various circumstances is measured depending on a couple of parameters. Those comprise the spatial form of the traveling wave, its spectral decomposition, the DC-part superposed by the flux pump, geometry details of the flux pump, etc. The flux pumping effect is to be explained systematically by combining measurement results with corresponding simulations. At the same time a knowledge-base is established for an accurately fitting design of a flux pump and its control. The applicability of the developed simulation framework to engineering problems will finally be proved by the design of a demonstrator-system that will be built and tested.

• DFG Programme: Research Grants