High Temperature Superconducting Flux Pumps for Contactless Energization

The development of superconducting technology has seen continuously increasing interest, especially in the area of clean power systems and electrification of transport with low CO2 emission. Electric machines, as the major producer and consumer of the global electrical energy, have played a critical role in achieving zero carbon emission. The superior current carrying capacity of superconductors with zero DC loss opens the way to the next-generation electric machines characterized by much higher efficiency and power density compared to conventional machines. The persistent current mode is the optimal working condition for a superconducting magnet, and thus the energization of superconducting field windings has become a crucial challenge to be tackled, to which high temperature superconducting (HTS) flux pumps have been proposed as a promising solution. An HTS flux pump enables current injection into a closed superconducting coil wirelessly and provides continuous compensation to offset current decay, avoiding excessive cryogenic losses and sophisticated power electronics facilities. Despite many publications regarding the design and analyses of various types of HTS flux pumps, the practical application of HTS flux pumps in a high-performance superconducting machine has been rarely reported. Therefore, it is of significance to specify the main challenges for building and implementing a reliable HTS flux pump. In addition, the physical mechanisms of distinct HTS flux pumps have caused some confusion, which should be clarified. Above all, a systematic review of the recent development and progress of HTS flux pumps remains lacking. Given the above-mentioned issues, this paper summarized the most up-to-date advances of this emerging technology, clarified the working mechanisms and commonly adopted modeling approaches, presented objective analyses of the applicability of various HTS flux pumps, specified the primary challenges for implementing HTS flux pumps, and proposed useful suggestions to improve this wireless excitation technology. The overall aim of this work is to bring a deep insight into the understanding of HTS flux pumps and provide comprehensive guidance for their future research and applications