Selection of superconducting machine concepts with direct liquid hydrogen cooling for electric aircraft

Abstract

The urgency for environmentally sustainable electric aircraft is driving the development of electric propulsion systems, with superconducting electrical machines (SCEMs) offering high efficiency and specific power. This thesis identifies suitable SCEM concepts for electric aircraft. The identifying is based on selection criterion aiming at stationary superconducting windings cooled directly by liquid hydrogen (LH₂). These criteria avoid the complexities of cooling the windings which are rotating and reduces total system weight compared to cryocooler based methods. A literature review of conceptual SCEMs is conducted in line with the criteria. The review shows high potential of a few SCEM concepts for the particular application although their performances are merely theoretical or from simulations. This was followed by a case study on the superconducting homopolar machine with finite element analysis to find any limiting factors. The machine concept selected fits the criteria very well and has a simple structure and working principle for ultra-high-speed operation. It is found that iron saturation and underutilization of the superconducting winding are the limiting factors for this SCEM concept. Improved magnetic circuit design is needed to address the limitations, otherwise adopting superconducting windings will result in no improvements over conventional copper windings.