This work describes the architecture and evaluation of a turbo-electric distributed propulsion microgrid for ECO-150, a NASA funded 154 passenger subsonic fixed wing commercial transport aircraft concept for entry into service by 2035. Three different microgrid types are considered: ac synchronous distribution, dc distribution, and a hybrid approach. A high level architecture for each grid type is proposed, considering requirements for single point failure accommodation, redundancy and reconfigurability, and electrical protection. Component sizing models were developed for rotating electrical machines, power converters, distribution, and protection equipment, targeting a technology readiness level (TRL) of TRL-6 by 2025. These tools are combined to evaluate the mass and efficiency metrics for each microgrid type. Sensitivity sweeps on grid voltage and frequency were completed in order to determine optimal choices for both parameters. Results indicate that microgrid performance metrics are optimized for ECO-150 near 6 kilovolts (kV) and 1 kilohertz (kHz), with the dc and hybrid grids having a greater sensitivity to voltage than the ac grid. Advantages of the dc and hybrid grids include ability to provide powered yaw, and ability to incorporate energy storage. However, powered yaw control was investigated and determined to be less effective than a conventional tail on a per mass basis. After accounting for the mass of the associated thermal management system (TMS), the dc grid emerges as the lowest mass option above 3 kV, followed by the ac and the hybrid grid. However, ac grid achieves a transmission efficiency 2-3% higher than the dc grid, which will have system level effects on fuel burn, fuel weight, and overall propulsive efficiency. For near term practical implementation of turbo-electric distributed propulsion, the ac synchronous system should be considered seriously as a strong candidate.

This paper describes a detailed design of a 6-T Nb 3 Sn superconducting racetrack coil designed for conduction cooling. We then describe a bench test pursued as a proof of concept for one winding of an actively shielded air-core electric machine with superconducting field windings. Electromagnetic design selection is drawn from previous optimization work. The coil former design is then discussed. Numerical simulations of thermal and structural features are pursued to determine temperature distribution and strain within the winding. A coil instrumentation and experimental setup of a quasi-conduction cooled system is described. Finally, test results are presented; a maximum critical current of 480 A was reached at a peak temperature of 7.9 K, surpassing the operational current goal of 435 A. Future work and planned improvements to the test setup are discussed.

Superconducting technology applications in electric machines have long been pursued due to their significant advantages of higher efficiency and power density over conventional technology. However, in spite of many successful technology demonstrations, commercial adoption has been slow, presumably because the threshold for value versus cost and technology risk has not yet been crossed. One likely path for disruptive superconducting technology in commercial products could be in applications where its advantages become key enablers for systems which are not practical with conventional technology. To help systems engineers assess the viability of such future solutions, we present a technology roadmap for superconducting machines. The timeline considered was ten years to attain a Technology Readiness Level of 6+, with systems demonstrated in a relevant environment. Future projections, by definition, are based on the judgment of specialists, and can be subjective. Attempts have been made to obtain input from a broad set of organizations for an inclusive opinion. This document was generated through a series of teleconferences and in-person meetings, including meetings at the 2015 IEEE PES General meeting in Denver, CO, the 2015 ECCE in Montreal, Canada, and a final workshop in April 2016 at the University of Illinois, Urbana-Champaign that brought together a broad group of technical experts spanning the industry, government and academia.

This paper describes a detailed design of a 6 Tesla Nb3Sn superconducting racetrack coil designed for conduction cooling. We then describe a bench test pursued as a proof of concept for one winding of an actively-shielded, air core electric machine with superconducting field windings. Design selection from a previously computed pareto-optimal front as well as electromagnetic performance of the test coil is discussed. The winding and support structure design is discussed. Analysis of the thermal performance is carried out to verify required temperatures given the cryostat and cryocooler setup. Finally, a strain analysis is performed in order to verify that the superconducting windings are within an acceptable strain level to avoid mechanical breakage as well as excessive degradation of the critical surface. Additionally, the structural integrity of the support components is verified. Test procedures and preliminary results are described.

This paper describes an approach for obtaining very high power density in an electrical machine by significantly increasing the air-gap magnetic flux density and eliminating the ferromagnetic steel traditionally employed to carry and shield magnetic flux. A novel concept is used to address a key challenge with this topology, that of containing the magnetic fields within the machine. An arrangement of main coils and a set of compensating coils, inspired by actively shielded magnetic resonance imaging magnet designs, are employed to cancel out the field outside the machine without the use of iron while maintaining air-gap field levels that are three to five times greater than conventional machines. For an example 10-MW motor study, the outer diameter is reduced by 35%, with corresponding weight reduction, using only 17% more superconductors.

An important challenge in the design of air-core superconducting machines is the containment of the magnetic fields within the electric machine. Current solutions result in large reductions of the high power density achievable through the use of superconducting windings. To address this challenge, an actively shielded electromagnet design, an approach commonly used in MRI magnet designs, is considered. This topology utilizes a set of main coils to produce armature MMF, while including another set of oppositely excited compensating coils to mitigate the fields radiating outside the machine. This approach eliminates or reduces the use of steel in a passive magnetic shield, allowing for very high power density machines. Furthermore, a multi-objective optimization scheme is introduced to minimize two competing objectives, superconducting coil usage and machine radius. Results show a 32% decrease in machine radius with a 33% increase in coil size.