Increasing air transportation can be a cause of global warming due to the emission of CO2. One of the solutions is an e-aircraft that has a distributed propulsion system using multiple motors and generators. Motors and generators used in this system require a high efficiency of more than 98% with a high-power density of 20 kW/kg. However, it is not easy to achieve the target efficiency and power density by conventional rotating machines composed of cooper wire and permanent magnets. REBCO wires have high critical densities, which allows superconducting motors to be smaller and lighter than conventional ones. For that reason, our research group aims to develop the 10 MW REBCO fully superconducting synchronous generator. Our previous research compared the field winding operating at 64 K with one operating at 20 K. In both cases, the armature windings cooled 64 K. We concluded that the field winding operating at 64 K was optimal because it had a simple structure and high safety [1]. In this study, we investigated methods of reducing the AC loss generated by a 10 MW superconducting synchronous generator operating at 64 K. The AC loss must be at least 200 kW or less to meet the efficiency of 98%. The AC loss from the armature winding is dominant in comparison with that from the field winding. Thus, we increased the magnetic field generated by the field winding and reduced the length of the armature winding. We calculated the power density, the leakage field, and the AC loss and achieved the target loss of 200 kW or less and the target power density of over 20 kW/kg.
[1] M. Komiya et al., “Conceptual Design and Numerical Analysis of 10 MW Fully Superconducting Synchronous Generators Installed with a Novel Casing Structure”, IEEE Transactions on Applied Superconductivity, vol. 30, no. 4, Jun 2020, Art no. 5206607.
Acknowledgments:
This research is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO), the Japan Science and Technology Agency (JST): Advanced Low Carbon Technology Research and Development Program (JPMJAL1405), and the Japan Society for the Promotion of Science (JSPS): Grant-in-Aid-for Scientific Research (JP18H03783 and JP19K14964).
Keywords: aircraft, synchronous generator, REBCO, AC loss reduction