Electromagnetic Characteristic Comparison of Superconducting Synchronous Motors for Electric Aircraft Propulsion Systems 2019-01-1912
Aircraft service has been increasing today and it also results in the increase of the greenhouse gas emission. To solve this problem, the electric aircraft propulsion system is the key solutions to realize the clean and high efficiency aircraft, while demanding higher output density motors. So far, though 5 kW/kg is realized with permanent magnet type synchronous motors, the electric aircraft for over 100 passengers demands motors with 16 -20 kW/kg.
Superconducting (S.C.) technology is one of the effective candidates for higher output density motors. In comparison with copper wires, the S.C. wires have higher current density at less than –200 ℃. And we can make a lighter weight coil with the S.C. wires. So far, many groups have been studying the S.C. motors over 16 kW/kg. Generally, there are two kinds of S.C motors. One is the S.C. motors made of the S.C. field coils and copper armature windings. The other is the fully S.C. motors using S.C. field and armature windings.
We have been studying the fully S.C. motors with two kinds of S.C. wires. The motors are operated at 20 K with liquid hydrogen. The field coils use YBCO wires, whose critical temperature is over 90 K. The wires have wide temperature margins and good mechanical characteristics under high magnetic flux density. Also, MgB2 wire is employed for the armature windings to realize lower AC loss reduction. The MgB2 wire has multifilament structure and can contribute to AC loss reduction.
In this presentation, we compare and discuss the electromagnetic characteristics of the two S.C. motors under some unified design conditions: output, rotational speed, cooling temperature and so on. We estimate output density and losses of S.C. motors based on FEM analysis and discuss the advantages of S.C. motors for future electrical aircraft.