Electromagnetic design for high power density of fully superconducting synchronous motor with through-shaft type field coil for electric aircraft

Abstract

The global demand for aircraft is currently increasing, paralleled by a growing emphasis on decarbonization through the replacement of fossil fuel engines with electric propulsion. In response to this trend, we have developed a superconducting motor distinguished by its high efficiency, output, and low weight. Our focus centers on two critical aspects. Firstly, we addressed the issue of the field coil’s shape. The widely used REBCO wire in high-temperature superconductivity is tape-shaped, making a racetrack coil the most straightforward method for winding the wire. However, this configuration necessitates dividing the motor shaft as it comes in contact with the field coil, raising concerns about the mechanical durability of motors. To overcome this challenge, we introduce a saddle-type coil and design a coil shape that achieves a single continuous through-axis. Utilizing the Frenet-Serre formula, we created a 3D model of the coil’s end without applying load to the wire. This method, previously employed in accelerators, enhances durability, potentially leading to increased output due to higher rotation speeds and reduces weight through part savings. Secondly, introducing a saddle coil presents challenges in forming an ideal magnetic field distribution. In a rotating-field-type motor using an iron core, the winding can be directly wound around it, resulting in multiple coils forming similar magnetic fields that can be superimposed to create one large magnetic pole. However, with a saddle coil, coils are arranged along the circumference, and the magnetic field distribution and an anticipated decrease in output. To address this, we aimed to optimize the magnetic field distribution and increase output through a parameter survey. Specifically, we conducted an analysis under fixed armature conditions (current, number of turns, and shape) in three cases. In Case1, with a fixed total number of turns for the field coil, we compared magnetic field distributions and output by varying the number and arrangement of coils. In Case2, building on the findings of Case1, we aimed to enhance output by fixing the coil arrangement and increasing the number of turns. Finally, in Case 3, we examined the change in motor size with fixed coil parameters while altering the coil arrangement and pitch.