Design of a High Specific Power Electric Machine for Turboelectric Propulsion

Abstract

The benefits of turboelectric propulsion for aviation, in which a gas generator core electrically drives motor-powered propulsors, are limited by the mass and losses of the electric components introduced into the drivetrain. These propulsion systems are predicted to result in a 15\% fuel savings provided that megawatt-class electrical machines (EMs) and power electronics (PEs) are available with power-to-mass ratios exceeding 13 kW/kg and 16 kW/kg, respectively.

This thesis proposes an integrated prime mover concept enabled by the material choices and cooling technology available today. In this concept, an outer rotor, tooth-and-slot Halbach array is integrated with the low pressure compressor of a low fan pressure ratio aeroengine. The specific power of the integrated compressor generator is estimated to be 14.8 kW/kg, exceeding the NASA 2030 goal for aviation applications of 13 kW/kg for a standalone electric machine for aviation applications.

Relative to a standalone, optimized electrical machine, co-optimization of the EM, PEs, thermal management system, and turbomachine rim suggests a 38\% increase in system specific power.

Based on these findings and supported by 2D and 3D finite element analysis, a 19.7 kW/kg, megawatt-class, air-cooled tooth-and-slot Halbach array electrical machine demonstrator is conceived. A detailed design study together with risk mitigation experiments of key components are carried out, setting the stage for megawatt-class, high power density, and high efficiency electrical machines for aerospace applications.