Modeling, Manufacturing, and Experimental Validation of an Electric Machine for Aircraft Propulsion

Abstract

The work presented in this thesis is part of an effort at MIT to develop a 1-MW electric machine which achieves the specific power necessary for hybrid-electric aviation: 13 kW/kg [1]. The models for torque and core loss used in the design of the 1-MW machine are revised and expanded based on experimental results obtained from a partially-manufactured prototype to guide the design of future high specific-power electric machinery.

To calculate the torque produced by the machine, the air-gap field created by a segmented Halbach array rotor is derived from Maxwell’s Equations. The closed-form solution for the air-gap field matches Finite Element Analysis (FEA) to within 1% and experimental data from the manufactured prototype to within the tolerance of the experiment. A method for modeling a slotted stator as a smooth cylinder with a surface current is applied to the stator of the 1-MW machine, and the average torque and torque ripple are calculated using the Lorentz-Kelvin force density. The analytical torque calculation computes 100,000 times faster than 2D FEA (0.56 ms vs. 44 s), and matches FEA to within 1.2%, making it ideal for initial machine design.

An experimental procedure is developed to measure the core loss and B-H curve of an iron lamination stack. This procedure is applied to various toroid samples and a stack of slotted stator laminations. A conventional lamination bonding process is found to raise core loss by 20% for 0.1-mm iron-cobalt laminations. An alternative stator-core manufacturing process, which results in no impact on core loss, is identified and experimentally verified. Based on the measured core loss of a stack of stator laminations, the 1-MW prototype is expected to remain within the thermal limits imposed by the winding insulation.