PhD student Shivang Agrawal with advisor A. Banerjee

Turboelectric propulsion uses no batteries for propulsive energy during any phase of flight (unlike hybrid and all-electric systems) and is considered a critical enabler for low-carbon emissions in the aircraft industry. As batteries with high enough power capacity and the specific power required for commercial aircraft are unlikely to be developed within the next 30 years, turboelectric systems are the only feasible option.
A brushless doubly-fed machine (BDFM) is an attractive option for megawatt-scale turbo-electric propulsion systems due to use of a partially-rated power converter, reduced maintenance, and absence of permanent magnets. However, BDFRMs have inherently poor torque density and high torque ripple as they utilize a sub-optimal rotor. We have proposed an analytical model to compute the air-gap flux density and torque characteristics, with the aim of modeling the effect of the flux barriers on the mean and ripple torques. Through analytical and finite element analysis, it has been verified that the position of the flux-barrier ends highly influences the torque waveform, and thus cannot be arbitrarily designed. The rotor geometry along with the stator current excitations are optimized to achieve a torque-dense BDFRM. The prototype motor is shown in Figure 1. This research is supported by the Grainger Center for Electric Machinery and Electromechanics.


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Figure 1. Hardware prototype of an optimized torque-dense BDFRM