Combined Analysis of NASA's High Efficiency Megawatt Motor and Its Converter

NASA’s High Efficiency Megawatt Motor (HEMM) is being developed to achieve the performance needed by single aisle class electrified aircraft. It is a 1.4 MW electric machine designed as a generator for NASA’s STARC-ABL concept vehicle. It has performance objectives of greater than 16 kW/kg electromagnetic specific power and efficiency of greater than 98%. The key enabling technology for HEMM’s high performance metrics is a superconducting rotor cooled by an integrated cryocooler. HEMM’s integrated cryocooler is being designed to only lift 50 W of heat at its target 50 K cold tip operating temperature. HEMM’s superconducting rotor therefore needs to have essentially zero electromagnetic losses in order to stay below the 50 W heat rejection limit of the cryocooler. This paper presents the combined analysis of HEMM and a preliminarily designed HEMM converter to analyze the rotor loss impact of several potential converter filter topologies. The analysis results point to interleaving and series inductance filters not being sufficient to suppress switching harmonic caused rotor loss. Paths forward to develop a converter to eliminate rotor loss are discussed.