High Efficiency Megawatt Motor Rotating Cryocooler Conceptual Design

Abstract

Some of the challenges associated with developing electric aircraft propulsion systems include developing powertrain components that are both efficient and light-weight. In particular, electric motors must simultaneously achieve high efficiency by minimizing electrical and mechanical losses while also achieving high specific power by increasing the torque and/or speed. Normally, increasing torque or speed will increase electrical and mechanical losses. The High Efficiency Megawatt Machine (HEMM) minimizes electrical losses by incorporating a superconductor to enable increased current on the rotor. The rotor spins in a vacuum to minimize thermal and mechanical losses. Some organizations have been developing superconducting rotors for similar reasons using either cryogenic fluid transfer systems, fully immersed cryogenic cooling, and in a few cases, built-in cryogenic cooling on the rotor using a Brayton or Stirling system; however, the implementation was too large or inefficient for effective motor integration. Instead, a new approach for cryogenically cooling the superconducting rotor coil with an embedded rotating cryocooler is presented that fits completely within the rotating shaft.