NASA is investigating advanced turboelectric aircraft propulsion systems that utilize superconducting motors to drive a number of distributed turbofans. Conventional electric motors are too large and heavy to be practical for this application, and so superconducting motors are required. In order to improve maneuverability of the aircraft, variable speed power converters would be required to throttle power to the turbofans. The low operating temperature and the need for lightweight components that place a minimum of additional heat load on the refrigeration system opens the possibility of incorporating extremely efficient cryogenic power conversion technology. This Phase II program will develop critical components required to meet NASA's size, weight, and performance goals.