Impact of cryogenic temperatures on high-power semiconductor performance

Power electronics is necessary for the independent control of the stator windings of electric aircraft motors. The benefit of using liquid fuel to cool conductors to utilize their high current density has enabled power electronics to be cooled by proxy. While small scale semiconductors have been found to be degraded during operation at cryogenic temperatures, results for systems rated for high power cryogenic applications have not been explored as much. In this work we test the performance of IGBT power electronics from room temperature to 77 K, with a focus on temperatures expected for electric aircraft motors using liquid natural gas (LNG, BP about 120 K) as the cooling medium. In this work, the measure of performance was taken to be the ability to be turned on and off (switched) by an input signal provided by a function generator. We also tested the cold-start ability i.e., the lowest temperature in which the power inverter will start. The lowest cold-start temperature was measured as 140 K. Experimentally, we also observed that both conduction losses and switching loss from a low-power constant current with an operational frequency of 10 kHz were sufficient to allow the inverter to work down to 105 K (below the LNG boiling point).