A Mission Profile-Based Reliability Modeling Framework for Fault-Tolerant Electric Propulsion

This article proposes a thermally enhanced reliability modeling framework which works from the mission profile of an electrified aviation propulsion system, incorporating known fault-tolerant power electronics, motor drives, control, and their pre and postfault behaviors. The reliability framework is presented in a hierarchical fashion. Multiphysics modeling is used, incorporating electromechanical states, power losses, and thermal behaviors. The approach includes the device thermal stress in healthy and postfault operating states in the failure rate calculations. Markov chain models are then used with the calculated failure rates to form system level reliability models. A case study of an electric vertical takeoff and landing urban aerial vehicle (eVTOL UAV) walks through the proposed method, modeling multiple versions of the propulsion system, with various levels of fault tolerance and redundancy. The proposed reliability modeling framework captures the operating temperatures and thermal swings seen by the components due to the flight mission, enhancing the failure rate calculation. Further, since the postfault operating mode of the fault tolerant system causes higher component currents and temperatures, different component failure rates are calculated for postfault operation. Finally, the Markov chain modeling allows for a reliability comparison between various UAV propulsion systems, including the effect of combining fault tolerance at the subsystem level, with redundancy at the system level.