NASA’s System-Wide Safety (SWS) project is developing innovative data solutions to assure safe, rapid, and repeatable access to a transformed National Airspace System. The increasing number of electric propulsion systems that will enter the airspace will require systems that ensure high safety standards in the low-altitude airspace. One element that can help ensure safety is proper diagnosis of failures via Fault Detection and Isolation (FDI). NASA Ames has developed a fault isolation approach for electric powertrains of unmanned aerial vehicles.
The approach leverages a combination of Failure Mode and Effect Analysis (FMEA) and Bayesian Networks (BN) to create a dependability structure within a diagnostic framework-mapping fault and failure events from the FMEA within a BN. This framework helps the fault isolation process by identifying the probability of occurrence of specific fault or root causes given evidence observed through sensor signals.
The tool developed through this work merges information from the electric propulsion system design phase with diagnostic tools. Information from the FMEA from the system design phase is embedded within BN. Each node in the network can represent either a fault, failure mode, root cause or effect, and the causal relationships between different elements are described through the connecting edges.
This novel approach can help FDI, producing a framework capable of isolating the cause of sub-system level fault and degradation. This system: Identifies and quantifies the effects of the identified hazards, the severity and probability of their effects, their root cause, and the likelihood of each cause; Uses a Bayesian framework for FDI; Based on the FDI output, estimates health of the faulty component and predicts the remaining useful life (RUL) by also performing uncertainty quantification (UQ); Identifies potential electric powertrain hazards and performs a functional hazard analysis (FHA) for unmanned aerial vehicles (UAVs)/Urban Air Mobility (UAM) vehicles.
Despite being developed for and demonstrated with an application to an electric UAV, the methodology is generalized and can be implemented in other domains. These domains range from manufacturing facilities to various autonomous vehicles.