This Small Business Innovation Research Phase I project will prove the feasibility of a high reliability motor drive optimized for lightweight propulsion systems for electric aircraft. The NASA green flight challenge proved the viability of electric flight with a 400 passenger mile per gallon pure electric flight last year, but products specific to this market are not yet available. Presently available motor drives limit the reliability of electric propulsion system to unacceptably low levels. These drives are designed for ground vehicles and have reliability significantly less than general aviation planes. These drives also require heavy load inductors to interface with the highest power density electric motors. The novel drive architecture proposed will provide high reliability and operate directly with low inductance motors in the 10 kW to >250 kW range. Rigorous reliability analysis techniques from the commercial aviation industry will be applied to system models to optimize the architecture for reliability and power density. The design will be validated in hardware by fabricating and testing a single phase of the drive. This drive coupled with an advanced motor will form an electric aircraft propulsion system with the highest power density available and a reliability level consistent with aviation usage.
The broader impact/commercial potential of this project is to address a developing market for propulsion systems that will enable non-polluting and reliable electric aviation in the small aircraft and Unmanned Aerial Vehicle (UAV) sectors. UAV use is expanding rapidly. Many domestic applications of UAVs such as law enforcement or surveying could be served by electric UAVs. Congress has mandated that the FAA integrate UAVs into the airspace, but present UAVs do not have reliability levels consistent with use in the civilian airspace. General aviation is looking to electric flight as a way to reduce operating costs and greenhouse emissions in an age of ever increasing fuel prices and concern for the environment. The FAA is updating regulations to create a class of "Electric Light Sport Aircraft" (eLSA), but no commercially available motor drives meet general aviation reliability levels. This project will combine rigorous commercial aviation high reliability electronics design techniques with power electronics designs from heavy industry motor drives to create an electric aviation motor drive that is lightweight, fault tolerant, and highly reliable. The proposed drive will have reliability levels consistent with operation of electric aircraft in the civilian airspace while still retaining exceptional power density.
The NASA green flight challenge proved the viability of electric flight with a 400 passenger mile per gallon pure electric flight two years ago. General aviation is looking to electric flight as a way to reduce operating costs and greenhouse emissions in an age of ever increasing fuel prices and concern for the environment. However, there are no electric motor drive electronics commercially available that meet the reliability levels required by FAA general aviation airworthiness requirements. Additionally, Unmanned Aerial Vehicle (UAV) use is expected to expand rapidly. Many domestic applications of UAVs such as law enforcement or surveying could be served by electric UAVs. This is a rapidly growing market where the lightest weight electric propulsion system will offer payload and/or range performance advantages to the product. Congress has mandated that the FAA integrate UAVs into the airspace. One of the requirements that the FAA has signaled will definitely be in the final regulations is that UAVs over a few kilograms of mass will be required to meet airworthiness requirements just like manned air vehicles. Thus commercial UAVs will require high reliability and fault tolerance in their electric propulsion systems. Electric propulsion products specific to the aviation market are not commercially available with the exception of hobbyist quality components. Presently available motor drives which are made for industrial use, ground vehicles, or R/C aircraft hobbyists have reliability significantly less than general aviation planes. These drives also require heavy load inductors to interface with the highest power density electric motors. Finally, these off-the-shelf drives typically have fault mode behaviors that are incompatible with aviation usage. A fault tolerant drive architecture is required because the reliability of electric drive systems is limited to unacceptable levels by the summed failure rate of the many individual components in the system. Thus the system must be tolerant to some component failures to achieve acceptable failure rates. We proposed to develop a motor controller that could achieve reliability better than 10^-6 failures per hour through a fault-tolerant architecture; have good power density and efficiency; and work with the low inductances typical of high performance motors. We proposed to take cutting edge aerospace design methodologies and architectures used in highly reliable Fly-By-Wire systems for commercial transport jets and bring bring them out of the large aerospace corporations to a commercial level; making this technology available to the many smaller entities who wish to enter the UAV and electric aircraft market. Through the Phase I research we have developed a design that will be able to achieve these goals and validated key parts of the design through in-depth modeling, analysis, and hardware validation. Fault Tree Analysis and Failure Modes and Effects analyses were used to determine the fault tolerant architecture and mitigate all single point failures. MIL-HDBK-217 methods were used to calculate estimated reliability and per hour failure rates. A paper design and CAD models were created for the entire drive and costs, weights, and efficiencies calculated and simulated. Prototype circuit boards containing representative power electronics were designed, fabricated, and tested to validate the modeling and simulation results. When our fault tolerant drive is coupled with an advanced permanent magnet motor it will form an electric aircraft propulsion system with the highest power density available and a reliability level consistent with aviation usage. The proposed motor drive will help address the unmet need for an aviation specific, high power density electric aircraft propulsion system which will enable "greener" flight.
