Researchers have successfully tested a new type of motor drive for hybrid-electric aircraft, using advanced silicon carbide components to create a system that is significantly smaller, lighter, and more efficient than current technology. The experimental inverter, developed by the UA Power Group at the University of Arkansas, powered the rear electric engine of a hybrid Cessna 337 during a test flight in Southern California. The flight successfully demonstrated the system’s viability in a real-world aviation environment, representing a critical advance in the effort to make electric flight more practical.
This breakthrough addresses two of the biggest obstacles for electric aviation: the weight and size of the necessary power electronics. By replacing traditional silicon with silicon carbide in the motor drive, the team created a powertrain that reduces energy consumption during takeoff and cruising. This improved efficiency can lead to extended range or increased payload capacity, moving hybrid-electric aircraft closer to commercial reality for applications ranging from air taxis to regional transport and helping to reduce greenhouse gas emissions.
The Silicon Carbide Advantage
The core of the innovation lies in the use of silicon carbide, a wide-bandgap semiconductor material with properties superior to conventional silicon for high-power applications. Transistors, which act as the fundamental switches in an electric circuit, lose a small amount of energy as heat each time they switch between on and off states. Silicon carbide transistors can switch up to 1,000 times faster than their silicon counterparts.
This rapid switching capability drastically improves energy efficiency, as the transition periods where energy is lost are much shorter. Because the silicon carbide components generate less waste heat, the entire system can operate more effectively with less cumbersome cooling equipment. This efficiency gain allows for a cascading size reduction in all the surrounding passive components, including inductors, transformers, and capacitors, which are essential for managing the flow of electricity. The result is a much lighter and more compact motor drive system.
Engineering a More Compact Powertrain
The device developed by the University of Arkansas team is a 250 kW inverter, a crucial component that converts the direct current (DC) from the aircraft’s battery into the alternating current (AC) required to power the electric motor. In an aircraft, where every pound and every inch of space counts, the reductions enabled by silicon carbide are transformative. The lighter weight directly translates to lower energy use, while the smaller footprint can free up space for passengers or cargo.
Chris Farnell, an assistant professor and the first author of the research paper published in IEEE Transactions on Power Electronics, illustrated the scale of the improvement with an analogy. “Imagine a race car with a big 350 engine that weighs hundreds of pounds,” he stated. “What if you had that same power, but I gave you something that would fit in your hand?” This highlights the level of power density achieved, a key metric for all-electric and hybrid vehicle development on the ground and in the air.
Overcoming Aviation-Specific Hurdles
Designing power electronics for aircraft presents a unique set of engineering challenges that the team had to overcome. The system must be robust enough to withstand the constant vibrations of flight and the shocks experienced during takeoffs and landings. Furthermore, the electrical systems must be designed to function reliably at high altitudes, where the thinner, drier air provides less insulation and can lead to electrical discharge issues.
Another potential issue arises from the very property that makes silicon carbide so effective: its fast switching speed. This rapid electrical activity can create electromagnetic interference that could disrupt other sensitive aircraft electronics. The UA Power Group’s design successfully managed these challenges, with the 2023 test flight serving as the ultimate validation that their engineering met the rigorous demands of aviation.
Broader Implications for Electric Flight
The successful flight test is a milestone not just for the university researchers but for the entire burgeoning electric aviation industry. The demonstrated performance shows a clear path to overcoming the power-to-weight ratio problems that have constrained electric aircraft designs. This progress is inspiring further research and development into electric airplanes and other forms of transportation. The technology is a key enabler for a wide range of electric aircraft, from small urban air mobility vehicles to larger regional turboprops. The trend is being pursued across the sector, with companies like ZeroAvia also developing high power-density silicon carbide inverters for its hydrogen-electric engines, targeting over 20 kW/kg of power density.
The Path to Commercial Adoption
Despite its superior performance, the widespread adoption of silicon carbide has been hindered by its historically high cost compared to silicon. Alan Mantooth, the project’s lead researcher and a Distinguished Professor at the university, noted that silicon is fundamentally inexpensive. “Silicon is made from dirt, and nothing is cheaper than dirt,” Mantooth said.
However, the cost of producing silicon carbide is steadily decreasing. Crucially, because SiC-based systems require smaller and less expensive supporting components, the total cost of the entire motor drive system is reduced, making it increasingly attractive to manufacturers in both the automotive and aerospace industries. The research project, which was supported by a grant from the Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E), is a key part of this push toward commercial viability. To further this work, the UA Power Group is opening a new Multi-User Silicon Carbide Research and Fabrication Laboratory to advance microchip production and foster collaboration between academia and industry.
