Redundancy is one of the core concepts in aviation engineering. Commercial aircraft are designed with multiple backup systems for hydraulics, electronics, flight controls, navigation, and fuel supply. The result is ultra-high reliability for engines and control systems—in fact, most multi-engine aircraft are capable of staying aloft even if one of their engines fails during flight.
As aviation begins to transition from combustion-powered jet engines to cleaner electric motors, designers need to make sure that electrically propelled aircraft can achieve the same level of reliability via redundancy. That’s why engineers at the University of Wisconsin-Madison are working on a NASA-funded project to develop ultra-reliable fault-tolerant electric motor drives for future aircraft propulsion systems.
“Fault tolerance is key to insuring that if one drive unit fails, the rest of the drive system continues operating,” says project leader Tom Jahns, the Grainger Professor Emeritus of Power Electronics and Electric Machines in the Department of Electrical and Computer Engineering. “If you have four modules and one fails, you still have three good ones left that will continue operating without any interruption.”
The challenge is that electric propulsion motor drives require many components that are susceptible to damage from demanding operating conditions including high temperatures and vibration. High fluctuations in power loads can also cause problems, as anyone who has blown a fuse by turning on a toaster while the microwave is already operating can attest.
In their project, Jahns, ECE Professor Bulent Sarlioglu and graduate students in the Wisconsin Electric Machines and Power Electronics Consortium (WEMPEC) are designing and testing innovative fault-tolerant modular motor drives that overcome these serious reliability issues.
The research began in 2017, when the team joined a multi-university project funded by NASA to develop a lightweight 1-megawatt integrated motor drive that set new records for high power density in electrified aircraft propulsion equipment. That project concluded with a successful test in 2022 and resulted in major advances, including incorporation of wide-bandgap power semiconductor switches to create compact, ruggedized drive units that were packaged in the same enclosure as the motor to reduce weight.
But that project didn’t focus much on reliability and redundancy. To fill that gap, Jahns convinced NASA to support a separate project that is now in its fifth year. The unique fault-tolerant machine drive design that resulted from this effort uses four separate electronic inverters that adjust the frequency and voltage of the power applied to the motor. Each of these inverters excites its own set of coiled windings in an integrated module to create a rotating magnetic field that causes the rotor to spin. The individual motor drive modules are magnetically and thermally isolated from the other three, preventing a fault in any one of the four modules from interfering with the normal operation of its neighboring modules.
“Imagine that the motor loses one of its four inverter-windings modules,” says Sarlioglu. “Can you recover from that failure by pushing the other three remaining healthy modules enough to get back to your original output power before the fault occurred? And what if you lose two modules? Those are the kinds of questions that we are investigating.”
The researchers designed a cutting-edge 40-kilowatt fault-tolerant modular motor drive incorporating these features which they built from scratch over the last four years. They then evaluated the performance of their prototype fault-tolerant modular motor drive on a testbed in UW-Madison’s Engineering Hall. A technical paper that they wrote to summarize their accomplishments was recognized in October 2025, with a first-prize paper award presented by the Electric Machines Technical Committee at the IEEE Energy Conversion Congress and Exposition (ECCE), one of the most renowned international conferences in their field.
Electric motors in the tens or hundreds of megawatts range required to power a full-size passenger airliner are still in the design stage, but Jahns says that small electric vertical takeoff-and-landing (e-VTOL) air taxis could take to the skies in the next few years. These much smaller aircraft with lower power requirements are prime candidates to take advantage of the team’s fault-tolerant modular motor drive technology.
But that’s not the endpoint. “The objectives that we’re setting are really aimed at something more ambitious, for the day when large commercial aircraft will be electrified,” says Sarlioglu. “That won’t be tomorrow or the day after tomorrow; we’re talking 10 or 20 years down the road. But we need to work on addressing the major technical challenges today in order to be ready.”
Jahns says he fully expects that UW-Madison engineers will be at the forefront of these new technologies, pointing out that Badgers are already important players in electric aviation, founding leading-edge companies like H3X and working in research and development at other innovative electric aviation startups.
“We make a real point of ensuring that every student who graduates from our master’s or PhD programs has spent a significant amount of time working in the lab on real motor drive equipment,” he says. “As a result, when they start a job, they’re able to hit the ground running. That is one of the things that’s really valued in WEMPEC graduates.”
Top photo caption: WEMPEC graduate students Xiaoyuan Zhang, Antonio Trujillo Parra and Ken Chen analyze the fault-tolerant motor drive they helped build as part of a NASA supported project. Submitted photo.