Stardust and Ohio State’s next-generation electric machine
A mineral found in stardust helped electrical engineers at The Ohio State University win a large-scale, $3.7 million overall, power efficiency project sponsored by the United States Department of Energy (DOE).
“The dream system now is in front of us,” Longya Xu said, director of Ohio State’s Center for High Performance Power Electronics (CHPPE). “We have operated the system. It does reach the goal.”
The world market for medium voltage electric motors is growing fast. They are the backbone of international industry. Power systems for oil and gas companies, refineries, or water treatment facilities all require a range of fans, pumps, compressors, grinding mills, metal rolling, and hoists in order to get results.
Ohio State was among five winning teams earning DOE funding to develop the next-generation electric machines and drives. Buckeye researchers see the value in pursuing the most efficient systems.
“Compared to traditional gas turbine or diesel engine solutions, the power electronics-based motor drive has almost double efficiency,” according to the group proposal abstract.
Electrical and Computer Engineering (ECE) professors Xu and Jin Wang, along with Assistant Professor Julia Zhang, make up the Ohio State team to create the first next-generation, silicon carbide-based medium voltage megawatt level converter -A 7 kV, 1 MVA SiC based Modular Multilevel Converter, or MMC.
SiC is a semiconductor containing silicon and carbon, ideal in high-power systems for its ability to achieve better efficiency and power density in harsh working environments.
Rare on Earth, the mineral is found naturally in meteorites and stardust, believed to have originated outside our solar system.
Synthetic SiC, however, has been mass produced as a powder for hundreds of years to create high endurance car brakes, bulletproof vests, LEDs, or components in early radios.
In the CHPPE lab located in the basement of Caldwell Hall, Wang and students in CHPPE gave a live demonstration of MMC, running the system from 0 hertz to 1000 hertz and back again. As the frequency increases, the voltage and current waveforms remain under control.
“You can see that our capacitor voltage keeps very stable,” CHPPE Graduate Research Assistant Ziwei Ke said.
“It’s a very interesting research project,” Xu said. “Our target is very ambitious. We want to reduce the size of the drive system 30 percent, and we want to improve the efficiency from 98 percent to 99.3 percent. That sounds like not that big of a number, but let me tell you, the losses will be reduced by 20 kw to 7 kw.”
It paves the way for an efficiency increase of 30 percent, he said.
“Which means your cooling system will be much simpler, and the size of your inverter will be way smaller,” Xu said.
Wang said silicon carbide significantly improves power density.
“By using the high-switching capability of silicon carbide devices, we can do high frequency injection at low fundamental frequencies. The capacitor voltage can be kept almost constant. We are fully utilizing the capability of silicon carbide to really increase the power density of our MMC,” he said.
Zhang said they incorporated a half-bridge structure for each of the 36 submodules, which gives a total of 72 switches to control the hardware in-the-loop system, allowing them to test all the control algorithms beforehand.
“It really helps us to reduce all the de-bugging efforts and possible damage to the hardware while we’re doing high-powered tests,” she said.
Wang said the success of the project has already led to multiple new million-dollar research awards from the Department of Energy and the Advanced Research Projects Agency-Energy.
Story by Ryan Horns, ECE/IMR Communications Specialist (Horns.firstname.lastname@example.org)