Prof. Al-Thaddeus Avestruz and ECE PhD student Xin Zan work to improve the efficiency and reliability of wireless power transfer. They focus on high-frequency and very high-frequency power conversion, which is best for miniaturization.
Their paper, “Performance Comparisons of Synchronous and Uncontrolled Rectifiers for 27.12 MHz Wireless Power Transfer Using CMCD Converters,” won a Best Paper Award at the last IEEE Energy Conversion Congress and Exposition, which is the top IEEE conference in the field of electrical and electromechanical energy conversion.
In their paper, Avestruz and Zan examine different designs of rectifiers, which are electrical devices that convert alternating current to direct current. Because rectifiers exist within many electronics, improving rectifier design helps improve the function and lifespan of the electronics.
Uncontrolled rectifiers automatically manipulate the conversion, but synchronous rectifiers can be programmed to commence power conversion at specific times, reducing power loss in the process. They also examined active vs. passive conversion. Active conversion allows for bi-directional power transfer but is a more complex design, whereas passive conversion is a simpler design that only allows for power transfer in one direction.
“What we found was that uncontrolled rectifiers are more efficient at higher power levels, but if bidirectional power transfer is needed, synchronous rectifiers are necessary,” Avestruz says. “It really depends on the application.”
Wireless power transfer (WPT) has many applications, such as charging your cell phone. It is particularly helpful for people with implanted medical devices because it can recharge and prolongate the life of the devices. Avestruz and Zan developed a simpler design that not only allows the devices to be smaller and therefore less invasive, but also facilitates higher power and higher efficiency.
“For these high frequencies, not many circuits work, but our circuit has fewer components, so it’s more robust and easier to design,” Zan says. “I think that’s what people think is an advantage in our paper.”
For this paper, Avestruz and Zan focused on 27.12 MHz, and they are now working on 100 MHz and beyond.
“The big challenge is that as you go higher in frequency, semiconductors are less efficient in the transmitter and receiver,” Avestruz says. “So we’re working to improve that trade-off with better circuits.”
Avestruz is a member of the Michigan Power and Energy Laboratory and director of the Power Electronics and Energy Research Studios (PEERS) at the University of Michigan. Zan is a fourth year PhD student who won the Richard F. and Eleanor A. Towner Prize for Distinguished Academic Achievement last year.