Getting in Tune: Researchers Solve Tuning Problem for Wireless Power Transfer Systems

Researchers from North Carolina State University have developed a new way to fine-tune wireless power transfer (WPT) receivers, making the systems more efficient and functional. WPT systems hold promise for charging electric vehicles, electronic devices and other technologies.

Researchers have shown that it is possible to transmit power wirelessly by using magnetic resonance. Even minor changes in how the transmitter or receiver is tuned, however, can result in faulty power transmission.

A new prototype developed at NC State addresses the problem by automatically – and precisely – re-tuning the receivers in WPT systems. The researchers focused on receivers because methods already exist that allow researchers to use electronics to precisely tune the transmitters.

“We’re optimistic that this technology moves us one step closer to realizing functional WPT systems that can be used in real-world circumstances,” says Dr. Srdjan Lukic, an assistant professor of electrical and computer engineering at NC State and co-author of a paper on the research.

WPT systems work by transmitting magnetic waves on a specific frequency from a transmitter to a receiver. These magnetic waves interact with a coil in the receiver to induce an electric current. If the coil is tuned so that its resonant frequency matches the frequency of the magnetic waves, the current it produces is amplified. However, if the receiver and the transmitter are out of tune, the system becomes inefficient and doesn’t transfer a significant amount of power. The receiver coil still picks up a trace amount of current, but it is not amplified.

This is a problem because many factors can affect the tuning of a receiver or transmitter, such as temperature or proximity to other magnetic objects. In other words, a hot summer day could wreak havoc on the tuning of a receiver.

Lukic and NC State Ph.D. student Zeljko Pantic developed an electronic prototype that incorporates additional circuitry into the receiver that does two things: it injects small amounts of reactive power into the receiver coil as needed to maintain its original resonant frequency; and, if the transmitter’s tuning changes, the prototype can read the trace amount of current being transmitted and adjust the receiver’s tuning accordingly.

“Because we are using electronics to inject reactive power into the receiver coil, we can be extremely precise when tuning the receiver,” Lukic says. “This degree of fine-tuning maximizes the efficiency of the WPT system.

“The next step is to try incorporating this work into technology that can be used to wirelessly charge electric vehicles.”

The paper, “Framework and Topology for Active Tuning of Parallel Compensated Receivers in Power Transfer Systems,” is published online in IEEE Transactions on Power Electronics and was supported by the Advanced Transportation Energy Center at NC State. The paper was co-authored by Pantic and Lukic.

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Note to Editors: The study abstract follows.

“Framework and Topology for Active Tuning of Parallel Compensated Receivers in Power Transfer Systems”

Authors: Zeljko Pantic, Srdjan Lukic, North Carolina State University

Published: online, IEEE Transactions on Power Electronics

Abstract: Wireless power transfer (WPT) based on magnetic coupling is becoming widely accepted as a means of transferring power over small to medium distances. An unresolved issue is the source and receiver resonance matching in multi-receiver systems where the source operating frequency adjustment is not possible. This paper presents a framework to analyze the effect of parallel-compensated receiver detuning on the power transfer in WPT systems. Building on this analytical study, we present a new receiver design for WPT systems. The proposed design combines a parallel compensated resonant tank with a tri-state boost converter. By synchronizing the tri-state boost switching period with the half-period of the resonant tank voltage, we position the inherently discontinuous current pulse drawn by the tri-state boost to control both active and reactive power flow from the resonant circuit to the tri-state boost. Controllable reactive current can be used effectively to emulate appropriate inductance or capacitance to tune the resonant tank and achieve optimal power transfer.

One response on “Getting in Tune: Researchers Solve Tuning Problem for Wireless Power Transfer Systems

  1. Patrick Bruce says:

    The N.C. State University mechanical Engineering Department won a Nobel prize in engineering in the years 1928 for the invention of the steam engine car. Please talk to the Nobel Committee in Olso, Norway to take position of your award and the money that goes with it.
    If you put a standard regular alternator on a electric car it would never need to be recharged. It is a closed electrical curcuit. (Trillion Dollar Idea…please help with the lost state history with regards to NCAA championships) The NCAA admits it was founded in 1910 but does not say anything thing about giving out championships until 1939 but the Official University of Southern California sports website(athletic dept site) states very clearly that USC won a Track and Field NCAA championship in 1921, It would seem very strange if that was the only thing the NCAA did from 1910 to 1939.

    Patrick Bruce

    (My phone will be off until sunday of this coming week but feel free to check things out and get back with me thru email)

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