A team led by physicists Christoph Utschick and Professor Rudolf Gross at the Technical University of Munich (TUM) has succeeded in fabricating a coil of superconducting wires capable of transmitting power on the order of more than five kilowatts without contact and with only minimal losses. The wide range of potential applications includes autonomous industrial robots, medical equipment, vehicles, and even aircraft.

Contactless power transmission has already established itself as a key technology for charging small devices such as mobile phones and electric toothbrushes. Users would also like to see contactless charging available for larger electrical machines, such as industrial robots, medical equipment, and electric vehicles.

These devices could be placed at a charging station whenever they are not in use. This would allow even short periods of downtime to be used effectively to recharge their batteries. However, the transmission systems currently available for high-performance charging in the kilowatt range and above are large and heavy, as they rely on copper coils.

In collaboration with the companies Würth Elektronik eiSos and the superconducting coating specialist Theva Dünnschichttechnik, a team of physicists led by Christoph Utschick and Rudolf Gross has succeeded in creating a coil with superconducting wires capable of transmitting contactless energy on the order of more than five kilowatts (kW) without significant losses.

Reducing AC Losses in Superconductors:
To achieve this, researchers had to overcome a challenge. Small AC losses also occur in superconducting transmission coils. These losses increase as transmission efficiency increases, with a decisive impact: the surface temperature of the superconducting wires rises, and superconductivity plummets.

The researchers developed a special coil design in which the individual coil windings are separated from each other by spacers. "This trick significantly reduces alternating current loss in the coil," says Christoph Utschick. "As a result, power transmission up to the kilowatt range is possible.".

Optimization with analytical and numerical simulations.
The team chose a coil diameter for their prototype that resulted in a power density higher than that possible in commercially available systems. "The basic idea with superconducting coils is to achieve the lowest possible resistance to alternating current within the smallest possible winding space and thus compensate for the reduced geometric coupling," says Utschick.

This forced researchers to resolve a fundamental conflict. If they made the distance between the windings of the superconducting coil small, the coil would be very compact, but there would be a risk of superconductivity collapsing during operation. On the other hand, larger separations would result in lower power density.

"We optimized the distance between the individual windings using analytical and numerical simulations," says Utschick. "The spacing is approximately equal to half the width of the tape conductor." The researchers now want to work on further increasing the amount of transmissible power.

Exciting application areas:
If they succeed, the door will open to a host of exciting application areas, such as industrial robotics, autonomous vehicles, and high-tech medical equipment. Utschick even envisions electric racing cars that can be dynamically charged on the track, as well as autonomous electric aircraft.

However, the system's large-scale applicability still faces a hurdle. The coils require constant cooling with liquid nitrogen, and the cooling vessels used cannot be made of metal. Otherwise, the walls of the metal vessels would heat up considerably in the magnetic field, much like a pot on an induction cooktop.

"There is no cryostat of this type currently available on the market. This will require a major development effort," says Rudolf Gross, Professor of Technical Physics at the Technical University of Munich and Director of the Walther-Meissner Institute of the Bavarian Academy of Sciences and Humanities. "But the achievements so far represent a major step forward for contactless energy transmission at high power levels.".

Publication:

Christoph Utschick, Cem Som, Ján Souc, Veit Große, Fedor Gömöry, and Rudolf Gross.
Superconducting wireless power transfer beyond 5 kW with high power density for industrial applications and fast battery charging.
IEEE Transactions on Applied Superconductivity, February 2, 2021.
Link: https://ieeexplore.ieee.org/document/9345521

More information:

The cooperation partner Würth Elektronik eiSos defined the topic and funded the industrial promotion underlying this publication. Essential parts of the research were carried out at the Walther-Meissner Institute (WMI) of the Bavarian Academy of Sciences and Humanities. The high-temperature superconductors used were supplied by Theva Dünnschichttechnik, a spin-off company of the Technical University of Munich.