Superconducting Wires Make Contactless High Performance Power Transmission Possible

Contactless power transmission is a hot topic in the power industry today. We’re seeing more and more wireless charging capabilities for phones, and other small electronics, sometimes even at distances over a meter, as EE Power previously covered. These applications are just the beginning. Some groups are finding applications in charging industrial robots, medical equipment, electric vehicles (EVs), and electric aircraft. 

This coil made of superconducting wires can contactlessly transmit power of more than five kilowatts without major losses. Image courtesy of C. Utschick / Würth Elektronik eiSos.

 

Conventionally, an engineer would use a copper coil to solve these problems, as they can achieve >90% efficiency and high power densities, but they come at the cost of size as they are very large and heavy. For this reason, a research team at the Technical University of Munich (TUM) has created a successful prototype of a superconducting coil for up to 5kW contactless power transmission with low losses, according to a new release from the school. The team is led by physicists Christoph Ultschick and Professor Rudolf Gross. The team also had industry partnerships with Wurth Elektronik, and Theva Dunnschichttechnik, a superconductor coating specialist.

According to the abstract of the team’s published research paper, the coils are built using high temperature superconducting (HTS) coils. Don’t get too excited, these “high temperatures” are still very cold in reality, as the prototype requires constant cooling in liquid nitrogen. The novel aspect of the team’s design however comes in its optimization.

The novel aspect of the team’s design however comes in its optimization. Alternating current losses in the coil grow with the performance of the coil, and it causes coil temperature to rise as well. This rising temperature can put the superconductor out of its required temperature range, causingsuperconductor collapse. This inverse relationship between performance and stability of the superconducting state required the team to separate individual windings of the coil with spacers. This significantly reduced the AC loss in the coil according to Christoph Utschick. The team then chose a coil diameter that would guarantee higher power density than in today’s commercial systems. 

However, to optimize performance, once had to achieve minimum AC resistance with the smallest winding space. These parameters, when minimized, can cause superconductor collapse. The team used simulations to find the optimal point between superconductor collapse and performance of the system, finding the ideal distance between windings. Designing under these parameters resulted in a coil with an experimentally measured DC-DC efficiency of 97% at 6kW power.

 

A closer look at the coils. Image courtesy of  C. Utschick / Würth Elektronik eiSos.

 

While all of these results are exceptionally promising, this technology has a ways to go prior to commercialization. As discussed prior, these coils need to be immersed in liquid nitrogen. However, metal vessels cannot be used, as their thermal properties will cause temperatures inside to rise above that of the superconductor’s range, and the superconductor will then collapse. Thus, as Rudolf Gross says, there is still an extensive amount of work to be done, but this innovation is a major step forward for contactless power transmission.

"There is as yet no cryostat like this which is commercially available. This will mean an extensive amount of further development effort,” Gross said. 

As our world continues to move towards a seemingly all-electric future, contactless charging is a huge benefit for larger machines like EVs and robotics. In order to achieve this though, there is a lot of research ahead, but the path is seeming to be set by the recent innovations at TUM.