Electric Aircraft Motor Gets Superconducting Upgrade

Among the countless technologies invented during the last half century, super-temperature superconductors are among the most promising and yet the most frustrating. Decades of research have given an assortment of materials which remove at temperatures up to -140 ° C (133 kelvins) at the ambient pressure. And yet, commercial applications were elusive.

Now, however, some developments could finally push superconductors to high temperature in commercial use. One is the availability, at a relatively moderate cost, of the copper -based superconductive band, which is produced by a few companies for startups working on Tokamak fusion reactors. The reactors use the superconductive ribbon, which is generally composed of barium yttrium copper oxide, in powerful electromagnetic. The other development involves a different group of startups that use the ribbon to build electric motors with powerful relationships / very high weight, mainly for use in electric aircraft.

Among this last group of startups, there is Hinetics, trained in 2017 to market research by Kiruba Haran at the University of Illinois Urbana-Champaign. Last April, the company tested an engine prototype equipped with superconductive rotor magnets. According to Haran, the tests, which included the rotation of a propeller in a laboratory configuration, validated key components of the company’s conceptions for superconductive engines that will operate at power levels of 5 and 10 megawatts. These levels would be high enough to supply a regional passenger airliner with several engines. The work was funded in part by an Advanced Research Projects Agency – Energy (ARPA -E) subsidy.

“HTS [high temperature superconductors] Have a moment, because the costs drop quickly, fired by all the work on the merger, “explains Haran.” Many people accelerate production, and new startups and new capacities are coming to the market. “”

Hinetics are a dozen companies, large and small, trying to use high temperature superconductors to build extremely effective engines with a very high power density. These include the aerospace giant Airbus, which works on a superconductive airliner under a program called Zeroe, as well as Toshiba, Raytheon and Startup UK Hyflux. However, Hinetics adopts an unusual approach.

Common approaches to build a superconductive machine use the superconductive material for rotor or stator coils, or both. As a rule, the coils are cooled with a liquid or gas preserved at a sufficiently low temperature by an external cryocoling system. The fluid cools the superconducting coils by convection, physically crossing the heat exchangers in contact with the coils and taking the heat as it does. The system has been successfully used in certain experimental engines and generators, but it suffers from several fundamental problems. A large is the need to circulate the cooling fluid through the rotor coils, which are integrated into a set of rotor which may turn into thousands of revolutions per minute. Another problem is that this approach requires a complicated cryocoling system which includes pumps, joints, joints, pipes, insulation, rotary coupling that transfers cryogen in and out of the rotor, and other components that can fail and add a considerable weight.

Rotor coils in an experimental hinetic electric motor are made of a high temperature superconductor. They are cooled by a cryocooler who has axially flowing in the center of the engine. The assembly of the rotor and the cryocooler are locked in an empty container.Hinetic

The revolutionary idea of ​​the hinetic: spin the cryocooler

The Hinetics system, on the other hand, uses an autonomous cryocooler which is small enough to be attached to the rotor, and which turns with it, eliminating the need to pass fluids in and out of a rotation container. With this arrangement, “you do not have to dive the superconductor into the liquid,” notes Laurent Pilon, associate director of technology at Arpa-E. Instead, “there is a cryocooler and a cold connection, and you withdraw the warmth of the superconducting magnetic coils at the cryocooler, performing a refrigeration cycle. Beauty here is that it simplifies everything because now you just have the cryocooler that turns with the rod.”

In this configuration, the assembly of the rotor, including the coils, is cooled by conduction rather than by convection. The rotor is installed in an empty room. The heat of the assembly of the superconductor magnet is transferred through a “thermal bus”, which is essentially only a copper structure in the shape of a disc which leads heat to the cryocooler, which is attached to the other side of the copper disc.

One of the challenges, said Haran, was to find a small and light cryocooler to turn at high rates and continue to work by doing so. For its concept proof unit, the hinetic team used a Sunpower Standard Stirling Cycle Cycle Cycle. It can only eliminate 10 Watts of heat from the assembly of the rotor, but, in this configuration, that is all that is necessary to keep the superconductive rotor coils, says Haran.

A potential disadvantage of the system is that due to this relatively low heat emitting capacity, the cryocooler takes a few hours to cool the superconductive magnet enough to start working. Future versions will reduce the necessary period, according to Haran. And on the right side, the low heat reinforcing rate means high efficiency, because the cooling is just enough power to maintain the low temperatures necessary during operation, and not much excessive capacity.

To provide electrical power to cryostat and rotation rotation magnets, the prototype used a sliding ring. But future versions of the engine will use a wireless system, perhaps based on inductive coupling, says Haran.

The superconductive hinetan engine tests last April validated the basic design and paved the way for the construction of more powerful units.Hinetic

Ship applications are also possible

He chose not to make the superconductive statistics, because in a typical configuration, the stator is under tension by an alternating current wave (AC). The superconductors are only completely lossless for direct current. Thus, AC application to superconductive coils in the stator would cause power losses that would require another cooling system to remove heat from the stator.

Haran thinks it is not necessary. With superconductors only in rotor coils, the engine will reach efficiency gains in the beach from 98 to 99.5%, or about four or five percentage points higher than realistic with a permanent magnet engine. Haran also insists that the superconductive design would reach this great efficiency without any reduction in power density, a combination difficult to make in a conventional engine.

Four or five percentage points may not seem much, but it would matter in typical aviation applications, known as pestle, in particular when associated with a higher power density. On its website, Hinetics says that its engine has a specific power continues 10 kilowatts per kilogram, which would place the machine among the densest units available, on a continuous basis. According to Haran, the next generation of the superconductive engine will reach 40 kW / kg, which would be much higher than anything that will be available in the trade.

Although aviation is the initial target, Haran sees potential applications in the propulsion of the ship, where the high volumetric power density of the engine would be a draw. “What is really exciting is that we see new transformational technology becoming practical,” he says. “Once you arrive at megawatts and low speed, wherever you need a high couple, it could be very interesting.”