Electric aircraft motor gets superconducting upgrade

Of the countless technologies invented in the previous half century, high -temperature superconductors are the most promising and still the most disappointing. Decades of research have made a classification of materials that superconds at temperatures in the form of -140 ° C (133 kelvins) under ambient pressure. And yet commercial applications have been elusive.

Now, however, some developments may eventually push superconductors with high temperatures into commercial use. There is an availability, at relatively moderate costs, of copper-oxide-based superconducting tape, which is being manufactured by some companies for startups working on Tokakam fusion reactors. Reactor uses superconducting tapes, usually made of yttrium barium copper oxide in powerful electromagnets. Other growths include a separate group of startups that are using tapes to manufacture electric motors with very high power-to-west ratio, mainly for use in electric aircraft.

From the later group of startups HeitixTo lead the business under the leadership of research formed in 2017 Kiruba Haran But University of Illinois Urabana-Shampain. Last April, the company tested a prototype motor with superconducting rotor magnets. According to Haran, the test, which included spinning a propeller in a laboratory setup, was validated by the major components of the company’s designs for superconducting motors that would work at the power level of 5 and 10 MW. Such levels will be sufficient to provide electricity to a regional passenger airliner with several motors. Work was funded in part from a grant Advanced Research Project Agency -Energy (Arpa-e).

“HTS (high temperature superconductors) are getting a moment, as the cost is rapidly decreasing, operated by all work on fusion,” Haran says. “A lot of people are accelerating production, and new startups, and new capabilities, are coming in the market.”

Hinetics is probably one of a dozen companies, trying to use high -temperature superconductors to manufacture extremely efficient motors with large and small, very high strength density. These include aerospace giant Airbus, working on a superconducting airline under a program. ZeroAs well as Toshiba, Rethionon and UK Startups HyphelusHowever, Hinetics is taking an unusual approach.

The general approach to manufacture a superconducting machine uses superconducting materials for rotor or stator coil, or both. Typically, the coil is cooled with a liquid or gas placed at a sufficiently low temperature by the external crychuling system. Colds the superconducting coil by fluid convection, physically does so as exposure to the coil through heat exchanges and takes away the heat. The system has been successfully used in some experimental motors and generators, but it suffers from many fundamental problems. There is a need to transmit cooling fluid through a large rotor coil, which are embedded in a rotor assembly which is probably moving on thousands of revolutions per minute. Another problem is that this approach requires a complex cryocholing system that includes pumps, seals, gaskets, pipes, insulation, a rotary coupling that transfers cryogen to and out in the rotor, and other components that can fail and which add a lot of weight.

The rotor coil in an experimental Hettics electric motor is made of a high -temperature superconductor. They are cooled by a crychuller that run axially under the center of the motor. Rotor assembly and crychullers are attached within a vacuum vessel.Heitix

Revolutionary idea of ​​Hinetics: Spin Cryoculler

On the other hand, the system of Hinetics uses a self-contained cryocular, which is quite small to be connected to the rotor, and which rotates with it, eliminates the need to pass fluids inside and out of a spinning vessel. With this arrangement, “you do not have to immerse the superconductor in the fluid,” noted Laurent Pilon, an associate director for technology in ARPA-E. Instead, “there is a crychuller, and a cool connection, and you exclude heat from superconducting magnetic coil to crychuller, performing a refrigeration cycle. The beauty here is that it simply simplifies everything because now you have only a crocular that rotates with the shaft.”

In this configuration, the rotor assembly, including the coil, is cooled by conduction instead of convection. The rotor is installed within a vacuum chamber. The heat from the superconducting magnet assembly is transferred through a “thermal bus”, originally just a disc-shaped copper structure that operates heat to the crychuller, which is connected to the other side of the copper disc.

One of the challenges, Haran says, a crychuller was looking for small and light to spin at high rates and work while doing so. For its proof-of-concept unit, Hinetics team used an off-the-shelf Sterling-cycle Cooler from Sun PowerThis can remove only 10 watts of heat from the rotor assembly, but, in this configuration, it is all necessary to keep the rotor coil superconducting, says Haran.

A potential defect of the system is that, due to this relatively low heat-rugable capacity, the cryocullator takes a few hours to cool the superconducting magnets to start operating. According to Haran, the future versions will reduce the required period. And on the bright side, low heat-ruin rate means high efficiency, as the cooler has sufficient power to maintain the required low temperature during operation, and not too much capacity.

Prototype used a slip ring to provide electric power to spinning cryostat and rotor magnets. But the future versions of the motor will use a wireless system, possibly based on inductive coupling, Haran.

In the last April last April, the tests of the superconducting motor of HINTICS valid the original design and cleared the way for the manufacture of more powerful units.Heitix

Applications on ships are also possible

He opted not to make the status not to make superconducting, as the stator is activated by an alternative-current (AC) wave in a specific configuration. Superconders are only completely defective for direct current. So the application of AC for the superconducting coil in the stator will result in power losses, which will require another cooling system to remove heat from the stator.

Haran’s figures are not necessary. Only with superconductors in the rotor coil, the motor will gain capacity in the range of 98 to 99.5 percent, which is actually more than four or five percent more than the permanent-magnet synchronous motor. Haran also insists that the superconducting design will achieve this high efficiency without any decrease in the power density, a combination that is difficult to get in a traditional motor.

Four or five percentage points may not take too much, but it matters in specific aviation applications, especially when coupled with high strength density. On its website, Hinetics claims that its motor has a constant specific power. 10 kW per kilogramWhich will put the machine in one of the most electrical-waste units available on a constant power basis. According to Haran, the next generation of superconducting motor will receive 40 kW/kg, which will be more than commercially available.

Although the aviation is initial goal, the haran sees the possible applications in the ship’s propulsion, where the high volumetric power density of the motor will be a draw. “It is really exciting that we are looking practical looking at a transformative new technique,” he says. “Once you reach the megawatt and low speed, anywhere you need high torque, it can be very interesting.”