Helmholtz Electric Machine

The HEMM is a is a wound-field partially superconducting machine that implements a combination of rotor superconducting and stator normal conductor elements, along with an integrated acoustic cryocooler, to achieve some of the benefits of a superconducting motor without the need for an external cryogenic system. The combination of the described elements allows a motor to be built which essentially operates like any other motor when viewed as a black box, but substantially enhanced performance can be achieved. The incorporation of superconductors on the rotor to create a high-level magnetic field results in a specific power and efficiency that could not be achieved any other way. The HEMM can achieve over 98% efficiency in a lightweight electric machine with an operating power greater than 1.4 MW, a specific power greater than 16 kW/kg (ratio to electromagnetic mass), and a rated operating speed of 6800 RPM. The HEMM can be used as both a motor or a generator, offering a wide range of applications including propulsion systems for hybrid aircraft, electric trains, hybrid cars, and turboelectric ships, as well as generator systems for wind turbines, power plants, or motors for other industrial machinery.

Glenn's novel system supports the NASA Aeronautics Research Mission Directorate (ARMD) strategic plan to leverage advancements in technologies over the next 25 years and beyond, leading to new aircraft configurations with enhanced performance, improved energy efficiency, and reduced CO2 emissions. The electric system is a multi-megawatt micro-grid that converts mechanical energy to electric via generators, and electric energy to mechanical via motor-driven fans. This innovation would use the variation in aircraft throttle settings to produce a high-voltage (20 kilovolts), variable-frequency 9-phase AC distribution system. Using doubly fed electric machines (generator, propulsor, and flywheel) allows for field excitation that can cause variable-frequency or variable speed operation around the commanded throttle setting. The flywheel enables an energy storage system that recovers and reuses energy, while the flywheel slews with the throttle control using the electromagnetic torque produced by the doubly fed electric machine. This design permits both sub-synchronous and super-synchronous operation using limited field excitation power provided through power converters. Finally, the reduced switchgear mass facilitated through the use of a high-frequency AC system, setting-less protection zones, and simplified switches for fault clearance provides enhanced operational capability. This system can be controlled so that fault energy is minimized, preventing collateral damage to aircraft structures even with high voltage distribution. Glenn's innovative system adds performance, efficiency, reliability, and cost savings to cutting-edge hybrid electric technology. This is an early-stage technology requiring additional development, and Glenn welcomes co-development opportunities.

Distilled to its core components, the cable is composed of either a flexible or rigid transmission line with integrated oil-based cooling. Instead of solid wire, current flows through small conductive tubes made of aluminum or copper, which are actively cooled by pump-driven oil flowing through them. Although these smaller conductors have higher resistance and generate more heat, the active cooling offsets this heat generation. This integrated design results in a cable with up to a tenfold improvement in weight per megawatt of power delivered compared to existing solutions. The use of smaller conductive cables with active cooling reduces the temperature requirements for insulation because more current can be run through the cable. As such, voltage can be reduced, mitigating partial discharge issues, and making insulation an easier engineering challenge. Due to significant weight reductions, specialized duct work is no longer needed. A collection of junction, splicing, and termination components allow the cable to be built into a power and thermal bus to service multiple electrical components. Initial tests demonstrated the ability to conduct 1,000 amps through actively cooled cables at lower mass than state-of-the-art alternatives, confirming feasibility for next-generation aircraft electrification. However, the cable has broad applications across all vehicle electrification where weight and thermal management are high priorities and is now available for patent licensing.

Aircraft thermal management systems typically comprise over half the mass associated with full electric power propulsion systems, with significant negative impact on fuel efficiency. In addition, the traditional method of using jet fuel to cool aircraft generators does not provide enough cooling for use in flight-weight cryogenic systems. Lastly, the much higher bus voltages required for flight-weight systems (4.5 kV vs. 270 V) introduce additional spark-ignition hazards associated with alternative cryogenic cooling fuels, including liquid methane or liquid hydrogen. The Glenn flight-weight thermal management system addresses all of these problems by using the considerable waste heat energy from turbogenerators to create a pressure wave thermoacoustically. This wave can then be delivered quietly and efficiently via routed ductwork to hollow pulse-tube coolers located near any component in the aircraft that requires cooling. The tubes can be fabricated in any length and can be curved to fit any space. This technology also allows waste heat energy to be used in at least four ways: 1) the waste heat energy can drive a thermoacoustics-based ambient or cryogenic heat pump; 2) it can be channeled directly into a thermoacoustic engine that generates power; 3) it can convectively preheat the fuel/ or air supplied to the aircraft engine; 4) it can drive a pulse-tube generator providing power. The delivered thermoacoustic power can provide cabin cooling as well as ambient/cryogenic cooling of converter, cables, and motors. In addition, this power can be converted to local electric power through the use of a transducer (such as a linear alternator) or piezoelectrics. Further, the efficient thermal management system enables the size, mass, and resultant cost of the radiating fins to be reduced. Glenn's system offers an efficient method of cooling next-generation flight-weight electric aircraft with significant benefits for fuel efficiency and safety.

The innovation uses the rotating blades of the compressor section to act as structural support for the generator. Since the compressor is the coolest part of the engine, it will reduce the potential for interference with magnetics and associated curie points of the permanent magnets. The placement of the generator in the cooler part of the engine flowpath (fan or compressor) will also improve the electrical insulation system's degradation and serve to improve overall system lifetime. The configuration proposed by Armstrong's design would be an axial magnetic flux permanent magnet generator or motor. The electrical/mechanical interface could serve to deliver power to the shaft of the turbojet/fan or extract power from the shaft. This axial electromagnetic flux design is more efficient for the combined function of aero-thermal heat transfer and generation of electricity. This is due to the relative amount of available cooling surface area, which has an advantage over radial designs given the total system volumetric aspect ratio of the generator/compressor section. When the system is viewed as a thermodynamic cycle, it is more efficient because it is essentially a regenerative cycle, with the heat of generation being fed back into the cycle instead of being released into the ambient surroundings