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Abstract:The demand for alternative fueling methods to reduce the need for fossil fuels is not limited to the electrification of ground vehicles. More-electric and all-electric aircraft pose challenges, with extensive requirements in terms of power density, efficiency, safety, and environmental sustainability. This paper focuses on electrical machines and their components, especially for high-power applications like the main propulsion. The electrical machine is evaluated from different aspects, followed by a closer look at the components and materials to determine the suitability of the current standard materials and advanced technologies. Furthermore, the mechanical and thermal aspects are reviewed, including new and innovative concepts for the cooling of windings and for the use of additive manufacturing. Aircraft have special demands regarding weight and installation space. Following recent developments and looking ahead to the future, the need and the possibilities for light and efficient electrical machines are addressed. All of the approaches and developments presented lead to a better understanding of the challenges to be expected and highlight the upcoming opportunities in electrical machine design for the use of electric motors and generators in future aircraft. Several prototypes of electrical machines for smaller aircraft already exist, such as the electric drive of the Siemens powered Extra 330LE. The focus of this paper is to provide an overview of current technical possibilities and technical interrelations of high performance electric drives for aviation. A 1 MW drive is exemplified to present the possibilities for future drives for airplanes carrying a larger number of passengers. All presented techniques can also be applied to other drive power classes.

Results on an established batch process preparing melt-textured YBCO of high quality and in large quantities are reported. We used a standard composition Y1.5Ba2Cu3O7−x+1 wt % CeO2 without further doping to fabricate single domain YBCO monoliths in different sizes and shapes (cylindrical, quadratic) as well as rectangular multi-seeded YBCO monoliths. Up to 2–3 kg of melt-textured YBCO blocks were grown, reproducible in one box furnace run. Top seeding by a self-made SmBCO was improved and rationalized. Optimization of an oxygen annealing treatment led to macro-crack free YBCO monoliths. Each YBCO monolith was characterized by integral levitation force and field mapping. In a single domain, a quadratic monolith with a edge length of 38 mm, a maximum induction of 1.44 T at 77 K and a distance of 0.5 mm was frozen. The reproducibility of the batch process is guaranteed. Mean maximum induction from 1.1 to 1.2 T at 77 K per batch was reached. A trapped magnetic field of 2.5 T was achieved between two single domain monoliths in a gap of 1.5 mm at 77 K. Depending on the application, function elements with different sizes, designs and more or less complex geometry are constructed in several working steps by cutting, machining, bonding and passivation. Selected function elements were checked with field mapping at 77 K. The results of our function elements in HTSC reluctance motors with an output power of up to 200 kW using single domain material are shown. We report on a fly wheel system DYNASTORE and a system to levitate people.

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This paper is aimed at giving an overview of possible cooling technologies for electrical machines and their assessment for aviation applications, e.g., fan or propeller drives. The most important demand for aircraft is the minimization of the drive system weight comprising electrical machine, power electronics, and the cooling system. The potential of aluminum winding an overview about several cooling technologies with the Rankine or Brayton cycle or utilizing the phase change of the cooling fluid is given. As an alternative approach, the cooling structure inside the machine is studied. A very interesting potential was discovered with direct slot cooling (DSC) removing the heat where it is produced and, thus, simplifying the cooling system effort and its weight. Since it is one of the most promising approaches, this cooling method is studied in depth. Furthermore, it can also be combined with one of the cooling technologies discussed above.In the overview paper [6], focus is set on the most recent progress in thermal management of electric motors for aviation. Besides air cooling, oil bath cooling, water jacket cooling, heat pipe cooling, intra winding cooling channels with a thermal conductive polymer [7], and direct winding cooling with tube-like conductors are cited. In this case, the problem of large pressure drops in the cooling ducts of six bars or more occurs. As experimental results, current densities of 24.7 A/mm 2 and transient current density of more than 40 A/mm 2 with class F insulation were achieved. With class H insulation even higher, values up to 58 A/mm 2 could be possible. By using conductors with integrated cooling channels, current densities possibly reaching 130 A/mm 2 were anticipated. However, the losses increase with the square of the current density and are linear with the volume of the winding even though the temperature is within the limits of the insulation system. The extremely high copper losses will increase weight and size of the cooling system and the reduced efficiency also requires an increase of the on-board power supply (generators and prime movers, fuel tank or energy storages, wiring, switchgear).The weight advantages of such machines can be quickly overcompensated by the weight of the cooling system and the increased power supply. Therefore, an accurately balanced design of the drive system is necessary. A proposal for the improvement of this approach is given in Section 5.A reduction of the winding temperature level by lowering the coolant temperature below standard ambient temperature promises a reduction of the copper losses in the electrical machine and a longer lifetime of the insulation. The higher effort for such cooling systems may be compensated by the higher efficiency of the drive. Due to the usually high temperature drop between winding and cooling fluid, this requires low ambient temperatures-as given in high cruising altitudes-or the use of refrigerant cooling systems, which allow coolant temperatures below ambient temperatures. In a literature study, no pap...

Single-domain crack-free CeO2-doped YBCO monoliths synthesized in a conventional box furnace using a top-seeded-melt-growth process with an optimized time–temperature profile exhibit trapped magnetic fields of up to 1.4 T and self-field critical current densities at 77 K of up to 1.3 × 105 A cm−2. The observed magnetic properties of the samples correlate with the microstructure, which was studied using optical and scanning electron microscopy. With these high quality high temperature superconductor samples a superconducting magnetic bearing for a 2 MW/10 kW h class flywheel energy storage system was designed and has been tested in a model arrangement.

The paper deals with a new analytical approach for calculating eddy current losses in permanent magnet synchronous machines with tooth windings. The analytical method presented here differs from known approaches in two points: The field is calculated using an all-in-one method, so the simultaneous calculation of stator and no-load field is possible. To take finite magnet dimensions into account, the calculation of an easy-to-use correction factor for endless dimensions is introduced. Losses caused by stator slotting as well as losses caused by stator harmonics are included. To allow for several load cases the stator current phase angle and the eddy current reaction field is considered. Index Terms-eddycurrents, permanent magnet, loss l l l l J x t J t a x J t ax

Modified concept of permanent magnet excited synchronous machines with improved high-speed features Permanent magnet (PM) excited synchronous machines used in modern drives for electro-mobiles suffer in high speed regions from the limited battery-voltage. The field weakening requires designing machines with reduced power conversion properties or increasing the size of the power converter. A new concept of such a machine features PM excitation, single-tooth winding and an additional circumferential excitation coil fixed on the stator in the axial center of the machine. By the appropriate feeding of this coil, the amplitude of the voltage effective excitation field can be varied from zero to values above those of the conventional PM-machines. The capability of reducing the excitation field to zero is an important safety aspect in case of failing of the feeding convertor.