Although the electromagnetic performance of superconducting machines has received considerable attention, their thermal analysis remains largely unaddressed. In particular, there is no consensus on the feasible operating temperature of superconducting armature windings, even though this is a critical design parameter. To address this problem, this paper proposes a cryogenic lumped-parameter thermal network (LPTN) to quantify the temperature drop between the superconducting armature and the cryogenic coolant. As a case study, the model is used to analyze and improve a 2.5 MW cryo-electric aviation motor. For the liquid hydrogen–cooled design, it is found that the armature temperature could not be reduced below 32 K without compromising the machine performance. This is further increased to 35 K when gaseous helium is used as a coolant. Moreover, heat leaks through the thermal insulation were found to double the temperature rise of the armature windings. These findings emphasize that detailed thermal constraints need to be considered in the design of superconducting machines and to predict their achievable performance.

Accurate estimation of AC losses is crucial to successfully implement high-temperature superconductors (HTS) in the armature of electric machines. In this estimation, a purely sinusoidal current is often assumed. However, the connection to power electronic converters will introduce harmonics in the transport current, generally leading to higher losses. In this paper, four separate distorted current waveforms produced by space vector modulation were implemented to assess how harmonics from power electronics influence the HTS AC losses in a 2.5 MW superconducting aviation motor. By varying the switching frequency between 5 and 40 kHz, the amount of harmonic distortion was varied between the four cases. The ReBCO and copper layers were both modeled using a multilayer H-A-formulated model. While the harmonic distortion was found to have a minor impact on ReBCO layer hysteresis losses, it increased eddy current losses in the copper stabilizer by between 250 % and 471 %, depending on the amount of distortion. Consequently, the total losses increased by between 60 % and 123 %, with a higher copper loss fraction.

Numerical analysis of high-temperature superconductors (HTS) commonly addresses AC losses in the superconducting REBCO layer. However, alternating magnetic fields also induce eddy current losses in the metallic non-superconducting (non-SC) substrate, silver, and copper layers of the HTS, which cannot be overlooked for certain operating temperatures and frequencies. Previously, non-SC losses have been estimated numerically for simple geometries at 77 K. Using a multilayer H-A-formulated model, this paper estimates the eddy current losses for a full-scale 2.5 MW superconducting aviation motor for frequencies between 50 and 1000 Hz and temperatures between 25 and 60 K. Furthermore, a sensitivity study is presented to show how AC losses are impacted by specific design parameters such as the copper purity, angle of the external field, tapes per turn, tape height, and copper layer thickness. The results show that eddy current losses are negligible for high HTS temperatures and low frequencies. However, at low temperatures and high frequencies, these losses represent a significant share of the total, meaning that while they can be neglected for low-speed machinery, they must be considered for power-dense machinery, particularly if the planned cooling method involves liquid hydrogen (LH2) temperatures.

This paper presents a homogenized electro-thermal model for high-temperature superconductor (HTS) stacks made of multiple REBCO tapes, which reduces the computational complexity of their thermal analysis. The electromagnetic analysis is performed in both the H- and Tâ\euro“A-formulation. An average heat capacity and an orthotropic heat conductivity are derived for the equivalent thermal properties of the HTS coil. The proposed homogenization method is verified to produce the same results as the full model with an error below 5% for a range of scenarios, including transport losses, magnetization losses, AC frequencies from 50 to 300 Hz and a temperature range from 25 to 80 K. Finally, the model is applied to study a permanent magnet motor with HTS armature windings, and is verified to produce accurate results as long as the stabilizer eddy current losses are low. Compared to the full multilayer model, the newly proposed model allows for the use of a significantly coarser mesh, which reduces the computation time by an order of magnitude.

This article describes the design and analysis of a 2.5-MW, 5000-rpm electric motor with a slotted armature employing REBCO high-temperature superconductors (HTS). The alternating current and field in the armature induces AC losses in the superconductors, requiring cryogenic cooling. Therefore, the aim is to design a machine with sufficiently low losses to make this cooling realistic, which simultaneously outperforms the state-of-the-art. The reasoning behind the key design choices is presented before the model used for two-dimensional (2-D) finite element analysis (FEA) is described. Then, HTS AC losses are studied with the T-A-formulation, examining the impact of various operating conditions. Aligning the HTS tapes with the field was found to successfully reduce AC losses, while filamentization was only successful for more than 10 filaments. The final design had an estimated efficiency of 99.8%, an active torque density of 50.9 Nm/kg, and a cryogenic cooling power requirement of 0.05% of the output power.

Macroscopic superconductivity models have improved significantly over the last decades. Formulations and methods have been developed to faster solve problems involving high-temperature superconductors (HTS). Despite these developments, finite element analysis (FEA) of AC superconducting machines (SCMs) with HTS coils still remains time-consuming. The combined burden from the HTS models and the moving mesh makes the models complex and slow. To deal with this challenge, a new framework for FEA of AC superconducting SCMs with surface-mounted permanent magnet (PM) rotors and HTS armature windings is proposed in this paper. In this approach, the rotating rotor geometry is emulated with a stationary array of small PM segments excited with time-varying boundary sources. The major benefit of this approach is that the models can be realized without moving meshes, which increases the computation speed by more than one order of magnitude. In our dedicated case study of a complete SCM design, the speedup factors are 17.4x and 38.5x for the H-A and T-A formulations, respectively. Over a large parametric space of 18 design permutations, the highest relative error in calculated HTS loss was 4.12 percent. As a result, this work enables the designer to perform much more comprehensive performance studies of SCMs.

Hydrogen-powered airplanes have recently attracted a revitalized push in the aviation sector to combat CO2 emissions. However, to also reduce, or even eliminate, non-CO2 emissions and contrails, the combination of hydrogen with all-electric solutions is undoubtedly the best option to move toward the ambitious goal of climate-neutral aviation. Another important design choice is to store hydrogen cryogenically in its liquid form (LH2) to reduce space occupation compared to storage as compressed gas. However, the LH2 fuels cannot be utilized directly in fuel cells. It needs to be brought from liquid to a gas at about 350 K, where large amounts of heat must be added. Thus, a synergy can be made from this otherwise wasted cryogenic refrigeration power where superconducting machines (SCMs) and cold power electronics (CPE) are low-hanging fruits that could lead to radical space and weight reductions onboard the aircraft. These opportunities can be realized without having to pay the price, nor the volume occupation and mass needed for the cooling ability usually needed to achieve these extraordinary performances. In fact, this ground-breaking synergy makes cryogenic energy conversion relevant in a whole new way for aviation. The SCMs’ more than five times higher power densities than their conventional counterparts are exceptionally significant. This article introduces the recently proposed cryo-electric drivetrain initiatives and explores the opportunities of using direct hydrogen cooling as a potential heating solution to enhance the overall performance and scalability of zero-emission propulsion systems in future regional aircraft.

In this paper, we present a comprehensive sizing and performance analysis framework for a disruptive cryo-electric propulsion system intended for a hydrogen-powered regional aircraft. The main innovation lies in the systematic treatment of all the electrical and thermal components to model the overall system performance. One of the main objectives is to study the feasibility of using the liquid hydrogen (LH\textsubscript{2}) fuel to provide cryogenic cooling to the electric propulsion system, and thereby enable ultra-compact designs. Another aim has been to identify the optimal working point of the fuel cell to minimize the overall propulsion system’s mass. The full mission profile is evaluated to make the analysis as realistic as possible. Analyses are done for three different 2035 scenarios, where available data from the literature are projected to a baseline, conservative, and optimistic scenario. The analysis shows that the total propulsion system’s power density can be as high as 1.63 kW/kg in the optimistic scenario and 0.79 kW/kg in the baseline scenario. In the optimistic scenario, there is also sufficient cryogenic cooling capacity in the hydrogen to secure proper conditions for all components, whereas the DC/DC converter falls outside the defined limit of 110 K in the baseline scenario.