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.

This paper aims to shed light on the possibility of first-generation electric aviation in Norway by looking at both the potential and the limitations of today’s technology while emphasizing Norway’s geographical opportunities and unique regional network as a pioneer in this field. Operating a flight distance up to 400 km would cover around 77 % of all domestic flights in Norway. In this work, the key factors influencing the scalability of electric flight are investigated and critically discussed, including battery technologies, propulsion systems, aircraft designs, and important aspects of the flight profile. A case study is presented based on five different flight distances in Norway (from 77 km to 392 km) and two different aircraft bodies. Our proposed framework is used to make detailed-level calculations for the required power, energy, and battery state of charge. The results show that slight energy density improvements in the battery technology would facilitate the implementation of electric aircraft, rendering the possibility of retrofitting already existing planes. However, other alternatives, such as novel aircraft design and adjusted mission profiles, are also viable options for complying with weight and power capability requirements to scale up all-electric aircraft for distances up to 400 km.

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.

One of the attractive benefits of slotless machines is low losses at high speeds, which could be emphasized by a careful stator core loss assessment, potentially available already at the pre-design stage. Unfortunately, mainstream iron loss estimation methods are typically implemented in the finite element analysis (FEA) environment with a constant-coefficients dummy model, leading to weak extrapolations with huge errors. In this paper, an analytical method for iron loss prediction in the stator core of slotless PM machines is derived. It is based on the extension of the 2-D field solution over the entire machine geometry. Then, the analytical solution is combined with variable- or constant-coefficient loss models (i.e., VARCO or CCM), which can be efficiently computed by vectorized post-processing. VARCO loss models are shown to be preferred at a general level.Moreover, the paper proposes a lookup-table-based (LUT) solution as an alternative approach. The main contribution lies in the numerical link between the analytical field solution and the iron loss estimate, with the aid of a code implementation of the proposed methodology. First, the models are compared against a sufficiently dense dataset available from laminations manufacturer for validation purposes. Then, all the methods are compared for the slotless machine case. Finally, the models are applied to a real case study and validated experimentally.

This paper presents the exact transient solution to the unbalanced and balanced faults in the doubly-fed induction machine (DFIM). Stator currents, rotor currents, and stator fluxes have been validated using simulation and experiment. The work is meant to strengthen and fasten the predictability of large DFIMs in the design stage to comply with mechanical constraints or grid fault issues. Moreover, the analytical approach reduces the computational costs of large-scale stability studies and is especially suited to the initial phase where a plethora design computations must be carried out for the DFIM before it is checked for its transient interaction with the power system. The possibility to dynamically estimate DFIM performance is simplified by original equations derived from first principles. First, a case study of a large 265.50 MVA DFIM is used to verify the proposed “large machine approximation” using simulation, achieving an exact match. Then, laboratory measurements were conducted on a 10.96 kVA and a 1.94 kVA DFIM to validate the transient current peaks predicted in the proposed analytic expressions for two-phase and three-phase faults, respectively.

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.

The sudden short-circuit is considered the gold-standard parameter measurement method for wound-field synchronous machines (WFSMs) as it enables the recording of the characteristic quantities in near-to-real conditions. However, the test needs huge pieces of equipment, but even worse, it reduces the lifetime of the electrical components by up to 10 years due to the high winding overhang mechanical forces. The DC-Decay tests are low-power alternatives to obtain the characteristic quantities without damaging the machinery. To allow wider use of this method, there are a couple of challenges left that are tackled by this paper. The two main open challenges are, firstly, the number of measurements needed to reach a particular precision, and secondly, a comparison of the DC-Decay with the sudden short-circuit test to allow the validation against the gold standard. More detailed, this paper explores the main challenges associated with the practical use of the DC decay method, which is a non-conventional and detailed-level approach to characterize WFSMs. We provide replies and recommendations regarding the number of measurements, suggesting the minimum number of recorded tests needed to obtain the equivalent diagram with a given accuracy, which has been further validated with an experimental case study. Moreover, the potential enhancement and precision of the parameter identification algorithm are studied in detail. Finally, the equivalent parameters of the DC decay method are compared to the gold standard, which concludes on what the characterization means in terms of predicting accurate transient short-circuit currents for WFSMs.

A new approach to predict the additional costs of reactive power system services delivered by large hydrogenerators is proposed in this letter. It is based on the application of the accumulated average efficiency (AAE), which has recently been proposed. An optimal operational path within the capability diagram with minimal losses is derived. This path can be used to calculate additional losses from operational regimes deviating from the optimal one for each active power level. Finally, the additional losses are accumulated in a similar manner as the AAE to estimate the extra cost of the operational regime, with ideal operation as the reference. In addition, the accuracy of a data clustering approach is explored to speed up the computation of the AAE and the accumulation of additional costs.

The energy transition is aimed to take advantage of the operational flexibility of hydropower to extend the in- tegration of intermittent renewable sources. Consequently, the hydrogenerators will have to operate in regimes far away from their designed best-point operation. In order to accurately assess the impact, this paper presents a useful approach to determine the overall operating efficiency of synchronous generators under intermittent operation. An accumulated average efficiency (AAE) model is proposed and compared against an alternative approach; the weighted average efficiency (WAE) model. It is found that the WAE approach produces unrealistic low efficiencies when the generator operates in synchronous condenser mode (SCM) for long periods. In general, the AAE supersedes the WAE for all the different load distributions that were investigated. This was further illustrated by a worked example and by constructing more complex load distributions. A load distribution dominated by SCM yields a difference as high as 33.18%, while an even distribution deviates 1.43 % in their respective efficiencies. Finally, a yearly on-site measurement of our studied 103MVA generator’s concentrated load distribution revealed a discrepancy of 0.67 %, which is a significant deviation considering what the operating regime would mean in terms of economic implications.

In this paper, an AC superconducting multi-phase symmetric-winding machine is designed for a wind power generator to improve its performance and reduce losses, where four handpicked topological designs were explored and compared. In particular, it is found that using high-phase order of unique phasors further improves the performance. The iron losses are reduced, and the rippling behaviour is reduced due to the smoother airgap magnetic flux density. Furthermore, a higher LCM is achieved due to a better slot-pole combination for fractional slot concentrated windings without having space sub-harmonics. Nonetheless, it is shown that creating a smooth air gap magnetic flux density does not improve the AC hysteretic superconducting losses; thus, further analysis with another approach must be done. Moreover, it is found that the Meisner effect is present in the machine and is inversely proportional to the AC hysteretic superconducting losses. Finally, it shows that a 13-phase AC-superconducting machine can achieve a theoretical limit approaching 101.7017 Nm/kg for the torque-to-weight (TTW) ratio, outperforming a classic winding layouts.

Safety-critical power conversion systems play a major role in the paradigm shift towards more electric aircraft (MEA) architectures. This paper reviews the electrical machines and their power electronic systems that are currently competing in the application of integrated starter-generators (S/Gs) in MEA power systems. Motivated by the strict requirements of sufficient electrical starting capability, super-high power density and ultra-high reliability, additional considerations on the overall system design are necessary, including the power electronic converters (PECs) and integrated thermal designs. These aspects are discussed not only in the light of their many benefits but also of the challenges introduced by the continuous advancements and emerging innovations in the power conversion technology. In achieving the MEA goals and capitalize on all potential benefits, optimization-based design approaches will be necessary, where the aggregation of electric machines, PECs and the aircraft grid is considered as an integrated system to be optimized. This review highlights the importance of these aspects and offers a view on future perspectives and open issues.

This paper investigates and implements a procedure for parameter identification of salient pole synchronous machines that is based on previous knowledge about the equipment and can be used for condition monitoring, online assessment of the electrical power grid, and adaptive control. It uses a Kalman filter to handle noise and correct deviations in measurements caused by uncertainty of instruments or effects not included in the model. Then it applies a recursive least squares algorithm to identify parameters from the synchronous machine model. Despite being affected by saturation effects, the proposed procedure estimates 8 out of 13 parameters from the machine model with minor deviations from data sheet values and is largely insensitive to noise and load conditions. Submitted to IEEE IECON 2019.