91 research outputs found
Prediction of superconducting properties of materials based on machine learning models
The application of superconducting materials is becoming more and more
widespread. Traditionally, the discovery of new superconducting materials
relies on the experience of experts and a large number of "trial and error"
experiments, which not only increases the cost of experiments but also prolongs
the period of discovering new superconducting materials. In recent years,
machine learning has been increasingly applied to materials science. Based on
this, this manuscript proposes the use of XGBoost model to identify
superconductors; the first application of deep forest model to predict the
critical temperature of superconductors; the first application of deep forest
to predict the band gap of materials; and application of a new sub-network
model to predict the Fermi energy level of materials. Compared with our known
similar literature, all the above algorithms reach state-of-the-art. Finally,
this manuscript uses the above models to search the COD public dataset and
identify 50 candidate superconducting materials with possible critical
temperature greater than 90 K
A Data-Driven Methodology for Modelling Losses in HTS Power Systems
When designing a superconducting device one of the main obstacles is the AC losses.
These losses created numerous difficulties, particularly in the design of the cryogenic system:
the heat created from these losses must be removed in such a way that the cryogenic
temperature is not affected, as to not change the materials state from superconductor
to normal. Currently, most simulations of AC losses in superconductors are done using
numerical methods, such as the finite element method. This type of simulation requires
a significant amount of time and computational power.
A data-driven model is proposed in this work to make determining AC losses in
a superconducting device easier. A lock-in amplifier method of AC loss measuring is
applied to superconducting coils and transformers, as well as a direct VâI method. With
these results, an artificial neural network is constructed, trained and optimized in order
to accurately predict AC losses in such devices.
This approach is meant to determine AC losses quickly and without the requirement
for significant computational power by using only a macro description of a device, such
as the number of turns in a coil and the core size of the transformer.
This work was developed in the ambit of the tLOSS project âTransforming Losses
Calculation in High Temperature Superconducting Power Systemsâ (reference PTDC/EEIEEE/
32508/2017_LISBOA-01-0145- FEDER-032508).Ao conceber um dispositivo supercondutor, um dos principais obstĂĄculos sĂŁo as perdas
AC. Estas perdas criam numerosas dificuldades, particularmente na conceção do
sistema criogénico: o calor devido a estas perdas deve ser removido de forma que as
temperaturas criogénicas não sejam afetadas, para não alterar o estado do material de
supercondutor para normal. Atualmente, a maioria das simulaçÔes de perdas de AC em
supercondutores são feitas utilizando métodos numéricos, nomeadamente o método dos
elementos finitos. Este tipo de simulação requer uma quantidade significativa de tempo
e poder computacional.
Um modelo orientado por dados é proposto neste trabalho para facilitar a determinação
de perdas AC num dispositivo supercondutor. Um método de amplificador lock-in
para medição de perdas AC é aplicado a bobinas supercondutoras e transformadores,
bem como um mĂ©todo direto VâI. Com estes resultados, uma rede neural artificial Ă©
construĂda, treinada e otimizada de modo a prever com precisĂŁo as perdas AC em tais
dispositivos.
Esta abordagem destina-se a determinar perdas AC rapidamente e sem necessidade de
poder computacional significativo, utilizando apenas uma descrição macro de um dispositivo,
tal como o nĂșmero de voltas numa bobina e o tamanho do nĂșcleo do transformador.
Este trabalho foi desenvolvido no Ăąmbito do projeto tLOSS âTransformando o CĂĄlculo
de Perdas em Sistemas de PotĂȘncia com Supercondutores de Alta Temperaturaâ (referĂȘncia
PTDC/EEI-EEE/32508/2017_LISBOA-01-0145- FEDER-032508)
Surface and inter-phase analysis of Composite Materials using Electromagnetic Techniques based on SQUID Sensors
In this thesis an electromagnetic characterization and a non-destructive evaluation of new advanced composite materials, Carbon Fiber Reinforced Polymers (CFRP) and Fiber-Glass Aluminium (FGA) laminates, using an eddy-current technique based on HTS dc-SQUID (Superconductive QUantum Interference Device) magnetometer is proposed. The main goal of this thesis is to propose a prototype based on a superconducting sensor, such as SQUID, to guarantee a more accuracy in the quality control at research level of the composite materials employed in the aeronautical applications.
A briefly introduction about the superconductivity, a complete description of the SQUID properties and its basic working principles have been reported. Moreover, an overview of the most widely used non destructive technique employed in several industrial and research fields have been described. Particular attention is given to the eddy current testing and the technical improvement obtained using SQUID in NDE. The attention has been focused on two particular application, that are the main topics of this thesis. The first concerns with the investigation of the damage due to impact loading on the composites materials, and the second is the study of the corrosion process on the metallic surface. The electrical and mechanical properties of the tested advanced composite materials, such as Carbon Fiber Reinforced Polymers (CFRPs) and Fiber-glass Aluminium (FGA) laminates are investigated. The experimental results concern the non-destructive evaluation of impact loading on the CFRPs and FGA composites, by means of the electromagnetic techniques; the investigation of the electromechanical effect in the CFRPs using the SQUID based prototype and the AFM analyses; and the study of corrosion activity of the metallic surface using magnetic field measurement
Design of a superconducting DC wind generator
The trend towards larger power ratings of wind turbines asks for innovations in power generation, which requires lower weight and cost, smaller size, higher efficiency and reliability. Due to high current-carrying capability and no DC losses of superconductors, a superconducting wind generator can have a superior power to weight/volume ratio with high efficiency. The work in the book mainly focuses on the feasibility study and design of a superconducting DC wind generator
Design of a superconducting DC wind generator
Offshore wind energy has received a lot of interest as one important renewable energy source. One promising way to reduce the Levelized Cost of Electricity (LCOE) of offshore wind energy is by developing large wind farms and turbines with large ratings. The average wind turbine size has reached 4.2 MW in 2015 and turbine sizes of 6-8 MW have already been seen in the wind market. Even larger turbine sizes are managing to pave their way from studies to market. The trend towards larger ratings and more offshore installations asks for innovations in power generation, which requires lower weight and cost, smaller size, higher efficiency and reliability. Due to the high current-carrying capability and no DC losses of the superconductors, superior power to weight/volume ratio with high efficiency of a superconducting generator can be achived. Moreover, direct current (DC) transmission has been put forward for the offshore wind farms mainly due to the overall economic benefit, as they are located far away from the land. Hence, this thesis introduces a DC generation and transmission scheme which consists of superconducting DC wind generators and superconducting DC cables as a possible technical solution. This enables a highly efficient and compact generator and in addition a new and also very efficient generator connection scheme at DC.
The work presented in the thesis focuses on the feasibility study and design of a superconducting DC wind generator. In part, an optimisation method will be developed by taking superconducting tape length (cost), mass, volume, and efficiency into a simplified objective function. All necessary analytical equations will be derived to connect the electromagnetic design and mechanical design with properties of the superconducting tapes and iron materials. To increase the design accuracy, analytical equations to calculate flux density distribution in the superconducting DC generator will be verified by finite element analysis. Not only the active parts but also inactive structural materials will be included in the mass calculation. Based on the design method, the design of a 10 kW superconducting DC generator demonstrator will be described. The losses of the demonstrator and its commutation, torque and efficiency at different wind speeds will be addressed. As first steps towards the demonstrator, properties of key components, superconducting tapes, iron materials and a superconducting coil, will be tested and characterized. Moreover, a preliminary test of a superconducting coil at 77 K will be completed. In order to identify the potientials that a large scale superconducting DC wind generator could offer, a 10 MW superconducting DC generator will be designed and a comparison with conventional synchronous generators will be made. Additionally, this work will also discuss the savings of HTS tapes by optimizing outer rotor diameter, pole pair number, and superconducting coil height, which contribute to a more competitive alternative to conventional generators
Computational design of new superconducting materials and their targeted experimental synthesis
In the last six years (2015-2021), many superconducting hydrides with
critical temperatures of up to 253 K, a record for today, have
been discovered. Now, a special field of hydride superconductivity at ultrahigh
pressures has developed. For the most part, the properties of superhydrides are
well described by the Migdal-Eliashberg theory of strong electron-phonon
interaction, especially when anharmonicity of phonons is taken into account.
The isotope effect, the effect of the magnetic field (up to 60-70 T) on the
critical temperature and critical current in the hydride samples, the
dependence of on the pressure and degree of doping - all data
indicate that polyhydrides are conventional superconductors, the theory of
which was created by Bardeen, Cooper, and Schrieffer in 1957.
This work presents a retrospective analysis of data for 2015-2021 and
describes the main directions for future research in the field of hydride
superconductivity. The thesis consists of six chapters devoted to the study of
the structure and superconductivity of binary and ternary superhydrides of
thorium (ThH and ThH), yttrium (YH and YH), europium and
other lanthanides (Ce, Pr, Nd), and lanthanum-yttrium (La-Y). This work
describes the physical properties of cubic decahydrides, hexahydrides, and
hexagonal metal nonahydrides, demonstrates high efficiency of evolutionary
algorithms and density functional methods in predicting the formation of
polyhydrides under high-pressure and high-temperature conditions. We proposed a
theoretical-experimental algorithm for analyzing the superconducting properties
of hydrides, which makes it possible to systematize the accumulated
experimental data. In general, this research is a vivid example of the
effectiveness and synergy of modern methods for studying the condensed state of
matter under high pressures
Superconducting wireless power transfer for electric vehicles
Electric vehicles (EVs) are an important pillar for the transition towards a cleaner and more
sustainable future as renewable energy can penetrate into the transportation section and act as
energy storage to cope with the intermittent supply of such energy sources. EVs have recently
been significantly developed in terms of both performance and drive range. Various models are
already commercially available, and the number of EVs on roads increases rapidly. Rather than
being limited by physical cable connections, the wireless (inductive) link creates the opportunity
of dynamic charging â charging while driving. Once realised, EVs will no longer be limited by
their achievable range and the requirement for battery capacity will be greatly reduced. However,
wireless charging systems are limited in their transfer distance and power density. Such drawbacks
can be alleviated through high-temperature superconductors (HTS) and their increased current
carrying capacity, which can substitute conventionally used copper coils in the charging pads.
This thesis investigates the effectiveness of wireless power transfer (WPT) systems as a whole
and when HTS coils are used as well as HTS performance at operating frequencies commonly
used in WPT-systems. Initially, the fundamentals of superconductivity are outlined to give some
background on how such conductors can help tackle problems occurring in WPT-systems and how
their behaviour can be simulated. Subsequently, key technical components of wireless charging
are summarised and compared, such as compensation topologies, coil design and communication.
In addition, health and safety concerns regarding wireless charging are addressed, as well as their
relevant standards. Economically, the costs of a wide range of wireless charging systems has also
been summarised and compared.
To explore the benefits of WPT-system for EVs, a force-based vehicle model is coupled with an
extended battery model to simulate the impact of wireless charging on the state of charge of the
accumulator sub-system. In total, three different scenarios, i.e. urban, highway and combined
driving are presented. The trade-off between having a standalone charging option versus combined
dynamic (or on-road charging) and quasi-dynamic (stationary charging in a dynamic environment)
wireless charging is outlined and minimum system requirements, such as charging power levels
and road coverage, for unlimited range are established. Furthermore, the effects of external factors
such as ambient temperature, battery age and wireless transfer efficiency are investigated. It is
shown that employing combined charging at medium power levels is sufficient to achieve
unlimited range compared to high power requirements for standalone charging.
HTS coils show great potential to enhance the WPT-system performance with high current-carrying capability and extremely low losses under certain conditions. However, HTS coils exhibit
highly nonlinear loss characteristics, especially at high frequencies (above 1 kHz), which
negatively influence the overall system performance. To investigate the improvements, copper,
HTS and hybrid wireless charging systems in the frequency range of 11-85 kHz are experimentally
tested. Results are compared with finite element analysis (FEA) simulations, which have been
combined with electrical circuit models for performance analysis. The measurements and
modelling results show good agreement for the WPT-system and HTS charging systems have a
much higher transfer efficiency than copper at frequencies below 50 kHz. As the operating
frequency increases towards 100 kHz, the performance of HTS systems deteriorates and becomes
comparable to copper systems. Similar results are obtained from hybrid systems with a mixture of
HTS and copper coils, either as transmitting or receiving coils. Nevertheless, it has been
demonstrated that HTS significantly improves the transfer efficiency of wireless charging within
a certain range of frequencies.
The AC losses occurring in HTS coils, particularly transport current loss, magnetisation loss and
combined loss, at high frequencies are studied further. A multilayer 2D axisymmetric coil model
based on H-formulation is proposed and validated by experimental results as the HTS film layer
is inapplicable at such frequencies. Three of the most commonly employed coil configurations,
namely: double pancake, solenoid and circular spiral are examined. While spiral coils experience
the highest transport current loss, solenoid coils are subject to the highest magnetisation loss due
to the overall distribution of the turns. Furthermore, a transition frequency is defined for each coil
when losses in the copper layer exceed the HTS losses. It is much lower for coils due to the
interactions between the different turns compared to single HTS tapes. At higher frequencies, the
range of magnetic field densities, causing a shift where the highest losses occur, decreases until
losses in the copper stabilisers always dominate. In addition, case studies investigating the
suitability of HTS-WPT are proposed.
Lastly, methods to reduce AC losses of HTS coils are investigated with particular focus on flux
diverters, which have been used for low frequency superconducting applications but their
effectiveness at high frequencies is unexplored. Therefore, the impact of flux diverters on HTS
double pancake coils operating at high frequencies up to 85 kHz is researched. Various geometric
characteristics of the flux diverter are investigated such as air gap between diverter and coil, width
and thickness. An FEA-model was used to examine the coil and diverter losses at such frequencies
and different load factors between 0.1 and 0.8. It is demonstrated that flux diverters are a viable
option to reduce the coil losses even at high frequencies and the width of the coil has the biggest
impact on the loss reduction. In general, flux diverters are more suitable for applications using
high load factors. Lastly, the impact of the diverter in terms of magnetic field distribution above
the coil and overall loss distribution in the HTS coil was examined
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