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ISSN: 2772-8307
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cited:12
AC loss mitigation for high temperature superconducting coils in wireless power transfer
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Article Number:Article 100044
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Abstract
Corresponding email:Hongye.Zhang@manchester.ac.uk
With the rapid development of high temperature superconducting (HTS) technology, second generation (2G) HTS materials have become a promising alternative to traditional conductive materials in the power transmission industry. Recently, the topic of using HTS materials in wireless power transfer (WPT) systems for electric vehicles (EVs) has attracted widespread attention in the background of net zero transport. With virtually zero DC resistance and superior current-carrying capacity, HTS materials can achieve high quality factor and power density in the WPT resonant circuits compared to conventional metals, e.g., copper. However, the optimal working frequency for the conventional WPT system is relatively high in the order of kilohertz level. Superconducting coils working at high frequencies could generate high AC losses, reducing the overall power transfer efficiency (PTE) and increasing the cooling burden. In order to improve the PTE of HTS-WPT systems, the AC loss mitigation methods for different HTS coil topologies have been investigated in this paper by varying the inter-turn gap and tape width. Three HTS coil structures, namely the spiral coil, the solenoid coil and the double pancake (DP) coil, have been studied with a 2D axisymmetric multi-layer numerical model based on the H - formulation, and the simulation results have been validated by the published experimental data. The general loss characteristics, loss distributions in each turn, as well as magnetic flux densities have been analysed in detail for three types of HTS coils. Moreover, the impact of these two loss reduction methods on the WPT performance has also been evaluated. Findings have shown that increasing the inter-turn gap and tape width can effectively reduce the AC power losses and increase the PTE of the HTS-WPT system. The spiral coil demonstrates the highest AC power loss reduction effect and PTE while maintaining a stable level of magnetic fields. This paper is believed to deepen the understanding of superconducting WPT and provide a useful reference for more efficient wireless energisation applications.
cited:9
Design of a finite impulse response filter for rapid single-flux-quantum signal processors based on stochastic computing
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Article Number:Article 100045
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Abstract
Corresponding email:tangguangming@ict.ac.cn
Rapid-Single-Flux-Quantum (RSFQ) circuit technology is well known for its low power consumption and latency, which enables digital signal processing up to tens of GHz. As a fundamental digital filter, the Finite Impulse Response (FIR) filter has wide applications in communication systems. A design of an FIR filter based on RSFQ circuit technology is proposed. However, the FIR filter consumes large amounts of adders and multipliers. Based on Stochastic Computing (SC) theory with which adder and multiplier are much simpler, the hardware cost of FIR filter is dramatically reduced. A novel stochastic number generator (SNG), a stochastic-to-binary converter (SBC), and the FIR filter were designed and verified via logic simulation with a target frequency of 10 GHz. The results indicated the FIR filter performs correct operations. The proposed FIR filter consists of 2255 Josephson junctions (JJs) without wiring cells (i.e., Josephson Transmission Lines (JTLs), Passive Transmission Lines (PTLs)), which is acceptable, making it possible to be used in RSFQ digital signal processors.
cited:89
Low-temperature superconductors: Nb3Sn, Nb3Al, and NbTi
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Article Number:Article 100047
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Corresponding email:banno.nobuya@nims.go.jp
Low-temperature superconducting (LTS) wires are of significant importance in high-field magnet applications. Current developments of the LTS wires are attributed to many studies. Particularly, Nb3Sn is an attractive superconductor with substantial potential for performance improvement in view of an ideal microstructure that maximizes flux pinning properties. To date, various reviews have been reported on the physical properties of low-temperature superconductors. Therefore, this review focuses on understanding the fundamental phase formations and microstructural controls of low-temperature superconductors from the perspectives of growth kinetics, nucleation theory, and chemical potentials to facilitate the syntheses of these superconductors and advancement of wire production. Taking Nb3Sn as an example, the effect of Cu addition to Nb3Sn on Nb/Sn reactive diffusion is briefly described. Then, representative Nb3Sn formations are schematically summarized to broaden our understanding of the development behaviors of Nb3Sn. These behaviors are qualitatively reviewed in terms of Sn chemical potential. After mentioning the potential for performance improvement of Nb3Sn, the influences of element additions, specifically those of Zr and Hf additions, resulting in breakthrough microstructural refinements, on Nb/Sn diffusion are investigated. Subsequently, strengthening of the matrix via element additions is reviewed. Thereafter, taking Nb3Al as an example, the features of Nb3Al formation and basic development processes, including low-temperature processes, metastable phase transformations, and microstructural control, are described. Strain sensitivity, one of the most important properties of Nb3Al, is also briefly reviewed. Then, taking Nb alloy as an example, α-Ti precipitation in a binary Nb–Ti system is concisely summarized. Subsequently, recently reported new artificial pin incorporation based on a powder method is introduced, followed by a unique study of the application of high-temperature-tolerable Nb superconducting alloys in superconducting joints. This review makes a novel contribution to the literature as it provides a comprehensive understanding of phase formation in low-temperature superconductors.
cited:8
Effect of Gd addition on the superconducting properties of Ti-based V, Nb, Ta alloys
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Article Number:Article 100048
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Corresponding email:sheikramjan1995@gmail.com
The critical current density () of the body centered cubic (bcc) V0.6Ti0.4 alloy enhances significantly after the addition of rare earth Gd as the latter is immiscible in the matrix [S. Paul, et.al, IEEE Trans. Appl. Supercond. 31, 5 (2021)]. Very low solubility of Gd in other bcc elements like Ta and Nb is also well known [Jr. KA Gschneidner in Prog Sci Technol Rare Earths, vol. 1, pp. 222–258, 1964 M Neuberger, et.al in Handbook of Electronic Materials, Vol 4, 1972]. We use these facts to find the effect of adding 1 at.% Gd into the Nb0.6Ti0.4 and Ta0.4Ti0.6 alloys on the superconducting properties e.g., the transition temperature (), , flux pinning force density () and the microstructure. In spite of Gd being ferromagnetic, the in these alloys change only marginally (increase by 0.3 K in Ta0.4Ti0.6 and decrease by 0.15 K in Nb0.6Ti0.4 after Gd addition. The ( T, T = 4 K) increases by 5 and 1.5 times respectively in the Gd containing Nb0.6Ti0.4 and Ta0.4Ti0.6 alloys, which is quite small as compared to the increase observed in the V0.6Ti0.4 (20 times) system. With Gd addition, the grain size reduces approximately by 65% and 10% respectively in Nb0.6Ti0.4 and Ta0.4Ti0.6. Our analysis indicates that grain boundaries are the major flux line pinning centres in these alloys and the role of Gd in increasing the depends on the effectiveness of Gd in reducing the grain size. The grain boundary density depends strongly on the distribution of Gd precipitates, which is quite different from each other for two alloy systems under study. Moreover, our results suggest that the addition of Gd to commercial Nb-Ti (Nb0.37Ti0.63) alloy is a new promising route for achieving higher values.
cited:48
J-A formulation: A finite element methodology for simulating superconducting devices
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Article Number:Article 100049
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Abstract
Corresponding email:gdsantos@id.uff.br
High-temperature superconductors are a powerful technological option to be applied in the current scenario of energy transition. Their applications include fault current limiters, power electrical cables, and electrical machines, for example. Due to the non-linearities of superconductors, it is computationally costly to run real models of superconducting equipment. Therefore, it is of paramount importance to have a reliable and fast formulation to model superconducting devices. This paper proposes a new hybrid J-A formulation to simulate superconducting devices. The new formulation is validated with 5 case studies, some of which are benchmarks. The J-A formulation agrees in all cases and has a smaller computation time when compared with the T-A formulation. Moreover, due to the simple implementation, the proposed formulation allows the possibility of running the J and A formulations in the same order and presents itself as a potential feature to speed up and help the design of the superconducting devices.
cited:42
Numerical modelling of high-temperature superconducting dynamos: A review
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Article Number:Article 100033
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Corresponding email:mark.ainslie@kcl.ac.uk
The high-temperature superconducting (HTS) dynamo enables injection of large DC currents into a superconducting coil, without the need for thermally-inefficient current leads. Because of this important advantage, there is significant interest in using such technology to energise superconducting coils in superconducting rotating machines and NMR/MRI magnets. Despite the extensive experimental work carried out over the past decade, there was – until very recently – considerable confusion and debate regarding the physical origin of the HTS dynamo’s DC output voltage. Numerical modelling has played a key role in elucidating the underlying physics of such devices and several different numerical models have now been developed as useful and cost-effective tools to not only explain and further examine experimental results, but also optimise and improve dynamo designs. This review summarises all of the developments in this important area over recent years, including modelling the open-circuit voltage behaviour in 2D and 3D, the definition of a new benchmark problem for the HTS modelling community, investigating key dynamo parameters, modelling dynamic coil charging behaviour and calculating losses. A view towards the future is provided, including the outstanding challenges and the developments required to address these.
Review