Modeling of airgap influence on DC voltage generation in a dynamo-type flux pump

Ghabeli, Asef; Pardo, Enric

doi:10.1088/1361-6668/ab6958

Cited by 21 publications

(48 citation statements)

References 36 publications

(89 reference statements)

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“…The gap dependence of the open-circuit voltage computed by Ghabeli and Pardo [14] also agrees with experiments. In [14], it is also shown that this voltage is independent of the critical current density, Jc, when the superconductor is fully penetrated by supercurrents. Since these overcritical eddy currents must recirculate in the HTS wire, and can co-exist with a transport current, the wire width is a key parameter and [15] shows that this should be sufficiently large so that the eddy and transport currents do not drive the full width of the wire into the fluxflow regime.…”

Section: Introductionsupporting

confidence: 81%

“…The DC output voltage obtained from an HTS dynamo arises naturally from a local rectification effect caused by overcritical eddy currents [7][8][9][10][11][12]: an effect that has been observed in HTS materials as far back as Vysotsky et al [13]. The gap dependence of the open-circuit voltage computed by Ghabeli and Pardo [14] also agrees with experiments. In [14], it is also shown that this voltage is independent of the critical current density, Jc, when the superconductor is fully penetrated by supercurrents.…”

Section: Introductionsupporting

confidence: 72%

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Modelling the Frequency Dependence of the Open-Circuit Voltage of a High-T _c Superconducting Dynamo

Ainslie

Quéval

Mataira

et al. 2021

IEEE Trans. Appl. Supercond.

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A high-Tc superconducting (HTS) dynamo enables the injection of large DC currents into a superconducting circuit, without the requirement for current leads. In this work, we attempt to explain the frequency dependence of such dynamos/flux pumps reported in the literature, where it is observed that the rate at which the open-circuit DC voltage increases reduces with increasing frequency, in contrast to the expected linear behaviour. Heat generated in the HTS wire has been the common explanation given to date for this phenomenon. Here we offer an alternative explanation: the interaction between and current flow in the different layers of the HTS wire as the frequency of the dynamo increases. Our claim is based on numerical analysis using a segregated H-formulation finite-element model of the HTS dynamo benchmark problem that is extended to include the full HTS wire architecture and coupled with a thermal model. This framework enables us to efficiently model the relative movement between the rotating room-temperature permanent magnet and the stationary HTS wire and to study the impact of the frequency of rotation and temperature on the open-circuit DC voltage of the dynamo.

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Section: Introductionsupporting

confidence: 81%

Section: Introductionsupporting

confidence: 72%

Modelling the Frequency Dependence of the Open-Circuit Voltage of a High-T _c Superconducting Dynamo

Ainslie

Quéval

Mataira

et al. 2021

IEEE Trans. Appl. Supercond.

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“…High-T c superconducting (HTS) dynamos [1][2][3][4][5][6][7][8][9][10][11][12][13] and other similar HTS "flux pumps" [14][15][16][17][18][19][20][21][22] have been receiving continuing attention recently, as they offer a potential solution to the dc current-injection problem in a wide range of superconducting machines [23] and magnets [24,25]. Specifically, the HTS dynamo is of interest for its predicted output produced by a HTS dynamo arises naturally from Maxwell's laws [12] when applied to a situation in which eddy currents flow in a thin sheet exhibiting a highly nonlinear local resistivity.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of the High- Tc Superconducting Dynamo: Models and Experiment

et al. 2020

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High-T c superconducting (HTS) dynamos are experimentally proven devices that can produce large (more than a kiloamp) dc currents in superconducting circuits, without the thermal leak associated with copper current leads. However, these dc currents are theoretically controversial, as it is not immediately apparent why a device that is topologically identical to an ac alternator should give a dc output at all. Here, we present a finite-element model and a comparison of it with experiment that fully explain this effect. It is shown that the dc output arises naturally from Maxwell's laws when time-varying overcritical eddy currents are induced to circulate in a HTS sheet. We first show that our finite-element model replicates all of the experimental electrical behavior reported so far for these devices, including the dc output characteristics and transient electrical waveforms. Direct experimental evidence for the presence of circulating eddy currents is also obtained through measurements of the transient magnetic field profile across the HTS tape, using a linear Hall array. These results are also found to agree closely with predictions from the finite-element model. Following this experimental validation, calculated sheet current densities and the associated local electric fields are examined for a range of frequencies and net transport currents. We find that the electrical output from a HTS dynamo is governed by the competition between transport and eddy currents induced as the magnet transits across the HTS tape. The eddy currents are significantly higher (approximately 1.5 times) than the local critical current density, and hence experience a highly nonlinear local resistivity. This nonlinearity breaks the symmetry observed in a normal ohmic material, which usually requires the net transport current to vary linearly with the average electric field. The interplay between local current densities and nonlinear resistivities (which both vary in time and space) is shown to systematically give rise to the key observed parameters of experimental HTS dynamo devices: the open-circuit voltage, the internal resistance, and the short-circuit current. Finally, we identify that the spatial boundaries formed by each edge of the HTS stator tape play a vital role in determining the total dc output. This offers the potential to develop alternative designs for HTS dynamo devices, in which the internal resistance is greatly reduced and the short-circuit current is substantially increased.

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“…In recent years, several numerical models have been developed, which can be categorized into two groups. The first group models the open-circuit mode, where the output current is zero [22][23][24][25][26][27][28]. All of these models could explore the essential mechanism of the flux pump to deliver a DC voltage by the assumption of constant critical current density J c for the HTS tape characteristic.…”

Section: Introductionmentioning

confidence: 99%

“…All of these models could explore the essential mechanism of the flux pump to deliver a DC voltage by the assumption of constant critical current density J c for the HTS tape characteristic. However, only some of them considered J c (B, θ) dependency, which enable the models to generate an output voltage much closer to reality and comparable to experiments [22,23,25]. The second group presented in [29] and [30] are capable of also modeling the HTS dynamo with an imposed DC transport current; using these models, the I-V curves of the flux pump and the associated effective resistance at different frequencies could be obtained.…”

Section: Introductionmentioning

confidence: 99%

Modeling the charging process of a coil by an HTS dynamo-type flux pump

Ghabeli,

Ainslie,

Pardo

et al. 2021

Preprint

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The high-T c superconducting (HTS) dynamo exploits the nonlinear resistivity of an HTS tape to generate a DC voltage when subjected to a varying magnetic field. This leads to the so-called flux pumping phenomenon and enables the injection of DC current into a superconducting coil connected to the dynamo without current leads. In this work, the process of charging a coil by an HTS dynamo is examined in detail using two numerical models: the Minimum Electromagnetic Entropy Production and the segregated H-formulation finite element model. The numerical results are compared with an analytical method for various airgaps and frequencies. Firstly, the I-V curves of the modeled HTS dynamo are calculated to obtain the open-circuit voltage, shortcircuit current and internal resistance. Afterward, the process of charging a coil by the dynamo including the charging current curve and its dynamic behavior are investigated. The results obtained by the two models show excellent quantitative and qualitative agreement with each other and with the analytical method. Although the general charging process of the coil can be obtained from the I-V curve of the flux pump, the current ripples within a cycle of dynamo rotation, which can cause ripple AC loss in the HTS dynamo, can only be captured via the presented models.

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Modeling of airgap influence on DC voltage generation in a dynamo-type flux pump

Abstract: High-temperature superconducting (HTS) Flux pumps are promising devices to maintain steady current mode in HTS magnets or to energize rotor windings in motors and generators in a contactless way. Among different types of flux pumps, the

Cited by 21 publications

References 36 publications

Modelling the Frequency Dependence of the Open-Circuit Voltage of a High-T _c Superconducting Dynamo

Modelling the Frequency Dependence of the Open-Circuit Voltage of a High-T _c Superconducting Dynamo

Mechanism of the High- Tc Superconducting Dynamo: Models and Experiment

Modeling the charging process of a coil by an HTS dynamo-type flux pump

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Modeling of airgap influence on DC voltage generation in a dynamo-type flux pump

Abstract: High-temperature superconducting (HTS) Flux pumps are promising devices to maintain steady current mode in HTS magnets or to energize rotor windings in motors and generators in a contactless way. Among different types of flux pumps, the

Cited by 21 publications

References 36 publications

Modelling the Frequency Dependence of the Open-Circuit Voltage of a High-T c Superconducting Dynamo

Modelling the Frequency Dependence of the Open-Circuit Voltage of a High-T c Superconducting Dynamo

Mechanism of the High- Tc Superconducting Dynamo: Models and Experiment

Modeling the charging process of a coil by an HTS dynamo-type flux pump

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Product

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Modelling the Frequency Dependence of the Open-Circuit Voltage of a High-T _c Superconducting Dynamo

Modelling the Frequency Dependence of the Open-Circuit Voltage of a High-T _c Superconducting Dynamo