Showing papers in "IEEE Transactions on Applied Superconductivity in 2020"
TL;DR: The results show that the ADRC-BP has strong robustness and adaptability to the uncertainty of magnetic bearing model and the variation of external disturbance, and the decoupling control effect of AD RC-BP is better than that of conventional ADRC.
Abstract: In order to decouple the three-degree-of-freedom six-pole active magnetic bearing (3-DOF 6-pole AMB) with strong couplings, nonlinear and unstable disturbance, an active disturbance rejection control strategy based on BP neural network (ADRC-BP) is put forward. Firstly, the configuration, magnetic circuit, working principle and mathematical model of 3-DOF 6-pole AMB are introduced and established. Then, taking the 3-DOF 6-pole AMB as the controlled object, an ADRC-BP system is designed and a method of parameter tuning is proposed. Finally, the effectiveness of the control strategy is verified by simulation and experiments. The results show that the ADRC-BP has strong robustness and adaptability to the uncertainty of magnetic bearing model and the variation of external disturbance. The decoupling control effect of ADRC-BP is better than that of conventional ADRC.
51 citations
TL;DR: The objective and R&D activities of the 40 T all superconducting user magnet project are presented andInitial analysis of different HTS magnet designs, based upon the three presently viable HTS conductors: REBCO, Bi-2212, and bi-2223, has determined that each technology faces significant challenges.
Abstract: The National High Magnetic Field Laboratory has launched an innovative project to develop a 40 T all superconducting user magnet. The first year funding was awarded by the National Science Foundation in September 2018. Consideration of a 40 T superconducting user magnet sets target specifications of a cold bore of 34 mm with a homogeneity of 500 ppm over a 1 cm diameter of spherical volume, a better than 0.01 T set-ability and stability, and with an ability to ramp up to full field 50,000 times over its 20 years design lifetime. It will be a fully superconducting magnet that can withstand quenches at its full 40T field and provide a very low noise environment for experimentalists. These capabilities will enable the 40 T SC magnet to support higher-sensitivity measurements than possible in present-day resistive and hybrid magnets; high-magnetic-field measurements that will be uniquely capable of addressing physics questions on a number of expanding frontiers in condensed matter physics. A 40 T SC magnet would enable more users to run long experiments at peak field with much less power consumption compared with resistive and hybrid magnets. However, realization of such a 40 T SC magnet requires magnet technology well beyond the present state-of-the-art. Initial analysis of different HTS magnet designs, based upon the three presently viable HTS conductors: REBCO, Bi-2212, and Bi-2223, has determined that each technology faces significant challenges. Hence, we decided that four HTS magnet technologies consisting of Insulated REBCO, No-Insulation REBCO, Bi-2212, and Bi-2223 would be developed in parallel and technology gaps based on major risks will be closed in the R&D phase. The candidate technologies will be narrowed down at the decision points. The objective and R&D activities of the 40 T all superconducting user magnet project are presented.
47 citations
TL;DR: In this paper, the authors investigated the effect of an inhomogeneous hoop stress distribution induced by the screening current on a small REBCO coil with a strain measurement and a numerical simulation and showed that a large hoop stress modification causes not only a hoop stress increase, but also buckling of the conductor.
Abstract: Degradation of a REBCO coil under external magnetic fields is one of the major technical problems in the field of HTS magnet technology. A possible cause of such degradation is an inhomogeneous hoop stress distribution, or hoop stress modification (both increase and decrease), induced by the screening current. In this work, we investigate such a hoop stress modification by a small coil experiment with a strain measurement and a numerical simulation. An experimental result shows a very high stress increase factor of >4.1, defined by the maximum circumferential stress over BzJR stress, and the simulated result is in qualitative agreements. The strain (stress) shows a hysteresis effect corresponding to the screening current behavior. A large hoop stress modification causes not only a hoop stress increase, but also buckling of the conductor, which induces delamination and micro-clacks of the superconducting layer. We also show the stress modification can be reduced by bonding turns with epoxy.
43 citations
TL;DR: In this paper, a 2D time dependent model is proposed to assess the ac losses of superconducting motors based on the T-A-formulation, which by using the finite element method, allows its implementation in commercial software.
Abstract: Modeling high temperature superconductor (HTS) motors remains challenging mainly due to the high aspect ratio of these conductors but also because of the properties of the magnetic materials. This article presents a 2-D time dependent model to assess the ac losses of superconducting motors based on the new T-A-formulation, which by using the finite-element method, allows its implementation in commercial software. The T-A-formulation computes the magnetic flux density with different Maxwell's equations depending on the areas of the motor and makes it possible to use the thin strip approximation i.e., the HTS tapes are modeled as infinitely thin lines. The model is then expected to tackle the high aspect ratio of the HTS as well as decreasing both the mesh complexity and the computing time. The first objective of the article is to validate the method in 2-D by evaluating the ac losses of a specific synchronous motor called superconducting torque motor; the computed results are compared with good agreements to those assessed with the minimum electromagnetic entropy production method, already validated. In a second part, the same losses are computed, taking into account the field anisotropy of $J_{c}$ with the implementation of a dataset based on experimentally measured $I_{c}$ at 65 and 77 K. With the model proposed in this article, it is possible to calculate the magnetic field of a whole electrical machine cross section and compute the ac losses in the individual tapes of its windings within the same numerical model.
41 citations
TL;DR: In this paper, a dynamic circuit model of a single-sided figure-eight-shaped null-flux electrodynamic suspension (EDS) system was established, and the magnetic coupling calculation was carried out between the onboard superconducting magnets and ground coils by a semianalytical method.
Abstract: Superconducting electrodynamic suspension (EDS) train has the unique advantages of excellent levitation and guidance stabilities, large levitation gap, and so on. All of these merits make it a promising candidate for the future ultrahigh-speed transportations. In order to explore the dynamic characteristics of the EDS system with a figure-eight-shaped coil (ground coil), this article transforms the complex electromagnetic field coupling between the superconducting magnets and ground coils into a reduced circuit relationship based on the dynamic circuit theory. Meanwhile, the motion characteristics are introduced to establish the field-circuit-motion-coupled model. In this article, a faster and more convenient semianalytical method was proposed to solve mutual inductance. First, the dynamic circuit model of a single-sided figure-eight-shaped null-flux EDS system was established. The magnetic coupling calculation was carried out between the onboard superconducting magnets and ground coils by a semianalytical method. Furthermore, the time-step iteration method was utilized to solve the induced current governing equation of the ground coil under different operating conditions. The energy method was employed to find the transient solution of the levitation force, guidance force, and drag force. Second, the field-circuit-motion-coupled model was validated by the experimental data of MLX01 on the Japanese Yamanashi testline. To investigate the influence upon the suspension and guidance caused by the different connection types of figure-eight-shaped coil, a cross-connected EDS train dynamic circuit model was built. Finally, based on the field-circuit-motion-coupled model, the essential parameters affecting the stability of the system were explored, and the characteristics of the system when vertical or lateral displacement occurs were calculated and analyzed. The achievements of this article can provide a reference for the design of the EDS train for future even higher speed transportation.
39 citations
TL;DR: A novel high-temperature superconductive power flow controller and current limiter (PFCCL), which limits fault currents and manages power flow in the intended transmission line, is presented.
Abstract: This article presents a novel high-temperature superconductive (HTS) power flow controller and current limiter (PFCCL), which limits fault currents and manages power flow in the intended transmission line. The proposed device includes series HTS reactors, HTS controlling dc coil, recovery resistive coil, and power electronic switches, which protects the microgrid from the upstream ac grid, short-circuit faults, and it controls the power flow between a microgrid and the upstream grid. Performance of the proposed PFCCL is mathematically analyzed, utilizing MATLAB and Maxwell software, and then validated by laboratory scaled-down experimental setup. It is shown that the simulation results are in fair agreement with the developed experimental laboratory setup results.
39 citations
TL;DR: It has been shown that utilizing this optimized flux diverter, the axial short circuit forces have been reduced significantly.
Abstract: The appealing advantages of high-temperature superconducting (HTS) power transformers over conventional ones have attracted transformer manufacturing companies, power companies, research institutes, and universities worldwide to conduct research and development in this field. Unfortunately, HTS transformers are more vulnerable to mechanical stresses than conventional transformers. The results of the interaction between current carrying windings and leakage magnetic fluxes are the electromagnetic forces, which act on transformer windings. Under short circuit events, these forces are remarkable, and, therefore, catastrophic failure of transformer may arise. Flux-diverter applications have been reported in earlier literatures for increasing critical current or decreasing ac losses in HTS transformers. In this paper, a genetic algorithm based method is employed for the optimal design of flux diverter to minimize the axial short circuit force, in design stage of a sample 132/13.8 kV, 50 MVA three-phase core type HTS transformer. In this paper, the optimal dimensions, placement, and permeability of a flux diverter have been determined. It has been shown that utilizing this optimized flux diverter, the axial short circuit forces have been reduced significantly. Electromagnetic modeling and simulations, by the application of finite element method, have been employed for the verification of the analytical method results. A high degree of consistency has been observed between the analytical results and the simulation results.
33 citations
TL;DR: In this paper, the authors used the CryoSoft code THEA to simulate the quench behavior of various subscale CICCs in view of a quench experiment in SULTAN facility.
Abstract: Quench protection is a critical issue for magnet using high-temperature superconducting (HTS) materials such as REBCO. For cable-in-conduit conductor (CICC) with twisted REBCO tapes, which is considered for high-current HTS conductor for fusion magnet, the anisotropic critical current density (Jc) of tape and complex conductor layout will further complicate the quench behavior. The CryoSoft code THEA is used to simulate the quench behavior of various subscale CICCs in view of a quench experiment in SULTAN facility. The CICCs are composed of twisted tape stack assembled into copper shell (strand). It has been found that neglecting the anisotropy of Jc in quench simulation will significantly underestimate the hot spot temperature by about 40 K. Therefore, it could leave potential risk to damage the magnet. It is also shown that the thermal contact resistance between strand and the steel jacket (the conduit) plays a very important role on quench behavior. The hot spot temperature can be reduced by more than 100 K if the thermal resistance is reduced by two order of magnitude. On the other hand, variations of interstrand electrical and/or thermal resistance have only very little influence (few kelvin).
30 citations
TL;DR: The permanent magnets are not conducive to improving the power of LSRM and the PMA-LSRM is not outstanding compared with LFSPM motor under the condition of large air gap for rail transit.
Abstract: Linear switched reluctance motor (LSRM) has been investigated and supposed as a good candidate in railway system. Recently, permanent magnet assisted switched reluctance motor (PMA-SRM) has attracted extensive attention because of the high torque, robust structure and low cost. However, all these researches focus on the application of small air gaps. How does PMA-SRM perform in large air gap? No research has been conducted until now. As we know, there are many similarities between linear flux switching permanent magnet (LFSPM) motor and permanent magnet assisted linear switched reluctance motor (PMA-LSRM) such as similar primary iron, winding structure, robust secondary and a small amount of permanent magnets. In this case, what are the similarities and differences between these two kinds of motors in terms of electromagnetic characteristics? This paper will compare these two kinds of motors based on the volume of rail transit from the following aspects: thrust force, thrust ripple, efficiency. First, the topology, operation principle of the two LSRMs are introduced and designed. Then, the electromagnetic performance of LSRM is optimized through two dimensional finite element analysis (FEA) based on ANSYS software. The optimization objectives of PMA-LSRM are to maximize the thrust and to minimize the ripple at the given dimensions and the rated condition. The comparison of electromagnetic characteristics between LFSPM motor and PMA-LSRM is completed. Finally, it is concluded that the permanent magnets are not conducive to improving the power of LSRM. And the PMA-LSRM is not outstanding compared with LFSPM motor under the condition of large air gap for rail transit.
29 citations
TL;DR: In this paper, a closed-form expression describing the dependence of the resonance frequency on the length of the PTL is presented, which describes a set of forbidden lengths for PTL interconnect segments in RSFQ circuits.
Abstract: Superconductive passive transmission lines (PTL) are widely used for signal routing in large-scale rapid single flux quantum (RSFQ) circuits. Due to the imperfect matching of the transmission lines between the driver and receiver, single flux quantum (SFQ) pulses are partially reflected. The round trip propagation time of these reflections can coincide with the following SFQ pulse, resulting in a decrease in bias margins or incorrect circuit behavior. This resonant effect depends upon the length of the PTL and the clock frequency of the signal. A methodology to reduce and manage this effect is the focus of this article. A closed-form expression describing the dependence of the resonance frequency on the length of the PTL is presented. This expression describes a set of forbidden lengths for PTL interconnect segments in RSFQ circuits. The proposed methodology and algorithm insert active PTL-based repeaters into long superconductive interconnect while ensuring the length of the line segment is outside the forbidden region and increasing bias margins.
29 citations
TL;DR: In this paper, the authors present results of an experimental and analytical study on screening-current-induced strain gradients, performed with small REBCO pancake coils, wound with monofilament and 3-striate/4-filament tape.
Abstract: Screening currents in REBCO conductors, induced by time-varying magnetic fields, not only affect the field quality of HTS coils but also cause strain gradients along REBCO tape width that may overstress REBCO conductors used in NMR and other high-field magnets. In this paper, we present results of an experimental and analytical study on screening-current-induced strain gradients, performed with small REBCO pancake coils. Because we believe that screening current effect is reduced in multifilament conductor, we have studied 2 test coils, φ150 mm, one wound with monofilament and the other with 3-striate/4-filament REBCO tapes. A 5-T/ 300-mm room-temperature bore magnet was used not only to excite a strong screening current but also apply the nonuniform Lorentz force to each coil at 4.2 K. Our experiment and analysis have quantitatively demonstrated that we can effectively suppress the screening-current effect on strain gradient, not surprisingly, by using striated multifilament REBCO conductor.
TL;DR: In this article, a resistive-type dc superconducting fault current limiter (SFCL) is developed for the fault current limiting at the Suzhou Nami substation.
Abstract: A resistive-type dc superconducting fault current limiter (SFCL) is developed for the fault current limiting at the Suzhou Nami substation. The rated voltage and current are 20 kV and 400 A, respectively. The prospective peak value of the short-circuit current is about 3.5 kA, and the current could be limited to less than 2.1 kA by the SFCL. The SFCL uses about 1800-m stainless steel reinforced yttrium barium copper oxide (YBCO) conductor. According to the testing results, the developed SFCL has passed the dc withstand voltage test at 50 kV/min, the full-wave lightning impulse voltage at 95 kV, and the dc power switching test with a peak value of 2.26 kA and a fault duration of 16.5 ms.
TL;DR: In this article, the authors compare two dual formulations, either magnetic-field conforming or magnetic-flux-density conforming, for high-temperature superconductors and compare their results against benchmarks.
Abstract: In this article, we consider finite-element models for high-temperature superconductors and compare two dual formulations, either magnetic-field conforming or magnetic-flux-density conforming. The electrical resistivity of superconductors is described by a power law and is strongly nonlinear. We compare the accuracy and the efficiency of the dual formulations by starting from simple considerations on the concavity/convexity of the constitutive law involved in each case. We then study the numerical behavior of each formulation in one-, two-, and three-dimensional problems and compare their results against benchmarks. We draw general recommendations for the choice of a formulation, an iteration scheme for treating the corresponding linearized constitutive law, and a time-stepping extrapolation scheme. This approach is extended to soft ferromagnetic materials with a saturation law. Since the outcome of our analysis shows that recommended formulations for treating ferromagnets are just the opposite of those for treating superconductors, we suggest a coupled formulation for systems where both types of materials are present. The coupled formulation is shown to be accurate and more efficient than single formulations applied indistinctly to all materials.
TL;DR: In this article, the outer rotor permanent magnet brushless DC motor (BLDC) with halbach magnet array was studied to improve the power characteristics of BLDC for drones, which can reduce the leakage flux and improve the efficiency by reducing the iron loss of the motor.
Abstract: In this paper, the outer rotor permanent magnet brushless DC motor (BLDC) with halbach magnet array was studied to improve the power characteristics of BLDC for drones. First, the BLDC motor applied to the currently commercial drone was selected as the target model and improved design was carried out. Spec generation was carried out for target BLDC model and the base model was designed and manufactured. Based on the base model, am improved design was applied using the halbach mag-net array using Response Surface Method (RSM). Applying the halbach magnet array can reduce the leakage flux and improve the efficiency by reducing the iron loss of the motor. In addition, the design for reducing the weight of the motor was carried out using RSM. It was confirmed by Finite Element Analysis (FEA) that the power characteristics of the designed improved model improved compared to the target BLDC model.
TL;DR: The SFCL can positively stabilize the VSG by enhancing the power delivery, mitigating the frequency fluctuation and consuming the excess energy, and can visibly decrease the fault current of each phase within the permissible level.
Abstract: To solve the low-voltage ride-through (LVRT) issue of a virtual synchronous generator (VSG) under severe grid fault, our research group proposes to use a modified flux-coupling-type superconducting fault current limiter (SFCL). In this study, the configuration structure of the VSG with the SFCL at the point of common coupling (PCC) is designed. The fault analytical circuit of the VSG is presented, and the functions of the SFCL are stated from the aspects of current restraint, voltage compensation, and energy dissipation. Using MATLAB/Simulink, symmetrical and asymmetrical faults are both simulated to assess the transient behaviors of the VSG, and the SFCL parameters are changed to clarify the quantitative effects. From the comparison results, the SFCL parameters are properly determined to provide favorable performance. The SFCL can visibly decrease the fault current of each phase within the permissible level, and facilitate the VSG to have a preferable voltage profile. Furthermore, the SFCL can positively stabilize the VSG by enhancing the power delivery, mitigating the frequency fluctuation and consuming the excess energy. A satisfactory LVRT operation is gained, and the efficacy of the SFCL on reinforcing the VSG robustness is validated.
TL;DR: An experimental platform of high temperature superconducting (HTS) synchronous motor with HTS flux pump has been designed and under construction in this article, where a finite element model (FEM) using T-A formulation was developed to analyze the electromagnetic characteristics of a double-pancake (DP) racetrack coil.
Abstract: An experimental platform of high temperature superconducting (HTS) synchronous motor with HTS flux pump has been designed and under construction. The HTS flux pump as an exciter eliminates thermal load from the metal current leads, which will reduce the cryogenic volume and improve the efficiency of the HTS machine. A finite element model (FEM) using T-A formulation was developed to analyze the electromagnetic characteristics of a double-pancake (DP) racetrack coil. The no-insulation (NI) racetrack coil wound by YBCO tapes was fabricated with a winding machine in our lab. We proposed a novel mechanical structure to avoid the impregnation of epoxy resin and make the coil more reliable. The turn-to-turn pressure of the racetrack coil can be changed by driving the screws on the straight section. Besides, we manufactured a rotating HTS flux pump as a DC power supply to charge the racetrack coil without contact. The self-field critical current test with a direct current (DC) power supply and the charging experiment with the HTS flux pump of the constructed YBCO racetrack coil were performed at 77 K.
TL;DR: In this article, the authors explore the dependency of harmonic ac losses of different coil configurations carrying nonsinusoidal current, and they find that AC loss in coils monotonically increases with the increase of the fifth harmonic, drastically.
Abstract: Application of high-temperature superconducting devices become promising in power networks, and transportation, including ship, train, and electric aircraft propulsion systems, with the advantages of light weight, compact size, and high efficiency, compared to conventional devices. In reality, electric networks—either in grid or transportation propulsion system—are polluted with harmonics due to the widespread use of power electronic devices and nonlinear loads. It is essential to explore the dependency of harmonic ac losses of different coil configurations carrying nonsinusoidal current. We modeled and compared harmonic ac loss behaviors in three coil configurations, single pancake coil (SPC), double pancake coil (DPC), and solenoid coil (SNC), where SPC and SNC are wound by identical wire length and DPC has twice conductor number compared to SPC. The research work has been carried out by means of H-formulation finite element method in a 2-D axisymmetric modeling environment of COMSOL Multiphysics. We explored and reported ac losses in these three coil structures carrying nonsinusoidal current with the third and the fifth harmonic orders, respectively, under different total harmonic distortion (THD) and fundamental current levels. It has been concluded that ac loss in these coils first decreases with the increase of the third harmonic content, when THD of the third harmonic 0.2. AC loss in coils monotonically increases with the increase of the fifth harmonic, drastically. We found that ac loss in SPC carrying the third harmonic and the fifth harmonic at different THD are more than 3.8 times of that in DPC; ac loss in SPC carrying either third or fifth harmonics at different THD are around 4.5 times of that in SNC.
TL;DR: In this article, a hybrid central solenoid is proposed based on ten layer-wound sub-coils using HTS, Nb3Sn and Nb-Ti conductors respectively for the high, medium, and low field sections.
Abstract: State-of-the-art high field solenoids make use of hybrid designs exploiting the superior high field performance of High Temperature Superconductors (HTS) in the innermost region. The benefits of a hybrid Central Solenoid in a pulsed tokamak like the EU DEMO can be two-fold: either to reduce its outer radius (which would result in a reduced overall size and cost of the tokamak), or to increase the generated magnetic flux (which could extend the plasma burn time and possibly increase the power plant efficiency). In the framework of the pre-conceptual design studies for DEMO coordinated by EUROfusion, a hybrid Central Solenoid is proposed based on ten layer-wound sub-coils using HTS, Nb3Sn, and Nb-Ti conductors respectively for the high, medium, and low field sections. The design exploits the flexibility of layer winding by grading both the superconductor and the stainless steel cross sections in each sub-coil, which has the potential for space and cost savings. Mechanical analyses have identified fatigue as the main design driver for the EU DEMO Central Solenoid. Possible alternatives to reduce the sensitivity of the proposed design to fatigue are currently under investigation.
TL;DR: In this paper, a new 2.8m long CORC CICC has been prepared to replace a degraded sample, which has a design critical current of 100kA at 10 T and 4.5 K at 4 K. The voids between CORC strands in the new sample are filled with solder alloy to provide increased mechanical support to the strands.
Abstract: In recent years, three unique Re BCO-CORC CICC samples with six-around-one cable layout were developed as technology demonstrators at CERN in collaboration with Advanced Conductor Technologies. The tests of these conductors at low temperature in external magnetic field yielded very promising results, but also showed several issues requiring improvement. A new 2.8 m long CORC CICC has been prepared to replace a degraded sample. The voids between CORC strands in the new sample are filled with solder alloy to provide increased mechanical support to the strands, however, this yielded an additional set of new challenges. The conductor has a design critical current of 100 kA at 10 T and 4.5 K and is designed specifically for high-current bus-bars and large detector-type magnets. It therefore features a copper jacket and practical conduction cooling via a cooling line embedded in the jacket.
TL;DR: Asynchronous logic gates greatly reduce the complexity of the clock network in large-scale RSFQ circuits, thereby alleviating certain timing issues and reducing the required bias currents.
Abstract: Among the major issues in modern large-scale rapid single-flux quantum (RSFQ) circuits are the complexity of the clock network, tight timing tolerances, poor applicability of existing CMOS-based design algorithms, and extremely deep pipelines, which reduce the effective clock frequency. In this article, asynchronous dynamic single-flux quantum majority gates are proposed to solve some of these problems. The proposed logic gates exhibit high bias margins and do not require significant area or a large number of Josephson junctions as compared to existing RSFQ logic gates. These gates exhibit a tradeoff among the input skew tolerance, clock frequency, and bias margins. Asynchronous logic gates greatly reduce the complexity of the clock network in large-scale RSFQ circuits, thereby alleviating certain timing issues and reducing the required bias currents. Furthermore, asynchronous logic allows existing design algorithms to utilize CMOS approaches for synthesis, verification, and testability. The adoption of majority logic in complex RSFQ circuits also reduces the pipeline depth, enabling higher clock speeds in very large scale integration RSFQ circuits.
TL;DR: The curve radius of HTS maglev line, the superelevation outer rail, and the suspension parameters of maglev vehicle are suggested and results show the H TS maglev freight vehicle can safely pass through the curves at a certain speed without external rail supereslevation.
Abstract: High-temperature superconducting (HTS) maglev has the potential in high-speed transportation owning to its capability of passive stabilization. As an important research field of vehicle dynamics in HTS maglev area, the curve negotiation performance is in connection with the vehicles’ operational safety and comfort. This article reports the curve negotiation performance of the HTS maglev through three steps. First, the guidance force is measured to determine the safe motion range, and the range will be used as the indicator of the safety. Second, the dynamic model of HTS maglev vehicle “Super-Maglev” is established and compared with the experimental results to verify the correctness. The magnetic guideway irregularity is measured, and the measured value is used as the input of dynamic simulation. Finally, the dynamic curve negotiation characteristics of maglev vehicle are simulated. Results show the HTS maglev freight vehicle can safely pass through the curves at a certain speed without external rail superelevation. However, as a passenger vehicle, it can pass through the curve safely and smoothly when the suspension system and the superelevation are added. The curve radius of HTS maglev line, the superelevation outer rail, and the suspension parameters of maglev vehicle are also suggested in this article.
TL;DR: In this paper, the first magnet assembly was done with lower coil pre-load to achieve 14 T and minimize the risk of coil damage during assembly, and the results of its cold tests were reported.
Abstract: Fermilab in the framework of the U.S. Magnet Devel-opment Program (MDP) has developed a $Nb_3Sn$ dipole demonstrator for a post-LHC hadron collider. The magnet uses 60-mm aperture 4-layer shell-type graded coils. The cable in the two inner-most layers has 28 strands 1.0 mm in diameter and the cable in the two outermost layers has 40 strands 0.7 mm in diameter. An inno-vative mechanical structure based on aluminum I-clamps and a thick stainless steel skin is used to preload $Nb_3Sn$ coils and support large Lorentz forces. The maximum field for this magnet is limited by 15 T due to mechanical considerations. The first magnet assembly was done with lower coil pre-load to achieve 14 T and minimize the risk of coil damage during assembly. This paper describes the magnet design and the details of its assembly procedure, and re-ports the results of its cold tests.
TL;DR: In this article, a coupled A-H field formulation for the analysis of magneto-thermal transients in accelerator magnets is presented, where the magnetic field strength H accounts for the eddy current problem in the source regions containing the superconducting domains, while the magnetic vector potential A represents the magnetoquasistatic problem in normal and nonconducting domain.
Abstract: The application of high-temperature superconductors to accelerator magnets for future particle colliders is under study. Numerical methods are crucial for an accurate evaluation of the complex dynamical behavior of the magnets, especially concerning the magnetic field quality and thermal behavior. We present a coupled A-H field formulation for the analysis of magneto-thermal transients in accelerator magnets. The magnetic field strength H accounts for the eddy current problem in the source regions containing the superconducting domains, while the magnetic vector potential A represents the magnetoquasistatic problem in the normal and nonconducting domains. Furthermore, we include a thin-shell approximation for the source regions, making the formulation suitable for large-scale models composed of thousands of tapes. In this article, the relevant equations are derived and discussed, with emphasis on the coupling conditions. The weak formulation is derived, and numerical results are provided in order to both verify the formulation and scale it to the size of an accelerator magnet.
TL;DR: Camouflaging superconducting electronics, specifically, rapid single flux quantum (RSFQ) technology, from reverse engineering requires near-zero area, power, and performance overhead even when 100% of the sensitive parts of the processor are camouflaged.
Abstract: Integrated circuit (IC) camouflaging is a defense to defeat image-based reverse engineering. The security of CMOS ICs has been extensively studied and camouflage techniques have been developed. A camouflaging method is introduced here to protect superconducting electronics, specifically, rapid single flux quantum (RSFQ) technology, from reverse engineering. RSFQ camouflaged units have been developed by applying the structural similarity of RSFQ standard cells. A defense using camouflaged RSFQ cells combined with obfuscating the temporal distribution of inputs to the IC increases the attacker's effort to decamouflage. The approach establishes the complexity class of RSFQ decamouflaging and a model checker is applied to evaluate the strength of the defenses. These techniques have been evaluated on ISCAS’85 combinational benchmarks and the controllers of the OpenSPARC T1 microprocessor. A dummy Josephson junction fabrication process adds two additional mask steps that increase the cost overhead. Camouflaging 100% of the benchmark circuits results in an area and power overhead of almost 40%. In the case of the OpenSPARC processor, the approach requires near-zero area, power, and performance overhead even when 100% of the sensitive parts of the processor are camouflaged.
TL;DR: In this article, the characteristics were analyzed by applying permanent magnets without conductivity, and the analysis of the electromagnetic field as well as the mechanical loss were also considered to show which magnet type is advantageous.
Abstract: In the coaxial magnetic gear, the permanent magnets of each rotor face each other, and the driving frequency of each rotor has different values according to the gear ratio. The magnetic flux that changes with time is transmitted to each permanent magnet. If the permanent magnet has conductivity property, losses by eddy currents are occurred in the permanent magnet. It is a major loss of a magnetic gear. Because the loss causes demagnetization by heat, it is mentioned a fatal problem at high speed. In this paper, the characteristics were analyzed by applying permanent magnets without conductivity. In addition, the analysis of the electromagnetic field as well as the mechanical loss were also considered to show which magnet type is advantageous.
TL;DR: In this paper, the effect of increasing the stator width through using recent advances in modeling superconducting dynamos has been explored, and it has been shown that given enough space in the stators, the total sum of circulating and transport currents do not drive the full width of the stor into the flux-flow regime.
Abstract: High- $T_c$ superconducting (HTS) dynamos are simple devices for injecting and sustaining dc currents in superconducting coils/magnets. The simple geometry of these devices consists of a superconducting stator(s) and one or more rotor magnets arranged in identical fashion to a classical alternator. However, unlike the classical alternator, the HTS dynamo gives a self-rectified dc output. This somewhat anomalous result is caused by the non-linear resistivity of HTS materials and the large over-critical eddy currents that flow in the stator. As these over-critical currents must recirculate in the HTS stator, the stator's width becomes a key parameter in the physics of the device. In this work we explore the effect of increasing the stator width through using recent advances in modeling these systems. We find that given enough space in the stator, the total sum of circulating and transport currents do not drive the full width of the stator into the flux-flow regime. Operation of the device in this regime results in a non-linear $I$ – $V$ curve, a marked decrease in the internal resistance at open circuit $R_{oc}$ , a saturation of the open circuit voltage $V_{oc}$ , and a short-circuit current $I_{sc}$ that approaches the in-field critical current of the stator itself $I_{c,min}$ . These behaviors lead to the conclusion that optimal HTS dynamo design should ensure that the stator width be sufficient to avoid current saturation of the superconductor at the target operating current.
TL;DR: In this article, a numerical model based on the $T - A$ formulation and moving mesh method is adopted to simulate the superconducting rotating machine, and the electromagnetic and mechanical behaviors of the rotating machine are investigated.
Abstract: Due to the excellent electromagnetic properties of superconductor materials, superconducting generators have higher efficiency, lower weight and volume than traditional rotating machines. However, it is difficult to simulate the electromagnetic behavior in the superconducting generator due to the nonlinear $E - J$ relationship. A numerical model based on the $T - A$ formulation and moving mesh method is adopted to simulate the superconducting rotating machine, and the electromagnetic and mechanical behaviors of the superconducting rotating machine are investigated. The fully superconducting generator investigated in this article is radial type, which consists of field windings and armature windings made from YBa2Cu3O $_{7 - \delta}$ (YBCO) superconducting race-track coils. The anisotropic field-dependent critical current density and the $E - J$ power law relationship are considered in our model. The “virtual tape” model is introduced to calculate the induced current in the $T - A$ formulation. The numerical results are obtained by the finite element method. The electromagnetic results calculated by our model are compared with results from the $H - A$ formulation. The ac losses and stress distributions in superconducting coils are presented based on the $T - A$ formulation. The results show that the body force and stress are periodic, and the stress will concentrate on the boundary of the coil. The magnetic field in the rotor is larger than that in the stator, and the field windings suffer greater body force and stress than the armature windings. This model has acceptable relative error with the $H - A$ model for the time saved following $T - A$ approach and relevance to mechanical calculations. Thus, this model can aid the design of superconducting rotating machines.
TL;DR: In this article, a high temperature superconducting double stator machine (HTS-DSM) based on the magnetic field modulation principle is proposed, where the HTS field winding and the copper armature winding are separately located on the two stators, so that it overcomes the drawbacks caused by the coupling device for cryogenic transfer, the torque tube, the carbon brushes, and slip rings in the conventional HTS synchronous machines with the rotating field winding.
Abstract: This paper proposes a high temperature superconducting (HTS) double stator machine (HTS-DSM), based on the magnetic field modulation principle. In the proposed HTS-DSM, the HTS field winding and the copper armature winding are separately located on the two stators, so that it overcomes the drawbacks caused by the coupling device for cryogenic transfer, the torque tube, the carbon brushes, and slip rings in the conventional HTS synchronous machines with the rotating field winding, bringing the merits of high reliability and low maintenance cost. Moreover, a method of amounting a ferromagnetic ring outside the HTS field winding is also proposed to reduce the negative effects of the armature reaction field on the HTS field winding, since the alternating current (AC) losses induced by the armature reaction field easily cause the quench of the HTS field winding. Totally four different topologies are proposed, and the operation principle of the HTS-DSMs is analyzed based on the magnetic field modulation principle. Then the design and optimization of the HTS-DSM is discussed in detail to present the main design parameters of the four topologies. Finally, the performance of the four different topologies are compared by the finite element analysis, the results reveal that the HTS-DSM with modular dewar and iron-teeth inner stator exhibits the merits of higher power density.
TL;DR: The proposed coordination of resistive superconducting fault current limiters (SFCLs) and hybrid-type DC circuit breakers (HDCBs) for dealing with the DC line fault is verified to be very effective in handling the fault.
Abstract: Directing at the robustness increase of a high voltage direct current (HVDC) system with line commutated converter (LCC) and voltage source converter (VSC), this paper proposes to coordinate resistive superconducting fault current limiters (SFCLs) and hybrid-type DC circuit breakers (HDCBs) for dealing with the DC line fault. The theoretical modeling of the SFCLs is presented, and the DC fault current characteristics are analyzed. Considering that the fault interruption involves multi-stages, the coordination of the SFCL and the HDCB in the LCC/VSC station is elaborated. Using PSCAD/EMTDC, the simulation model of a 320 kV HVDC system is built. Changing the SFCL size and the HDCB operation delay is simulated, and the performance indexes such as the fault current level, breaking time and dissipated energy are compared. The proposed coordination is verified to be very effective in handling the fault. Especially for the VSC station, it enables to visibly limit the fault current rising, shorten the transient voltage duration, and facilitate a significant decrease in the dissipated energy of the HDCB. For the LCC station, the proposed coordination can serve as a competitive backup to ensure a timely fault breaking. Consequently, the DC line fault is removed more rapidly and reliably.
TL;DR: In this paper, a 3D-printed permanent magnet synchronous motors (AFPMSMs) shoe was used to mold existing soft magnetic composite (SMC) into shape when producing the AFPMSM using 3D printing.
Abstract: Axial-flux permanent-magnet synchronous motors (AFPMSMs) have a higher torque density than radial-flux permanent-magnet synchronous motors (RFPMSMs); therefore, AFPMSMs are widely used in high-power and high-efficiency motors. However, in the case of AFPMSMs, three-dimensional production is limited, less mass production is available, and the production unit cost is high because the shape of the motor is implemented by rolling the amorphous electrical steel sheet or molding the soft magnetic composite (SMC) to manufacture the motor. Therefore, in this paper, a 3D-printed AFPMSM is proposed, which takes high torque density including the AFPMSM shoe to mold existing SMC into shape when producing the AFPMSM using 3D printing. Further, hybrid AFPMSM, which is made by heeding, is proposed. To reduce core loss with 3D-printed AFPMSM, the core loss of the proposed hybrid AFPMSM was compared to that of the target RFPMSM in this study. The 3D-printed AFPMSM showed a 48% increase in core loss compared to the target motor. However, the proposed hybrid AFPMSM reduced the ratio of the electrical steel sheet by more than 25% compared to 3D-printed AFPMSM. The validity of the proposed model was verified using the finite element method.