High-temperature superconducting (HTS) magnets are promising in high-field applications. However, due to inevitable joint resistance, HTS magnets still face challenges in maintaining a persistent current in their closed-loop operation. HTS flux pumps are devices that can charge closed HTS magnets wirelessly in the way of electromagnetic coupling. Thus, high-capacity DC power supplies and thick resistive current leads, which are generally used for charging superconducting magnets, can be replaced by HTS flux pumps. Hence, on the one hand, the extra heat load caused by the resistive current leads are avoided, improving the safety operation of HTS magnets. On the other hand, the cost of charging HTS magnets can be reduced. In this review, published works about HTS flux pumps and dynamic resistance are summarized. These studies have laid a foundation for the follow-up researches of flux pumps applied in high-field HTS magnets.

With the widespread application of high-temperature superconducting (HTS) magnets in power systems, accurately describing their inductance characteristics has become crucial. However, most studies have neglected the effect of AC loss on the calculated inductance value of the HTS magnets, and neglected the effect of screening currents on inductance of the HTS magnets. Firstly, this work analyzes the inductance characteristics of HTS magnets during the charging and discharging processes. It is found that when AC loss is neglected, the calculated inductance exhibits a discontinuity between the charging and discharging stages, and the distribution of screening currents varies with the operating current, which in turn leads to changes in the inductance of the HTS magnet. Secondly, we propose a novel inductance evaluation method based on experimental and equivalent circuit, which takes into account the combined effects of AC losses and screening currents. Thirdly, we use the proposed method to calculate the inductance of an HTS magnet, compare it with the result calculated by neglecting AC losses, and analyze how the inductance varies with the operating current. Furthermore, based on the finite element method, the evolution of inductance in HTS coils with different topological configurations is further studied and compared. The results demonstrate that the proposed method effectively captures the true inductance characteristics of HTS magnets and yields more accurate inductance values.

Modern active suspensions require controllers that can suppress vibration, satisfy hard physical constraints, and remain robust under nonlinear dynamics, road disturbances, and parameter uncertainties. Robust sliding mode control (SMC) is well suited to this task, but its performance strongly depends on the sliding-surface and switching parameters, whose tuning involves a conflicting trade-off between ride comfort and energy consumption. Although multi-objective particle swarm optimization (MOPSO) is a natural solver for this problem, standard variants often suffer from premature convergence because their search parameters are scheduled in an open-loop manner and cannot react to the real-time diversity state of the swarm. To address this tuning bottleneck, this paper proposes an entropy-driven adaptive MOPSO (EAMOPSO) for robust SMC co-design. The proposed method introduces a normalized disorder coefficient derived from Shannon entropy to quantify the swarm’s exploration-exploitation state and adaptively regulate the velocity-update parameters and Gaussian mutation process. A Lyapunov analysis proves the stability of the robust SMC under bounded uncertainties, and the computational complexity of EAMOPSO is analyzed. The proposed framework is validated on a nonlinear quarter-car active suspension model under slope-step, impulsive bump, non-stationary random, and parameter-uncertainty scenarios. Compared with non-optimized SMC, EAMOPSO-SMC reduces the vehicle body acceleration index by 47.26

Photovoltaic (PV) has become a crucial support for energy transformation and the development of clean energy. Superconducting fault current limiters (SFCLs), with their superconducting and quench characteristics, are considered to be effective in limiting the fault currents and enhancing the low-voltage ride-through (LVRT) capability of PV plants. However, the current-limiting impedance of SFCLs will affect the relay protection for PV plants, particularly their distance protection. In this work, investigations are carried out to explore the impacts of SFCLs on the distance protection for PV plants, revealing that SFCLs may cause maloperation of distance protection under asymmetric short-circuit faults. An improved protection method is designed to eliminate the negative impacts of SFCLs and precisely identify short-circuit faults. A model of the grid-connected PV plant with SFCLs is constructed using the PSCAD/EMTDC software package, and the simulation results validate the accuracy of the improved protection method, serving as a reference for the application of SFCLs in PV plants.

With the global energy transition, the proportion of renewable energy power generation in total electricity production has exceeded 30% and continues to rise, even the ratio is higher in China. Multi-terminal high-voltage direct-current (MT-HVDC) transmission systems have advantages of integration of distributed renewable energy sources, dynamic grid interconnections, and reliable islanding operation capabilities, being critical for next-generation power grid. Current limiting technologies are pivotal in maintaining grid safety and stability, especially for HVDC systems without natural zero-crossing point in fault currents. In this perspective, a superconducting fault current limiter (SFCL) with combination of resistance and inductance is necessary and more effective solution in protecting MT-HVDC transmission systems.

The conductor on round core (CORC) cable spirally wound by second-generation high temperature superconducting (HTS) tapes is considered as a good candidate conductor for high-field magnets due to its good isotropy and low AC losses. Simulation is an effective way to clarify the electromagnetic characteristics of CORC cables. In this work, a 3D finite element model of the CORC cable based on H formulation is proposed, which considers the influence of magnetic field on critical current. The influence of the winding direction on the transport current distribution and the AC loss of the CORC cable is investigated based on the proposed model. The simulation results clearly illustrate the electromagnetic characteristics of CORC cables wound in the same and opposite directions. This work provides an important reference for the design and practical application of CORC cables.

In this paper, we proposed a new axial-type superconducting magnetic bearing (SMB) based on the interaction behavior between a permanent magnet and two closed superconducting coils. Firstly, the principle of the new SMB was presented. Then, the axial restoration characteristic is simulated based on a finite element simulation model. With the simulation results, the optimized parameters for designing the new SMB are obtained. Finally, we built a prototype of the axial SMB and a testing platform for measuring its axial restoring force. The experimental results indicated that the new axial-type SMB has practical axial double-direction stiffness and stability, and may provide an alternative technology for horizontal axle type flywheel energy storage system.

Due to the excellent properties, high-temperature superconducting (HTS) magnets are promising in high-intensity magnetic field applications. However, HTS magnets face a long-standing challenge of field decay due to connecting joint resistance and flux creep in superconductors. In this article, a novel full-wave HTS rectifier based on ac field-controlled switches is proposed to charge closed HTS magnets inductively. With advantages of compact structure, low cost and low heat load, the proposed full-wave HTS rectifier is capable of replacing the bulky dc power supply and thick current leads, which are required for maintaining the field stability of HTS magnets. An experimental prototype has been developed to verify its working principle. Tests have been carried out to illustrate parameters impacting the working characteristics. The proposed HTS rectifier can expand application scenarios and reduce the costs of HTS magnet significantly.

The conductor on round core (CORC) cable has attracted increasing attention due to its strong and high-efficient current carrying capacity. It is considered as one of ideal candidate cables for manufacturing nuclear fusion magncets. Under the circumstance, the transport current distribution of the coils wound by CORC cables has significant impacts on the operating performance of nuclear fusion magnets. Considering the difficulty in experimental tests, numerical model is an effective way to illustrate transport current distribution of the multi-layer CORC coil and provide further insights into its working performance. Therefore, in this work, A 3D finite element model based on the H formulation is proposed to simulate a single-turn and multi-layer CORC coil. The validity of the model has been verified by experimental results. Based on the proposed model, the transport current distribution of the multi-layer straight CORC cable and the multi-layer CORC coil is compared and discussed. In addition, the current density distribution on the superconducting tapes of the multi-layer CORC coil is also investigated. This work can provide an important reference for the design and practical application of multi-layer CORC coils.

Due to excellent properties of large current-carrying capability and high critical magnetic field, high-temperature superconducting (HTS) materials play an increasingly important role in the field of energy storage. The superconducting magnetic energy storage generally needs power electronic converters to realize the power exchange, where the loss is inevitable. In this paper, the interaction between a closed HTS coil and in-series permanent magnets are investigated, which can realize the efficient storage and release of electromagnetic energy without power electronic converters. The working principle and performance of the proposed structure have been verified through both simulation and experimental tests. The results can provide an insight into constructing high-performance superconducting magnetic energy storage devices.

Two categories of high-temperature superconducting (HTS) tapes, the silver-sheathed BSCCO tape (1G HTS tape) and REBCO coated conductor (2G HTS tape), have been commercialized worldwide and widely used in applications. In this study, the 1G HTS tape produced by Sumitomo and 2G HTS tape produced by Superpower were selected for a systematic comparative study in critical current (I c) performances under various temperature and magnetic field conditions. The anisotropy and I c variation patterns of these two types of samples in the temperature range of 25-77 K, magnetic field from 0 to 7 T and field angle from 0 to 90 degrees were compared and analyzed. The results of this study reveal certain comprehensive characteristic features of these two categories of HTS tapes, supplementing some new systematic information to the literature.

In recent years, a new type of superconducting energy storage is proposed based on the interaction of a permanent magnet and a superconducting coil, and many studies on the superconducting energy storage have been conducted. Based on its unique ability of directly realizing energy conversion of mechanical → electromagnetic → mechanical, the new energy storage has promising potential in the applications of utilizing mechanical energy, such as the aircraft catapult. In this paper, we proposed an auxiliary system for the aircraft catapult using the new superconducting energy storage. It works with the conventional aircraft catapult, such as steam catapult and electromagnetic catapult, to realize the catapult capability improvement and energy regeneration. The expected structure and working principle are introduced. The simulation results indicate that a meter-scale auxiliary system can provide propulsion force of average about 100 kN at the beginning of launching, which is significantly helpful. Therefore, we confidently believe that the auxiliary system will greatly enhance the capability of aircraft catapults, both the steam catapult and electromagnetic catapult, which brings a breakthrough in aircraft catapult technology.

Devices made of High Temperature Superconductor (HTS) will suffer AC loss during AC operations, which has unnegligible influence on energy consumption, overall efficiency, cooling cost, and operational stability of the devices. In this study, comparative measurements on 1G and 2G HTS coil samples with an identical structure, geometry, and number of turns were systematically conducted with a calorimetric method at different current values ( I rms s) and frequencies ( f s). The AC loss characteristics of the HTS samples were analyzed and compared based on the experimental results. The results show that eddy current and coupling play a more dominant role than magnetic hysteresis in the total AC loss of coils made of HTS tapes. The AC loss of both samples increases with I rms and f , but the AC loss is more sensitive to I rms than to f . Under the same conditions, the 1G coil sample has a slightly larger AC loss than the 2G one.

In order to reduce vibration and noise with wide frequency, a new extended arrow tetragonal lattice topology is proposed. The band gap characteristics are discussed by combining the finite element method and Bloch's theorem. The generation principle of band gap is explained by vibration mode analysis. By topological optimization of the structure, band gap has obvious optimization effect. The propagation characteristics of elastic waves with a specific frequency in the structure are studied from the point of view of energy. Finally, the band gap frequency range is compared with the transmission function, and the stress cloud diagram is analyzed. The research shows that the structure has good band gaps and can play a good role in vibration and noise reduction. Through the topological design of the structure, the band gap frequency range of the structure is optimized, which provides a new design idea for wide frequency vibration attenuation.

High-temperature superconducting (HTS) magnets are promising in the application of high-intensity magnetic field. HTS flux pumps are devices that can charge closed HTS magnets without direct electrical contact. Simulation is an effective way to clarify the physical mechanism and provide further insight into the design of the device. In this work, we propose an accurate and efficient modeling methodology to simulate the transformer-rectifier HTS flux pump, which has considered electromagnetic and thermal coupling. The validity of the model has been verified by experimental results and theoretical calculations. The working characteristics of the HTS flux pump are investigated based on the proposed model, including DC bias component in the charging loop, the voltage recovery delay of the dynamic bridge and the temperature distribution in the dynamic bridge. The simulation results clearly depict working details of the device, in terms of electricity, magnetism and heat. The proposed model can serve as a powerful tool to design the HTS flux pump in practical applications.

The conductor on round core (CORC) cables with multi-layer structure show great potential for superconducting magnetic energy storage (SMES) because of their low AC losses and large current carrying capacity. The dynamic resistance is an important electro-magnetic property of CORC cables for SMES. Considering that experimental results of multi-layer CORC cables are usually difficult to obtained, numerical model is an efficient method to demonstrate their electro-magnetic properties. In the work, a numerical model is proposed to illustrate the dynamic resistance of the multi-layer CORC cables. Then, an analytical model using method of rotating magnetic field is proposed to provide mathematical expressions for computing the dynamic resistance, which verifies the numerical model. According to the numerical model, the impacts of DC current and AC magnetic field on dynamic resistances of the multi-layer CORC cables are investigated respectively. The simulation clearly illustrates the dynamic resistance characteristics of CORC cables, showing dynamic resistances and currents in individual layers. This study can serve as a valuable guidance for the implementation of multi-layer CORC cables in SMES systems.

The high temperature superconductor (HTS) maglev train has several merits in compare with other ones. In our previous work, the feasibility of using electromagnetic guideway (EMG) in HTS maglev trains has been verified and the HTS bulk is proved to gain repulsive force in a reversed magnetic field, which can be used for propulsion function based on EMG in HTS maglev train. In this paper, the repulsive force under different factors are experimented in both EMG unit and segment. With the single EMG unit, the propulsion force under different levitation height, different operation velocities and the hysteresis of propulsion force are discussed. With a 60 cm EMG segment, the periodicity of propulsion forces is discussed and a free propulsion experiment were conducted. The results verify the feasibility of a levitation, guidance and propulsion integrated operation system in HTS maglev train and can support the further development of it.

Due to the high isotropy and low AC losses, the multi-layer conductor on round core (CORC) cable is a good candidate for high field magnets, such as central solenoid magnets in fusion. Considering the difficulty in experimental measurement, numerical model is an effective way to illustrate the electromagnetic characteristics of the multi-layer CORC cable and provide further insights into its working performance. In this work, a 3D finite element model based on H formulation is proposed to simulate a CORC cable with as many as 18 layers considering electromagnetic coupling. The validity of the model has been verified by experimental results. Based on the proposed model, the DC transport current distribution characteristics and charge-discharge loss characteristics of multi-layer CORC cables wound in the same and opposite winding directions are investigated respectively. This work can provide an important reference for the design of multi-layer CORC cables for high-current or high-field application.

High-temperature superconducting (HTS) magnets are promising in high field applications. However, due to inevitable joint resistance and flux creep, HTS magnets still face challenges in maintaining field stability in their closed-loop operation. HTS flux pumps can charge closed HTS magnets wirelessly, thus allowing lower cryogenic loading and more flexible arrangements in HTS magnet systems. In this work, a full-bridge flux pump using two AC field-controlled switches is proposed, which can charge HTS magnets during whole cycles. Therefore, the charging speed of the proposed full-bridge flux pump is at least one time larger than half-bridge flux pumps. A numerical model and an experimental prototype are developed to verify the working principle of the proposed full-bridge flux pump. Simulation and experimental tests are carried out to investigate the working characteristics of the proposed flux pump. The proposed flux pump has huge potential in the application scenarios where high charging speed is required.

Abstract Due to the excellent electrical conductivity, superconducting materials are playing an increasingly important role in high-field applications. Lots of superconducting applications rely on the electromagnetic interaction between the permanent magnet (PM) and superconductors in different forms of tapes, bulks and coils. Recently, an electromagnetic interaction between the closed superconducting coil (SC) and the moving PM has been researched with interest. This electromagnetic interaction can both induce and utilize the current in the closed SC, thus achieving the mutual conversion between mechanical and electromagnetic energy wirelessly. In this review, all recently published works about this electromagnetic interaction have been summarized, from aspects of interaction behaviors, mechanism, numerical models, key influence factors and applications. These studies have laid a solid foundation for the follow-up researches.