Superconducting generators offer a promising solution for far-offshore wind power that has a capacity of 20 MW and above. This paper proposes a novel configuration for high-power low-temperature superconducting (LTS) wind generators with a thermosiphon helium pipe cooling system on the superconducting excitation rotor. Three groups of cold heads, each with a condenser, are symmetrically arranged circumferentially around the excitation rotor, which has been preliminarily validated to enable natural circulation of helium along the helium cooling pipes without any pump no matter the rotor rotates or keeps standstill at any angle. A conceptual design for a 20 MW LTS wind generator incorporating the novel configuration has been developed, covering electromagnetic, structural, and cryogenic aspects. The design features 72 LTS excitation coils, achieving a radial air-gap flux density of 2.5 T with rated armature voltage and current of 3300 V and 3500 A, respectively. The generator has an air-gap diameter of 7.2 m, an axial length of 1.6 m and an active weight of roughly 130 tons. Preliminary analysis of electromagnetic, structural, and cryogenic performances of the generator has been conducted by 2D finite element simulations and analytical calculations. The maximum magnetic field on the superconducting coils is 6.6 T, and the maximum stresses on the superconducting coils and the torque tubes are 37 MPa and 137 MPa, respectively. The total heat leakages from 300 K to 50 K and from 50 K to 4.2 K within the cryostat are 174.8 W and 4.65 W respectively, sufficiently covered by the combined cooling capacity of nine cold heads in the system, each providing 70 W at 50 K and 1.25 W at 4.2 K. The highest temperature on the superconducting coils is 4.3 K.

Offshore wind power is trending towards larger capacities and deep-water applications. To accommodate floating platforms in deep water and to avoid reliability issues related to gearboxes, it is essential to enhance the power density of direct-drive wind generators thereby reducing their weight and volume. This paper presents a conceptual design for a 20 MW low-temperature superconducting (LTS) wind generator. A thermosiphon helium piping cooling system, which rotates with the LTS excitation coils as the rotor, is proposed to keep the coils at 4.2 K by circulating helium through gravitational force while rotating without any pump. Using NbTi wires for the excitation coils, the designed sample generator features a radial magnetic flux density of 3 T in the air gap at a rated speed of 10 rpm. The rated voltage and current are 3300 V and 3500 A respectively. By a 2D finite element model, the basic electromagnetic structure is designed that has an air gap diameter of 6 m, an axial length of 1.1 m with 48 poles and 576 slots. The maximum magnetic field of 4.3 T locates inside the NbTi excitation coils. The cryogenic cooling system employs 8 cryostats, each containing six NbTi coils with a carbon fiber reinforced plastic suspension system and a GM cryocooler. The estimated heat leaks for a single cryostat are 0.382 W at 4.2 K and 39.8 W at 50 K.

The bump motion of in-wheel motors (IWMs) is a key concern in addition to motor vibration, which have significant influence on motor's mechanical and thermal dynamics. In comparison to motor vibration, the frequency of bump motion is considerably lower, whereas its amplitude is significantly higher. This paper develops a physical simulation platform to experimental simulate the bump motion of an electric vehicle (EV) on a standard sine-wave track, and the mechanical and thermal dynamic characteristics of IWMs under bump motion could be further tested. A cam-roller mechanism is designed to drive the tested IWM system up and down vertically, according to the specifications of an automotive proving sine-wave track constructed by BYD, an EV manufacturer located in Shenzhen, China. The target vertical amplitude of bump motion is designed as 4.5 cm, and the maximum vertical frequency of bump motion is 1.59 Hz at the cam's rotation speed of 95.4 r/min. By adjusting the profile and rotation speed of the cam, the desired vertical amplitude and bump frequency can be modified to meet various test requirements. A speed control algorithm with torque feedforward is proposed for a 3 kW, 1435 r/min asynchronous motor equipped with a gear reducer, which is used to compensate the variation of the cam's load torque and ensure the highly stable rotation speed of the cam. An online torque feedforward correction method is proposed to compensate errors in parameters of torque feedforward calculation, and avoid frequent manual parameter calibrations. Moreover, the parametric sensitivity of torque feedforward is analyzed. Simulation and experimental results demonstrate that the cam rotates smoothly at the maximum speed of 95.4 r/min under a full heavy load of 415 kg. The measured speed fluctuation is less than 2.04%, and the measured displacement, velocity, and acceleration curves of the tested IWM system in the vertical direction are consistent with the target values of IWMs on the sine-wave track.

A 14 T actively shielded animal MRI magnet has been designed and is currently under construction. The magnet has a warm bore of 175 mm diameter and consists of Nb3Sn and NbTi solenoid coils. This paper presents the results of electromagnetic, structural and quench protection designs of the magnet. The magnetic field homogeneity is 0.9 ppm within a 60 mm diameter of spherical volume. The distance of 5 Gauss line from the magnet center is 2.4 m radially and 2.9 m axially. Stress analysis shows that the maximum axial and circumferential stresses in the coils are -73 MPa and 144 MPa, respectively. Under the worst quench scenarios, the maximum hotspot temperature and inter-layer voltage in the coils are constrained to 169 K and 720 V, respectively.

Objective With the rapid advancement of electric vehicle technology, in-wheel motors (IWMs) have emerged as a novel solution for transportation electrification because of their distributed drive characteristics. IWMs simplify mechanical transmission systems, enhance overall transmission efficiency and torque output performance, and improve vehicle torque control flexibility through force distribution control, making them ideal for navigating intricate terrain. Consequently, IWMs are increasingly applied in high-torque-density scenarios such as mining dump trucks and military tractors. Liquid cooling, characterized by its high convective heat transfer coefficient at the fluid-solid interface and the coolant's high specific heat capacity, has emerged as a crucial solution for managing thermal loads during short-term high-overload operations. This ability is crucial because IWMs are directly integrated into vehicle wheels, exposing them to more direct impacts from road vibrations compared to centralized drive systems. High-frequency small-amplitude vibrations caused by minor road deformations coexist with low-frequency large-amplitude bump motion resulting from substantial road undulations. Although tires can mitigate the effects of minor road shapes, low-frequency large-amplitude bump motion considerably affects the vertical acceleration of IWMs and their cooling systems, impacting fluid dynamics and heat dissipation performance. Methods To assess these impacts, this research adopts advanced simulation techniques, including the finite element method for thermal analysis and computational fluid dynamics to fluid flow analysis under dynamic conditions, alongside experimental validation using a custom-designed physical simulator replicating real-world bumpy road scenarios. Theoretical models based on the Navier-Stokes equations describe the fluid behavior under bump motion by considering additional forces induced by vertical acceleration. By integrating multiphysics modeling and employing simplified 1D-3D coupling approaches, the study effectively simulates the entire cooling circuit, achieving a balance between accuracy and computational efficiency. A multiphysics model integrating electromagnetic, thermal, and fluid dynamics fields was developed and validated against experimental data obtained from the physical simulation platform. Results The simulations reveal that under the specified bump conditions (an amplitude of 4.5 cm and a frequency of 2 Hz), the average flow rate decreases by approximately 3.8%, peak-to-peak fluctuation reaches up to 23.2%, and the IWM's maximum internal temperature increases by approximately 1.2 u2103, demonstrating a moderate yet considerable effect on the overall cooling efficacy. The experimental results show that the average flow rate decreases by 2.7% and the peak-to-peak fluctuation reaches 20.8% under bump conditions compared to those under the steady-state operation, and the IWM's maximum internal temperature is approximately 1.2 u2103. The comparison between the simulation and experimental results validates the effectiveness of the proposed multiphysics modeling and simulation. Furthermore, this paper analyzes the impact of transient bump motion on the IWM's temperature increase. The analysis reveals that during such conditions, the cooling circuit flow experiences reduced average flow and fluctuates at the bump frequency. Through fluid-thermal coupling simulations, this paper examines how varying the bump motion's amplitude, frequency, and steady-state flow rate affects these fluctuations, leading to considerable changes in IWM wall temperature increase. Increased amplitude and frequency exacerbate flow rate fluctuations and temperature increases, while higher steady-state flow mitigates these effects. Conclusions This research highlights the importance of understanding and addressing the thermal management challenges faced by IWMs under real-world bump motion, paving the way for their broader application in the future. The insights gained from this study suggest that further optimization of cooling system designs and thermal management strategies will be crucial for enhancing the reliability and performance of IWMs in challenging environments such as bumpy roads.

This paper presents the manufacture process of the Nb 3 Sn coils for a 14 T animal MRI magnet. The magnet consists of two NbTi-CuNi reinforced bronze-processed Nb 3 Sn solenoid coils, which contribute 6.6 T to the central magnetic field. The manufacture process of the Nb 3 Sn coils includes the following steps: bobbin design, coil winding, heat treatment, epoxy impregnation, binding installation, superconducting joint fabrication, and bobbin removal. The coil bobbin is designed with a draft angle and a liquid nitrogen chamber. Decarbonized fiberglass cloth is wrapped between coil layers during winding. A heat treatment tooling is designed and utilized to control the dimensions and positions of the Nb 3 Sn coils after heat treatment. The epoxy resin used for impregnation is CTD-101K, and a 6061-T6 aluminum cylinder is utilized as the binding for Nb 3 Sn coils. Superconducting joints are fabricated by the solder matrix replacement method. Finally, the bobbin is removed from the coils using liquid nitrogen and hydraulic jacks.

The 14-T magnetic resonance imaging (MRI) superconducting magnet utilizes reinforced multifilament Nb 3 Sn wires and multifilament NbTi wires to generate the required magnetic field. The resistances of the Nb 3 Sn-NbTi superconducting joints are crucial to the temporal field stability of the magnet operation in persistent mode. The resistance of each joint is required to be lower than 10 −11 Ω under a 0.5 T background magnetic field to keep the temporal field drift lower than 0.1 ppm/hour. This paper presents the fabrication of multifilament Nb 3 Sn-NbTi superconducting joints and the measurement of their resistances. The joints were fabricated by the solder matrix replacement method using PbBi as the solder in an open-air environment. The samples were tested by an apparatus that was developed based on the current-decay method and can provide a background field up to 1 T. The sample loop with a Nb 3 Sn wire and a NbTi wire contains two Nb 3 Sn-NbTi joints. The Nb 3 Sn wire undergoes the heat treatment before the fabrication of superconducting joints with the NbTi wire. The measured results indicate that the joints can carry a current up to 809.8 A with a resistance lower than 6.20 × 10 −13 Ω without a background field. Under a 1 T background field, the joints can carry a current up to 481.5 A with a resistance lower than 1.24 × 10 −12 Ω, which meet the requirement of the 14-T MRI superconducting magnet.

A novel control algorithm for the phase-shifted full bridge converter is proposed that employes proportional controller for the voltage loop and proportional-integral controller for the current loop. Besides, estimated load feedforward is adopted using the filtered primary current. Moreover, the voltage integrator is removed to avoid its deterioration to transient response. In such a way, both infinity open-loop dc gain and attenuated output impedance are achieved, leading to precise regulation and fast response. Only output voltage and primary current are sensed, whose sampling-gain drifts are tolerable. Simulation and experiment results verify the methodology.

A hybrid energy transmission pipeline is proposed with the aim of long-distance cooperative transmission of electricity and chemical fuels, which is composed of an inner high-temperature superconducting (HTS) power cable and outer liquefied natural gas (LNG) pipeline. The flowing LNG could maintain the operating temperature of the inner HTS power cable within the range of 85 K-90 K, thus the Bi-2223 superconductors in the HTS power cable produce little Joule loss with the transmission current below the critical current. Owing to the advantages of high power density, low transmission losses and economical manufacturing costs, the hybrid energy transmission pipeline is expected to be widely utilized in the near future. In order to ensure the safety of the HTS power cable and explosive LNG in case of short-circuit faults, this paper tests and analyzes the characteristics of Bi-2223 HTS tapes of the Type HT-CA, Type HT-SS and Type H models under short-circuit current impacts at the LNG cooling temperature (85 K-90 K). An experimental platform is designed and established for the ampacity tests of HTS tapes above LN2 cooling temperature (77 K). The AC over-current impact tests at 85 K-90 K are carried out on each sample of Bi-2223 tapes respectively, and the experimental results are analyzed and compared to evaluate their performances under different operating conditions. The results indicate that the Type HT-CA tape can withstand 50 Hz short-circuit current impact with the amplitude of 1108 A (10 times of critical current $I_{\mathrm{c}}$ ) for 100 ms at 90 K, and its resistance is the smallest of the three tested samples under similar current impacts. Therefore, the Type HT-CA Bi-2223 tape is the optimal superconductor of the HTS power cable in the hybrid energy transmission pipeline.

This paper analyses harmonic distortion caused by the narrow pulse problem in matrix converters, and presents an improved switching pattern that is based on the basic five vector switching pattern. With limited switching frequencies, the improved pattern solves the narrow pulse problem by applying an additional zero vector and adjusting the sequence of the four active vectors at the same time to minimize the switching times. Simulation results show that in the six vector switching pattern, a) the low-frequency harmonics caused by the narrow pulse problem are greatly reduced; b) the average switching frequency is reduced compared with the five vector pattern; c) the sampling frequency harmonics are apparently attenuated though a little 1/2 and 3/2 sampling frequency harmonics are produced; d) the THD of the output current is improved to the same level of the three zero vector switching pattern (TZVSP); e) the proposed switching pattern has benefits in both normal and unbalance input voltage conditions. Experimental results on a matrix converter platform, verify the benefits of the six vector switching pattern. Faster dynamic, lower harmonics and lower losses can be achieved by using the proposed six vector switching pattern.

Resistive-type superconducting fault current limiters (R-SFCLs) can limit short-circuit fault currents and have a good future in HVdc systems. The system can be reclosed when the R-SFCLs return from the quenched state to the superconducting state. If the short-circuit fault is permanent, the R-SFCLs will be quenched for the second time after the system is reclosed. The second quench and recovery characteristics of R-SFCLs in liquid nitrogen (LN 2 ) are crucial for the reclosing of a flexible dc systems. However, the recovery characteristics of high temperature superconducting (HTS) tapes after the second quench are still unclear. Thus the objective of this article is to obtain the effect of the quench-recovery-requench process in LN 2 on the current-limiting and recovery characteristics of HTS tapes. In this article, both experimental and simulation methods are used to study the recovery characteristics of HTS tapes after two quenches. The effects of the amplitude of the current and the requench speed on the recovery time of the HTS tape are also analyzed. The results showed that when the HTS tape was in a “critical recovery” state, the HTS tapes does not recover to 77 K after the first quench. The recovery time for the second quench was 2.48 times that of the first quench; when the reclosing time is reduced from 0.5 to 0.3 s, the maximum temperature of tape after the second quench has a 17.3% increase. Finally, by comparing the simulation with the experimental data the maximum error is less than 20%, which verifies the feasibility of the simulation design method.

Superconducting energy pipeline (SEP) is a new type of electrical energy transmission. It contains high-temperature superconducting cables and liquefied natural gas pipelines and can simultaneously transmit electricity and liquefied natural gas (LNG). However, when the superconducting tapes in the superconducting cables in SEP quench and generate heat, bubbles will generate in the butt-gaps of the insulation layer of superconducting cables, which can reduce the insulation strength of the cables significantly. In addition, the effects of bubbles in the butt-gap of the insulation layer on the insulation properties of the superconducting cables are unknown. The objective here is to obtain the influences of bubbles in the insulation layer of superconducting cables in capacitive field, transitional field, and resistive field. Simulation results show that: Compared with the absence of bubbles, the big bubbles can increase the capacitive field strength of the PP film, the butt-gap, and the kraft by 37.54%, 30.89%, and 18.5%, and increase the transition time from the capacitive field to the resistive field, but has almost no effect on the butt-gap in the resistive field.

Superconducting energy pipelines (SEPs) which can simultaneously transmit liquefied natural gas (LNG) and electricity over long distances are proposed these years. SEPs combining LNG pipelines and high-temperature superconducting (HTS) cables together have higher transmission efficiency. The stable and reliable operation of SEPs during short-circuit faults is important. The HTS cable generating heat may cause the liquid protective medium (LPM) inside the copper former of the cable to boil, endangering the safety of SEP during short-circuit faults. The objective of this paper is to obtain the influence of short-circuit faults on the temperature of HTS cables in SEPs. Three different structures of copper former in HTS cables of a ±100 kV/1 kA SEP are investigated including copper rod and two different copper tubes. One inside of the copper tube is vacuum calling internal vacuum copper tube (IVCT) and the other one is LPM calling internal LPM copper tube (ILCT). Simulation results show that the ILCT has the best properties due to its lowest temperature during short-circuit faults. When a fault current of 20 kA transports in the HTS cable for 100 ms, the cross-sectional area of the copper former should be larger than 187.46 mm 2 to ensure safety.

Medium-frequency transformer (MFT) dc bias is critical for the safe operation of dual-active-bridge (DAB) converters. To analyze the dc bias, expressions of dc bias are derived for SiC MOSFET DAB converters. It shows that the dc bias is a current source in steady state; thus, a dc bias current capacity is defined and used as a design constraint in the optimization of MFT. The dc bias current capacity is related to core materials, geometric parameters, and flux density, which is analyzed with analytical expression. Optimization equations with geometric variables are derived, which can be solved theoretically or numerically for both interleaved winding (IW) and separated winding (SW) MFT without and/or with leakage inductance design. Based on the optimization equations, different MFT designs for a 150-kW SiC MOSFET DAB converter are compared on the aspects of core materials, winding structures, and without/with leakage inductance design. The combination of IW structure MFT with auxiliary phase shift inductors is chosen, and the assembled prototype is tested with the 150-kW DAB converter. The designed dc bias capacity, temperature rise, and efficiency are verified.

Superconducting DC energy pipeline combines long-distanceelectricity and liquified natural gas transmission, which could improve the overall efficiency of the pipeline system and save construction space. The characteristics of superconducting DC energy pipelines with bipolar coaxial, double-core and partitioned structural layouts are analyzed and compared in this paper, which are significant for the selection of pipeline structure. The voltage levels are set as ±10 kV/±100 kV for electricity distribution and transmission applications, and the rated current is set as 1 kA. The simulation models of energy pipelines with each structural layout are established in order to evaluate the respective operation characteristics. The operation conditions of the steady state, the quench transient process under a short-circuited fault and the quench recovery transient process afterwards are analyzed in order to evaluate the stability and safety of the pipeline system. The comparison results illustrate the distinguishing features of each structural layout from various aspects. It is found that the double-core structure and the partitioned structure are the most suitable options at the voltage levels of ±10 kV and ±100 kV respectively.

将超导输电技术与液化天然气(LNG)管道输送技术相结合,形成能同时输送LNG与电力的能源管道,不仅可以节约能源通道,还可以利用LNG冷却超导电缆,提高能源输送效率和经济性,是一种极具前景的能源输送方式.在国家"智能电网与装备"重点研发计划的支持下,开展了超导直流能源管道的基础研究.该文主要介绍超导直流能源管道的基础研究项目近一年多的进展情况,主要包括:LNG混合工质的低温液固转变机理及传热流动特性,电力/LNG一体化输送动态稳定性判据,为安全性与故障演化分析而搭建的实验平台及初步实验结果,以及10m/10kV超导直流能源管道原理样机的研制与实验情况.

High-temperature superconducting (HTS) DC cables with the merits of light weight, large capacity and low loss provide a novel power transmission method for future utility grid. In this paper, the electromagnetic characteristics of unipolar and bipolar coaxial HTS DC cables are compared by finite element simulation. Besides, the 3D magnetic flux density distribution characteristics of HTS DC cable are obtained. The method to investigate the influence of winding angle on HTS DC cable magnetic flux density is also applied to 3D HTS DC analysis.

Superconducting DC energy pipeline incorporates HTS DC cables and the LNG pipeline, and the overall efficiency is improved compared to the conventional HTS DC cables. In the energy pipeline, LNG is cooled down to 90 K at which Bi2223 tapes can still conduct moderate currents although the critical current density J c at 90 K drops to about half of that at 77 K. According to the power law, three-dimensional models are constructed to investigate and contrast the current distributions and degradations on helical Bi2223 tapes of the bipolar double-core DC cables under different voltage levels. It is found that the current distributions on Bi2223 tapes tend to the sides which are closer to the cable of opposite polarity. Both the perpendicular and parallel magnetic fields on the surfaces of helical tapes are compared in ±100 kV and ±10 kV cables. The average degradations of critical current density of the cable influenced by the magnetic fields are estimated and the results indicate that the degradations of critical current density are similar with different insulation distance between poles.

High-temperature superconducting (HTS) DC cables have the advantages of low transmission loss, high current density and large transmission capacity, which have gained more and more attentions in recent years. The typical structures of HTS DC cables include unipolar and bipolar coaxial that doubles the cable's transmission capacity. Based on the critical state model, this article analyses and contrasts the critical current density distributions and degradations due to magnetic field in the HTS tapes of the unipolar and coaxial bipolar DC cables. The influences of the bipolar cables with different voltage levels are also compared. The results show that the critical current density degradations due to magnetic field are almost the same in both unipolar and coaxial bipolar structures, which are mainly caused by the self-field. For the bipolar cables, the current density distribution in the outer layer HTS tapes changes with the voltage level. To evaluate the influence of the axial magnetic field, a 3-D model of the unipolar cable is established with a helical wound pitch of the HTS tapes. The results show that the axial magnetic field is relatively low and the critical current density would not degrade if the helical angle of the HTS tapes is reasonably small.

A new superconducting energy pipeline (SEP) structure with high security is proposed due to the flammability of liquified natural gas (LNG). The structure is applied to a ±100 kV/1 kA SEP and the simulations considering the normal conditions and impact of short-circuit currents are carried out. The results show that the structure can realize the transmission of multiple energy. When the SEP is impacted by DC fault current, the temperature of the copper former is lower than the maximum allowable temperature during the fault. Then the cables recover to the superconducting state, and the temperature rises of liquid protective medium (LPM) and LNG are 0.68 K and 0.04 K, respectively. Therefore, the feasibility and security of the new structure are verified.