High-temperature Superconducting Maglev System Research Articles

A reconstructed three-dimensional HTS bulk electromagnetic model considering J c spatial inhomogeneity and its implementation in a bulks’ combination system

High-temperature superconducting (HTS) bulks in HTS Maglev systems are always arrayed in a combination to make full use of the applied magnetic field of the permanent magnet guideway (PMG). An excellent combination scheme improves the overall levitation and guidance performance significantly. In this paper, a three-dimensional (3D) electromagnetic model of the real HTS-PMG maglev system with an HTS bulk array was established. This model comprehensively expresses the influence of various factors on the E – J relationship and the 3D spatial distribution of J c, including internal factors such as the inhomogeneity and anisotropy of electromagnetic characteristics, as well as external factors such as applied magnetic field and working temperature. A ternary function was proposed to describe the uneven distribution of J c caused by the bulk’s growth process, which is an interesting phenomenological modeling attempt. In the simulations of the bulks’ combinations, perfect magnetic conductor boundary conditions were applied on the contact surface to simulate two bulks touching each other. Besides, the research target includes reproducing the shapes, the orientations, and the combination scheme of HTS bulks in the real PMG magnetic field. The calculation results of levitation force of the cylindrical bulk under different spatial orientations above the PMG were compared with the experimental results, through which the accuracy of the model was verified. On this basis, the influence of the magnetic field generated by the superconducting current on the nearby bulk was further explored. It was found that this magnetic field has a small contribution to the total levitation force and a relatively obvious influence on the guidance force. When the lateral displacement is large, such as 5 mm, the magnetic field generated by the superconducting current slightly increases the total guidance force stiffness. According to more simulated conditions, some optimization strategies on bulk combinations were proposed. This work provides not only a 3D descriptive model for fitting the real multi-bulk-combination maglev scenarios but also some optimization strategies for the HTS maglev transportation applications.

The magnetic and levitation characteristics of single-grain YBaCuO and GdBaCuO-Ag bulk superconductors in high magnetic fields

In principle, high-temperature superconducting (HTS) flux-pinning maglev has the advantage of self-stable levitation and is therefore a good development prospect as a new rail transit technology. The magnetic field intensity is one of the key factors affecting the levitation performance of single-grain bulk superconductors in the HTS maglev system. To date, however, most researchers have focused on the levitation performance of HTS bulk superconductors in magnetic fields within a permanent magnet guideway (PMG) configuration. The magnitude of the external working magnetic field provided by a PMG is limited to about 0.5 T at 77 K, given that the superconductor usually levitates at a typical working height of 10 mm above the PMG. Therefore, the weak magnetic fields generated by the PMG significantly limits the levitation performance of HTS maglev systems to that of the permanent magnet (PM). In this article, a superconducting magnet test bench was utilized to provide a 0–3 T external magnetic field (B) environment for the study of the levitation force in HTS single grains. The difference in levitation performance between YBaCuO (YBCO) and GdBaCuO-Ag (GdBCO-Ag) bulk superconductors under large, changing magnetic fields was studied systematically. The relationships between levitation force and magnetic field characteristics, including vertical magnetic field component (Bz), transverse magnetic field component (Br), and vertical magnetic field variation (ΔBz) were investigated. The result of variation curves about YBCO and GdBCO bulks' levitation forces under different ΔBz shows that the levitation force of the bulk, single-grain superconductors will reach saturation under a varying ΔBz environment (0.72 and 1.5 T). The values of ΔBz corresponding to the saturation positions are found to be independent of the sizes of the HTS samples. At the same time, GdBCO-Ag exhibits a levitation force that is 112.8% greater than YBCO in B = 3 T magnetic environment. As a result, it is demonstrated that the levitation potential of single-grain HTS bulks can be better exploited by optimizing the distribution of the magnetic field.

Influence of Electromagnetic Shunt Damper on Nonlinear Vibration of HTS Maglev System

The levitation force in the high temperature superconducting (HTS) maglev system has obvious nonlinear characteristics. When the excitation frequency and amplitude meet certain conditions, nonlinear vibration phenomena such as period-doubling bifurcation would appear. Nonlinear vibration will bring difficulties to dynamic analysis and even affect the safety and comfort of driving. While an electromagnetic shunt damper (EMSD) can effectively reduce the vibration amplitude. This paper analyzes the influence of EMSD on the nonlinear vibration of HTS maglev systems from the perspective of experiments and simulations. Firstly, free vibration and forced vibrations in the resonance interval are tested. Secondly, based on numerical simulations, the vibration response under various excitation was analyzed. The results show that the EMSD can effectively suppress its nonlinear vibration. This research has reference value for the detailed understanding of the dynamic characteristics of the HTS maglev and further vehicle design.

Vibration Reduction Using Eddy Current Damper in High-Temperature Superconducting Maglev System

Vibration Reduction Using Eddy Current Damper in High-Temperature Superconducting Maglev System

Experiments and Simulations of the Secondary Suspension System to Improve the Dynamic Characteristics of HTS Maglev

High temperature superconducting (HTS) magnetic levitation (maglev) has the potential as a high-speed passenger transportation mode owing to its passive stabilization. Our group is constructing a 1500 m-long HTS maglev high speed test line. As a kind of passenger transport, safety and comfort are primary factors for its operation quality. However, the weak damping in HTS maglev system is not enough to suppress the vibration. As a preliminary study of the test line, this article investigates an additional suspension system aiming to improve the dynamic characteristics of HTS maglev through experiments and simulation. We first built an HTS maglev model vehicle composed of a levitation frame and a car body. The dynamic responses were tested based on a dynamic measurement system. Second, a dynamic model of this kind of maglev device was established and the influence of suspension parameters on its vibration performance is analyzed theoretically. Third, this suspension system was applied to an HTS maglev engineering prototype through numerical simulations. Experimental and simulation results manifested that the suspension system can effectively reduce the vibration, especially with high frequencies. This article provides a reference for the design of HTS maglev vehicles.

Dynamic Studies of the HTS Maglev Transit System

With the advantages of high-speed, low-noise and environment-friendly, magnetic levitation (maglev) train has the potential to become a high-speed transportation mode. High-temperature superconducting (HTS) maglev, which can remain stable levitation without any control system, is a competitive type of maglev rail transit. As a kind of high-speed transit, the vibration of the HTS maglev system is inevitable. Hence, studies about its dynamics are necessary and significant. The developments and researches for the HTS maglev vehicle dynamics in Applied Superconductivity Laboratory (ASCLab) are elaborated in detail in this paper. Based on the improved HTS maglev ring test line “Super-Maglev”, a series of research works have been carried out. First, the mathematical model of the pinning force was proposed. Second, motion stability and nonlinear vibration characteristics were studied. Then, the dynamic simulation of vehicle-bridge coupled system of the HTS maglev train was performed. Finally, certain vibration reduction optimizations were added. These dynamics researches give a strong verification for the future application prospect and feasibility of HTS maglev transportation, and the results can provide reference for the engineering application.

Numerical Simulations on the Vertical Dynamic Characteristics of High-Temperature Superconducting Bulk

High-temperature superconducting (HTS) maglev, owing to its unique self-stability characteristic, has a wide range of application prospect in flywheel energy storage, magnetic levitation bearing, rail transportation, and other fields. As the important foundation of the engineering application, researches on the dynamic characteristics of HTS maglev have attracted more and more attention. As most of existing models adopted the power exponential function to approximately fit the relationship between the force and displacement, which can only qualitatively analyze the dynamic characteristics of HTS maglev, this paper employs the flux flow and creep model to deduce a 2D H formulation of the HTS maglev system to make up for this deficiency. Moreover, related experiments were also carried out to validate the accuracy of this simulation model and comparisons with other previous models have been achieved. The results prove that the simulation model can reduce the calculation time still with a good convergence. Then, an electromagnetic-thermal-force multiphysics coupling model was established to analyze the dynamic characteristics, especially the levitation height drift of an HTS bulk above the permanent magnet guideway. Results indicate that when the superconductor has an initial velocity that causes disturbance at the working position, vibration and drift phenomena will occur, and the vertical levitation drift also grows as the velocity increases. The simulation results also show that resonance will occur if the excitation frequency is close to the HTS maglev system’s resonance frequency, and a strong “beat” phenomenon will occur if the excitation frequency is close to twice the main vibration frequency of the system. Additionally, the HTS maglev system shows good anti-vibration ability on the relatively low-frequency region as well as the high-frequency region, which proves that it can be well applied to the rail transportation field. All results could be supported as references for the design of HTS maglev systems and its future application.

Vertical–Lateral Coupling Force Relation of the High-Temperature Superconducting Magnetic Levitation System

A high-temperature superconducting (HTS) magnetic levitation (maglev), based on YBaCuO bulk superconductors and permanent magnet guideways, shows the potential to be applied in the future rail transportation. The maglev forces (levitation and guidance force) of the HTS maglev system, which bond the vehicle and the guideway, are the key factors of its dynamics studies. In practical operation, the HTS maglev vehicle moves in both the vertical and lateral directions, but the previous force models are in single degree of freedom. In this article, an experiment was designed to study the vertical-lateral coupled effect of the levitation and guidance force. A 2-D coupling model was proposed to fit the experimental data. Furthermore, the motion stability and the dynamical characteristics of the HTS maglev system in 2-D space were studied. The simulation results show that the vertical-lateral coupling effect in maglev forces cannot be neglected, and one direction motion can affect the motion in the other direction. It also shows that the proposed force model is suitable for HTS maglev dynamics' calculations.

Dynamic Responses of HTS Maglev System Under Track Random Irregularity

High-temperature superconducting (HTS) magnetic levitation (maglev), with the advantages of low-energy consumption, simple mechanical structure and environment-friendly, has the potential to become a high-speed transportation. In rail track lines, the track random irregularity is ineluctable due to the defects of permanent magnets in production and construction, which will further affect the operation stationarity. In practical operation, the vibration is usually vertical-lateral coupled because of the lateral excitations from the track irregularity and the guideway deformation. In this paper, an HTS maglev vehicle-bridge coupled model considering vertical-lateral coupling effect is built based on the Universal Mechanism (UM) software. To study the dynamical response of the maglev system, a track irregularity spectrum was built based on our group's existing guideway. Different speeds and spans were adopted in this model. The Sperling index is used to evaluate the system stationarity performance under different working conditions. The results show that HTS maglev can run very safely and smoothly on existing guideway and more flexible bridges. This study suggests the limitation of the running speed and the designs of bridges in HTS maglev under track random irregularity, as well as provides references for the engineering.

Technical Feasibility Study of an E-Shaped Electromagnetic Guideway for HTS Maglev

High temperature superconducting (HTS) maglev technology has been developed for more than two decades. Permanent magnet guideway (PMG) has been always used for the rail of a HTS maglev system so far. For the long distance HTS maglev system, PMG has some disadvantages in practice. In last few years, we carried out studies to investigate the feasibility of using electromagnetic guideway (EMG) for a HTS maglev system. EMG is not only more reliable, but also more controllable and flexible. We have proposed an E-shaped electromagnet that could be the basic element for building an EMG with good controllability and flexibility. The geometrical and circuitry design of the E-shaped electromagnet were first suggested through theoretical magnetic circuit analysis. The design then was examined and optimized by computer simulation. Afterward, we made a prototype and conducted several levitation tests to verify the design with a high precision measuring platform. In this article, the performances of the prototype with different exciting modes and different dimensions are reported and discussed.

Modeling and identification of the hysteresis nonlinear levitation force in HTS maglev systems

High-temperature superconducting (HTS) maglev has great potential in the field of high-speed transportation due to its capability for passive stabilization. The levitation force between the bulk HTSs and the permanent magnet guideway is a significant parameter relating to operational safety and comfort. This force has an obvious hysteresis nonlinear characteristic, which can be represented by nonlinear stiffness and damping. The stiffness and the damping are functions of vertical displacement and velocity, respectively. The vibration velocity of a HTS maglev vehicle can at times exceed 100 mm s−1, but the existing levitation force test methods are almost quasi-static. These methods are unable to accurately measure the damping characteristic of the maglev system. In this paper, a viscoelasticity model is introduced to describe the dynamic force. The parameters in the model are identified using the least square method based on the vibration response of the HTS maglev system. Meanwhile, the effectiveness of the model and identification method are tested by numerical simulations. The hysteresis loops derived from the motion theory coincide with the practical ones. Finally, the method is applied to identify the parameters of hysteresis nonlinear levitation force in a previous experiment with dampers. Based on the established hysteretic model, the dynamic characteristics of the HTS maglev system can be well presented.

Study on Different YBCO Bulk Arrangements With a Fan-Shaped Electromagnetic Guideway of HTS Maglev

The application of High Temperature Superconducting (HTS) technology in the maglev field has met a giant improvement in the recent years. With the success in the laboratorial test lines, the scientists started to focus on the research of practical issues on reality applications. Lately, our team devoted ourselves into the study of Electromagnetic Guideway (EMG) for improve the flexibility and the practicability of guideway in an HTS maglev system. In this paper, a fan-shaped EMG was proposed, its basic unit was analyzed through magnetic equivalent circuit method, in order to decide the rated magnetomotive force. Afterward, a prototype was made to verify the design feasibility, the comparison among three arrangements of HTS bulks were carried out with the experiments under different measuring conditions. The levitation and guidance performances of each arrangement were comprehensively discussed as the summary.

Electromagnetic and Levitation Characteristics of a High-Temperature Superconducting Bulk Above an Electromagnet Guideway

An electromagnet guideway unit (EMGU) that can form an electromagnet guideway (EMG) with only a small gap, or even no gap, between multiple EMGUs was designed. The magnetic characteristics of such EMGU(s), including the homogeneity of the magnetic field along the EMGU(s) and the transverse magnetic field distribution were first investigated. As expected, the EMGU(s) can provide a homogeneous magnetic field in order to levitate bulk superconductors. Simulation results from an EMGU model implemented in COMSOL Multiphysics were verified using experimentally measured data, which indicated the established model can be used for further study and analysis. Next, the levitation characteristics of a high-temperature superconducting (HTS) bulk above the EMGU, including the levitation force acting on HTS bulk due to its interaction with the EMGU, as well as the stability of the bulk when experiencing a lateral disturbance and when varying the current of the EMGU, were investigated through experiment and simulation. The behavior of the levitation force during re-magnetization of the EMGU indicated that a larger re-magnetizing current is needed to suppress the internal magnetic field (trapped field) obtained from the pre-magnetization process, thereby providing a repulsive force to the superconductor. The stability study showed that the HTS maglev system with an EMGU with adjustable current can not only deal with a reduction of the levitation force but can also increase the restoring force when the superconductor is disturbed laterally. Finally, in order to clarify the mechanism of these levitation characteristics, the internal electromagnetic characteristics of the HTS bulk were analyzed using a 2D model.

Attenuation of Levitation Performance for Side-Suspending HTS Maglev System Under Vibration

The influences of vertical vibration on suspension stability and side-suspending gap for the side-suspending high-temperature superconducting (HTS) maglev system are investigated. The results show that the attenuations of side-suspending height and gap augment with the increases of vibration amplitude and initial side-suspending gap, respectively. These phenomena observed can be attributed to the fact that the vibration process causes ac loss effects. The results will be helpful for the future applications of HTS maglev system.

Feasibility Study of a DC Linear Motor Based on the Magnet Track of High-Temperature Superconducting Maglev

This article proposed a new design of a dc linear motor for the propulsion of high-temperature superconducting (HTS) magnet levitation (maglev) transports. This design is effective because it can reduce the HTS maglev system cost and compact the system components by improving the integration of the three main functions of levitation, guidance, and propulsion. The design was made for the desired onboard coil so that it is applicable to the existing magnet track of the HTS maglev system. Meanwhile, the previous independent linear motor can be replaced. The idea was first evaluated by the finite-element simulation and optimized to obtain an effective propulsion force. Based on the simulation results, a dc linear motor principle model was designed and fabricated. The propulsion force was obtained during experiments and verified the feasibility of the proposed idea. With further optimization, this method could be applied to the future HTS maglev system.

Numerical Simulation and Experimental Analysis on the AC Losses of HTS Bulks Levitating Under a Varying External Magnetic Field

Alternating current (AC) loss occurs when the high-temperature superconducting (HTS) maglev running on a permanent magnetic guideway (PMG) with a varying field. The running stability and safety of the HTS maglev vehicle will be influenced by the AC losses, which are closely related to the magnetic field fluctuation of the PMG and the levitation characteristics of HTS bulks. In order to study the AC losses of the HTS bulk under a varying field with different frequencies and amplitudes, numerical simulation and experimental analysis are employed. The simulation model was built by COMSOL Multiphysics with the partial differential equations module and heat transfer module. The experimental analysis of AC losses was designed based on a calorimetric method. The experiments are based on an HTS maglev dynamic measurement system, in which the rotational velocity of the PMG and working height of the HTS bulks are changed for simulating the experimental conditions of different frequencies and amplitudes of the AC field. And, the AC losses of HTS bulks are deduced from the evaporation amount of the liquid nitrogen. The simulation findings are consistent with the experimental phenomena qualitatively, which not only verify the rules of frequency and amplitude, but also the availability of the numerical simulation method. Moreover, the findings provide important hints for the future design of the HTS maglev systems.

Lateral drift of the HTS Maglev vehicle running on a ring test line under low pressure environment

With the development in recent years, high temperature superconducting (HTS) Maglev with self-stabilization characteristic has been regarded as a good candidate for evacuated tube transport (ETT). To ensure the safety and stability of the HTS Maglev vehicle running in a low pressure environment, results measured in the latest research of an HTS Maglev-ETT Test System were used to study the lateral drift (LD) of the Maglev vehicle under different low pressures. The field cooling heights (FCHs) of 20 mm, 30 mm, and 40 mm were studied under each pressure condition. The experimental results show that the low pressure environment and an appropriately low FCH condition are both beneficial to suppress the LD phenomenon. The low pressure environment will reduce the LD by lowering the temperature of the liquid nitrogen and increasing the pinning potential energy U0 of HTS bulk. The basic data of the pressure effects on the HTS Maglev system at different FCHs proves the low-pressure environment can improve the operating characteristics and further demonstrates the superiority of the HTS Maglev-ETT system.

Levitation Height Drifts of HTS Bulks under a Long-Term External Disturbance

High-temperature superconducting (HTS) maglev owns the capability of passive stabilization and has the potential to operate at a high speed with low energy consumption. However, the excitation caused by the irregular surface and inhomogeneous magnetic field of the permanent magnet guideway (PMG) will result in vibration between the superconductors and PMG, which could lead to some stability problems such as drift. To study the reliability of HTS maglev systems under a long-term disturbance, a tailored experimental device composed of a vibration table, a fixture, and HTS maglev model was employed. The effects of field-cooling height (FCH), external excitation frequencies, and amplitudes on the levitation height drift were investigated. It is found that under the same operating conditions, large excitation amplitude, high frequency, and low FCH would lead to a greater levitation height drift. There are three kinds of drift trends, i.e., downward, upward, or downward at first and then upward, and the phenomenon of drifting upward is more likely to occur under small excitation amplitude, high frequency, and low FCH conditions. Meanwhile, two simulation models employing the flux flow model and the flux flow and creep model were applied respectively. The simulation results show that the flux flow and creep model are more consistent with the experimental phenomena and the flux flow has a greater influence on the drift in the initial time period, while the flux creep has a slighter impact on the drift for a long time. These researches reveal the levitation height drift rules of the HTS maglev system and introduce proper simulation model for levitation height drift so that this work provides a reference for the design and safe operation of HTS maglev vehicles.

Subharmonic Resonance in Magnetic Levitation of the High-Temperature Superconducting Bulks YBa2Cu3O7‐<italic> <sub>x</sub> </italic> Under Harmonic Excitation

High-temperature superconducting (HTS) bulk YBa 2 Cu 3 O 7-x (YBCO) can achieve self-stable magnetic levitation (maglev) over a permanent magnet (PM) for its inherent flux pinning effect, which has considerable potential for engineering applications. The complicated vibration response, however, is lacking in research for the nonlinearity of the interaction force between the HTS bulks and PMs. This paper mainly focuses on the subharmonic resonance of the HTS bulks YBCO levitating above the PMs in Halbach array, which are in reciprocating motion, by numerical simulations. In general, the motion of HTS bulks is approximately harmonic under limited excitation. When the amplitude and frequency of the excitation satisfy certain conditions, the dynamical system undergoes a period-double bifurcation, and then, the subharmonic resonance occurs. Moreover, the period-double bifurcation brings the jump phenomenon when the frequency of excitation increases and decreases at the double of eigenfrequency nearby. Simulations show that a suitable damping is able to reduce the vibration markedly. The subharmonic resonance region in an amplitude-frequency plane is presented in this paper finally. In a word, the subharmonic resonance would occur in an HTS maglev system under certain conditions and its prediction is numerically studied here with a nonlinear mathematics model of the levitation force.

Simulation and Experiment Research on the Dynamic Levitation Force of Bulk Superconductors Under a Varying External Magnetic Field

In practical high-temperature superconducting (HTS) maglev systems, it was found that the levitation force of the onboard bulk superconductors may attenuate gradually under the inhomogeneous magnetic field. The corresponding phenomenon is that the levitation height will decay in the macroscopic and affects the long-term stability of the maglev vehicle. Thus, it is of great significance to study the dynamic levitation force of bulk superconductors under a varying external magnetic field and lay a foundation for the moderate and high-speed HTS maglev system application. In this paper, first, an experiment related to the dynamic levitation performance of YBCO bulks is carried out with a self-developed HTS maglev dynamic measurement system for the investigation of force attenuation. Then, a corresponding two-dimensional simulation model based on the finite element software of COMSOL Multiphysics 5.3 is built to research the dynamic levitation force of bulk superconductors moving above a nonuniform magnetic field. In the simulation, the electromagnetic properties are calculated using the H -formulation, and the moving mesh is employed to implement the relative movement between the bulk superconductors and permanent magnets. The experiment process is repeated in the simulation model, and the simulation results agree with the experimental results.