High Temperature Superconducting Maglev Vehicle Research Articles

Levitation performance evolution of high-temperature superconducting maglev vehicle under electromagnetism-heat-force strong coupling

ABSTRACT High-temperature superconducting (HTS) maglev is considered suitable for high-speed maglev systems because of its self-stability characteristic. However, when the HTS maglev vehicle vibrates, alternating current loss occurs in the onboard superconductor due to the change in the external magnetic field. It leads to the decrease of vehicle levitation height and seriously affects the safe and stable operation of the vehicle. So, in this paper, the levitation performance evolution of HTS maglev vehicle under the electromagnetism-heat-force strong coupling model is studied. The parameter of the air spring is optimized according to the ride index and levitation height decay. The effects of random irregularity at different speeds on vehicle levitation performance are compared. The influence of periodicity geometric irregularity on the levitation performance and ride comfort of HTS maglev vehicle are studied. This paper can provide data reference for the HTS maglev vehicle system in future engineering applications.

The effect of the modelling approaches in the assessment of comfort and curve negotiation performance of a small-scale maglev vehicle

In this article, a new co-simulation method was presented for high-temperature superconducting (HTS) magnetic levitation (Maglev) systems by utilizing H-formulation that is implemented in COMSOL Multiphysics®. A comparative study was conducted to evaluate the curve negotiation performance, which is closely related to its stability, of the HTS maglev vehicle running on a multi-surface permanent magnet guideway (PMG). Also, Sperling’s ride index method was used to evaluate ride comfort. Different from the existing related models of this subject, the dynamics of free-falling were incorporated into the modelling approach to simulate the actual running conditions of the vehicle. In addition, because of considering the non-stationary dynamics of the induced supercurrent in the HTS domain, the proposed approach and the selected route design provide simulation results that are close to the actual application of the HTS maglev vehicle. The results show that the performance indicators of the co-simulation greatly deviate from those of the existing curve-fitting-based models with increasing velocity.

Vertical Dynamic Response Analysis of HTS Maglev Vehicle Excited by a Designed Coreless-Typed PMLSM

High-temperature superconducting (HTS) pinning maglev has the potential for high-speed application because of its advantages of passive self-stabilization, energy conservation, environmental protection, and no inherent magnetic resistance along the forward direction. The HTS pinning maglev can realize non-contact levitation and guidance. Permanent magnet linear synchronous motor (PMLSM) is suitable for HTS pinning maglev to realize non-contact drive. However, in addition to the longitudinal driving force for the HTS pinning maglev train, the PMLSM also produces the normal force which will cause additional excitation on the maglev train and affect its levitation height and vertical dynamic response. In this paper, a coreless-typed PMLSM is designed for HTS pinning maglev driving system, and the driving force and normal force characteristics of the motor under different air gaps are calculated. Then, a vertical dynamic model of the HTS pinning maglev vehicle is established. The vertical dynamic response of the HTS pinning maglev vehicle excited by the normal force of PMLSM and permanent magnet guideway (PMG) irregularity is simulated and analyzed. This work can provide a reference for the study of the electromechanical coupling effect between the HTS pinning maglev levitation system and linear motor driving system.

Investigation on thermal effect of bulk high-temperature superconductors under varying external magnetic field

Superconducting bulks applied to high-temperature superconducting (HTS) maglev vehicles are susceptible to magnetic field, resulting in alternating current (AC) losses and heat generation, which affect the stability of the suspension system. Therefore, the thermal effect of superconducting bulk under external magnetic field is worth studying. The paper uses finite element software to establish a 2D electromagnetic-thermal coupling model. The distribution and variation of HTS bulks’ temperature under varying external magnetic field are simulated and analyzed, and the loss and temperature rise of rectangular bulks with different thicknesses are studied. Finally, the effect of increasing the critical current density on the thermal effect of the superconducting bulk is discussed. The results show that the temperature rise of bulk has a positive correlation with the amplitude and frequency of external magnetic field. The maximum temperature is affected by the angle of magnetic field. Under the same external magnetic field, the bulk with smaller thickness produces smaller loss and temperature rise. The research results can provide important references for the operation and furniture design of HTS maglev vehicles.

Simulation of the Braking Effects of Permanent Magnet Eddy Current Brake and Its Effects on Levitation Characteristics of HTS Maglev Vehicles

High-temperature superconducting (HTS) magnetic levitation (maglev) trains for designed high speed need a non-contact braking method that can produce stable and sufficient braking forces to ensure the safety of the train during emergency braking. In order to study the braking effects of permanent magnet eddy current braking (PMECB) used in HTS maglev vehicles and its effects on the levitation performance of HTS maglev vehicles, an equivalent two-dimensional simulation model of PMECB for a HTS maglev test vehicle under different working air gaps of 5 mm, 10 mm, 15 mm and 20 mm was established in Maxwell software. Then, a 6 degree of freedom dynamic model of the vehicle was established in Universal Mechanism software. In the dynamic simulation, the normal force of PMECB was not considered, and only the detent force of PMECB was taken as the excitation of the vehicle. The simulation results show that PMECBs can reduce the vehicle to relatively low speed in a few seconds. During the operation of PMECBs, the levitation height and levitation force of the maglev Dewar will be affected, and maximum variations in levitation heights and levitation forces occur on the Dewars at both ends of the vehicle. These help us to understand the braking and levitation performance of HTS maglev vehicles under the action of PMECBs and enrich the design idea of braking and levitation systems of HTS maglev vehicles equipped with PMECBs.

Influence of Traction Rod Arrangement on the Dynamic Performance of High-Temperature Superconducting Maglev Vehicle

High temperature superconducting (HTS) maglev, which uses the magnetic flux pinning effect to realize the levitation and operation, has attracted wide attention in the field of transportation due to its advantages of high efficiency, energy saving, safety and comfort. As the connection components between the bogie and vehicle body, and the transmission components of tractive and brake force, traction rods not only satisfy the relative motion between vehicle body and the bogie, but withstand the pounding of bogie relative to body as well. There is a great need to research the influence of traction rod parameters to HTS vehicle on its dynamic performance, which can prolong the life of the traction transmission device and enhance the running stability of vehicles. In this paper, a vehicle-bridge coupled dynamics model, considering different traction device arrangements, is established by means of multibody dynamics software Universal Mechanism (UM). And the influence of the traction transmission devices on the vehicle's dynamic performance is analyzed. The analysis results provide a reference for designing and optimizing the parameter of traction drive transmission devices.

Vibration Suppression of HTS Maglev System Based on Negative Resistance Electromagnetic Shunt Damper

The high-temperature superconducting (HTS) maglev system has tremendous possibilities for future high-speed transportation application owing to its salient advantages of self-stable levitation and zero pollution operation. However, previous study indicated that the relatively low damping of HTS system may lead the undesired large-amplitude nonlinear vibration in system. Thus, electromagnetic shunt damper (EMSD), which usually consists of electromagnets, permanent magnets and shunt impedance connected to the terminals of the coils, is introduced in the system to improve the damping of the system. The effect of EMSD is to transfer the mechanical energy to electrical energy and consume it in the form of Joule heat. For better vibration suppression performance, this paper proposes a negative resistance electromagnetic shunt damper (NR-EMSD) in HTS maglev vehicle model. The negative resistance can offset the inherent resistance of the electromagnet coils and as a consequence, the induced current of the circuit will increase as well as the induced electromagnetic force. Also, the change of total resistance of the circuit will influence the vibration reduction performance. In this paper, the effect of NR-EMSD is tested by experiment under different working conditions compared with the model without EMSD. The results are analyzed and basic conclusions are summarized. This work may provide references for further practical application in HTS system.

The SCML-05 Developed for Studying the 3D Force and PMG Irregularities Characteristics of HTS Maglev

In order to promote the application of high temperature superconducting (HTS) maglev vehicle, the series of superconducting maglev (SCML) measurement devices — 01, 02 & 03 have been developed in Southwest Jiaotong University. During the course of research, the importance of three-dimensional (3D) study of the interaction between HTS bulks and permanent magnet guideways (PMGs) has become evident. More specifically, when the HTS vehicle is moving at a high speed, small irregularities of the PMG's magnetic field become the source of vibration. Therefore, in order to study the 3D force and the characteristics of HTS maglev under PMG irregularities, a new measurement device called SCML-05 was designed, constructed, and validated. This newly developed measurement device consists of two major parts. The first one is a closed-loop sliding platform providing 3D motion. The second part is measurement and data acquisition system with the software developed for this purpose. In addition, a laser displacement sensor is used to measure the geometry irregularities of the PMG. Overall, the SCML-05 is flexible and light. The force characteristics of the HTS bulks placed above the PMG can be precisely investigated by means of this system. Additionally, the PMG irregularities including geometry and magnetic field irregularities can be measured. These parameters are required to analyze the relationship between the PMG irregularities and the force of HTS maglev vehicle. The test process and typical results obtained by this system are presented in this paper.

Design of the Onboard Cryogenic System for High-Temperature Superconducting Maglev Vehicle

In the high-temperature superconducting (HTS) maglev system, the cryogenic system is used to eliminate the thermal load of the low-temperature unit in time to maintain the superconducting state of the superconductor, which is the prerequisite of the application. At present, liquid nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) immersion cryogenic system is used in HTS maglev vehicles, but the operation efficiency of the vehicles will be reduced because of the LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> replenishment. Therefore, according to the application environment of HTS maglev vehicles, an onboard LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> natural circulation cryogenic system based on the principle of thermosiphon is designed. This paper focuses on the design of the structure of the cryogenic box, including the design of the vacuum system, the selection of refrigerator, the design of heat exchanger, and the selection of materials. Finally, it is calculated that the thermal load of the cryogenic system during the normal operation of the HTS maglev vehicle is 25.09 W, which is less than the cooling capacity of 120 W when the cryogenic system is working at 65 K. The feasibility of the cryogenic system is verified, which will provide a reference for the design of the cryogenic system in the engineering of the HTS maglev vehicles.

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 Characteristics of the New High-Temperature Superconducting Maglev Vehicle Based on Operation Test

A new HTS maglev vehicle called “KENYON” that can carry 8 passengers was successfully developed in December 2019. The vehicle adopted the bogie structure of independent running gear, which brings the improvement of curve passing performance. In order to further optimize vehicle curve passing performance in view of the small radius curve of the ring test line, corresponding experimental research was carried out in this paper. The experimental results show that the small wheelbase and centripetal arrangement were beneficial to improve the vehicle's curve passing ability.

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.

A new guideway design for the HTS Maglev vehicles considering curve negotiation

High-temperature superconducting (HTS) magnetic levitation (maglev) systems have been studied by various research groups regarding both experimental and modelling point of view. However, there exists a trade-off between levitation and guidance forces acting on the vehicle, especially in the case of high-speed curve negotiation. To overcome this trade-off, we proposed a multi-surface permanent magnet guideway (PMG) design, for the small-scale maglev vehicle, in which polarization of the permanent magnets (PM) changing with track segments. The HTS-PM interaction model was constructed by utilizing H-formulation implemented in COMSOL Multiphysics®. The hysteretic levitation and guiding force expressions used in the dynamic simulation have been obtained by a polynomial fit to force-displacement curves obtained by the finite element model built in COMSOL Multiphysics® environment. Also, the damping effect derived from free-fall dynamic tests is incorporated into the model to construct a more realistic simulation model. The effectiveness of the proposed track design has been validated through comparisons with Halbach-derived PMG. Finally, it can be thought that the proposed PMG design is a good candidate for the high-speed operation of a maglev system when the increased levitation and guiding stiffness values are considered.

Active vibration control of secondary suspension based on high-temperature superconducting maglev vehicle system

The high-temperature superconducting (HTS) magnetic levitation (maglev) vehicle system is a kind of self-stable levitation mode, which is benefited from the characteristic of flux pinning of non-ideal type II superconductor. And this novel prototype has the outstanding advantages of simple structure, reliable principle, friendly environment and so on. But in the HTS maglev vehicle system, the damping coefficients of the primary suspension are very small. The vibration of the YBCO bulks over a permanent magnet guideway (PMG) will be incurred by the fluctuant external magnetic field, which is easily transmitted to the car body to affect the running comfort. The primary goal of this paper is to apply active vibration control into two linear electromagnetic actuators on each bogie. Each electromagnetic actuator is combined with an air spring as a kind of active suspension system in secondary suspension. Initially, the primary suspension stiffness coefficient and damping coefficient of YBCO bulks are measured by experiments. And the mathematical model of HTS maglev vehicle with active actuators was built using the German track spectrum of low interference as PMG irregularity. Then, the dynamic responses of HTS maglev vehicle system were simulated with PID and Fuzzy-PID controllers used in the active actuator to verify the feasibility of the control methods, and compared with the uncontrolled system. Finally, the results of the simulation indicate that both control strategies could improve vehicle comfortable and greatly improve the stability of the system compared to the passive bogie system.

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.

The Stability of HTS Maglev Vehicle Through Grade Change Point

High-temperature superconducting (HTS) maglev system, based on the magnetic flux pinning characteristic of non-ideal type II superconductors, can realize self-stable above permanent magnets. HTS maglev possesses the advantages of low-energy consumption, simple mechanical structure and environment-friendly, which make it an ideal high-speed transportation mode. When an HTS maglev vehicle crosses a ramp, the levitation height will fluctuate due to the rapid change of the track curve, which may affect the safety and stability of the system. In this paper, first, a levitation force model was obtained based on experimental data. Based on this model, a dynamic model of the HTS maglev vehicle-bridge coupled system was established. The dynamic response of the maglev train was simulated and analyzed when it operated through track grade change points under different track slopes, vertical curve radii and speeds. The influence of these parameters on the stability of the system was investigated, and the optimized design parameters for the vehicle and the track slope are proposed as well. This study provides references for the future engineering development of HTS maglev transportation.

Design and Implementation of auto-filling liquid nitrogen for HTS maglev vehicles based on Kalman filter algorithm

The cryostat equipped with superconducting materials is one of the most important component of high-temperature superconducting maglev vehicles. However, due to the multiple energy disturbance forms in the cryostat, such as AC losses of superconductors, vibration of the cryostat and so on, the evaporation of liquid nitrogen (LN2) will be stimulated to accelerate, which will seriously threaten the vehicle safety. Therefore, this paper designs an intelligent controller which can realize the function of auto-filling LN2 based on the Kalman filter (KF) algorithm. Moreover, in this publication the corresponding methodology will be described as well in detail. Initially, the platinum resistance sensors were used to study the relationship between the temperature and LN2 level, meanwhile, the system state equation and observation equation were established. Then, the KF algorithm was introduced to estimate the true LN2 level. Based on the feedback signal of LN2 level, the system utilizes the STM32 microprocessor as control chip to control the solenoid valves and realizes the function of auto-filling. The controller has been implemented and the total time for filling one cryostat was reduced from 86 min to 16 min. This result is very encouraging and inspiring for the practical application of HTS maglev systems.

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.

Vertical and lateral drift behavior of a linear superconducting magnetic bearing system under multi-operating modes

Since the discovery of high temperature superconducting (HTS) material, HTS maglev with the characteristics of self-stabilization and zero magnetic drag, has shown excellent potential for future transportation applications. However, this stability characteristic of HTS maglev is difficult to fully ensure in a spatial position, because of the magnetic flux flow and creep of the HTS bulk. Hence, to study the drift phenomenon of the HTS maglev vehicle excited by this unguaranteed stability characteristic, the linear superconducting magnetic bearing system, composed of a ring permanent magnetic guideway line (double track) and a HTS maglev vehicle, the ‘Super-Maglev’, was utilized. This system aims to explore the drift phenomenon in the vertical and lateral directions of the whole maglev vehicle under various operating conditions: different running speeds, unbalanced loading and cyclic loading situations. As an illustration induced by the experimental results, the lateral drift (LD) at a faster running speed (15 km h−1) is twice than that at 10 km h−1. Also, compared to the constant load condition, the vertical drift (VD) under cyclic load is larger. Moreover, with time going by, both LD and VD tend to be stable. Specifically, for the LD curve, it can be fitted by an exponential function. Finally, all the above experimental results support references for the future design and study of linear SMB systems.

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.