Showing papers by "Guangtong Ma published in 2021"

Coupled Magnetic Field-Thermal Network Analysis of Modular-Spoke-Type Permanent-Magnet Machine for Electric Motorcycle

Abstract: Brushless modular spoke type permanent magnet (MSTPM) machine has exhibited prior electromagnetic (EM) performance over conventional surface-mounted PM machines for in-wheel traction system in electric vehicles (EVs) However, analysis of thermal behavior of MSTPM machines is rather insufficient, even accurate thermal analysis is of significant importance due to poor heat dissipation condition inside the wheel hub Conventionally, the losses produced in electrical machines by EM prediction is equivalent to the heat source in normal thermal analysis, and only the resultant thermal behavior is investigated However, the reaction of temperature rising on the EM performance is neglected In this article, a bi-directional coupled electromagnetic-thermal analysis method is proposed and carried out by a combination of lumped parameter thermal network (LPTN) model and finite element method (FEM), where both steady-state temperature distribution and transient-state temperature rise are investigated for MSTPM machines By finite number of iterations between magnetic and thermal fields, the electromagnetic performance and thermal behavior can be predicted more accurately due to the coupling effect considered The coupled model-predicted results are verified by 3D-FEM and experimental measurement, which shows that the proposed method has advantages in both computational efficiency and accuracy as well as can be applied to other electrical machines

3-D FEM Modeling of the Superconducting EDS Train With Cross-Connected Figure-Eight-Shaped Suspension Coils

Abstract: Superconducting electrodynamic suspension (EDS) train has become a suitable candidate for the future ultra-high-speed ground transportation because of its unique advantages of self-stability suspension and guidance performances, large suspension gap, and high suspension/drag ratio. It is indispensable to develop an efficient electromagnetic modeling method for the EDS train. An analytical model based on the dynamic-circuit theory and virtual displacement method has been proposed, but it has to know exactly the mutual inductance between the on-board magnet and ground suspension coil before calculating the induced current and electromagnetic force. Thus, this article is to establish an efficient 3-D finite element method (FEM) model for the EDS train, in which the mutual inductance is not required. First, the critical current of the REBCO magnet serving as the on-board magnet of the EDS train is estimated. Second, based on the vector magnetic potential method and circuit principle, the 3-D FEM model of the EDS train is established with the magnetic potential boundary condition employed to avoid the moving mesh of on-board magnet. Third, the 3-D FEM model is validated by comparing the analytical results as well as the published measurement data. Finally, the electromagnetic behaviors of EDS train under the guidance offset and suspension offset conditions are investigated with the validated 3-D FEM model.

Improved Current Dynamics of Proportional-Integral-Resonant Controller for a Dual Three-Phase FSPM Machine

Abstract: Resonant controllers are commonly used in parallel with proportional–integral controllers in the current control of multiphase machines and other three-phase drives where current harmonics need elimination. However, additional oscillatory and slow poles arise with the resonant controllers, resulting in a degradation in both reference tracking and disturbance rejection. In this article, an improved current control scheme with a discrete-time PI-resonant controller is proposed for a dual three-phase flux switching permanent magnet (FSPM) machine to eliminate the current unbalance and harmonics. First, a partial prefilter is used in the resonant controller path, yielding a pole-zero cancelation for the resonant poles in the closed-loop system; thus, the oscillation in command response becomes negligible. Then, the active resistance method is employed to improve the low-frequency disturbance rejection, and the resonant poles are damped with a pole-placement strategy. Finally, the experimental results on a dual three-phase FSPM machine validate the effectiveness of the proposed method, which can be extended to other ac drives for harmonic suppression.

Operation of a Seven-Level T-Type Active Neutral-Point-Clamped Converter With Modified Level-Shifted PWM

Abstract: This article presents novel control strategies for a seven-level (7L) T-type active neutral-point-clamped (T-ANPC) converter based on the level-shifted pulse width modulation (LS-PWM) technique. Compared with classical 7L topologies, such as NPC, flying capacitor converter, and cascaded H-bridge converter, the 7L T-ANPC converter can reduce the device requirements while reserving the advantages of high redundancy and low conduction losses. Furthermore, the internal switching state redundancy provides freedom to balance the flying capacitor (FC) voltage and realize the fault-tolerant operation flexibly. The control strategy with modified LS-PWM technique is developed for the T-ANPC to obtain desired outputs under normal and switch open fault modes. The proposed control strategy considers the complete balancing of dc-link neutral-point voltage and FC voltages. The feasibility of the proposed 7L T-ANPC and control strategy is evaluated by simulations and experimental tests under steady-state and several typical transient operating conditions.

Open-Switch Fault-Tolerant Operation of T-Type Active Neutral-Point-Clamped Converter Using Level-Shifted PWM

Abstract: The T-type active neutral-point-clamped (T-ANPC) converter is an emerging hybrid multilevel topology, which owns superior characteristics such as low conduction losses, flexible in control. Reliability improvement is essential for the T-ANPC due to the large number of power switches. For this motivation, this brief develops a carrier-based fault-tolerant control strategy for the T-ANPC converter in the case of typical open-switch faults. A modified level-shifted pulse width modulation (LS-PWM) is employed to control the converter to obtain the desired outputs under single/multiple open-switch fault modes. The fault-tolerant operations with full and reduced power ratings are realized by rearranging the carriers and modulation signals of the LS-PWM. Finally, the feasibility and effectiveness of the proposed control strategy for the T-ANPC is evaluated experimentally.

Performance Investigation of Contactless Self-Regulating HTS Flux Pump

Abstract: Self-regulating high temperature superconducting (HTS) flux pump is one of the most effective methods to compensate the current degradation of a closed HTS magnet for its stable operation. In this study, to understand the working principle as well as the influential factors regarding to its operation performance, a basic circuit model has been established. Based on that, we found the saturation load current is strongly related to the added secondary resistance, which could offset the DC bias current induced in the charging loop. Then, we built a prototype experimentally, in which, part of the load coil was used as a HTS bridge and bifilar bridge design has been adopted to minimize the possible flux fluctuation in the load loop. In the experiment, the dependence of the charging performance on the bridge length as well as the added secondary resistance at different frequencies has been clarified. The results show that, the load current is remarkably impacted by the aforementioned parameters. Specifically speaking, with an increasing added secondary resistance, the operating frequency needs to be higher to ensure the secondary current can follow the primary current, which is crucial for maintaining a larger load current.

Dynamic Simulation of Vibration Characteristics and Ride Quality of Superconducting EDS Train Considering Body with Flexibility

Abstract: A numerical model has been developed to investigate the dynamic characteristics of the Superconducting electrodynamic suspension (EDS) system. Modeling of the guideway with the surface irregularity and the Maglev vehicle are described. Numerical simulations were performed in Simulink to solve the coupled problem. A 3-D model of the electromagnetic system of the superconducting EDS train is established, and the computed real electromagnetic forces are coupled with the maglev train. The EDS train was simulated by using the SIMPACK multi-body dynamic program. The simulation was carried out by using two body models of rigid and flexible bodies. In order to use the modal information to construct the flexible car body, the finite element method and the ABAQUS software were used to construct it together with equivalent elements. The final framework is constructed in MATLAB/Simulink to simulate dynamics and electromagnetic forces together with the constructed simulation framework. In order to consider the interference caused by irregularities, randomness and power spectral density (PSD) are used to analyze vibration interactions. We compared random signal inputs with PSD, greatly enhancing accuracy, and analyzed the vibrational interaction between car body and ride quality.

The Underlying Mechanism of Faster Current Attenuation of HTS Magnet in Persistent Current Mode Subject to the Traveling Magnetic Fields

Abstract: High-temperature superconducting (HTS) magnet, due to its greater performance of magnetic field at higher temperature (20–40 K), better thermal stability, smaller volume and weight under the same requirements, and lower refrigeration costs, has attracted growing attention in the ultra-high-speed maglev system, high field magnet, and some other applications. Considering the practical requirements, closed-loop method is generally adopted in HTS magnet to maintain the persistent operation and to output the stable magnetic fields. But the accelerated current attenuation occurs when the HTS magnet is subjected to traveling magnetic fields, which is not conducive to the long-term operation. Therefore, this paper aims to investigate the essence of current attenuation of HTS magnet in persistent current mode under traveling magnetic fields and to further suppress this adverse behavior. In this study, to calculate the current distribution and dynamic resistance, a two-dimensional (2-D) finite element model (FEM) was established and verified by comparing with the experimental results. It can be seen from the simulation results that the dissipative losses caused by dynamic resistance present a non-negligible effect on the current attenuation of the magnet. And the mechanism of faster current attenuation was well explained by the variation of the dynamic resistance under the traveling magnetic fields.

Thermo-electromagnetic modeling of coated superconductor coils with metal insulation

Abstract: The use of metallic sheets as the insulator in a coated superconductor coil is able to increase its turn-to-turn contact resistance for shortening the charging/discharging delay while preserving the self-protection ability. To theoretically understand and predict the properties of the metal-insulation coils, we developed a thermo-electromagnetic model, in which a modified equivalent circuit for electrically representing the metal-insulation coils is built to take the effect of insulator into account. The effectiveness and versatility of this model are verified by different experimental scenarios, e.g., charging, sudden-discharging, and overcurrent. Enabled by the validated model, we carried out a set of case studies and observed that, (a) the metal-insulation coil with a low resistivity and high thermal conductivity metallic insulator is preferable to achieve a better thermal stability; (b) there exists an optimal insulator thickness for realizing the shortest charging delay, but a thicker insulator is superior for realizing a stronger thermal stability; (c) contact resistivity of over 104 μΩ· cm2 can weaken the current sharing in the radial direction, which would deteriorate the thermal stability of the metal-insulation coils, although it can significantly suppress the charging delay, implying that a tradeoff is always needed to balance the charging delay and thermal stability when determining the contact resistivity. These findings, mostly being inaccessible from the experiments, provide guidance toward practical applications of metal-insulated coated superconductor coils.

Comparison of Long Stator Three-Phase Winding Structures in a 2G HTS LSM for Maglev Application

Abstract: Superconducting magnetically levitated (SC maglev) trains have developed rapidly in recent decades due to their promising features, such as a high cruising speed. A series of RD the thermal load from the non-synchronous magnetic wave on the HTS magnet is also an important design issue. Consequently, double-layer short-pitch winding has been designed for the HTS LSM.

The Effect of Running Speed and Guideway Irregularity on the Levitation Performance of a Linear HTS Maglev Bearing

Abstract: High-temperature superconducting (HTS) magnetic levitation (maglev) bearing is regarded as a promising candidate for the future high-speed transportation system as a result due to the merits of passive stabilization, low power consumption and environmental-friendliness The dynamic characteristics are critical for its high-speed applications performance The current research on the dynamic characteristics of linear HTS maglev bearings is limited to small-scale, approximate harmonic excitation or low-speed In this paper, the expression of random guideway irregularity spectrum in time domain, which could describe the realistic guideway excitation in rail transportation system, was obtained by Inverse Fourier Transform method with a homemade code Based on a strong-coupled electromagnetic-thermal-mechanical model, the dynamic characteristic of a heavy-load linear HTS maglev bearing under the excitation of random guideway irregularity with different speeds (400, 500, 600 km/h) and guideway irregularity amplitudes were studied The results show that the influence of high speed and the temperature on the dynamic stability of linear HTS maglev bearing is quite limited, which is contrary to common concern On the other hand, the guideway irregularity amplitude plays a great effect on the system dynamic stability Thus cautious attention is still needed when selecting the line route and manufacturing the guideway These conclusions could serve as a design guideline for the future high-speed application of linear HTS maglev bearing

3-D Analysis of Electromagnetic Forces of a Real-Scale Superconducting Linear Synchronous Motor for EDS Train

Abstract: The superconducting linear synchronous motor (LSM) is considered as one of the most suitable propulsion approaches for the electrodynamic suspension (EDS) train whose operating speed exceeding 600 km/h has been realized. The performance of the superconducting LSM is directly influenced by the multi-degree-of-freedom motion of EDS train. Therefore, it is essential to carry out the characteristic analyses of superconducting LSM to verify its fitness in EDS system. In this paper, the characteristic analysis of superconducting LSM was implemented based on a real-scale 3-D finite element model. The variation trends of thrust force, levitation force and guidance force are investigated to confirm the stability of EDS train in consideration of both the lateral and vertical displacements. The obtained results show that the electromagnetic force of superconducting LSM can provide the excellent thrust force for EDS train, enhance the stability in lateral direction and worsen the stability in vertical direction of EDS train. Those results will be the significant guidance for promoting the application of superconducting LSM in EDS train.

Evaluation of the Structural Dynamics of a 2G HTS Magnet System Considering Electromagnetic and Thermal Stress

Abstract: Magnetically levitated (maglev) trains with superconducting technology has been developed rapidly in recent decades due to such promising features as high cruising speed. The second-generation high-temperature superconducting (2G HTS) magnets used on maglev trains are state-of-the-art among different types of magnets, like permanent magnets, electromagnets, or low-temperature superconducting magnets. A series of works have been done by the group on the development of the 2G HTS maglev, including optimal design, manufacturing, and testing of the ground propulsion system and on-board 2G HTS magnet system. In this work, as a continuation of the development progress, the structural dynamics of the on-board 2G HTS magnet system are evaluated. Since the HTS magnets are operated in a cryogenic environment featuring large current inflows, consideration of both the electromagnetic and thermal stresses on the maglev's structural dynamics is necessary. Modal analysis, harmonic response, random vibration, and shock response are conducted, based on standard IEC 61373. Fatigue assessment is also provided.

3-D Analytical Model of Racetrack HTS Coil Subject to Travelling Magnetic Fields

Abstract: Magnetic levitation (maglev) train has the unique advantages of no-mechanical contact, high operating speed, and so on. All those advantages indicate the potential of maglev in the future ultra-high-speed ground transit, in which the high-temperature superconducting (HTS) linear synchronous motor (LSM) is essential because of its sample structure and excellent performance. HTS LSM is a typical application of racetrack HTS coil subject to travelling magnetic field. Motivated by an efficient method to promote the application of maglev, a 3-D analytical model combining the dynamic circuit theory and virtual displacement method was proposed for estimating the performances of racetrack HTS coil in LSM. To verify the proposed 3-D analytical model, the calculated open-circuit magnetic field and back electromotive force were compared with the numerical results of a 3-D finite element model in which the actual geometry of HTS LSM and the nonlinear conductivity of HTS tapes were taken into account. Based on the validated 3-D analytical model, the characteristics of HTS LSM was analyzed. The obtained results indicate that the validated 3-D analytical model could be a very efficient tool for the characteristic analysis and optimization of HTS LSM.

Research on Braking Characteristics of Rail Eddy Current Brake with AC Excitation

Abstract: This paper describes an eddy current brake (ECB) device consisting of AC excitation and ferromagnetic railway. The braking force can be generated with non-contact and low noise caused by the reaction between the eddy current and excitation current. In this paper, the structure of the brake is introduced detailedly. In addition, the three-dimensional finite element analysis (FEA) model of ECB is established. Meanwhile, the experiment system of the rail ECB is built to study the braking characteristics. The validity of FEA simulation is verified by experimental results. It is found that with the increase of speed, the braking force increases linearly to a maximum value first, then slowly decreases, while the normal attractive force decreases continuously. The braking characteristic matches the requirements for the high-speed running trains which need large braking force and low normal force in the deceleration process, so it can be used as an auxiliary braking method in the high-speed railway.

Development of a Double-Side Transverse Flux Linear Motor for Direct Drive Applications

Abstract: The transverse flux linear motor (TFLM) can achieve high force density at low speed. But the special structure also leads to low utilization of PM materials. In this paper, a novel double-side TFLM is proposed and investigated. The magnets can provide effective flux linkage both in positive and negative operating period. Firstly, the basic structure of the double-side TFLM and operating principle is introduced. Then, the reluctance network of the proposed motor is established based on the flux path, and the expression of thrust force is deduced. Moreover, the electromagnetic performance of the proposed motor is investigated. The results show that the proposed motor is suitable for direct-drive applications.

Structure Optimization of a Superconducting Linear Generator With YBCO Tape Windings

Abstract: The paper proposed double-sided superconducting linear generator with YBCO tape windings. An analytical model of linear generator was developed based on electromagnetic field theory. A parameter-scanning method is used to search for optimal dimension parameters with the purpose of minimizing the non-sinusoidal components of the induced voltage curve. The results obtained show a significant improvement in the quality of air-gap magnetic field, and reduction of the higher harmonic in voltage wave obviously. The induction voltage in the generator coils at the speed of 130 m/s are studied. Finally, the feasibility of the superconducting linear generator was analyzed and confirmed.