The high-temperature superconducting (HTS) null-flux electrodynamic suspension (EDS) system is one of the most promising solutions for high-speed transportation. In this article, a 3-D model based on the finite-element method (FEM) is established to solve the electromagnetic forces in the HTS null-flux EDS system with the commercial software COMSOL Multiphysics. The current induced in the null-flux coils and the forces on the HTS magnets were studied and compared with the results from our dynamic circuit model. The two models agree with each other with a difference of less than 6%. The FEM model can deal with 3-D geometries, allowing the analysis of complex situations, such as the eddy current in the cryostat walls. Furthermore, the model can be readily extended to solve coupled problems, including the heat and mechanical behaviors of the HTS magnets and/or the null-flux coils, which are engineering concerns in real applications.

The existing time domain models for CLLLC class resonant converters have at least one of the following drawbacks: 1) the model cannot be applied for different resonant tanks and circuit topologies; 2) the effect of parasitic capacitors and deadtime is ignored; 3) large computation time is required to obtain steady state waveforms. To address these issues, an advanced state-space based analysis (ASSA) model is proposed in this article. The operation stages by considering parasitic capacitors and deadtime are proposed and equivalent to a universal circuit, which largely increases the accuracy with low model complexity. Additionally, the ASSA model is universal for different inverter structures, rectifier structures, and different resonant tanks, including LC, LLC, CLL, CLLC, and CLLLC . To improve the calculation speed, a hybrid operation mode analysis and ASSA model is proposed to obtain closer initial values and achieve steady state 2.15 times faster than traditional state-space based analysis methods. Finally, experimental results of CLLLC, CLLC , and LLC resonant converters working in multiple conditions are presented to validate the effectiveness and accuracy of the proposed ASSA model. Compared with the traditional time domain model, the relative error of resonant inductor current waveforms is reduced from 5.91%–43.54% to 2.83%–19.42%.

Owing to the presence of joint resistance and flux creep, high-temperature superconducting (HTS) coils without a power supply inevitably suffer from current decay. A flux pump is a voltage supply that requires connections with smaller footprints and a lower heat load than traditional current leads. In this study, we explain the principle of the upper limit for the output current of the traveling wave flux pumps. Based on this principle, a miniaturized linear flux pump device was developed. With narrow and misaligned iron teeth, elaborate 3D geometry of the iron pieces, and optimized driving current waveform, the miniaturized flux pump can support more than 120 A output current with only a 10 mm wide HTS tape and a compact size of 4.6 × 4.6 × 3.4 cm. Our experimental results show that the critical current of the HTS tape has a significant effect on the flux pump output. An HTS tape with a larger critical current supports a higher maximum transport current, whereas an HTS tape with a smaller critical current requires less applied current for positive output. Finally, excitation tests on HTS coils were performed. Charge/active discharge and field supplement experiments were done on a maglev HTS racetrack coil of 0.4 H, where charging/field supplement capability of the miniaturized flux pump were demonstrated up to 46.8 A (close to the critical current of the coil). It has also been proved that the flux pump can work together with an external power supply with persistent current switch. The miniaturized flux pump can also independently charge an HTS coil of 60 μH to 91.6 A, which is the critical current of the coil at a low voltage criterion.

Long wire critical current (Ic) characterization is important for fabrication of superconducting magnets. Many inductive and transport Ic measurement methods have been developed for km scale rare earth cuprate (REBCO) based Coated conductors (CC), which is a very promising high temperature superconduct-ing material for magnet applications. As a direct indication of the current carrying capability, transport measurement is fa-vored by most tape users. However, the traditional transport measurement technique has its limitations for long tape charac-terization. The speed of transport measurement is usually not high enough for km scale tapes, and direct current (DC) meas-urement also has a certain risk of tape damage due to the Joule heating at current contacts, especially for some special CCs with higher contact resistance, e.g. stainless-steel encapsulated CCs. For long wire measurements, the risk of tape damage is general-ly higher than acceptable. A pulse measurement method based on induction principle is proposed and tested in this work, the feasibility of this method is verified by experiments. Where pulsed current is used to reduce Joule heating thus reduce the risk of tape damage. Moreover, the speed of measurement can also be improved by the technique compared with DC measurements.

Persistent Current Switches (PCS) which switch between superconducting and resistive states enrich the operation scenarios of superconducting magnets. A commonly used thermally controlled PCS fits DC current feeding but too slow for AC or pulsed current feeding for the magnets. Thanks to the high thermal stability of high temperature superconductors, pulsed current feeding becomes feasible with a practical over current PCS control strategy, which is verified through experiments on a non-insulated coil made of ReBCO tapes in this work, leading to a novel charging procedure for superconducting magnets. The structure is simple and straightforward, and has a prospect in the field of excitation and field supplement for a superconductingmagnet.

The dynamic stability is crucial to successful operation and passenger comfort in zero-flux electric-dynamic suspension (EDS) systems. Usually, the stability problem is studied by a dynamic method where equations of motion are solved, with the electromagnetic interaction and the motion of the vehicle coupled in different levels. The dynamic studies provide information on operation strategies such as active or passive damping designs. In this work, the stability of the system is studied from another angle, where the vehicle body and bogie are taken as a whole and the stability is evaluated from the “potential energy surface” of the system. Although the system is not conservative, the difference between path integrals of electromagnetic force along different paths is small. For approximation, the stability is evaluated by taking the path integral as potential energy. Instead of dynamic stabilities, the method reveals the quasi-static stabilities. Instead of a damping strategy, the work is focused on the geometrical design parameters. The study is done with different system design parameters, which reveals that the height of the upper ground coil is one of the most important parameters that affect the lateral-roll coupled stability. The design principle is to have maximum mutual inductance between the on-board and upper ground coils, as well as maximum spatial derivative of the mutual inductance.