Wei Zhou

To meet the requirements of high thrust, low electromagnetic disturbance of both the overall mover and the local superconducting coil (SC) of superconducting linear synchronous motors (SLSMs) for the high-speed propulsion system such as electromagnetic sled and maglev launch system, a topology of SLSM with double-layered misaligned centralized windings (DLMCWs) is proposed in this article. The harmonic suppression mechanism of the SLSM with DLMCWs is introduced. An analytical model is established based on the line element equivalent model to calculate the comprehensive dynamic electromagnetic characteristics including back-electromotive force (back EMF), overall and local six degrees of freedom (6-DOF) electromagnetic loads of the SLSM. A multiobjective optimization process is carried out to complete the design of the SLSM. The characteristics of the designed DLMCW SLSM are analyzed and the benefits of the high thrust and low disturbance capacity are demonstrated. The accuracy of the analytical model and the capability to suppress electromagnetic vibration in superconducting magnets are verified via experimental tests.

The superconducting electrodynamic suspension (EDS) is one of the most promising technologies for developing an ultrahigh-speed maglev due to its special advantages. The superconducting coil (SC), which generates the force source for the EDS, is one of the key components. Improving the SC supporting characteristics, such as stiffness and damping, is an unavoidable challenge for enhancing the reliability and durability of the SC under long-term operation. Therefore, this article establishes a 3-D transient dynamic finite element model (FEM) to investigate the SC supporting characteristics. In this model, the frictional heat generation between the SC and the coil box is considered. First, the modeling method is verified by the one-degree-of-freedom (ODOF) vibration system, incorporating damping and friction. Second, the time-varying loads of suspension, guidance, and drag of 600 km/h are calculated based on dynamic-circuit theory and the virtual displacement method, and the stiffness of a self-developed SC support structure is tested. Third, based on the validated modeling method, the calculated time-varying loads, and the tested stiffness, the 3-D FEM of the SC is established. The dynamic response of the SC is estimated by the 3-D model, further, the support stiffness and damping are optimized. Finally, the influence of the friction coefficient on the frictional energy between the SC and coil box is investigated.

In a superconducting electrodynamic suspension train, a high temperature superconducting (HTS) magnet gradually accelerates to levitation speed under the action of the ground module traveling wave magnetic field, and then achieves levitation. During this process, propulsion coils and suspension coils will generate varying degrees of harmonic magnetic fields on the surface of the dynamic HTS magnet with variations in speed. Due to the influence of external harmonic magnetic fields, electromagnetic losses are generated in the HTS magnet’s outer Dewar, thermal shield, and inner Dewar, including eddy current loss, ac loss, etc. If the thermal load generated during operation is too large, it will increase the operating burden of cryogenic system, resulting in the inability of refrigerant to operate in a closed loop. Furthermore, without any effective measures, harmonic penetration into the interior of the HTS magnet may cause local overheating of the HTS coil, leading to quench accidents. Therefore, this article conducts a simulation study on the electromagnetic loss characteristics of magnets within the range of 0–600 km/h. The electromagnetic loss variation process of HTS magnets is analyzed from two parts: the launch phase and the suspension phase. The electromagnetic loss distribution characteristics and thermal load variation law of HTS magnets in the dynamic process are obtained, and the corresponding thermal stability of HTS coils is analyzed.

The suggested chapter will present the latest developments of the superconducting maglev in the world (especially in China). The chapter firstly introduces the classification of suspension, for example, the developments of electro-magnetic suspension (EMS), electro-dynamic suspension (EDS), and magnetic flux pinning suspension. Secondly, we explain the concept and principle of EMS, EDS, and so on. Thirdly, we give the introduction to the latest developments of the maglev in the world, such as China, Japan, the US, and so on. In particular, the chapter will give more details about the superconducting EDS developments in China. Finally, the chapter will present the key technologies and research prospect of the superconducting magnet of the EDS.

In view of the problems such as insufficient transmission capacity and reduced system reliability caused by the increasing proportion of new energy access in modern power grid, Distributed Static Series Compensator (DSSC) with high cost efficiency and reliability is the best choice for flexible regulation of future power grid. In this paper, the basic principle of multi-mode switching of DSSC is introduced in detail. Firstly, a three-loop control strategy with high robustness is constructed based on the mathematical model of DSSC, and the control principle of different working modes of DSSC is analyzed. Then, a multi-mode switching strategy of DSSC that can make different working modes switch smoothly is proposed, and the reset strategy of PI controller during mode switching is given. Finally, the electromagnetic transient model of DSSC is constructed based on PSCAD / EMTDC, and the effectiveness and reliability of the multi-mode switching strategy of DSSC are verified by simulation.

AC loss plays an important role in the design of the device employing HTS magnet. Therefore, it is important to measure the AC loss in HTS magnet. In this work, we studied the calorimetric self-field AC loss measurement of a four-tape HTS stacks using Fiber Bragg Grating (FBG) sensors. Three cryogenic FBG temperature sensors with different coating and installation were selected for the AC loss measurement. The calibration between power loss and wavelength shift was carried out by a resistance heater before the AC loss measurement. With the calibrated FBG sensors, the AC loss measurement was measured at 67 Hz and 89 Hz. These measurements were carried out at 77 K through conduction cooling by sealing the sample in a thermal insulator. The measured loss results were verified through comparison with the Norris models as well as the electrical measurements of AC loss. Finally, the magnetic strain effect on loss measurement was evaluated experimentally. The results in our paper shows that the calorimetric method based on the proposed FBG sensor can be used for the AC loss measurement of a four-tape HTS stack, and the magnetic strain of a four-tape stack has no effect on the AC loss measurement, which provides the possibility of using FBG sensors for ac loss measurement on HTS stacks.

This paper presents the power dissipation analysis on high-temperature superconducting (HTS) coated conductor tapes and coils under the action of various oscillating currents and fields. The loss calculation on HTS coil was carried out by the H-formulation model implemented in the finite-element method (FEM) software package COMSOL Multiphysics. There were four different oscillating (ac) signals in this paper: sine, triangle, sawtooth, and square. Two scenarios causing loss in HTS tapes and coils which have been analyzed: Scenario 1 ac transport current; Scenario 2 ac magnetic field. The simulation results were compared to the experiment results with the typical sinusoidal ac signal.

This paper mainly describe the designing progress of iron-core saturated high-temperature superconducting fault current limit-er(HTSFCL). Firstly, the relationship between magnetic field and current of high temperature superconducting coil are simu-lated in the finite element software. which can get the working current of superconducting coil is 70A. Then, using the simula-tion results of coil, the design formula is deduced, and the size of HTS current limiter and the number of coil turns are calculated. Thirdly, HTSFCL model is established in the finite element anal-ysis software to obtain the field distribution and short-circuit characteristics from the simulation results, and calculate the equivalent parameters. The equivalent circuit of HTSFCL is es-tablished in the circuit analysis software, and the correctness of the equivalent circuit is verified by comparing different simula-tion results.Finally, through the test of HTS coil, the working current of the superconducting coil is verified to be 70A.

Experimental and advanced superconducting Tokamak (EAST) was designed by the Institute of Plasma Physics Chinese Academy of Sciences. The magnet system of EAST includes poloidal field (PF) coils, central solenoid (CS) coils, and toroidal field coils. The heat generated by the ac losses of PF and CS coils increases the burden of the cooling system, which reduces the critical current of the superconducting cable. Once the superconducting magnet quenches, it will pose a serious threat to the stability of the whole device. In this paper, the piecewise linear method and the finite-element analysis were used to analyze the ac loss of the EAST PF and CS coils under the specific operating current. The whole calculation process is described in detail. The final results meet the stability margin of the design of the EAST device. Meanwhile, the ac losses of PF and CS coils for EAST are theoretically evaluated in terms of the structure of magnet, the simplified current, and the distribution of the coil. The results of this paper not only provide data support for the next design and experiment of the EAST device, but provide some references for similar calculation of other large nuclear fusion magnets.