Liwei Jing

Gravity energy storage systems (GESS) have emerged as a promising long-duration energy storage technology capable of supporting large-scale renewable integration and enhancing grid resilience. However, the modeling framework for the hoisting electromechanical subsystem in wire-rope-based GESS remains underdeveloped, thereby limiting the accurate characterization of its transient grid-connected behavior, dynamic operating response, and cross-domain coupling effects. Existing studies commonly simplify wire ropes and related transmission components as rigid bodies or low-dimensional mechanical elements, failing to adequately account for their flexibility and the resulting high-dimensional nonlinear dynamics. Although related studies in mine hoisting and elevator systems have addressed mechanical vibration phenomena, they primarily focus on mechanical-side effects, such as shock loading and guide-structure response, whereas the mechanism by which flexible mechanical vibrations propagate through electromechanical coupling and influence electrical dynamic performance remains inadequately understood. To address this gap, this study establishes a distributed-parameter model for the wire-rope hoisting mechanism based on Hamilton’s principle and solves the corresponding vibration governing equations using the Galerkin method to capture nonlinear multi-modal dynamics. An electromechanical coupling model is then developed to elucidate how rope-vibration-induced tension fluctuations propagate through the drive chain, resulting in torque ripple, electrical interharmonics, and low-frequency grid-side oscillations. A Bessel-function-based analytical representation is further introduced to explain the formation of interharmonic clusters and beat-frequency phenomena under converter modulation. An experimental prototype is constructed to validate the proposed modeling framework. The measured vibration spectra, beat-frequency characteristics, and torque ripple align closely with analytical predictions, confirming the model’s capability to capture key propagation paths from rope vibration to electromechanical oscillation and grid-side dynamic response. The results provide a solid theoretical foundation for vibration mitigation, dynamic analysis, and control design of hoisting electromechanical subsystems in gravity energy storage applications.

This paper presents a study on the impact of circuit parameters on the transmission of electrical energy in wireless power transfer systems designed for intelligent sensing devices within the urban electric power Internet of Things (IoT). Relying on the essential principles of resonant mutual inductance models, the paper conducts an analytical investigation into the phenomena of power-frequency splitting characteristics, efficiency-frequency splitting characteristics, and efficacy synchronization characteristics within wireless energy transmission technologies. The investigation includes a detailed analysis of a wireless power transfer system model operating at 100 kHz, delineating how varying circuit parameters influence the system’s efficiency. Via the utilization of graphical software and computational programming for simulation modeling, this research delved into the dynamics between key parameters such as equivalent load and coupling coefficient and their influence on distinct splitting phenomena. This rigorous approach substantiated the validity of the proposed power-frequency and efficiency-frequency splitting characteristics outlined in the study. Based on the analytical results, it is shown that selecting an appropriate equivalent load or utilizing impedance matching networks to adjust the equivalent load to a suitable size is crucial in consideration of the system’s output power, voltage withstand level, and transmission efficiency. The research findings provide a theoretical basis for the design of wireless power supply systems for non-directly buried cable front-end sensing devices.

Nowadays, copper Litz wire is widely used in the electrical applications. This wire is a particular type of multistrand wire, which is designed to reduce the skin effect and proximity effect losses in conductors. As the frequency dependence of losses in YBCO coils and Litz coils is different, how to determine the frequency band in which superconducting coils have an efficiency advantage over copper coils is a problem that needs to be solved. In response to the above concerns, a theory of the applicable frequency band of YBCO coils are proposed. Both experimental and numerical methods are used to study the characteristics of the applicable frequency band. Results show that the applicable frequency band of the YBCO coil decreases as the transport current increases, while its dependence on the radius of the coil is small. The obtained conclusions can be used as a reference when superconducting coils are used to replace copper coils.

Transport AC loss is a crucial reference for evaluating the performance of high-temperature superconducting (HTS) materials. Although the transport AC loss of $YBa_{2}Cu_{3}O_{7-\delta}$ (YBCO) single tapes has been well studied, the transport AC loss characteristic of YBCO coils with different substrates in the kHz frequency band is still unclear, which is important for a wide range of applications, such as wireless power supply systems and high frequency superconducting transformers. In response to the above concerns, both numerical and experimental methods are used to study the frequency dependence of transport AC loss in YBCO coils with magnetic and non- magnetic substrate over a frequency range, from 55 Hz to 10 kHz. The mechanism of the loss of each turn and the distribution of the transport current of each turn are clarified. It is found that there is a frequency dependence of the distribution of both the loss and the transport current in each layer of each turn, and this distribution is highly dependent on the spatial location and the magnetic properties of the substrate.

There are axial and radial electromagnetic forces between stator and rotor of axial flux disk motor besides the useful torque. The electromagnetic forces act on the rotor and are crucial to the stable operation in magnetic levitation applications driven by disk motor. This paper concerns the behaviors of axial and radial electromagnetic forces of disk motor using for cryogenic submersible pump. It is measured experimentally that the electromagnetic properties of motor materials, including the electrical conductor and magnetic conductor materials, in room temperature (RT) and liquid nitrogen (LN₂) environment. Then, the 3D FEM of three-phase asynchronous disk motor in RT environment is built which is also validated by the RT experimental tests. Finally, the behaviors of axial and radial electromagnetic forces in LN₂ environment are investigated using the modified FEM taking account of the effect of cryogenic environment on the motor material. It is concluded that the axial electromagnetic force decreases monotonously with the increasing air-gap thickness or the decreasing rotating speed. When the rotor exhibits radial eccentricity, there is a restoring radial electromagnetic force, trying to pull the rotor back to the central position. The radial electromagnetic force increases with the increasing rotational speed and radial eccentric displacement.

In this paper, a general scheme of a 40 kV/2 kA resistive type DC superconducting fault current limiter (SFCL) is suggested, which could be utilized to suppress the surge current caused by short-circuit faults in voltage-source-converter HVDC (VSC-HVDC) power grids. This DC SFCL is designed and fabricated with 6 coil modules in parallel and 4 in series. In order to investigate the current-limiting performance of the DC SFCL under the rapidly rising fault current, the SFCL is tested on the platform with a pulsed DC impact generator. Besides the property of current limitation, the current capacity, insulation and quench recovery performance of such SFCL are also tested. Results indicate that the critical current of SFCL is larger than 2050 A at 69 K, and the DC withstand voltage is larger than 74 kV in 2 hours. During the 9kV DC impact test, the short-circuit current could be limited to 8842 A, and the quench recovery time is less than 200ms.

The numerical study on the transport loss reduction in REBCO double pancake (DP) coil is presented in this paper. An axisymmetric finite element model based on H formulation and E-J power law is established. The influence of the gap between two pancakes on the transport losses of DP coils is investigated. The use of magnetic flux diverters to reduce the ac loss of the DP coil by decreasing the perpendicular magnetic field applied to the tape surface is also studied. It is found that the perpendicular magnetic field is decreased clearly by attaching the flux diverter in the middle and end positions of DP coil. Compared with the ac losses of DP coils without flux diverters, the use of flux diverters can decrease the ac losses by 70% when the applied current is at half the critical current of DP coil.

A 1MVA/1MJ superconducting fault current limiter-magnetic energy storage system (SFCL-MES) has been developed. The SFCL-MES utilizes one superconducting coil to both enhance low voltage ride through capability of wind turbine and smooth wind power output. The developed SFCL-MES was installed and put into operation in a wind farm northwest of China. This paper presents final design and test of the four major components of SFCL-MES: power conditioning system, cryogenic system, superconducting coil and monitoring system. Test results of the SFCL-MES are also presented. Test results show that the SFCL-MES has good performance and improves the power quality and reliability of wind power generation successfully.