Interaction of Electromagnetic Waves with Two-Dimensional Metal Covered with Radar Absorbing Material and Plasma

A two-dimensional metal model is established to investigate the stealth mechanisms of radar absorbing material （RAM） and plasma when they cover the model together. Using the finite-difference time-domain （FDTD） method, the interaction of electromagnetic （EM） waves with the model can be studied. In this paper, three covering cases are considered： a. RAM or plasma covering the metal solely; b. RAM and plasma covering the metal, while plasma is placed outside; e. RAM and plasma covering the metal, while RAM is placed outside. The calculated results show that the covering order has a great influence on the absorption of EM waves. Compared to case a, case b has an advantage in the absorption of relatively high-frequency EM waves （HFWs）, whereas case c has an advantage in the absorption of relatively low-frequency EM waves （LFWs）. Through the optimization of the parameters of both plasma and RAM, it is hopeful to obtain a broad absorption band by RAM and plasma covering. Near-field attenuation rate and far-field radar cross section （RCS） are employed to compare the different cases.

Architecture design and demand analysis on application layer of standard system for ubiquitous power Internet of Things

The ubiquitous power Internet of Things(UPIoT)is an intelligent service system with comprehensive state perception,efficient processing,and flexible application of information.It focuses on each link of the power system and makes full use of the mobile internet,artificial intelligence,and other advanced information and communication technologies in order to realize the inter-human interaction of all things in all links of the power system.This article systematically presents to the national and international organizations and agencies in charge of UPIoT layer standardization the status quo of the research on the Internet of Things(IoT)-related industry standards system.It briefly describes the generic standard classification methods,layered architecture,conceptual model,and system tables in the UPIoT application layer.Based on the principles of inheritance,innovation,and practicability,this study divides the application layer into customer service,power grid operation,integrated energy,and enterprise operation,emerging business and analyzes the standard requirements of these five fields.This study also proposes a standard plan.Finally,it summarizes the research report and provides suggestions for a follow-up work.

Engineering practices for the integration of large-scale renewable energy VSC-HVDC systems

With the continuous development of power electronic devices,intelligent control systems,and other technologies,the voltage level and transmission capacity of voltage source converter (VSC)-high-voltage direct current (HVDC) technology will continue to increase,while the system losses and costs will gradually decrease.Therefore,it can be foreseen that VSC-HVDC transmission technology will be more widely applied in future large-scale renewable energy development projects.Adopting VSC-HVDC transmission technology can be used to overcome issues encountered by large-scale renewable energy transmission and integration projects,such as a weak local power grid,lack of support for synchronous power supply,and insufficient accommodation capacity.However,this solution also faces many technical challenges because of the differences between renewable energy and traditional synchronous power generation systems.Based on actual engineering practices that are used worldwide,this article analyzes the technical challenges encountered by integrating large-scale renewable energy systems that adopt the use of VSC-HVDC technology,while aiming to provide support for future research and engineering projects related to VSC-HVDC-based large-scale renewable energy integration projects.

Self-consistent three-dimensional modeling and simulation of large-scale rectangular surface-wave plasma source

A self-consistent and three-dimensional （3D） model of argon discharge in a large-scale rectangular surface-wave plasma （SWP） source is presented in this paper, which is based on the finite-difference time-domain （FDTD） approximation to Maxwell＇s equations self-consistently coupled with a fluid model for plasma evolution. The discharge characteristics at an input microwave power of 1200 W and a filling gas pressure of 50 Pa in the SWP source are analyzed. The simulation shows the time evolution of deposited power density at different stages, and the 3D distributions of electron density and temperature in the chamber at steady state. In addition, the results show that there is a peak of plasma density approximately at a vertical distance of 3 cm from the quartz window.

Key design parameters and optimum method of medium- and high-velocity synchronous induction coilgun based on orthogonal experimental design

The energy conversion efficiency of a multistage synchronous induction coilgun(MSSICG) has become one of the key factors that restricts its industrialization. To improve the launch efficiency of medium-and high-velocity MSSICG,we propose an optimization design scheme combining orthogonal experimental design(OED) and self-consistent design method in this paper. The OED is introduced to reduce the number of iterations and improve the identification accuracy and efficiency. A self-consistent design model is established to overcome a defect that the parameters that need to be optimized will multiply as the number of coil stages increases. The influence of six factors(radial thickness of armature, axial length of armature, axial length of coil, capacitance, wire diameter, and slip speed) on the launch efficiency are then evaluated by range analysis. This work presents a valuable reference for optimizing medium-and high-velocity MSSICG.

Numerical studies of surface and bulk modes in attenuated total reflection spectra

The dispersion relations of normal modes in the layered constructions are studied. In the frequency region with negative permittivity, we investigate the normal modes near the air-metal and the air-matematerial interfaces and compare them. An extra bulk mode appearing in a pass band of two media is found near the air-matematerial interface, which is different from the air-metal case. Moreover, the bulk mode will be further proved by the attenuated total reflection （ATR） technique, in which the coupling between the incident electromagnetic waves and the normal modes is studied. For p-polarized incident waves, the ATR spectra based on the Otto and the Kretschmann configurations are obtained numerically, where the dips present the excitations of the surface and bulk modes. Furthermore, we also discuss the influences of the middle layer thickness, the incident angle and the damping term on the reflection in detail. It is found that the coupling frequencies and the maximum strength are strongly dependent on the above media parameters.

Preliminary Design and Analysis of the DC Reactor for the ITER Converter

The DC reactor is an important piece of equipment for restraining loop and ripple currents in the international thermonuclear experimental reactor （ITER） converter power supply system. As the reactor is operated at a steady state of 27.5 kA and needs to withstand a peak current of 175 kA, so the design of the DC reactor used in the ITER converter power supply system is necessary. A new water-cooling dry-type air-core reactor is designed in this work. The detailed structural parameters are calculated by theoretical formulas, and then the structure is optimized by electromagnetic simulation with ANSYS. Finally, thermal and dynamic stability analyses are performed to verify the temperature and stress at a rated current of 27.5 kA and pulsed current of 175 kA. The analysis results show that the temperature and stress meet the requirements of the ITER converter power supply system.

Temperature Dependence of Polarizability and Dispersion in Three,Two and One Dimensional Electron Gases

Both temperature dependence of polarizability and plasmon dispersion in unmagnetized metal （or semiconductor） electron gases are investigated in this paper. It is obtained that, with a continuous variation of temperature in a large region, the polarizability and dispersion change non-monotonously. The static polarizability X（q, w =0, μ, T） and dispersion wp（q, T） for finite T in three, two and one dimensional electron gases are calculated numerically. In addition, dispersion relation w（q） at a definite temperature （T ≠0） is similar to that at T = 0.

Stress and Thermal Analysis of the In-Vessel RMP Coils in HL-2M

A set of in-vessel resonant magnetic perturbation （RMP） coils for MHD instability suppression is proposed for the design of a HL-2M tokamak. Each coil is to be fed with a current of up to 5 kA, operated in a frequency range from DC to about I kHz. Stainless steel （SS） jacketed mineral insulated cables are proposed for the conductor of the coils. In-vessel coils must withstand large electromagnetic （EM） and thermal loads. The support, insulation and vacuum sealing in a very limited space are crucial issues for engineering design. Hence finite element calculations are performed to verify the design, optimize the support by minimizing stress caused by EM forces on the coil conductors and work out the temperature rise occurring on the coil in different working conditions, the corresponding thermal stress caused by the thermal expansion of materials is evaluated to be allowable. The techniques to develop the in-vessel RMP coils, such as support, insulation and cooling, are discussed.

Intermittency of the density fluctuations and its influence on the radial transport in the boundary of J-TEXT

To improve the understanding of the turbulence intermittency, a detailed investigation of the intermittency of the density fluctuations has been performed in the boundary of J-TEXT. The intermittency of the density fluctuations and its influence on the radial transport are reported. The probability distribution functions of the density fluctuations are not scale-invariant, being inconsistent with the self-organized criticality hypothesis. The underlying dynamics of the intermittency are detected using the quiet-time statistical method. The probability distribution function of the quiet times shows double-power-law regions, indicating the existence of correlations between the successive burst events.

Dispersion Relations of Longitudinal Plasmons in One,Two and Three Dimensional Electron Gas of Metals

The longitudinal plasmons are the electrostatic collective excitations of the solid electron gas. In this paper, the dispersion relations of these plasmons for one-, two- and threedimensional electron gas are compactly derived in two approaches with uniform disturbed Coulomb potentials. The first approach is adopted usually in solid state theory that is the so-called random phase approximation （RPA） with the Lindhard dielectric function in the long-wavelength and high-frequency limits. The second method is a typical plasma fluid description that includes the electron fluid equations with the adiabatic process in the jellium model. The disturbed electrostatic （Coulomb） potential produced by the oscillation of electron density is dimensionally dependent and derived from the Poisson equation in Appendix B.

Stress and Thermal Analysis of the In-Vessel Resonant Magnetic Perturbation Coils on the J-TEXT Tokamak

A set of four in-vessel saddle coils was designed to generate a helical field on the J- TEXT tokamak to study the influences of the external perturbation field on plasma. The coils are fed with alternating current up to 10 kA at frequency up to 10 kHz. Due to the special structure, complex thermal environment and limited space in the vacuum chamber, Jt is very important to make sure that the coils will not be damaged when undergoing the huge electromagnetic forces in the strong toroidal field, and that their temperatures don＇t rise too much and destroy the in- sulation. A 3D finite element model is developed in this paper using the ANSYS code, stresses are analyzed to find the worst condition, and a mounting method is then established. The results of the stress and modal analyses show that the mounting method meets the strength requirements. Finally, a thermal analysis is performed to study the cooling process and the temperature distribution of the coils.

Startup Speed with Dead Band in Wind Farms with Low-Medium Wind Speed Profile—Case Study of Hong Kong

Wind turbines are usually designed and operated with fixed startup speed. It could perform startup and shutdown operations repeatedly when the wind fluctuates around the startup speed. The excessive stress induced by frequent startup and shutdown could enhance the likelihood of component failure and hence negatively impact the availability of a wind turbine. Startup speed with dead band is proposed in this article to prevent the wind turbine from frequent startup. 22 years wind data from the Cheung Chau wind station in Hong Kong are analyzed to evaluate the reduction in the number of startup and potential loss of wind power production using the proposed approach. Numerical simulation suggests that the number of startup could be reduced by half with trivial reduction in potential wind power generation in most of investigated sites once an appropriate dead band is adopted.

Research and Application of Probability Distribution of Wind Power Fluctuation Characteristics

The fluctuation characteristics is the inherent property of wind power.Through analysis of a large number of wind t＇anns based on measured data,we find it describes the best probability distribution of wind power fluctuation for the mixed Gauss distribution of two components,and try to carry out the physical interpretation of two components.Further discussion is between the probability distribution of fluctuating wind power time difference and whole relationship.It is found that the two have basic similarity.Through comparing the different time level data quantified losses the information of wind power fluctuation,quantitative determination of the degree of impact prediction.We can summarize and understand of wind power fluctuation,constructing instance from the wind farm construction and monitoring prediction two aspect recommendations to overcome the adverse effects of wind power fluctuations on the power grid operation.

Relaxed Stability Criteria for Time-Delay Systems:A Novel Quadratic Function Convex Approximation Approach

This paper develops a quadratic function convex approximation approach to deal with the negative definite problem of the quadratic function induced by stability analysis of linear systems with time-varying delays.By introducing two adjustable parameters and two free variables,a novel convex function greater than or equal to the quadratic function is constructed,regardless of the sign of the coefficient in the quadratic term.The developed lemma can also be degenerated into the existing quadratic function negative-determination(QFND)lemma and relaxed QFND lemma respectively,by setting two adjustable parameters and two free variables as some particular values.Moreover,for a linear system with time-varying delays,a relaxed stability criterion is established via our developed lemma,together with the quivalent reciprocal combination technique and the Bessel-Legendre inequality.As a result,the conservatism can be reduced via the proposed approach in the context of constructing Lyapunov-Krasovskii functionals for the stability analysis of linear time-varying delay systems.Finally,the superiority of our results is illustrated through three numerical examples.

Suppression of intervalley scattering and enhanced phonon anharmonic interactions in 2D Bi_(2)TeSe_(2):Crystal-field symmetry and band convergence

The electron-phonon(el-ph)and phonon-phonon interactions play a key role in determining electronic and thermal transport properties,respectively,in promising two-dimensional(2D)semiconductor de-vices.In this study,we investigated el-ph interactions using Wannier-Fourier interpolation method and renormalized phonon scattering considering finite-temperature effects in Bi_(2)TeSe_(2)monolayer.The re-sults show that the optical phonon modes dominate the carrier scattering,where level repulsion induced by crystal field splitting and spin-orbit coupling(SOC)effect effectively suppresses intervalley scattering,leading to high hole mobility.Moreover,the strong anharmonicity in Bi_(2)TeSe_(2)monolayer results in the temperature-dependent softening of its optical phonons,along with a corresponding variation in interatomic force constants(IFCs).As a result,the lattice thermal conductivity is remarkably low and exhibits weak temperature dependence.Finally,the predicted dimensionless thermoelectric figure of merit exceeds unity in the range of 200-800 K,indicating the potential of Bi_(2)TeSe_(2)monolayer for thermoelectric applications.This work provides new insights into the elimination of intervalley scat-tering by crystal field splitting and SOC effects,and paves the way for the evaluation of thermoelectric properties of materials with complex scattering mechanisms and strong anharmonicity.

Comparative analysis of the characteristics of outlet short circuit and winding insulation fault of distribution transformer and its preventive measures

Outlet short circuit on the low-voltage(LV)side and winding inter-turn short circuit faults are hazardous to transformer operation.To investigate the formation mechanism of winding insulation faults of distribution transformer,ANSYS Maxwell was used to build a coupled magnetic field-circuit model with the same structural dimension as the actual distribution transformer.An outlet short circuit and winding inter-turn insulation faults were set by using the voltage-controlled switch in the external circuit of the model.Sub-sequently,the differences in the electromagnetic characteristics and the electrodynamic force distributions of the windings under three operating conditions,namely,nominal load,three-phase outlet short circuit on the LV side and inter-turn insulation failure were studied,respectively.The results show that compared with the rated load,in the cases of outlet short circuit and inter-turn insulation faults,the amplitude of winding current in-creases by 20 and 50 times,the magnetic field strength grows by 20 and 17 times,and the electrodynamic force rises by 400 and 230 times,respectively.Outlet short circuit fault is more likely to cause the winding instability and deformation,and inter-turn short circuit fault can easily burn out winding insulation.Therefore,corresponding preventive measures were proposed.

Dispersed Wind Power Planning Method Considering Network Loss Correction with Cold Weather

In order to play a positive role of decentralised wind power on-grid for voltage stability improvement and loss reduction of distribution network,a multi-objective two-stage decentralised wind power planning method is proposed in the paper,which takes into account the network loss correction for the extreme cold region.Firstly,an electro-thermal model is introduced to reflect the effect of temperature on conductor resistance and to correct the results of active network loss calculation;secondly,a two-stage multi-objective two-stage decentralised wind power siting and capacity allocation and reactive voltage optimisation control model is constructed to take account of the network loss correction,and the multi-objective multi-planning model is established in the first stage to consider the whole-life cycle investment cost of WTGs,the system operating cost and the voltage quality of power supply,and the multi-objective planning model is established in the second stage.planning model,and the second stage further develops the reactive voltage control strategy of WTGs on this basis,and obtains the distribution network loss reduction method based on WTG siting and capacity allocation and reactive power control strategy.Finally,the optimal configuration scheme is solved by the manta ray foraging optimisation(MRFO)algorithm,and the loss of each branch line and bus loss of the distribution network before and after the adoption of this loss reduction method is calculated by taking the IEEE33 distribution system as an example,which verifies the practicability and validity of the proposed method,and provides a reference introduction for decision-making for the distributed energy planning of the distribution network.

Experimental demonstration of a flexible-grid 1×(2×3)mode-and wavelength-selective switch using silicon microring resonators and counter-tapered couplers

A flexible-grid 1×(2×3)mode-and wavelength-selective switch which comprises counter-tapered couplers and silicon microring resonators has been proposed,optimized,and demonstrated experimentally in this work.By carefully thermally tuning phase shifters and silicon microring resonators,mode and wavelength signals can be independently and flexibly conveyed to any one of the output ports,and different bandwidths can be generated as desired.The particle swarm optimization algorithm and finite difference time-domain method are employed to optimize structural parameters of the twomode(de)multiplexer and crossing waveguide.The bandwidth-tunable wavelength-selective optical router composed of12 microring resonators is studied by taking advantage of the transfer matrix method.Measurement results show that,for the fabricated module,cross talk less than-10.18 dB,an extinction ratio larger than 17.41 d B,an in-band ripple lower than0.79 dB,and a 3-dB bandwidth changing from 0.38 to 1.05 nm are obtained,as the wavelength-channel spacing is 0.40 nm.The corresponding response time is measured to be 13.64μs.