Recent various experiments have provided evidence supporting the emergence of loop-current order in kagome metals. Particularly superconductivity in AV_(3)Sb_(5) is significantly enhanced when this charge order is sup...Recent various experiments have provided evidence supporting the emergence of loop-current order in kagome metals. Particularly superconductivity in AV_(3)Sb_(5) is significantly enhanced when this charge order is suppressed by pressure or doping. Distinct from magnetic order, loop-current order does not couple directly to spin and thus whether such fluctuations can enhance superconductivity remains elusive. We design a sign problem-free bilayer kagome model coupled to quantum Ising spins through bond currents and perform determinant quantum Monte Carlo simulations to explore single-particle properties and superconductivity arising from 2 × 2 loopcurrent fluctuations. We find that this loop-current order induces intriguing band folding, band broadening,and gap opening around saddle points. Remarkably, our pairing susceptibility analysis identifies a dominant enhancement of superconductivity due to loop-current fluctuations, with the dominant pairing being the chiral d-wave channel. This pairing primarily occurs within the intra-sublattice channel and involves third nearestneighbor sites, attributed to the unique sublattice texture associated with van Hove singularities. We also discuss potential experimental implications for kagome superconductors.展开更多
Recent modeling studies on the shedding of Loop Current rings suggest that the intensification of the dominant zonal wind field delays the detachment of rings and affects the Loop Current migrations. The atmospheric m...Recent modeling studies on the shedding of Loop Current rings suggest that the intensification of the dominant zonal wind field delays the detachment of rings and affects the Loop Current migrations. The atmospheric modulation of the Loop Current migrations is analyzed here using reanalysis winds and altimetry-derived observa- tions. A newly developed methodology is applied to locate the Loop Current front, and a wavelet-based semblance analysis is used to explore correlations with atmospheric forcing. The results show that weakening （intensification） of the zonal wind stress in the eastern Gulf of Mexico is related with the Loop Current excursions to the north （south）. Semblance analyses confirm negative correlations between the zonal wind stress and the Loop Current migrations during the past 20 years. The intrusions of the Loop Current might involve an increase of the Yucatan Transport, which would balance the westward Rossby wave speed of a growing loop and delay the ring shedding. The results of this study have consequences for the interpretation of the chaotic processes of ring detachment and Loop Current intrusions, which might be modulated by wind stress.展开更多
We propose a bulk negative refractive index （NRI） metamaterial composed of periodic array of tightly coupled metallic cross-pairs printed oR the six sides of a cube for applications of superlenses. The structural ch...We propose a bulk negative refractive index （NRI） metamaterial composed of periodic array of tightly coupled metallic cross-pairs printed oR the six sides of a cube for applications of superlenses. The structural characteristics of the three-dimensional （3D） metamaterial consist in the high symmetry and the superposition of metallic cross-pairs, which can increase the magnetic inductive coupling between adjacent cross-pairs and realize a broadband and isotropic NRI. The proposed 3D structure is simulated using the CS~ Microwave Studio 2006 to verify the design validity. The simulation results show that the proposed structure can not only realize simultaneously an electric and magnetic response to an incident electromagnetic （EM） wave, but also exhibit a broadband NRI whose relative bandwidth can reach up to 56.7%. In addition, the NRI band is insensitive to tile polarization and the incident angle of the incident EM wave. Therefore, the proposed metamaterial is a good candidate material as three-dimensional broadband isotropic NRI metamaterial.展开更多
With the advent of Computer Algebra System (CAS) such as Mathematica [1], challenging symbolic longhand calcula-tions can effectively be performed free of error and at ease. Mathematica’s integrated features allow th...With the advent of Computer Algebra System (CAS) such as Mathematica [1], challenging symbolic longhand calcula-tions can effectively be performed free of error and at ease. Mathematica’s integrated features allow the investigator to combine the needed symbolic, numeric and graphic modules all in one interactive environment. This assists the author to focus on interpreting the output rather than exerting the efforts of relating the scattered separate modules. In this note the author, utilizing these three features, explores the magneto-static field and its associated vector potential of a steady looping current. In particular by deploying the numeric features of Mathematica the exact value of the vector potential of the looping current conducive to its 3D graph is presented.展开更多
To reduce current harmonics caused by switching frequency,T-type grid-connected inverter topology with LCL filter is adopted.In view of the disadvantages of the slow response speed of the traditional current control a...To reduce current harmonics caused by switching frequency,T-type grid-connected inverter topology with LCL filter is adopted.In view of the disadvantages of the slow response speed of the traditional current control and the failure to eliminate the influence of the LCL filter on the grid-connected current by using current PI control alone,a current double closed loop PI current tracking control is proposed.Through the theoretical analysis of the grid-connected inverter control principle,the grid-connected inverter control model is designed,and the transfer functionmodel of each control link is deduced,and the current loop PI regulator is designed at last.The simulation results show that the control strategy is feasible.展开更多
A thin metallic wire loop of arbitrary curvature is rotated with respect to an arbitrary axis of its plane. The device is excited by an electric dipole of infinite length and constant current. The resistance of the lo...A thin metallic wire loop of arbitrary curvature is rotated with respect to an arbitrary axis of its plane. The device is excited by an electric dipole of infinite length and constant current. The resistance of the loop is computed rigorously as function of the position of the source. In this way, the induced voltage along the wire, under any kind of axial excitation, is given in the form of a superposition integral. The measured response is represented for various shapes of the coil, with respect to the time, the rotation angle and the position of the source. These diagrams lead to several technically applicable conclusions which are presented, discussed and justified.展开更多
【目的】跟网型换流器(grid-following converter,GFL)被广泛应用于新能源并网系统。电网发生故障引起电压跌落时,系统进入低电压穿越(low voltage ride-through,LVRT)过程。传统锁相环(phase-locked loop,PLL)的二阶模型因忽略电流暂...【目的】跟网型换流器(grid-following converter,GFL)被广泛应用于新能源并网系统。电网发生故障引起电压跌落时,系统进入低电压穿越(low voltage ride-through,LVRT)过程。传统锁相环(phase-locked loop,PLL)的二阶模型因忽略电流暂态过程,难以准确描述LVRT期间系统的动态特性,导致暂态同步稳定性的提升效果受限。为此,针对对称故障场景,提出一种适用于LVRT过程的电流内环协同控制策略,以增强系统暂态同步稳定性。【方法】基于PLL四阶动态方程,结合暂态能量函数法,分析PLL输出频率突变以及电流内环与PLL耦合作用对系统暂态同步稳定性的影响,并设计相应的控制策略:根据最优阻抗比动态调整电流参考值,以抑制故障期间暂态能量累积;通过在电流内环前馈解耦项中引入频率偏差补偿机制,加速暂态能量耗散过程。两者协同作用,提升系统在LVRT期间的暂态同步稳定性。【结果】PSCAD/EMTDC对称故障时域仿真结果表明:故障瞬间PLL输出频率突变量与电网电压跌落幅值成正比,增大系统失稳风险;所提控制策略能够有效抑制故障期间PLL输出频率偏差,显著降低虚拟功角首摆幅度,缩短故障清除后系统恢复时间,在不同电网参数下均表现出良好的适应性。【结论】所提电流内环协同控制策略,能够在对称故障期间有效抑制暂态能量累积,在故障清除后加速暂态能量耗散,有效提升了GFL并网系统在此类LVRT过程中的暂态同步稳定性。展开更多
针对微特电机驱动控制系统中,双有源桥(dual active bridge,DAB)变换器在高频调制过程中易产生较大电流应力,导致器件温升高、寿命衰减及负载扰动下系统稳定性下降等问题,本文提出一种改进型双移相优化调制策略。该方法基于双有源桥拓扑...针对微特电机驱动控制系统中,双有源桥(dual active bridge,DAB)变换器在高频调制过程中易产生较大电流应力,导致器件温升高、寿命衰减及负载扰动下系统稳定性下降等问题,本文提出一种改进型双移相优化调制策略。该方法基于双有源桥拓扑,建立双移相调制下的功率传输模型与电流应力数学模型,采用拉格朗日乘数法求解最优移相比组合,并进一步推导多功率场景下的电流应力解析表达式;在控制器设计方面,引入电感电流内环补偿机制,提高系统对电机驱动过程中负载变化的动态响应能力。MATLAB/Simulink仿真结果表明,该方法在典型微特电机负载工况下能有效降低变换器的电流应力,缩短暂态响应时间,并改善输出电压纹波,对提升微特电机控制系统的稳态与暂态性能具有良好效果,为高效能电机驱动供电模块的优化设计提供理论依据。展开更多
基于高速低功耗混合应用场景下对互补金属氧化物半导体(Complementary Metal Oxide Semiconductor,CMOS)比较器性能的综合需求,系统研究其结构优化设计。阐述动态比较器在响应速度、功耗控制、输入失调与噪声抑制等方面的关键技术,介绍...基于高速低功耗混合应用场景下对互补金属氧化物半导体(Complementary Metal Oxide Semiconductor,CMOS)比较器性能的综合需求,系统研究其结构优化设计。阐述动态比较器在响应速度、功耗控制、输入失调与噪声抑制等方面的关键技术,介绍前置放大器、电源控制、闭环反馈及偏置电路的协同优化策略。结合65 nm CMOS工艺下的仿真测试结果,分析主要性能指标在典型工况下的表现,验证所提结构的可实现性与工程适应性。结果表明,该设计能够在低功耗约束下保持高速响应。展开更多
Objective For the inverters used in UPS, it is important to maintain the pure sinusoidal AC output voltage waveform over all loading conditions and transients. Methods A novel sinusoidal output voltage control strat...Objective For the inverters used in UPS, it is important to maintain the pure sinusoidal AC output voltage waveform over all loading conditions and transients. Methods A novel sinusoidal output voltage control strategy is pregented in this paper. The output voltage is controlled by introducing filtering eapacitor current feedback. Two simple PI regulators are used for the current and voltage control loops. Results With the new control strategy, the inverter achieves very low output voltage distortion, good output voltage regulation and strong perturbation rejection, fast dynamic response, and good performance under nonlinear loads. The THD under capacitance rectifying load is better than 0.2%, the output voltage regulation within 0 to full load is less than 0.1%. The resting time under load transient is within 200?μ s . Conclusion The merits of the new control strategy include rapid response and good steady state stiffness.展开更多
Multiply-connected Hall plates show different phenomena than singly connected Hall plates. In part I (published in Journal of Applied Physics and Mathematics), we discussed topologies where a stream function can be de...Multiply-connected Hall plates show different phenomena than singly connected Hall plates. In part I (published in Journal of Applied Physics and Mathematics), we discussed topologies where a stream function can be defined, with special reference to Hall/Anti-Hall bar configurations. In part II, we focus on topologies where no conventional stream function can be defined, like Corbino disks. If current is injected and extracted at different boundaries of a multiply-connected conductive region, the current density shows spiral streamlines at strong magnetic field. Spiral streamlines also appear in simply-connected Hall plates when current contacts are located in their interior instead of their boundary, particularly if the contacts are very small. Spiral streamlines and circulating current are studied for two complementary planar device geometries: either all boundaries are conducting or all boundaries are insulating. The latter case means point current contacts and it can be treated similarly to singly connected Hall plates with peripheral contacts through the definition of a so-called loop stream function. This function also establishes a relation between Hall plates with complementary boundary conditions. The theory is explained by examples.展开更多
In order to control the lateral motion of a jet trencher which is important for stable trenching operation,the oscillation characteristics of the jet trencher are researched. The jet trencher is simplified into a sing...In order to control the lateral motion of a jet trencher which is important for stable trenching operation,the oscillation characteristics of the jet trencher are researched. The jet trencher is simplified into a single degree of freedom model with restoring and damping force. The nonlinear mathematical model of the trencher laterally oscillating in ocean currents is established,and its approximate analytical solution is obtained.Results show that the analytical solution has small differences with numerical solution based on the fourth-order Runge-Kutta method and can effectively describe the underwater oscillation. A double-loop PID controller is designed to control the lateral motion displacement of the trencher to return to the center of the pipeline route which is effective and robust for the propulsion system.展开更多
With the continuous development of urban distribution network, most of the distribution network has formed a dual power supply mode. The traditional way of distribution network load operating mainly adopts the power m...With the continuous development of urban distribution network, most of the distribution network has formed a dual power supply mode. The traditional way of distribution network load operating mainly adopts the power method, while satisfied the requirements of the safety of power grid, but will cause external short time power outages, poor user experience, realizing the distribution network outage rearrangement of load is a necessary means to improve power supply reliability. This paper presents mathematical model of load transfer in distribution network. The differences of voltage of amplitude and phase angle on both sides are calculated by the power flow. According to the differential pressure to determine whether the loop can be closed at the loop operation, thereby improving the success rate of operation.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 12447103)financial support from the MERIT-WINGS course provided by the University of Tokyo+10 种基金the Fellowship for Integrated Materials Science and Career Development provided by the Japan Science and Technology Agencysupport from the computational resource of Wisteria/BDEC-01 provided by Information Technology Center, the University of Tokyo, for the Monte Carlo simulationthe support by the National Natural Science Foundation of China (Grant No. 12404275)the Fundamental Research Program of Shanxi Province (Grant No. 202403021212015)support from the Würzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter-ct.qmat (EXC 2147, Project No. 390858490)supported by the National Natural Science Foundation of China (Grant No. 12274289)the National Key R&D Program of China (Grant Nos. 2022YFA1402702 and 2021YFA1401400)the Innovation Program for Quantum Science and Technology (Grant No. 2021ZD0301902)Yangyang Development Fund, and Startup Funds from SJTUsupported by the National Key R&D Program of China (Grant No. 2023YFA1407300)the National Natural Science Foundation of China (Grant No. 12047503)。
文摘Recent various experiments have provided evidence supporting the emergence of loop-current order in kagome metals. Particularly superconductivity in AV_(3)Sb_(5) is significantly enhanced when this charge order is suppressed by pressure or doping. Distinct from magnetic order, loop-current order does not couple directly to spin and thus whether such fluctuations can enhance superconductivity remains elusive. We design a sign problem-free bilayer kagome model coupled to quantum Ising spins through bond currents and perform determinant quantum Monte Carlo simulations to explore single-particle properties and superconductivity arising from 2 × 2 loopcurrent fluctuations. We find that this loop-current order induces intriguing band folding, band broadening,and gap opening around saddle points. Remarkably, our pairing susceptibility analysis identifies a dominant enhancement of superconductivity due to loop-current fluctuations, with the dominant pairing being the chiral d-wave channel. This pairing primarily occurs within the intra-sublattice channel and involves third nearestneighbor sites, attributed to the unique sublattice texture associated with van Hove singularities. We also discuss potential experimental implications for kagome superconductors.
文摘Recent modeling studies on the shedding of Loop Current rings suggest that the intensification of the dominant zonal wind field delays the detachment of rings and affects the Loop Current migrations. The atmospheric modulation of the Loop Current migrations is analyzed here using reanalysis winds and altimetry-derived observa- tions. A newly developed methodology is applied to locate the Loop Current front, and a wavelet-based semblance analysis is used to explore correlations with atmospheric forcing. The results show that weakening （intensification） of the zonal wind stress in the eastern Gulf of Mexico is related with the Loop Current excursions to the north （south）. Semblance analyses confirm negative correlations between the zonal wind stress and the Loop Current migrations during the past 20 years. The intrusions of the Loop Current might involve an increase of the Yucatan Transport, which would balance the westward Rossby wave speed of a growing loop and delay the ring shedding. The results of this study have consequences for the interpretation of the chaotic processes of ring detachment and Loop Current intrusions, which might be modulated by wind stress.
基金supported by the National Natural Science Foundation of China (Grant No. 51005001)the National Science Foundation for Post-doctoral Scientists in China (Grant No. 20090450226)+1 种基金the Research Foundation of Education Bureau of Heilongjiang Province, China (Grant No. 11551098)the Youth Foundation of Harbin University of Science and Technology, China (Grant No. 2009YF024)
文摘We propose a bulk negative refractive index （NRI） metamaterial composed of periodic array of tightly coupled metallic cross-pairs printed oR the six sides of a cube for applications of superlenses. The structural characteristics of the three-dimensional （3D） metamaterial consist in the high symmetry and the superposition of metallic cross-pairs, which can increase the magnetic inductive coupling between adjacent cross-pairs and realize a broadband and isotropic NRI. The proposed 3D structure is simulated using the CS~ Microwave Studio 2006 to verify the design validity. The simulation results show that the proposed structure can not only realize simultaneously an electric and magnetic response to an incident electromagnetic （EM） wave, but also exhibit a broadband NRI whose relative bandwidth can reach up to 56.7%. In addition, the NRI band is insensitive to tile polarization and the incident angle of the incident EM wave. Therefore, the proposed metamaterial is a good candidate material as three-dimensional broadband isotropic NRI metamaterial.
文摘With the advent of Computer Algebra System (CAS) such as Mathematica [1], challenging symbolic longhand calcula-tions can effectively be performed free of error and at ease. Mathematica’s integrated features allow the investigator to combine the needed symbolic, numeric and graphic modules all in one interactive environment. This assists the author to focus on interpreting the output rather than exerting the efforts of relating the scattered separate modules. In this note the author, utilizing these three features, explores the magneto-static field and its associated vector potential of a steady looping current. In particular by deploying the numeric features of Mathematica the exact value of the vector potential of the looping current conducive to its 3D graph is presented.
基金Supported by Science and Technology Projects of State Grid Corporation ofChina(J2022019).
文摘To reduce current harmonics caused by switching frequency,T-type grid-connected inverter topology with LCL filter is adopted.In view of the disadvantages of the slow response speed of the traditional current control and the failure to eliminate the influence of the LCL filter on the grid-connected current by using current PI control alone,a current double closed loop PI current tracking control is proposed.Through the theoretical analysis of the grid-connected inverter control principle,the grid-connected inverter control model is designed,and the transfer functionmodel of each control link is deduced,and the current loop PI regulator is designed at last.The simulation results show that the control strategy is feasible.
文摘A thin metallic wire loop of arbitrary curvature is rotated with respect to an arbitrary axis of its plane. The device is excited by an electric dipole of infinite length and constant current. The resistance of the loop is computed rigorously as function of the position of the source. In this way, the induced voltage along the wire, under any kind of axial excitation, is given in the form of a superposition integral. The measured response is represented for various shapes of the coil, with respect to the time, the rotation angle and the position of the source. These diagrams lead to several technically applicable conclusions which are presented, discussed and justified.
文摘【目的】跟网型换流器(grid-following converter,GFL)被广泛应用于新能源并网系统。电网发生故障引起电压跌落时,系统进入低电压穿越(low voltage ride-through,LVRT)过程。传统锁相环(phase-locked loop,PLL)的二阶模型因忽略电流暂态过程,难以准确描述LVRT期间系统的动态特性,导致暂态同步稳定性的提升效果受限。为此,针对对称故障场景,提出一种适用于LVRT过程的电流内环协同控制策略,以增强系统暂态同步稳定性。【方法】基于PLL四阶动态方程,结合暂态能量函数法,分析PLL输出频率突变以及电流内环与PLL耦合作用对系统暂态同步稳定性的影响,并设计相应的控制策略:根据最优阻抗比动态调整电流参考值,以抑制故障期间暂态能量累积;通过在电流内环前馈解耦项中引入频率偏差补偿机制,加速暂态能量耗散过程。两者协同作用,提升系统在LVRT期间的暂态同步稳定性。【结果】PSCAD/EMTDC对称故障时域仿真结果表明:故障瞬间PLL输出频率突变量与电网电压跌落幅值成正比,增大系统失稳风险;所提控制策略能够有效抑制故障期间PLL输出频率偏差,显著降低虚拟功角首摆幅度,缩短故障清除后系统恢复时间,在不同电网参数下均表现出良好的适应性。【结论】所提电流内环协同控制策略,能够在对称故障期间有效抑制暂态能量累积,在故障清除后加速暂态能量耗散,有效提升了GFL并网系统在此类LVRT过程中的暂态同步稳定性。
文摘针对微特电机驱动控制系统中,双有源桥(dual active bridge,DAB)变换器在高频调制过程中易产生较大电流应力,导致器件温升高、寿命衰减及负载扰动下系统稳定性下降等问题,本文提出一种改进型双移相优化调制策略。该方法基于双有源桥拓扑,建立双移相调制下的功率传输模型与电流应力数学模型,采用拉格朗日乘数法求解最优移相比组合,并进一步推导多功率场景下的电流应力解析表达式;在控制器设计方面,引入电感电流内环补偿机制,提高系统对电机驱动过程中负载变化的动态响应能力。MATLAB/Simulink仿真结果表明,该方法在典型微特电机负载工况下能有效降低变换器的电流应力,缩短暂态响应时间,并改善输出电压纹波,对提升微特电机控制系统的稳态与暂态性能具有良好效果,为高效能电机驱动供电模块的优化设计提供理论依据。
文摘Objective For the inverters used in UPS, it is important to maintain the pure sinusoidal AC output voltage waveform over all loading conditions and transients. Methods A novel sinusoidal output voltage control strategy is pregented in this paper. The output voltage is controlled by introducing filtering eapacitor current feedback. Two simple PI regulators are used for the current and voltage control loops. Results With the new control strategy, the inverter achieves very low output voltage distortion, good output voltage regulation and strong perturbation rejection, fast dynamic response, and good performance under nonlinear loads. The THD under capacitance rectifying load is better than 0.2%, the output voltage regulation within 0 to full load is less than 0.1%. The resting time under load transient is within 200?μ s . Conclusion The merits of the new control strategy include rapid response and good steady state stiffness.
文摘Multiply-connected Hall plates show different phenomena than singly connected Hall plates. In part I (published in Journal of Applied Physics and Mathematics), we discussed topologies where a stream function can be defined, with special reference to Hall/Anti-Hall bar configurations. In part II, we focus on topologies where no conventional stream function can be defined, like Corbino disks. If current is injected and extracted at different boundaries of a multiply-connected conductive region, the current density shows spiral streamlines at strong magnetic field. Spiral streamlines also appear in simply-connected Hall plates when current contacts are located in their interior instead of their boundary, particularly if the contacts are very small. Spiral streamlines and circulating current are studied for two complementary planar device geometries: either all boundaries are conducting or all boundaries are insulating. The latter case means point current contacts and it can be treated similarly to singly connected Hall plates with peripheral contacts through the definition of a so-called loop stream function. This function also establishes a relation between Hall plates with complementary boundary conditions. The theory is explained by examples.
基金Sponsored by the High Technology Ship Research and Program of Ministry of Industry and Information Technology of the People's Republic of China(Grant No.539[2012])the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20120073120014)
文摘In order to control the lateral motion of a jet trencher which is important for stable trenching operation,the oscillation characteristics of the jet trencher are researched. The jet trencher is simplified into a single degree of freedom model with restoring and damping force. The nonlinear mathematical model of the trencher laterally oscillating in ocean currents is established,and its approximate analytical solution is obtained.Results show that the analytical solution has small differences with numerical solution based on the fourth-order Runge-Kutta method and can effectively describe the underwater oscillation. A double-loop PID controller is designed to control the lateral motion displacement of the trencher to return to the center of the pipeline route which is effective and robust for the propulsion system.
文摘With the continuous development of urban distribution network, most of the distribution network has formed a dual power supply mode. The traditional way of distribution network load operating mainly adopts the power method, while satisfied the requirements of the safety of power grid, but will cause external short time power outages, poor user experience, realizing the distribution network outage rearrangement of load is a necessary means to improve power supply reliability. This paper presents mathematical model of load transfer in distribution network. The differences of voltage of amplitude and phase angle on both sides are calculated by the power flow. According to the differential pressure to determine whether the loop can be closed at the loop operation, thereby improving the success rate of operation.
