Metallic ring-shaped nanotube arrays are proposed and its optical transmission properties are studied by using finite-difference time-domain （FDTD） method. Compared with the transmission spectra of conventional circ...Metallic ring-shaped nanotube arrays are proposed and its optical transmission properties are studied by using finite-difference time-domain （FDTD） method. Compared with the transmission spectra of conventional circular nanotube arrays, two photonic band gaps are emerged in the transmission spectra offing-shaped nanotube arrays, the two band gaps and transmission spectra are adjusted by the length, inner radius, intertube spacing and the dielectric constants of the core and embedding medium, and magnitude modification, redshift and blueshift of the resonance modes are observed. A metallic ring-shaped nanotube arrays for subwavelength band-stop filter in the range of visible light can be achieved. To understand its physical origin, field-interference mechanism was suggested by the field distributions. The proposed nanostructures and results may have great potential applications in subwavelength near-field optics.展开更多
High Voltage Direct Current (HVDC) electric power transmission is a promising technology for integrating offshore wind farms and interconnecting power grids in different regions. In order to maintain the DC voltage, d...High Voltage Direct Current (HVDC) electric power transmission is a promising technology for integrating offshore wind farms and interconnecting power grids in different regions. In order to maintain the DC voltage, droop control has been widely used. Transmission line loss constitutes an import part of the total power loss in a multi-terminal HVDC scheme. In this paper, the relation between droop controller design and transmission loss has been investigated. Different MTDC layout configurations are compared to examine the effect of droop controller design on the transmission loss.展开更多
In the ring-shaped Su–Schrieffer–Heeger(SSH)double-chain,the quantum interference between the two different electron tunneling paths of the upper and lower chains has an important influence on the electron transport...In the ring-shaped Su–Schrieffer–Heeger(SSH)double-chain,the quantum interference between the two different electron tunneling paths of the upper and lower chains has an important influence on the electron transport properties of non-trivial topological edge states.Here,we have studied the electron transport signatures of non-trivial topological edge states in a ring-shaped SSH double-chain system based on the wave-guide theory and transfer-matrix method.In the ringshaped SSH double-chain with the upper chain being different from the lower one,it is demonstrated that the electron transmission probability displays the four and two resonance peaks associated with the non-trivial topological edge states in the weak and strong coupling regimes,respectively.Whereas in the case of the upper chain being the same as the lower one,the two transmission resonance peaks associated with the non-trivial topological edge states in the weak coupling regime are only found,and that in the strong coupling regime disappear that originated from the destructive interference between the two different electron tunneling paths of the upper and lower chains.Consequently,the variation of the number of transmission resonance peaks associated with the non-trivial topological edge states in the weak and strong coupling regimes suggests that an alternative scheme for detecting non-trivial topological edge states in the ring-shaped SSH doublechain system.展开更多
This work presents an optimal design method of antenna aperture illumination for microwave power transmission with an annular collection area.The objective is to maximize the ratio of the power radiated on the annular...This work presents an optimal design method of antenna aperture illumination for microwave power transmission with an annular collection area.The objective is to maximize the ratio of the power radiated on the annular collection area to the total transmitted power.By formulating the aperture amplitude distribution through a summation of a special set of series,the optimal design problem can be reduced to finding the maximum ratio of two real quadratic forms.Based on the theory of matrices,the solution to the formulated optimization problem is to determine the largest characteristic value and its associated characteristic vector.To meet security requirements,the peak radiation levels outside the receiving area are considered to be extra constraints.A hybrid grey wolf optimizer and Nelder–Mead simplex method is developed to deal with this constrained optimization problem.In order to demonstrate the effectiveness of the proposed method,numerical experiments on continuous apertures are conducted;then,discrete arrays of isotropic elements are employed to validate the correctness of the optimized results.Finally,patch arrays are adopted to further verify the validity of the proposed method.展开更多
由于换流站数目、控制模式以及指令值的不同,电压源换流器型多端直流(voltage source converter based multi terminal dc,VSC-MTDC)输电系统在实际运行中具有多种运行方式,并且随着电网运行条件的变化,VSC-MTDC输电系统的运行方式也随...由于换流站数目、控制模式以及指令值的不同,电压源换流器型多端直流(voltage source converter based multi terminal dc,VSC-MTDC)输电系统在实际运行中具有多种运行方式,并且随着电网运行条件的变化,VSC-MTDC输电系统的运行方式也随之改变。因此,直流运行中心需要根据换流站运行特性、电网条件和系统参数等快速确定VSCMTDC输电系统运行控制模式与系统状态量,这对系统调控和安全运行具有重要意义。基于此,分析主导换流站、辅助换流站、定有功功率控制换流站和风电场换流站的直流电压–电流运行特性,推导各换流站在不同控制模式下的特性方程,给出各换流站不同控制模式下的电气量范围。接着,提出VSC-MTDC输电系统稳态工作点的计算方法,完善换流站的控制模式修正方法。最后,以典型的五端直流输电系统为例,Matlab编程验证了直流运行特性分析方法和稳态工作点计算方法的准确性;计算结果表明,该稳态分析方法能够快速准确地计算出VSC-MTDC输电系统的稳态工作点。展开更多
随着国内柔性直流输电技术的快速发展,基于真双极接线的多端柔性输电技术将被越来越多地应用到实际工程中。不同于单极线路或换流器退出运行时,伪双极系统下会出现的线路过载和切机切负荷现象,对于运行方式更为灵活的真双极系统,由于非...随着国内柔性直流输电技术的快速发展,基于真双极接线的多端柔性输电技术将被越来越多地应用到实际工程中。不同于单极线路或换流器退出运行时,伪双极系统下会出现的线路过载和切机切负荷现象,对于运行方式更为灵活的真双极系统,由于非故障极可转代故障极的部分功率,使得电网可靠性和整体输电能力的提升成为可能。提出了一种适用于真双极多端柔性直流输电(VSC-MTDC)系统的功率转代策略:基于真双极系统正负极电网可独立控制功率的特点,当直流系统在非正常运行状况下出现非对称拓扑时,在确保各元件不越限的前提下使非故障极电网转代故障极电网部分功率,以提高VSC-MTDC系统的总传输容量。同时,基于张北±500 k V柔性直流输电示范工程,搭建了真双极四端柔性直流输电PSCAD/EMTDC仿真系统,对所提策略进行了有效性验证。展开更多
基金Projects(11164007,61275174)supported by the National Natural Science Foundation of ChinaProject(20100162110068)supported by the Doctoral Program of Higher Education of China+1 种基金Project(20132BAB212007)supported by the Natural Science Foundation of Jiangxi Province,ChinaProject(GJJ11107)supported by Scientific Foundation of Jiangxi Education Department,China
文摘Metallic ring-shaped nanotube arrays are proposed and its optical transmission properties are studied by using finite-difference time-domain （FDTD） method. Compared with the transmission spectra of conventional circular nanotube arrays, two photonic band gaps are emerged in the transmission spectra offing-shaped nanotube arrays, the two band gaps and transmission spectra are adjusted by the length, inner radius, intertube spacing and the dielectric constants of the core and embedding medium, and magnitude modification, redshift and blueshift of the resonance modes are observed. A metallic ring-shaped nanotube arrays for subwavelength band-stop filter in the range of visible light can be achieved. To understand its physical origin, field-interference mechanism was suggested by the field distributions. The proposed nanostructures and results may have great potential applications in subwavelength near-field optics.
文摘High Voltage Direct Current (HVDC) electric power transmission is a promising technology for integrating offshore wind farms and interconnecting power grids in different regions. In order to maintain the DC voltage, droop control has been widely used. Transmission line loss constitutes an import part of the total power loss in a multi-terminal HVDC scheme. In this paper, the relation between droop controller design and transmission loss has been investigated. Different MTDC layout configurations are compared to examine the effect of droop controller design on the transmission loss.
基金supported by the National Natural Science Foundation of China(Grant No.11974153)the Natural Science Foundation of Shanxi Province,China(Grant No.20210302123184)+1 种基金the Program for the Outstanding Innovative Teams of Higher Learning Institutions of Shanxi Province,China(Grant No.163220120-S)the Natural Science Foundation of Shandong Province,China(Grant No.ZR2020MA091)。
文摘In the ring-shaped Su–Schrieffer–Heeger(SSH)double-chain,the quantum interference between the two different electron tunneling paths of the upper and lower chains has an important influence on the electron transport properties of non-trivial topological edge states.Here,we have studied the electron transport signatures of non-trivial topological edge states in a ring-shaped SSH double-chain system based on the wave-guide theory and transfer-matrix method.In the ringshaped SSH double-chain with the upper chain being different from the lower one,it is demonstrated that the electron transmission probability displays the four and two resonance peaks associated with the non-trivial topological edge states in the weak and strong coupling regimes,respectively.Whereas in the case of the upper chain being the same as the lower one,the two transmission resonance peaks associated with the non-trivial topological edge states in the weak coupling regime are only found,and that in the strong coupling regime disappear that originated from the destructive interference between the two different electron tunneling paths of the upper and lower chains.Consequently,the variation of the number of transmission resonance peaks associated with the non-trivial topological edge states in the weak and strong coupling regimes suggests that an alternative scheme for detecting non-trivial topological edge states in the ring-shaped SSH doublechain system.
基金supported in part by the National Key Research and Development Program of China(2021YFB3900300)in part by the National Natural Science Foundation of China(62201416)+2 种基金in part by the Fundamental Research Funds for the Central Universities(QTZX23070)in part by the Qin Chuang Yuan High-Level Innovative and Entrepreneurial Talents Project(QCYRCXM-2022-314)in part by Singapore Ministry of Education Academic Research Fund Tier 1。
文摘This work presents an optimal design method of antenna aperture illumination for microwave power transmission with an annular collection area.The objective is to maximize the ratio of the power radiated on the annular collection area to the total transmitted power.By formulating the aperture amplitude distribution through a summation of a special set of series,the optimal design problem can be reduced to finding the maximum ratio of two real quadratic forms.Based on the theory of matrices,the solution to the formulated optimization problem is to determine the largest characteristic value and its associated characteristic vector.To meet security requirements,the peak radiation levels outside the receiving area are considered to be extra constraints.A hybrid grey wolf optimizer and Nelder–Mead simplex method is developed to deal with this constrained optimization problem.In order to demonstrate the effectiveness of the proposed method,numerical experiments on continuous apertures are conducted;then,discrete arrays of isotropic elements are employed to validate the correctness of the optimized results.Finally,patch arrays are adopted to further verify the validity of the proposed method.
文摘由于换流站数目、控制模式以及指令值的不同,电压源换流器型多端直流(voltage source converter based multi terminal dc,VSC-MTDC)输电系统在实际运行中具有多种运行方式,并且随着电网运行条件的变化,VSC-MTDC输电系统的运行方式也随之改变。因此,直流运行中心需要根据换流站运行特性、电网条件和系统参数等快速确定VSCMTDC输电系统运行控制模式与系统状态量,这对系统调控和安全运行具有重要意义。基于此,分析主导换流站、辅助换流站、定有功功率控制换流站和风电场换流站的直流电压–电流运行特性,推导各换流站在不同控制模式下的特性方程,给出各换流站不同控制模式下的电气量范围。接着,提出VSC-MTDC输电系统稳态工作点的计算方法,完善换流站的控制模式修正方法。最后,以典型的五端直流输电系统为例,Matlab编程验证了直流运行特性分析方法和稳态工作点计算方法的准确性;计算结果表明,该稳态分析方法能够快速准确地计算出VSC-MTDC输电系统的稳态工作点。
文摘随着国内柔性直流输电技术的快速发展,基于真双极接线的多端柔性输电技术将被越来越多地应用到实际工程中。不同于单极线路或换流器退出运行时,伪双极系统下会出现的线路过载和切机切负荷现象,对于运行方式更为灵活的真双极系统,由于非故障极可转代故障极的部分功率,使得电网可靠性和整体输电能力的提升成为可能。提出了一种适用于真双极多端柔性直流输电(VSC-MTDC)系统的功率转代策略:基于真双极系统正负极电网可独立控制功率的特点,当直流系统在非正常运行状况下出现非对称拓扑时,在确保各元件不越限的前提下使非故障极电网转代故障极电网部分功率,以提高VSC-MTDC系统的总传输容量。同时,基于张北±500 k V柔性直流输电示范工程,搭建了真双极四端柔性直流输电PSCAD/EMTDC仿真系统,对所提策略进行了有效性验证。
