Compared with the typical Ultra HVDC(UHVDC)system,the inverters of the UHVDC system with a hierarchical connection mode(UHVDC-HCM),connect two receiving-end systems with different operational conditions.This requires ...Compared with the typical Ultra HVDC(UHVDC)system,the inverters of the UHVDC system with a hierarchical connection mode(UHVDC-HCM),connect two receiving-end systems with different operational conditions.This requires the corresponding conversion units(CUs)at the different terminals to be differentiated in reliability modeling,and the spares should also be separately set.A reliability model of the UHVDCHCM system is proposed in this paper.The operating modes are classified by the capacities of the total system and the transmission powers to the two receiving-ends.Considering the independent spares of the components of the CUs at different terminals,the state space is derived.Two sets of indices are newly proposed to more accurately evaluate the system reliability.Based on the matrix description of the frequency&duration(F&D)method,the sensitivities of the reliability indices to the reliability parameters of the components are quantified.Numerical results validate the feasibility of the proposed model.The vulnerabilities are recognized by the sensitivity analysis,and the impact of different spare schemes on the reliability indices and sensitivities are compared.The proposed model and indices provide a reference for the practical UHVDC-HCM projects.展开更多
The aim of this work is to explore the impact of regional transit service on tour-based commuter travel behavior by using the Bayesian hierarchical multinomial logit model, accounting for the spatial heterogeneity of ...The aim of this work is to explore the impact of regional transit service on tour-based commuter travel behavior by using the Bayesian hierarchical multinomial logit model, accounting for the spatial heterogeneity of the people living in the same area.With two indicators, accessibility and connectivity measured at the zone level, the regional transit service is captured and then related to the travel mode choice behavior. The sample data are selected from Washington-Baltimore Household Travel Survey in 2007,including all the trips from home to workplace in morning hours in Baltimore city. Traditional multinomial logit model using Bayesian approach is also estimated. A comparison of the two different models shows that ignoring the spatial context can lead to a misspecification of the effects of the regional transit service on travel behavior. The results reveal that improving transit service at regional level can be effective in reducing auto use for commuters after controlling for socio-demographics and travel-related factors.This work provides insights for interpreting tour-based commuter travel behavior by using recently developed methodological approaches. The results of this work will be helpful for engineers, urban planners, and transit operators to decide the needs to improve regional transit service and spatial location efficiently.展开更多
信息时代网络赋能指挥控制(network enabled command and control,NEC2)的理念,是通过使联网作战兵力信息共享效益最大化,达到作战效能的最大化.通过分析NEC2信息布局应具有的属性要求,提出一种可实现的层次模式联合兵力指挥控制(comman...信息时代网络赋能指挥控制(network enabled command and control,NEC2)的理念,是通过使联网作战兵力信息共享效益最大化,达到作战效能的最大化.通过分析NEC2信息布局应具有的属性要求,提出一种可实现的层次模式联合兵力指挥控制(command and control,C2)连通结构,对其自适应C2特性进行分析,最后结合层次模式指挥控制连通结构信息交换示例,对信息标准交换和按需交换进行介绍,并论述了该连通结构的特性、优点和技术要求.展开更多
特高压直流分层接入交流电网的新方式可提高受端电网接纳直流功率的能力,从电网结构、直流控制方式等方面合理分析特高压直流分层落点近区500 k V层和1 000 k V层换流母线的电压稳定性问题亟待深入研究。为此首先分析了不同层逆变器的...特高压直流分层接入交流电网的新方式可提高受端电网接纳直流功率的能力,从电网结构、直流控制方式等方面合理分析特高压直流分层落点近区500 k V层和1 000 k V层换流母线的电压稳定性问题亟待深入研究。为此首先分析了不同层逆变器的功率输出特性,并基于降阶雅克比矩阵推导了换流母线处电压稳定性因子的计算方法,进而提出了分层接入方式下各层换流母线的电压稳定性判据,判据表明综合电压稳定性因子越接近于0说明系统的电压稳定水平越好。利用该判据,分析了不同直流控制方式下电压稳定性的差异,得到了不同控制方式下电压稳定性的排序。从排序看出,整流站采用定电流控制或定功率控制、逆变站高低端逆变器都采用定电压控制的综合电压稳定性因子最小,为0.314 0,说明各层换流母线电压稳定水平最好;整流站采用定功率控制、逆变站高低端逆变器都采用定熄弧角控制的综合电压稳定性因子最大,为0.672 8,说明各层换流母线电压稳定水平最差。同时研究了直流功率输送水平对换流母线电压稳定的影响。最终得出的结论为:整流站控制方式由定功率变为定电流,或者逆变站高低端逆变器控制方式由定熄弧角变为定电压都能够提高分层直流落点处电压稳定水平;相对低的直流功率输送水平也对提高各层换流母线处电压稳定性有利。最后,以锡盟—泰州直流输电工程为背景的算例仿真证明了该分析方法的合理性和有效性。展开更多
为满足快速发展的网侧分层接入特高压直流换流站建设需要,通过全面调研并综合比较±800 k V/8 000 MW及±800 k V/10 000 MW工程各技术路线下换流阀、换流变压器等交直流主要转换设备的概念设计方案,归纳了直流主设备的外形参数...为满足快速发展的网侧分层接入特高压直流换流站建设需要,通过全面调研并综合比较±800 k V/8 000 MW及±800 k V/10 000 MW工程各技术路线下换流阀、换流变压器等交直流主要转换设备的概念设计方案,归纳了直流主设备的外形参数,总结了阀厅概念设计的总体要求、控制阀厅防火墙间距、制约内部电气布置的关键因素,以及主、辅设备的安装布置原则。在优化交流1 000 k V典型电极形状下空气净距的基础上,兼顾功能性和经济性的原则,得出了网侧分层接入交流500 k V/1 000 k V下的±800 k V/10 000 MW特高压直流工程高、低压阀厅的概念设计尺寸。结合换流站站址实际情况,并兼顾所有技术路线设备尺寸,提出:±800 k V泰州站换流区域按照"一字型"方案布置,高、低端阀厅设计尺寸(长×宽×高)分别为83 m×35 m×28.5 m和89 m×24 m×18.7 m;±800 k V临沂站换流区域按照"背靠背"方案布置,高、低端阀厅设计尺寸分别为89.2 m×35 m×28.5 m和99 m×23.1 m×18.7 m。展开更多
针对±800 k V特高压直流系统首次采用逆变侧分层接入到1 000 k V特高压交流系统的需求,为了确定换流站中1 000 k V交流母线的过电压水平,分别在两种分层接入方案的多种严重工况下,对1 000 k V交流母线的工频暂时过电压和操作过电...针对±800 k V特高压直流系统首次采用逆变侧分层接入到1 000 k V特高压交流系统的需求,为了确定换流站中1 000 k V交流母线的过电压水平,分别在两种分层接入方案的多种严重工况下,对1 000 k V交流母线的工频暂时过电压和操作过电压水平进行了仿真计算。分析了最高过电压产生的原因,给出了最高过电压产生的工况以及过电压水平。方案1中泰州站相对地过电压标幺值最高为1.54,相间过电压标幺值最高为2.71;方案2中临沂站相对地过电压标幺值最高为1.57,相间过电压标幺值最高为2.97。提出了采用额定电压低的避雷器降低换流母线操作过电压的措施,为特高压换流站1 000 k V交流侧空气间隙距离的选取和绝缘配合提供依据。展开更多
基金This work was supported by the National Natural Science Foundation of China under Grant 51637004.
文摘Compared with the typical Ultra HVDC(UHVDC)system,the inverters of the UHVDC system with a hierarchical connection mode(UHVDC-HCM),connect two receiving-end systems with different operational conditions.This requires the corresponding conversion units(CUs)at the different terminals to be differentiated in reliability modeling,and the spares should also be separately set.A reliability model of the UHVDCHCM system is proposed in this paper.The operating modes are classified by the capacities of the total system and the transmission powers to the two receiving-ends.Considering the independent spares of the components of the CUs at different terminals,the state space is derived.Two sets of indices are newly proposed to more accurately evaluate the system reliability.Based on the matrix description of the frequency&duration(F&D)method,the sensitivities of the reliability indices to the reliability parameters of the components are quantified.Numerical results validate the feasibility of the proposed model.The vulnerabilities are recognized by the sensitivity analysis,and the impact of different spare schemes on the reliability indices and sensitivities are compared.The proposed model and indices provide a reference for the practical UHVDC-HCM projects.
基金Project(71173061)supported by the National Natural Science Foundation of ChinaProject(2013U-6)supported by Key Laboratory of Eco Planning & Green Building,Ministry of Education(Tsinghua University),China
文摘The aim of this work is to explore the impact of regional transit service on tour-based commuter travel behavior by using the Bayesian hierarchical multinomial logit model, accounting for the spatial heterogeneity of the people living in the same area.With two indicators, accessibility and connectivity measured at the zone level, the regional transit service is captured and then related to the travel mode choice behavior. The sample data are selected from Washington-Baltimore Household Travel Survey in 2007,including all the trips from home to workplace in morning hours in Baltimore city. Traditional multinomial logit model using Bayesian approach is also estimated. A comparison of the two different models shows that ignoring the spatial context can lead to a misspecification of the effects of the regional transit service on travel behavior. The results reveal that improving transit service at regional level can be effective in reducing auto use for commuters after controlling for socio-demographics and travel-related factors.This work provides insights for interpreting tour-based commuter travel behavior by using recently developed methodological approaches. The results of this work will be helpful for engineers, urban planners, and transit operators to decide the needs to improve regional transit service and spatial location efficiently.
文摘信息时代网络赋能指挥控制(network enabled command and control,NEC2)的理念,是通过使联网作战兵力信息共享效益最大化,达到作战效能的最大化.通过分析NEC2信息布局应具有的属性要求,提出一种可实现的层次模式联合兵力指挥控制(command and control,C2)连通结构,对其自适应C2特性进行分析,最后结合层次模式指挥控制连通结构信息交换示例,对信息标准交换和按需交换进行介绍,并论述了该连通结构的特性、优点和技术要求.
文摘特高压直流分层接入交流电网的新方式可提高受端电网接纳直流功率的能力,从电网结构、直流控制方式等方面合理分析特高压直流分层落点近区500 k V层和1 000 k V层换流母线的电压稳定性问题亟待深入研究。为此首先分析了不同层逆变器的功率输出特性,并基于降阶雅克比矩阵推导了换流母线处电压稳定性因子的计算方法,进而提出了分层接入方式下各层换流母线的电压稳定性判据,判据表明综合电压稳定性因子越接近于0说明系统的电压稳定水平越好。利用该判据,分析了不同直流控制方式下电压稳定性的差异,得到了不同控制方式下电压稳定性的排序。从排序看出,整流站采用定电流控制或定功率控制、逆变站高低端逆变器都采用定电压控制的综合电压稳定性因子最小,为0.314 0,说明各层换流母线电压稳定水平最好;整流站采用定功率控制、逆变站高低端逆变器都采用定熄弧角控制的综合电压稳定性因子最大,为0.672 8,说明各层换流母线电压稳定水平最差。同时研究了直流功率输送水平对换流母线电压稳定的影响。最终得出的结论为:整流站控制方式由定功率变为定电流,或者逆变站高低端逆变器控制方式由定熄弧角变为定电压都能够提高分层直流落点处电压稳定水平;相对低的直流功率输送水平也对提高各层换流母线处电压稳定性有利。最后,以锡盟—泰州直流输电工程为背景的算例仿真证明了该分析方法的合理性和有效性。
文摘为满足快速发展的网侧分层接入特高压直流换流站建设需要,通过全面调研并综合比较±800 k V/8 000 MW及±800 k V/10 000 MW工程各技术路线下换流阀、换流变压器等交直流主要转换设备的概念设计方案,归纳了直流主设备的外形参数,总结了阀厅概念设计的总体要求、控制阀厅防火墙间距、制约内部电气布置的关键因素,以及主、辅设备的安装布置原则。在优化交流1 000 k V典型电极形状下空气净距的基础上,兼顾功能性和经济性的原则,得出了网侧分层接入交流500 k V/1 000 k V下的±800 k V/10 000 MW特高压直流工程高、低压阀厅的概念设计尺寸。结合换流站站址实际情况,并兼顾所有技术路线设备尺寸,提出:±800 k V泰州站换流区域按照"一字型"方案布置,高、低端阀厅设计尺寸(长×宽×高)分别为83 m×35 m×28.5 m和89 m×24 m×18.7 m;±800 k V临沂站换流区域按照"背靠背"方案布置,高、低端阀厅设计尺寸分别为89.2 m×35 m×28.5 m和99 m×23.1 m×18.7 m。
文摘针对±800 k V特高压直流系统首次采用逆变侧分层接入到1 000 k V特高压交流系统的需求,为了确定换流站中1 000 k V交流母线的过电压水平,分别在两种分层接入方案的多种严重工况下,对1 000 k V交流母线的工频暂时过电压和操作过电压水平进行了仿真计算。分析了最高过电压产生的原因,给出了最高过电压产生的工况以及过电压水平。方案1中泰州站相对地过电压标幺值最高为1.54,相间过电压标幺值最高为2.71;方案2中临沂站相对地过电压标幺值最高为1.57,相间过电压标幺值最高为2.97。提出了采用额定电压低的避雷器降低换流母线操作过电压的措施,为特高压换流站1 000 k V交流侧空气间隙距离的选取和绝缘配合提供依据。