The coronavirus disease 2019(COVID-19)pandemic has greatly damaged human society,but the origins and early transmission patterns of the severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)pathogen remain unclea...The coronavirus disease 2019(COVID-19)pandemic has greatly damaged human society,but the origins and early transmission patterns of the severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)pathogen remain unclear.Here,we reconstructed the transmission networks of SARS-CoV-2 during the first three and six months since its first report based on ancestor-offspring relationships using BANAL-52-referenced mutations.We explored the position(i.e.,root,middle,or tip)of early detected samples in the evolutionary tree of SARS-CoV-2.In total,6799 transmission chains and 1766 transmission networks were reconstructed,with chain lengths ranging from 1-9 nodes.The root node samples of the 1766 transmission networks were from 58 countries or regions and showed no common ancestor,indicating the occurrence of many independent or parallel transmissions of SARS-CoV-2 when first detected(i.e.,all samples were located at the tip position of the evolutionary tree).No root node sample was found in any sample(n=31,all from the Chinese mainland)collected in the first 15 days from 24 December 2019.Results using six-month data or RaTG13-referenced mutation data were similar.The reconstruction method was verified using a simulation approach.Our results suggest that SARS-CoV-2 may have already been spreading independently worldwide before the outbreak of COVID-19 in Wuhan,China.Thus,a comprehensive global survey of human and animal samples is essential to explore the origins of SARS-CoV-2 and its natural reservoirs and hosts.展开更多
Transmission network analysis is a crucial evaluation tool aiming to explore the characteristics of the human immunodeficiency virus epidemic,develop evidence-based prevention strategies,and contribute to various area...Transmission network analysis is a crucial evaluation tool aiming to explore the characteristics of the human immunodeficiency virus epidemic,develop evidence-based prevention strategies,and contribute to various areas of human immunodeficiency virus/acquired immunodeficiency syndrome prevention and control.Over recent decades,transmission networks have made tremendous strides in terms of modes,methods,applications,and various other aspects.Transmission network methods,including social,sexual,and molecular transmission networks,have played a pivotal role.Each transmission network research method has its advantages,as well as its limitations.In this study,we established a systematic review of these aforementioned transmission networks with respect to their definitions,applications,limitations,recent progress,and synthetic applications.展开更多
This paper proposes an environment-aware best- retransmission count selected optimization control scheme over IEEE 802.11 multi-hop wireless networks. The proposed scheme predicts the wireless resources by using stati...This paper proposes an environment-aware best- retransmission count selected optimization control scheme over IEEE 802.11 multi-hop wireless networks. The proposed scheme predicts the wireless resources by using statistical channel state and provides maximum retransmission count optimization based on wireless channel environment state to improve the packet delivery success ratio. The media access control (MAC) layer selects the best-retransmission count by perceiving the types of packet loss in wireless link and using the wireless channel charac- teristics and environment information, and adjusts the packet for- warding adaptively aiming at improving the packet retransmission probability. Simulation results show that the best-retransmission count selected scheme achieves a higher packet successful delivery percentage and a lower packet collision probability than the corresponding traditional MAC transmission control protocols.展开更多
In this paper,we investigate the evolution of spatiotemporal patterns and synchronization transitions in dependence on the information transmission delay and ion channel blocking in scale-free neuronal networks.As the...In this paper,we investigate the evolution of spatiotemporal patterns and synchronization transitions in dependence on the information transmission delay and ion channel blocking in scale-free neuronal networks.As the underlying model of neuronal dynamics,we use the Hodgkin-Huxley equations incorporating channel blocking and intrinsic noise.It is shown that delays play a significant yet subtle role in shaping the dynamics of neuronal networks.In particular,regions of irregular and regular propagating excitatory fronts related to the synchronization transitions appear intermittently as the delay increases.Moreover,the fraction of working sodium and potassium ion channels can also have a significant impact on the spatiotemporal dynamics of neuronal networks.As the fraction of blocked sodium channels increases,the frequency of excitatory events decreases,which in turn manifests as an increase in the neuronal synchrony that,however,is dysfunctional due to the virtual absence of large-amplitude excitations.Expectedly,we also show that larger coupling strengths improve synchronization irrespective of the information transmission delay and channel blocking.The presented results are also robust against the variation of the network size,thus providing insights that could facilitate understanding of the joint impact of ion channel blocking and information transmission delay on the spatiotemporal dynamics of neuronal networks.展开更多
The limitations of the conventional master-slavesplitting(MSS)method,which is commonly applied to power flow and optimal power flow in integrated transmission and distribution(I-T&D)networks,are first analyzed.Con...The limitations of the conventional master-slavesplitting(MSS)method,which is commonly applied to power flow and optimal power flow in integrated transmission and distribution(I-T&D)networks,are first analyzed.Considering that the MSS method suffers from a slow convergence rate or even divergence under some circumstances,a least-squares-based iterative(LSI)method is proposed.Compared with the MSS method,the LSI method modifies the iterative variables in each iteration by solving a least-squares problem with the information in previous iterations.A practical implementation and a parameter tuning strategy for the LSI method are discussed.Furthermore,a LSI-PF method is proposed to solve I-T&D power flow and a LSIheterogeneous decomposition(LSI-HGD)method is proposed to solve optimal power flow.Numerical experiments demonstrate that the proposed LSI-PF and LSI-HGD methods can achieve the same accuracy as the benchmark methods.Meanwhile,these LSI methods,with appropriate settings,significantly enhance the convergence and efficiency of conventional methods.Also,in some cases,where conventional methods diverge,these LSI methods can still converge.展开更多
Wireless Mesh Network (WMN) is a new-type wireless network. Its core idea is that any of its wireless equipment can act as both an Access Point (AP) and a router. Each node in the network can send and receive signals ...Wireless Mesh Network (WMN) is a new-type wireless network. Its core idea is that any of its wireless equipment can act as both an Access Point (AP) and a router. Each node in the network can send and receive signals as well as directly communicate with one or several peer nodes. One important issue to be considered in wireless Mesh networks is how to secure reliable data transmission in multi-hop links. To solve the problem, the 3GPP system architecture proposes two functionalities: ARQ and HARQ. This paper presents two HARQ schemes, namely hop-by-hop and edge-to-edge, and three ARQ schemes: hop-by-hop, edge-to-edge, and last-hop. Moreover, it proposes three solutions for WMNs from the perspective of protocol stock design: layered cooperative mechanism, relay ARQ mechanism and multi-hop mechanism.展开更多
Using Linux server as a gateway between the local area network and the Internet may lead to slow pace in network transmission and even data loss. In this study,the above problem and its solution were discussed.
1 Technical Features of ZTE’sDWDM SystemThe toll backbone wave division equipmentof ZXWM M900 backbone transmissionplatform is well designed forlarge-capacity optical transmission. It canfully satisfy the networking ...1 Technical Features of ZTE’sDWDM SystemThe toll backbone wave division equipmentof ZXWM M900 backbone transmissionplatform is well designed forlarge-capacity optical transmission. It canfully satisfy the networking and managementrequirements of diversified users and be fit forvarious toll backbone networks. The systemsupports up to 40 working wavelengths and up to400 Gb/s transmission capacity, and thewavelength selection and interval are in strictcompliance with ITU-T Recommendations. It展开更多
To satisfy the requirements of accurate operationalrisk assessment of integrated transmission and distribution networks (I-T&D), an integrated operational risk assessment (IORA) algorithm is proposed. Specific cas...To satisfy the requirements of accurate operationalrisk assessment of integrated transmission and distribution networks (I-T&D), an integrated operational risk assessment (IORA) algorithm is proposed. Specific cases demonstrate thatan I-ORA is necessary because it provides accurate handlingof the coupling between transmission and distribution networks,accurate analysis of power supply mode (PSM) changes ofimportant users and helps to improve security and stability ofpower grid operations. Two key technical requirements in theI-ORA algorithm are realized, i.e., integrated topology analysisand integrated power flow calculation. Under a certain contingency, integrated topology analysis is used to assess the risksof substation power cuts, network split and PSM changes ofimportant users, while the integrated power flow calculation,based on the self-adaptive Levenburg-Marquard method andNewton method, can be implemented to assess risks of heavyload/overload and voltage deviation. In addition, the graphicsprocessing unit is used to parallelly process some computationintensive steps. Numerical experiments show that the proposedI-ORA algorithm can realize accurate assessment for the entireI-T&D. In addition, the efficiency and convergence are satisfying,indicating the proposed I-ORA algorithm can significantly benefitreal practice in the coordination operation of I-T&D in the future.展开更多
This paper reviews the recent advances in multi-terabit long-haul transmission technologies for terrestrial optical networks. The use of high performance new fibres, low-noise Raman amplification, optimised modulation...This paper reviews the recent advances in multi-terabit long-haul transmission technologies for terrestrial optical networks. The use of high performance new fibres, low-noise Raman amplification, optimised modulation formats, and forward error correction is shown to be effective for capacity and distance expansion.展开更多
The identification of influential nodes in complex networks is one of the most exciting topics in network science.The latest work successfully compares each node using local connectivity and weak tie theory from a new...The identification of influential nodes in complex networks is one of the most exciting topics in network science.The latest work successfully compares each node using local connectivity and weak tie theory from a new perspective.We study the structural properties of networks in depth and extend this successful node evaluation from single-scale to multi-scale.In particular,one novel position parameter based on node transmission efficiency is proposed,which mainly depends on the shortest distances from target nodes to high-degree nodes.In this regard,the novel multi-scale information importance(MSII)method is proposed to better identify the crucial nodes by combining the network's local connectivity and global position information.In simulation comparisons,five state-of-the-art algorithms,i.e.the neighbor nodes degree algorithm(NND),betweenness centrality,closeness centrality,Katz centrality and the k-shell decomposition method,are selected to compare with our MSII.The results demonstrate that our method obtains superior performance in terms of robustness and spreading propagation for both real-world and artificial networks.展开更多
We discuss the concept of coarse wavelength-division multiplexing (CWDM) for metro networks. After reviewing the requirements on components such as lasers and fiber, we propose different architectures for a flexible u...We discuss the concept of coarse wavelength-division multiplexing (CWDM) for metro networks. After reviewing the requirements on components such as lasers and fiber, we propose different architectures for a flexible upgrade of existing CWDM systems.展开更多
The presentation will give an overview over different classes of signal impairments in ultra-long-haul and high-speed optical WDM transmission systems and adequate approaches for suppression, mitigation or compensatio...The presentation will give an overview over different classes of signal impairments in ultra-long-haul and high-speed optical WDM transmission systems and adequate approaches for suppression, mitigation or compensation are discussed.展开更多
Super High Definition (SHD) movies were successfully transmitted as streaming contents at about 300 Mbps for the first time over a long distance IP network (more than 3,000 km), in conjunction with the experimental ve...Super High Definition (SHD) movies were successfully transmitted as streaming contents at about 300 Mbps for the first time over a long distance IP network (more than 3,000 km), in conjunction with the experimental verification of traffic control and scalable multicast technologies.展开更多
Network virtual social life and social life of the intimate contact, gaining experience through the network are growing acceptance of a new kind of practice writing behavior. In this paper, closely related to the new ...Network virtual social life and social life of the intimate contact, gaining experience through the network are growing acceptance of a new kind of practice writing behavior. In this paper, closely related to the new direction of life experience of the Internet age forms, and characteristics of practical writing life experience development under the network environment and study of teaching strategy analysis, think the Internet+ provided by the social forms life mirror, fits the practical writing “material needs” obtaining through the network to the indirect way to gain life experience of social forms, and has become a new kind of practical writing teaching methods. Network life experience is not only a practical writing, and also will use literature writing, news writing, such as writing behavior.展开更多
Time synchronization systems that utilize the global navigation satellite systems(GNSS)are widely used in the monitoring,control,and protection of transmission networks.They ensure that phasor measurement units(PMUs)c...Time synchronization systems that utilize the global navigation satellite systems(GNSS)are widely used in the monitoring,control,and protection of transmission networks.They ensure that phasor measurement units(PMUs)can accurately monitor voltage phase angles,increase the accuracy of fault locators,enhance the capabilities of disturbance recorders,and allow differential feeder protection to use re-routable communication networks.However,concern about the reliability of GNSS receivers used in intelligent electronic devices(IEDs)have been reported;problems include mal-operations of differential protection,erroneous satellite timing/location messages,inappropriate installations,and blocking of satellite signals due to illegal use of GNSS jammers in vehicles.Utilities now require a timing system less dependent on the use of low cost GNSS receivers integrated into IEDs,but one that uses Grandmaster clocks,slave and transparent clocks,and an Ethernet communication network.The IEEE 1588-2008 synchronization protocol uses the Ethernet to disseminate a global time reference around a substation.A future substation will probably include duplicate 1588 grandmasters,each incorporating stable oscillators with GNSS and terrestrial receivers,in conjunction with a 1588 compliant Ethernet data network with slave and transparent clocks,and redundancy boxes for interfacing with IEDs.Although IEEE 1588 protocol is promising for future substation automation systems,its performance and impact has to be fully evaluated before it can be used in real substations.This paper describes how an IEEE 1588 time synchronization testbed is designed,constructed,and tested.Testing involves measuring the time offset when the Ethernet is heavily loaded with other traffic and the holdover capability of 1588 clocks.Additional delay introduced by IEEE 1588 traffic is also measured.As there is limited testing on GPS receivers within the power industry,this paper also uses the testbed to evaluate the steady state and transient behavior of GPS receivers.The results show a 1588 time synchronization system is accurate,secure,and ideally suited for protection and control applications,compared to a timing system merely based on GPS receivers.The information described in this paper should increase a utility’s confidence in applying IEEE 1588 timing in a real substation.展开更多
This paper proposes a novel method for transmission network expansion planning(TNEP)that take into account uncertainties in loads and renewable energy resources.The goal of TNEP is to minimize the expansion cost of ca...This paper proposes a novel method for transmission network expansion planning(TNEP)that take into account uncertainties in loads and renewable energy resources.The goal of TNEP is to minimize the expansion cost of candidate lines without any load curtailment.A robust linear optimization algorithm is adopted to minimize the load curtailment with uncertainties considered under feasible expansion costs.Hence,the optimal planning scheme obtained through an iterative process would be to serve loads and provide a sufficient margin for renewable energy integration.In this paper,two uncertainty budget parameters are introduced in the optimization process to limit the considered variation ranges for both the load and the renewable generation.Simulation results obtained from two test systems indicate that the uncertainty budget parameters used to describe uncertainties are essential to arrive at a compromise for the robustness and optimality,and hence,offer a range of preferences to power system planners and decision makers.展开更多
基金supported by the Ministry of Science and Technology of the People’s Republic of China(2021YFC0863400)Institute of Zoology,Chinese Academy of Sciences(E0517111,E122G611)。
文摘The coronavirus disease 2019(COVID-19)pandemic has greatly damaged human society,but the origins and early transmission patterns of the severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)pathogen remain unclear.Here,we reconstructed the transmission networks of SARS-CoV-2 during the first three and six months since its first report based on ancestor-offspring relationships using BANAL-52-referenced mutations.We explored the position(i.e.,root,middle,or tip)of early detected samples in the evolutionary tree of SARS-CoV-2.In total,6799 transmission chains and 1766 transmission networks were reconstructed,with chain lengths ranging from 1-9 nodes.The root node samples of the 1766 transmission networks were from 58 countries or regions and showed no common ancestor,indicating the occurrence of many independent or parallel transmissions of SARS-CoV-2 when first detected(i.e.,all samples were located at the tip position of the evolutionary tree).No root node sample was found in any sample(n=31,all from the Chinese mainland)collected in the first 15 days from 24 December 2019.Results using six-month data or RaTG13-referenced mutation data were similar.The reconstruction method was verified using a simulation approach.Our results suggest that SARS-CoV-2 may have already been spreading independently worldwide before the outbreak of COVID-19 in Wuhan,China.Thus,a comprehensive global survey of human and animal samples is essential to explore the origins of SARS-CoV-2 and its natural reservoirs and hosts.
文摘Transmission network analysis is a crucial evaluation tool aiming to explore the characteristics of the human immunodeficiency virus epidemic,develop evidence-based prevention strategies,and contribute to various areas of human immunodeficiency virus/acquired immunodeficiency syndrome prevention and control.Over recent decades,transmission networks have made tremendous strides in terms of modes,methods,applications,and various other aspects.Transmission network methods,including social,sexual,and molecular transmission networks,have played a pivotal role.Each transmission network research method has its advantages,as well as its limitations.In this study,we established a systematic review of these aforementioned transmission networks with respect to their definitions,applications,limitations,recent progress,and synthetic applications.
基金supported by the National Basic Research Program of China(2013CB329005)the National Natural Science Foundation of China(61101105+9 种基金6120116261302100)the Basic Research Program of Jiangsu Province(BK2011027BK2012434)the Natural Science Foundation of the Higher Education Institutions of Jiangsu Province(12KJB51002212KJB510020)the Postdoctoral Science Foundation of China(2013M531391)the State Grid Project(52090F135015)the Scientific Research Foundation for Nanjing University of Posts and Telecommunications(NY211006NY211007)
文摘This paper proposes an environment-aware best- retransmission count selected optimization control scheme over IEEE 802.11 multi-hop wireless networks. The proposed scheme predicts the wireless resources by using statistical channel state and provides maximum retransmission count optimization based on wireless channel environment state to improve the packet delivery success ratio. The media access control (MAC) layer selects the best-retransmission count by perceiving the types of packet loss in wireless link and using the wireless channel charac- teristics and environment information, and adjusts the packet for- warding adaptively aiming at improving the packet retransmission probability. Simulation results show that the best-retransmission count selected scheme achieves a higher packet successful delivery percentage and a lower packet collision probability than the corresponding traditional MAC transmission control protocols.
基金supported by the National Natural Science Foundation of China(11172017 and 10972001)the Fujian Natural Science Foundation of China(2009J05004)a Key Project of Fujian Provincial Universities(Information Technology Research Based on Mathematics)
文摘In this paper,we investigate the evolution of spatiotemporal patterns and synchronization transitions in dependence on the information transmission delay and ion channel blocking in scale-free neuronal networks.As the underlying model of neuronal dynamics,we use the Hodgkin-Huxley equations incorporating channel blocking and intrinsic noise.It is shown that delays play a significant yet subtle role in shaping the dynamics of neuronal networks.In particular,regions of irregular and regular propagating excitatory fronts related to the synchronization transitions appear intermittently as the delay increases.Moreover,the fraction of working sodium and potassium ion channels can also have a significant impact on the spatiotemporal dynamics of neuronal networks.As the fraction of blocked sodium channels increases,the frequency of excitatory events decreases,which in turn manifests as an increase in the neuronal synchrony that,however,is dysfunctional due to the virtual absence of large-amplitude excitations.Expectedly,we also show that larger coupling strengths improve synchronization irrespective of the information transmission delay and channel blocking.The presented results are also robust against the variation of the network size,thus providing insights that could facilitate understanding of the joint impact of ion channel blocking and information transmission delay on the spatiotemporal dynamics of neuronal networks.
基金supported by the National Natural Science Foundation of China(52077193).
文摘The limitations of the conventional master-slavesplitting(MSS)method,which is commonly applied to power flow and optimal power flow in integrated transmission and distribution(I-T&D)networks,are first analyzed.Considering that the MSS method suffers from a slow convergence rate or even divergence under some circumstances,a least-squares-based iterative(LSI)method is proposed.Compared with the MSS method,the LSI method modifies the iterative variables in each iteration by solving a least-squares problem with the information in previous iterations.A practical implementation and a parameter tuning strategy for the LSI method are discussed.Furthermore,a LSI-PF method is proposed to solve I-T&D power flow and a LSIheterogeneous decomposition(LSI-HGD)method is proposed to solve optimal power flow.Numerical experiments demonstrate that the proposed LSI-PF and LSI-HGD methods can achieve the same accuracy as the benchmark methods.Meanwhile,these LSI methods,with appropriate settings,significantly enhance the convergence and efficiency of conventional methods.Also,in some cases,where conventional methods diverge,these LSI methods can still converge.
文摘Wireless Mesh Network (WMN) is a new-type wireless network. Its core idea is that any of its wireless equipment can act as both an Access Point (AP) and a router. Each node in the network can send and receive signals as well as directly communicate with one or several peer nodes. One important issue to be considered in wireless Mesh networks is how to secure reliable data transmission in multi-hop links. To solve the problem, the 3GPP system architecture proposes two functionalities: ARQ and HARQ. This paper presents two HARQ schemes, namely hop-by-hop and edge-to-edge, and three ARQ schemes: hop-by-hop, edge-to-edge, and last-hop. Moreover, it proposes three solutions for WMNs from the perspective of protocol stock design: layered cooperative mechanism, relay ARQ mechanism and multi-hop mechanism.
文摘Using Linux server as a gateway between the local area network and the Internet may lead to slow pace in network transmission and even data loss. In this study,the above problem and its solution were discussed.
文摘1 Technical Features of ZTE’sDWDM SystemThe toll backbone wave division equipmentof ZXWM M900 backbone transmissionplatform is well designed forlarge-capacity optical transmission. It canfully satisfy the networking and managementrequirements of diversified users and be fit forvarious toll backbone networks. The systemsupports up to 40 working wavelengths and up to400 Gb/s transmission capacity, and thewavelength selection and interval are in strictcompliance with ITU-T Recommendations. It
基金the State Grid Zhejiang Electric Power Co.,Ltd.(Science and Technology Project under Grant 5211JH180081:Research on security evaluation and control technology of smart platform based on dispatch cloud.)。
文摘To satisfy the requirements of accurate operationalrisk assessment of integrated transmission and distribution networks (I-T&D), an integrated operational risk assessment (IORA) algorithm is proposed. Specific cases demonstrate thatan I-ORA is necessary because it provides accurate handlingof the coupling between transmission and distribution networks,accurate analysis of power supply mode (PSM) changes ofimportant users and helps to improve security and stability ofpower grid operations. Two key technical requirements in theI-ORA algorithm are realized, i.e., integrated topology analysisand integrated power flow calculation. Under a certain contingency, integrated topology analysis is used to assess the risksof substation power cuts, network split and PSM changes ofimportant users, while the integrated power flow calculation,based on the self-adaptive Levenburg-Marquard method andNewton method, can be implemented to assess risks of heavyload/overload and voltage deviation. In addition, the graphicsprocessing unit is used to parallelly process some computationintensive steps. Numerical experiments show that the proposedI-ORA algorithm can realize accurate assessment for the entireI-T&D. In addition, the efficiency and convergence are satisfying,indicating the proposed I-ORA algorithm can significantly benefitreal practice in the coordination operation of I-T&D in the future.
文摘This paper reviews the recent advances in multi-terabit long-haul transmission technologies for terrestrial optical networks. The use of high performance new fibres, low-noise Raman amplification, optimised modulation formats, and forward error correction is shown to be effective for capacity and distance expansion.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11801430,11801200,61877046,and 61877047).
文摘The identification of influential nodes in complex networks is one of the most exciting topics in network science.The latest work successfully compares each node using local connectivity and weak tie theory from a new perspective.We study the structural properties of networks in depth and extend this successful node evaluation from single-scale to multi-scale.In particular,one novel position parameter based on node transmission efficiency is proposed,which mainly depends on the shortest distances from target nodes to high-degree nodes.In this regard,the novel multi-scale information importance(MSII)method is proposed to better identify the crucial nodes by combining the network's local connectivity and global position information.In simulation comparisons,five state-of-the-art algorithms,i.e.the neighbor nodes degree algorithm(NND),betweenness centrality,closeness centrality,Katz centrality and the k-shell decomposition method,are selected to compare with our MSII.The results demonstrate that our method obtains superior performance in terms of robustness and spreading propagation for both real-world and artificial networks.
文摘We discuss the concept of coarse wavelength-division multiplexing (CWDM) for metro networks. After reviewing the requirements on components such as lasers and fiber, we propose different architectures for a flexible upgrade of existing CWDM systems.
文摘The presentation will give an overview over different classes of signal impairments in ultra-long-haul and high-speed optical WDM transmission systems and adequate approaches for suppression, mitigation or compensation are discussed.
文摘Super High Definition (SHD) movies were successfully transmitted as streaming contents at about 300 Mbps for the first time over a long distance IP network (more than 3,000 km), in conjunction with the experimental verification of traffic control and scalable multicast technologies.
文摘Network virtual social life and social life of the intimate contact, gaining experience through the network are growing acceptance of a new kind of practice writing behavior. In this paper, closely related to the new direction of life experience of the Internet age forms, and characteristics of practical writing life experience development under the network environment and study of teaching strategy analysis, think the Internet+ provided by the social forms life mirror, fits the practical writing “material needs” obtaining through the network to the indirect way to gain life experience of social forms, and has become a new kind of practical writing teaching methods. Network life experience is not only a practical writing, and also will use literature writing, news writing, such as writing behavior.
文摘Time synchronization systems that utilize the global navigation satellite systems(GNSS)are widely used in the monitoring,control,and protection of transmission networks.They ensure that phasor measurement units(PMUs)can accurately monitor voltage phase angles,increase the accuracy of fault locators,enhance the capabilities of disturbance recorders,and allow differential feeder protection to use re-routable communication networks.However,concern about the reliability of GNSS receivers used in intelligent electronic devices(IEDs)have been reported;problems include mal-operations of differential protection,erroneous satellite timing/location messages,inappropriate installations,and blocking of satellite signals due to illegal use of GNSS jammers in vehicles.Utilities now require a timing system less dependent on the use of low cost GNSS receivers integrated into IEDs,but one that uses Grandmaster clocks,slave and transparent clocks,and an Ethernet communication network.The IEEE 1588-2008 synchronization protocol uses the Ethernet to disseminate a global time reference around a substation.A future substation will probably include duplicate 1588 grandmasters,each incorporating stable oscillators with GNSS and terrestrial receivers,in conjunction with a 1588 compliant Ethernet data network with slave and transparent clocks,and redundancy boxes for interfacing with IEDs.Although IEEE 1588 protocol is promising for future substation automation systems,its performance and impact has to be fully evaluated before it can be used in real substations.This paper describes how an IEEE 1588 time synchronization testbed is designed,constructed,and tested.Testing involves measuring the time offset when the Ethernet is heavily loaded with other traffic and the holdover capability of 1588 clocks.Additional delay introduced by IEEE 1588 traffic is also measured.As there is limited testing on GPS receivers within the power industry,this paper also uses the testbed to evaluate the steady state and transient behavior of GPS receivers.The results show a 1588 time synchronization system is accurate,secure,and ideally suited for protection and control applications,compared to a timing system merely based on GPS receivers.The information described in this paper should increase a utility’s confidence in applying IEEE 1588 timing in a real substation.
基金supported by the National Basic Research Program of China(2012CB215106).
文摘This paper proposes a novel method for transmission network expansion planning(TNEP)that take into account uncertainties in loads and renewable energy resources.The goal of TNEP is to minimize the expansion cost of candidate lines without any load curtailment.A robust linear optimization algorithm is adopted to minimize the load curtailment with uncertainties considered under feasible expansion costs.Hence,the optimal planning scheme obtained through an iterative process would be to serve loads and provide a sufficient margin for renewable energy integration.In this paper,two uncertainty budget parameters are introduced in the optimization process to limit the considered variation ranges for both the load and the renewable generation.Simulation results obtained from two test systems indicate that the uncertainty budget parameters used to describe uncertainties are essential to arrive at a compromise for the robustness and optimality,and hence,offer a range of preferences to power system planners and decision makers.