During faults in a distribution network,the output power of a distributed generation(DG)may be uncertain.Moreover,the output currents of distributed power sources are also affected by the output power,resulting in unc...During faults in a distribution network,the output power of a distributed generation(DG)may be uncertain.Moreover,the output currents of distributed power sources are also affected by the output power,resulting in uncertainties in the calculation of the short-circuit current at the time of a fault.Additionally,the impacts of such uncertainties around short-circuit currents will increase with the increase of distributed power sources.Thus,it is very important to develop a method for calculating the short-circuit current while considering the uncertainties in a distribution network.In this study,an affine arithmetic algorithm for calculating short-circuit current intervals in distribution networks with distributed power sources while considering power fluctuations is presented.The proposed algorithm includes two stages.In the first stage,normal operations are considered to establish a conservative interval affine optimization model of injection currents in distributed power sources.Constrained by the fluctuation range of distributed generation power at the moment of fault occurrence,the model can then be used to solve for the fluctuation range of injected current amplitudes in distributed power sources.The second stage is implemented after a malfunction occurs.In this stage,an affine optimization model is first established.This model is developed to characterizes the short-circuit current interval of a transmission line,and is constrained by the fluctuation range of the injected current amplitude of DG during normal operations.Finally,the range of the short-circuit current amplitudes of distribution network lines after a short-circuit fault occurs is predicted.The algorithm proposed in this article obtains an interval range containing accurate results through interval operation.Compared with traditional point value calculation methods,interval calculation methods can provide more reliable analysis and calculation results.The range of short-circuit current amplitude obtained by this algorithm is slightly larger than those obtained using the Monte Carlo algorithm and the Latin hypercube sampling algorithm.Therefore,the proposed algorithm has good suitability and does not require iterative calculations,resulting in a significant improvement in computational speed compared to the Monte Carlo algorithm and the Latin hypercube sampling algorithm.Furthermore,the proposed algorithm can provide more reliable analysis and calculation results,improving the safety and stability of power systems.展开更多
The jacket structure has become more popular as the offshore wind-turbine support structure. K-type and inverted-K-type jacket support structures have superior potential due to their fewer joints and lower cost of man...The jacket structure has become more popular as the offshore wind-turbine support structure. K-type and inverted-K-type jacket support structures have superior potential due to their fewer joints and lower cost of manufacture and installation. A numerical study was presented on the dynamic responses of K-type and inverted-K-type jacket support structures subjected to different kinds of dynamic load. The results show that the inverted-K-type jacket structure has higher natural frequencies than the K-type. The wave force spectrum response shows that the maximum displacement of the K-type jacket structure is larger than that of the inverted-K-type. The time-history responses under wind and wave-current load indicate that the inverted-K-type jacket structure shows smaller displacement and stress compared with the K-type, and presents different stress concentration phenomena. The dynamic responses reveal that the inverted-K-type of jacket support structure has greater stiffness and superior mechanical properties, and thus is more applicable in the offshore area with relatively deep water.展开更多
In this paper, the output quantum correlations of three fields interacting with inverted Y-type atoms inside a three-mode cavity are investigated. By numerically calculating the stationary noise spectra of the fields,...In this paper, the output quantum correlations of three fields interacting with inverted Y-type atoms inside a three-mode cavity are investigated. By numerically calculating the stationary noise spectra of the fields, we show that it is possible to generate the genuine tripartite continuous variable entanglement outside the cavity by coherently preparing the atoms in a superposition of the upper excited state and two ground states initially. Our numerical results demonstrate that both zero frequency entanglement and sideband frequency entanglement can be obtained under different initial coherent conditions. In addition, we investigate the thermal fluctuation effects on the quantum entanglement. It is found out that the entanglement occurring in a high frequency regime is more robust against thermal noise than the zero frequency entanglement, which may be useful for quantum communication.展开更多
This paper studies a heavy snowfall in Beijing that took place on 1 November 2009. The date of the snowfall was about one month earlier than the average. The National Centers for Environmental Prediction (NCEP) reanal...This paper studies a heavy snowfall in Beijing that took place on 1 November 2009. The date of the snowfall was about one month earlier than the average. The National Centers for Environmental Prediction (NCEP) reanalysis data, conventional data, and Automatic Weather Station (AWS) data are utilized to explore the reasons for the snowfall and the influencing systems. The main conclusions are as follows: (1) It is revealed from the average geopotential height and average temperature fields at 500 hPa that the large scale circulation in November 2009 was favorable to snowfall. The cold-dry air from West Siberia and the warm-moist air from the Bay of Bengal converged in North China. In addition, it was found from the average moisture flux field at 700 hPa that the main water vapor source was in the Bay of Bengal. (2) Not only the "return current", as usually accepted, but also the inverted trough on the current had an important contribution to the snowfall. The inverted trough could produce the obvious upward motion that is an important environmental condition of snowfalls. (3) More attention should be paid to mesoscale systems such as mesolows during the cold season because of their importance, though they do not occur as frequently as in the warm season. It should be pointed out that AWS data are very useful in mesoscale system analysis during both warm and cold seasons.展开更多
基金This article was supported by the general project“Research on Wind and Photovoltaic Fault Characteristics and Practical Short Circuit Calculation Model”(521820200097)of Jiangxi Electric Power Company.
文摘During faults in a distribution network,the output power of a distributed generation(DG)may be uncertain.Moreover,the output currents of distributed power sources are also affected by the output power,resulting in uncertainties in the calculation of the short-circuit current at the time of a fault.Additionally,the impacts of such uncertainties around short-circuit currents will increase with the increase of distributed power sources.Thus,it is very important to develop a method for calculating the short-circuit current while considering the uncertainties in a distribution network.In this study,an affine arithmetic algorithm for calculating short-circuit current intervals in distribution networks with distributed power sources while considering power fluctuations is presented.The proposed algorithm includes two stages.In the first stage,normal operations are considered to establish a conservative interval affine optimization model of injection currents in distributed power sources.Constrained by the fluctuation range of distributed generation power at the moment of fault occurrence,the model can then be used to solve for the fluctuation range of injected current amplitudes in distributed power sources.The second stage is implemented after a malfunction occurs.In this stage,an affine optimization model is first established.This model is developed to characterizes the short-circuit current interval of a transmission line,and is constrained by the fluctuation range of the injected current amplitude of DG during normal operations.Finally,the range of the short-circuit current amplitudes of distribution network lines after a short-circuit fault occurs is predicted.The algorithm proposed in this article obtains an interval range containing accurate results through interval operation.Compared with traditional point value calculation methods,interval calculation methods can provide more reliable analysis and calculation results.The range of short-circuit current amplitude obtained by this algorithm is slightly larger than those obtained using the Monte Carlo algorithm and the Latin hypercube sampling algorithm.Therefore,the proposed algorithm has good suitability and does not require iterative calculations,resulting in a significant improvement in computational speed compared to the Monte Carlo algorithm and the Latin hypercube sampling algorithm.Furthermore,the proposed algorithm can provide more reliable analysis and calculation results,improving the safety and stability of power systems.
基金Project(51509081)supported by the National Natural Science Foundation of ChinaProject(B12032)supported by the “111 Project” of ChinaProjects(BK20150037,BK20150811)supported by the Natural Science Foundation of Jiangsu Province,China
文摘The jacket structure has become more popular as the offshore wind-turbine support structure. K-type and inverted-K-type jacket support structures have superior potential due to their fewer joints and lower cost of manufacture and installation. A numerical study was presented on the dynamic responses of K-type and inverted-K-type jacket support structures subjected to different kinds of dynamic load. The results show that the inverted-K-type jacket structure has higher natural frequencies than the K-type. The wave force spectrum response shows that the maximum displacement of the K-type jacket structure is larger than that of the inverted-K-type. The time-history responses under wind and wave-current load indicate that the inverted-K-type jacket structure shows smaller displacement and stress compared with the K-type, and presents different stress concentration phenomena. The dynamic responses reveal that the inverted-K-type of jacket support structure has greater stiffness and superior mechanical properties, and thus is more applicable in the offshore area with relatively deep water.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.1137418 and 11104163)the Science Foundation of Three Gorges University,China(Grant No.KJ2011B019)
文摘In this paper, the output quantum correlations of three fields interacting with inverted Y-type atoms inside a three-mode cavity are investigated. By numerically calculating the stationary noise spectra of the fields, we show that it is possible to generate the genuine tripartite continuous variable entanglement outside the cavity by coherently preparing the atoms in a superposition of the upper excited state and two ground states initially. Our numerical results demonstrate that both zero frequency entanglement and sideband frequency entanglement can be obtained under different initial coherent conditions. In addition, we investigate the thermal fluctuation effects on the quantum entanglement. It is found out that the entanglement occurring in a high frequency regime is more robust against thermal noise than the zero frequency entanglement, which may be useful for quantum communication.
基金supported by the National Basic Research Program of China (Grant No. 2009CB421401)the National Natural Science Foundation of China (Grant No. 40930951)
文摘This paper studies a heavy snowfall in Beijing that took place on 1 November 2009. The date of the snowfall was about one month earlier than the average. The National Centers for Environmental Prediction (NCEP) reanalysis data, conventional data, and Automatic Weather Station (AWS) data are utilized to explore the reasons for the snowfall and the influencing systems. The main conclusions are as follows: (1) It is revealed from the average geopotential height and average temperature fields at 500 hPa that the large scale circulation in November 2009 was favorable to snowfall. The cold-dry air from West Siberia and the warm-moist air from the Bay of Bengal converged in North China. In addition, it was found from the average moisture flux field at 700 hPa that the main water vapor source was in the Bay of Bengal. (2) Not only the "return current", as usually accepted, but also the inverted trough on the current had an important contribution to the snowfall. The inverted trough could produce the obvious upward motion that is an important environmental condition of snowfalls. (3) More attention should be paid to mesoscale systems such as mesolows during the cold season because of their importance, though they do not occur as frequently as in the warm season. It should be pointed out that AWS data are very useful in mesoscale system analysis during both warm and cold seasons.
