Line parameters play an important role in the control and management of distribution systems.Currently,phasor measurement unit(PMU)systems and supervisory control and data acquisition(SCADA)systems coexist in distribu...Line parameters play an important role in the control and management of distribution systems.Currently,phasor measurement unit(PMU)systems and supervisory control and data acquisition(SCADA)systems coexist in distribution systems.Unfortunately,SCADA and PMU measurements usually do not match each other,resulting in inaccurate detection and identification of line parameters based on measurements.To solve this problem,a data-driven method is proposed.SCADA measurements are taken as samples and PMU measurements as the population.A probability parameter identification index(PPII)is derived to detect the whole line parameter based on the probability density function(PDF)parameters of the measurements.For parameter identification,a power-loss PDF with the PMU time stamps and a power-loss chronological PDF are derived via kernel density estimation(KDE)and a conditional PDF.Then,the power-loss samples with the PMU time stamps and chronological correlations are generated by the two PDFs of the power loss via the Metropolis-Hastings(MH)algorithm.Finally,using the power-loss samples and PMU current measurements,the line parameters are identified using the total least squares(TLS)algorithm.Hardware simulations demonstrate the effectiveness of the proposed method for distribution network line parameter detection and identification.展开更多
Phasor measurement units(PMUs)provide useful data for real-time monitoring of the smart grid.However,there may be time-varying deviation in phase angle differences(PADs)between both ends of the transmission line(TL),w...Phasor measurement units(PMUs)provide useful data for real-time monitoring of the smart grid.However,there may be time-varying deviation in phase angle differences(PADs)between both ends of the transmission line(TL),which may deteriorate application performance based on PMUs.To address that,this paper proposes two robust methods of correcting time-varying PAD deviation with unknown parameters of TL(ParTL).First,the phenomena of time-varying PAD deviation observed from field PMU data are presented.Two general formulations for PAD estimation are then established.To simplify the formulations,estimation of PADs is converted into the optimal problem with a single ParTL as the variable,yielding a linear estimation of PADs.The latter is used by second-order Taylor series expansion to estimate PADs accurately.To reduce the impact of possible abnormal amplitude data in field data,the IGG(Institute of Geodesy&Geophysics,Chinese Academy of Sciences)weighting function is adopted.Results using both simulated and field data verify the effectiveness and robustness of the proposed methods.展开更多
利用实况资料和再分析资料,结合WRF(weather research and forecasting)模式对南通一次极端大风过程进行诊断分析及数值模拟。分析了该个例发生的天气形势背景和系统的水平、垂直结构,探究大风天气成因,并进一步对比不同参数化方案的模...利用实况资料和再分析资料,结合WRF(weather research and forecasting)模式对南通一次极端大风过程进行诊断分析及数值模拟。分析了该个例发生的天气形势背景和系统的水平、垂直结构,探究大风天气成因,并进一步对比不同参数化方案的模拟效果。结果表明:1)大风过程发生在高空深厚冷涡和地面强暖湿低压的环流背景下,上空存在不稳定层结和不稳定能量的累积;雷暴大风在12—13时经历了发展、成熟、消散3个阶段,飑线以碎块型的方式形成。2)3种微物理方案中,MG方案模拟出更大面积的层云、强回波和极端大风,模拟的最大地面阵风为44.47 m·s^(-1)。Lin方案较好地模拟出飑线的演变过程和垂直结构特征,模拟的最强上升气流达23.55 m·s^(-1),下沉气流达-13.21 m·s^(-1)。3)水平方向上,雷暴大风附近存在成熟的飑线地面中尺度系统,地面存在深厚冷池出流、变压梯度大值区和冷锋过境,它们共同促进了地面大风的生成。4)垂直方向上,对流单体上空高层辐散、低层辐合,存在强上升气流和水汽潜热释放;后侧的干空气蒸发和粒子的拖曳加强下沉运动,配合地面冷池出流和辐散气流,造成了极端大风天气。展开更多
The paper deals with the tests on the first 500 kV compact transmission line. The transmission line stretches from Fangshan Substation to Changping Substation nearby Beijing with a length of 83 km. In order to investi...The paper deals with the tests on the first 500 kV compact transmission line. The transmission line stretches from Fangshan Substation to Changping Substation nearby Beijing with a length of 83 km. In order to investigate the characteristics of the transmission line, many tests were performed on the line before and after its operation. The results indicate that all electrical parameters are perfectly identical to the design.展开更多
We present an exercise that intends to establish a relationship between the strength of nebular emission lines and optical stellar features in the spectrum of a galaxy. After accurately subtracting the stellar continu...We present an exercise that intends to establish a relationship between the strength of nebular emission lines and optical stellar features in the spectrum of a galaxy. After accurately subtracting the stellar continuum and the underlying stellar absorption, we made reliable measurements of the emission lines of all the galaxies in the Sloan Digital Sky Survey Data Release 2 (SDSS DR2). More than 4000 star-forming galaxies with high S/N ratio of both the stellar spectrum and the emission lines are selected. These galaxy spectra are fitted with the 10 PCs of Yip et al., after all the emission line regions have been filtered out. We find that the flux of hydrogen Balmer emission lines, Ha and Hβ can be well recovered from the PCs, while the metal lines are not well reproduced. The fluxes of Ha and Hβ measured from the PC-reconstructed spectra and from the observed spectra agree well with an rms scatter of only - 0.1 dex. This result suggests that, with moderate spectral resolution and S/N ratio, the optical stellar spectrum of a galaxy can serve as an indicator of star formation rate.展开更多
基金supported by the National Key Research and Development Program under Grant 2017YFB0902900 and Grant 2017YFB0902902。
文摘Line parameters play an important role in the control and management of distribution systems.Currently,phasor measurement unit(PMU)systems and supervisory control and data acquisition(SCADA)systems coexist in distribution systems.Unfortunately,SCADA and PMU measurements usually do not match each other,resulting in inaccurate detection and identification of line parameters based on measurements.To solve this problem,a data-driven method is proposed.SCADA measurements are taken as samples and PMU measurements as the population.A probability parameter identification index(PPII)is derived to detect the whole line parameter based on the probability density function(PDF)parameters of the measurements.For parameter identification,a power-loss PDF with the PMU time stamps and a power-loss chronological PDF are derived via kernel density estimation(KDE)and a conditional PDF.Then,the power-loss samples with the PMU time stamps and chronological correlations are generated by the two PDFs of the power loss via the Metropolis-Hastings(MH)algorithm.Finally,using the power-loss samples and PMU current measurements,the line parameters are identified using the total least squares(TLS)algorithm.Hardware simulations demonstrate the effectiveness of the proposed method for distribution network line parameter detection and identification.
基金This work was supported by the National Key Research and Development Program of China(2017YFB0902901)National Natural Science Foundation of China(51627811).
文摘Phasor measurement units(PMUs)provide useful data for real-time monitoring of the smart grid.However,there may be time-varying deviation in phase angle differences(PADs)between both ends of the transmission line(TL),which may deteriorate application performance based on PMUs.To address that,this paper proposes two robust methods of correcting time-varying PAD deviation with unknown parameters of TL(ParTL).First,the phenomena of time-varying PAD deviation observed from field PMU data are presented.Two general formulations for PAD estimation are then established.To simplify the formulations,estimation of PADs is converted into the optimal problem with a single ParTL as the variable,yielding a linear estimation of PADs.The latter is used by second-order Taylor series expansion to estimate PADs accurately.To reduce the impact of possible abnormal amplitude data in field data,the IGG(Institute of Geodesy&Geophysics,Chinese Academy of Sciences)weighting function is adopted.Results using both simulated and field data verify the effectiveness and robustness of the proposed methods.
文摘利用实况资料和再分析资料,结合WRF(weather research and forecasting)模式对南通一次极端大风过程进行诊断分析及数值模拟。分析了该个例发生的天气形势背景和系统的水平、垂直结构,探究大风天气成因,并进一步对比不同参数化方案的模拟效果。结果表明:1)大风过程发生在高空深厚冷涡和地面强暖湿低压的环流背景下,上空存在不稳定层结和不稳定能量的累积;雷暴大风在12—13时经历了发展、成熟、消散3个阶段,飑线以碎块型的方式形成。2)3种微物理方案中,MG方案模拟出更大面积的层云、强回波和极端大风,模拟的最大地面阵风为44.47 m·s^(-1)。Lin方案较好地模拟出飑线的演变过程和垂直结构特征,模拟的最强上升气流达23.55 m·s^(-1),下沉气流达-13.21 m·s^(-1)。3)水平方向上,雷暴大风附近存在成熟的飑线地面中尺度系统,地面存在深厚冷池出流、变压梯度大值区和冷锋过境,它们共同促进了地面大风的生成。4)垂直方向上,对流单体上空高层辐散、低层辐合,存在强上升气流和水汽潜热释放;后侧的干空气蒸发和粒子的拖曳加强下沉运动,配合地面冷池出流和辐散气流,造成了极端大风天气。
文摘The paper deals with the tests on the first 500 kV compact transmission line. The transmission line stretches from Fangshan Substation to Changping Substation nearby Beijing with a length of 83 km. In order to investigate the characteristics of the transmission line, many tests were performed on the line before and after its operation. The results indicate that all electrical parameters are perfectly identical to the design.
基金Supported by the National Natural Science Foundation of China.
文摘We present an exercise that intends to establish a relationship between the strength of nebular emission lines and optical stellar features in the spectrum of a galaxy. After accurately subtracting the stellar continuum and the underlying stellar absorption, we made reliable measurements of the emission lines of all the galaxies in the Sloan Digital Sky Survey Data Release 2 (SDSS DR2). More than 4000 star-forming galaxies with high S/N ratio of both the stellar spectrum and the emission lines are selected. These galaxy spectra are fitted with the 10 PCs of Yip et al., after all the emission line regions have been filtered out. We find that the flux of hydrogen Balmer emission lines, Ha and Hβ can be well recovered from the PCs, while the metal lines are not well reproduced. The fluxes of Ha and Hβ measured from the PC-reconstructed spectra and from the observed spectra agree well with an rms scatter of only - 0.1 dex. This result suggests that, with moderate spectral resolution and S/N ratio, the optical stellar spectrum of a galaxy can serve as an indicator of star formation rate.
