直流微电网中常常含有恒功率负载(constant power loads,CPLs),其负阻抗特性会降低系统的稳定性,造成直流母线电压波动甚至崩溃。因此,首先建立了直流微电网的小信号模型,使用根轨迹法分析了恒功率负载对系统稳定性的影响;其次提出一种...直流微电网中常常含有恒功率负载(constant power loads,CPLs),其负阻抗特性会降低系统的稳定性,造成直流母线电压波动甚至崩溃。因此,首先建立了直流微电网的小信号模型,使用根轨迹法分析了恒功率负载对系统稳定性的影响;其次提出一种基于混合灵敏度优化的电压控制策略,提升了直流微电网系统的稳定性,并采用改进粒子群优化(particle swarm optimization,PSO)算法对权函数进行了优化,进一步提升了鲁棒控制器的性能;最后采用Matlab/Simulink仿真算例进行验证,仿真结果表明提出的鲁棒控制器减小了母线电压的波动,有效提升了直流微电网系统的稳定性。展开更多
The Turonian Notom Delta is one of the Ferron fluvial-deltaic wedges deposited in the foreland basins of the Cretaceous Seaway of North America.The wedge is exposed three dimensionally in the Henry Mountains region Ut...The Turonian Notom Delta is one of the Ferron fluvial-deltaic wedges deposited in the foreland basins of the Cretaceous Seaway of North America.The wedge is exposed three dimensionally in the Henry Mountains region Utah,USA.High-resolution sequence stratigraphic analysis along a 35 km dip-oriented outcrop belt shows that the wedge consists of six depositional sequences.Ammonite and Inoceramid biostratigraphy and 40Ar/39Ar age dating of various bentonites show that the wedge was deposited from 91.25 Ma to 90.63 Ma,an interval of merely 0.62 Ma.Assuming each sequence is formed over a similar time span,each sequence,thus,represents about 105 yr,suggesting high-frequency depositional sequences.Amplitude of relative sea-level changes,built on shoreline trajectory,is 2-61 m,with an average of only 20 m.Fluvial incision during high-frequency and low-amplitude relative sealevel fall is mainly around the highstand prism.Incision diminishes rapidly up dip and down dip,and the resultant incised valleys are narrow and shallow.Such sea-level fluctuations also result in small,stratigraphically complex shoreline sandstones that need special attention during hydrocarbon exploration.展开更多
MODTRAN model was used for the atmospheric correction of one HJ-1B / CCD2 image,and the effect of atmospheric correction was evaluated from the changes of spectral characteristics of typical ground objects,the compari...MODTRAN model was used for the atmospheric correction of one HJ-1B / CCD2 image,and the effect of atmospheric correction was evaluated from the changes of spectral characteristics of typical ground objects,the comparison with the MODIS surface reflectance product,and the effect on normalized differential vegetation index( NDVI). The results show that atmospheric correction eliminated the increase effect in visible bands and the absorption in near-infrared band. Atmospheric correction results and the MODIS surface reflectance product with high accuracy were highly consistent in the reflectance of vegetation,water and residents,and the average error of vegetation was 12.8%. According to the comparison of changing characteristics of NDVI before and after atmospheric correction,it could be found that atmospheric correction had corrected NDVI of mixed pixels and made it more reasonable. NDVI of each kind of ground objects improved,among which NDVI of vegetation increased most greatly,which can help differentiate vegetation from other ground objects. In a word,MODTRAN model has a good effect on atmospheric correction of HJ /CCD images.展开更多
文摘直流微电网中常常含有恒功率负载(constant power loads,CPLs),其负阻抗特性会降低系统的稳定性,造成直流母线电压波动甚至崩溃。因此,首先建立了直流微电网的小信号模型,使用根轨迹法分析了恒功率负载对系统稳定性的影响;其次提出一种基于混合灵敏度优化的电压控制策略,提升了直流微电网系统的稳定性,并采用改进粒子群优化(particle swarm optimization,PSO)算法对权函数进行了优化,进一步提升了鲁棒控制器的性能;最后采用Matlab/Simulink仿真算例进行验证,仿真结果表明提出的鲁棒控制器减小了母线电压的波动,有效提升了直流微电网系统的稳定性。
文摘The Turonian Notom Delta is one of the Ferron fluvial-deltaic wedges deposited in the foreland basins of the Cretaceous Seaway of North America.The wedge is exposed three dimensionally in the Henry Mountains region Utah,USA.High-resolution sequence stratigraphic analysis along a 35 km dip-oriented outcrop belt shows that the wedge consists of six depositional sequences.Ammonite and Inoceramid biostratigraphy and 40Ar/39Ar age dating of various bentonites show that the wedge was deposited from 91.25 Ma to 90.63 Ma,an interval of merely 0.62 Ma.Assuming each sequence is formed over a similar time span,each sequence,thus,represents about 105 yr,suggesting high-frequency depositional sequences.Amplitude of relative sea-level changes,built on shoreline trajectory,is 2-61 m,with an average of only 20 m.Fluvial incision during high-frequency and low-amplitude relative sealevel fall is mainly around the highstand prism.Incision diminishes rapidly up dip and down dip,and the resultant incised valleys are narrow and shallow.Such sea-level fluctuations also result in small,stratigraphically complex shoreline sandstones that need special attention during hydrocarbon exploration.
基金Supported by National Natural Science Foundation of China(41171336)
文摘MODTRAN model was used for the atmospheric correction of one HJ-1B / CCD2 image,and the effect of atmospheric correction was evaluated from the changes of spectral characteristics of typical ground objects,the comparison with the MODIS surface reflectance product,and the effect on normalized differential vegetation index( NDVI). The results show that atmospheric correction eliminated the increase effect in visible bands and the absorption in near-infrared band. Atmospheric correction results and the MODIS surface reflectance product with high accuracy were highly consistent in the reflectance of vegetation,water and residents,and the average error of vegetation was 12.8%. According to the comparison of changing characteristics of NDVI before and after atmospheric correction,it could be found that atmospheric correction had corrected NDVI of mixed pixels and made it more reasonable. NDVI of each kind of ground objects improved,among which NDVI of vegetation increased most greatly,which can help differentiate vegetation from other ground objects. In a word,MODTRAN model has a good effect on atmospheric correction of HJ /CCD images.
