针对传统加权平均电流(weighted average current,WAC)控制策略未考虑数字控制延时使系统出现相位滞后而导致系统带宽减小、鲁棒性差的问题,提出了基于准比例谐振控制和超前补偿器结合的WAC控制策略。首先,引入电容电流反馈,抑制反向谐...针对传统加权平均电流(weighted average current,WAC)控制策略未考虑数字控制延时使系统出现相位滞后而导致系统带宽减小、鲁棒性差的问题,提出了基于准比例谐振控制和超前补偿器结合的WAC控制策略。首先,引入电容电流反馈,抑制反向谐振峰;其次,在逆变桥传递函数处串联超前补偿器,提高系统的相位裕度;最后,应用准比例谐振控制器作为电流调节器,提高基频增益、降低系统的静态误差。经仿真验证,所提控制策略对弱电网具有良好的适应能力,并网电流谐波畸变率从1.84%降低到0.26%,增强了系统的鲁棒性、改善了并网电流的质量。展开更多
Aeolian processes have been studied extensively at low elevations,but have been relatively little studied at high elevations.Aeolian sediments are widely distributed in the Yarlung Zangbo River basin,southern Tibetan ...Aeolian processes have been studied extensively at low elevations,but have been relatively little studied at high elevations.Aeolian sediments are widely distributed in the Yarlung Zangbo River basin,southern Tibetan Plateau,which is characterized by low pressure and low temperature.Here,we comprehensively analyzed the wind regime using data since 1980 from 11 meteorological stations in the study area,and examined the interaction between the near-surface wind and aeolian environment.The wind environment exhibited significant spatial and temporal variation,and mean wind speed has generally decreased on both annual and seasonal bases since 1980,at an average of 0.181 m/(s•10a).This decrease resulted from the reduced contribution of maximum wind speed,and depended strongly on variations of the frequency of sand-driving winds.The drift potential and related parameters also showed obvious spatial and temporal variation,with similar driving forces for the wind environment.The strength of the wind regime affected the formation and development of the aeolian geomorphological pattern,but with variation caused by local topography and sediment sources.The drift potential and resultant drift direction were two key parameters,as they quantify the dynamic conditions and depositional orientation of the aeolian sediments.Wind affected the spatial variation in sediment grain size,but the source material and complex topographic effects on the near-surface wind were the underlying causes for the grain size distribution of aeolian sands.These results will support efforts to control aeolian desertification in the basin and improve our understanding of aeolian processes in high-elevation environments.展开更多
Coastal dune is a common aeolian geomorphology in a sandy coast,which records the evolution process of the aeolian landscape system and reflects the complex interaction among land surface,atmosphere and ocean.Coast is...Coastal dune is a common aeolian geomorphology in a sandy coast,which records the evolution process of the aeolian landscape system and reflects the complex interaction among land surface,atmosphere and ocean.Coast is a sensitive area to global climate change.Restricted by chronology,most previous researches in China focused only on the cause of formation of coastal dunes.In recent years,the development of optically stimulated luminescence （OSL） dating provides a good method and acts as a carrier for coastal dunes to paleoclimate and paleoenvironmental studies.In this study,we selected an aeolian dune at the Anshan archaeological site,Fujian,China as the research object based on field observations.For determining their sedimentary stages and the primary influencing factors,we used the OSL dating method to construct a chronological framework for the aeolian dune.In addition,the sizes of grains were analyzed for identifying factors influencing the winter monsoon during the Medieval Warm Period （MWP） and the Little Ice Age （LIA） in this area.The results showed that the deposition of the aeolian dune was closely related to variations in the winter monsoon intensity.The changes of the winter monsoon were similar to the tendency of the East Asian winter monsoon,although there were several sub-fluctuations.From an overall perspective,the winter monsoon was strengthened during the MWP （1050–1300） .The results of a power spectrum analysis showed that the intensity of the East Asian winter monsoon is correlated with sunspot activity.展开更多
雅江流域风成沉积广泛发育,其气候指示意义及年代的界定尚不够清晰。从雅江全流域视角出发,全面分析了不同区域风成沉积的发育机制及模式,同时对风成沉积年代数据归一化处理,并与全球气候对比研究。结果表明:①流域内风成沉积有盛行风...雅江流域风成沉积广泛发育,其气候指示意义及年代的界定尚不够清晰。从雅江全流域视角出发,全面分析了不同区域风成沉积的发育机制及模式,同时对风成沉积年代数据归一化处理,并与全球气候对比研究。结果表明:①流域内风成沉积有盛行风场发育模式和局地风场发育模式,不同模式对环境的指示意义不同。②雅江流域风成沉积多堆积于末次盛冰期(LGM)以后,且主要发育于晚冰期(15 ka BP)以来的不同时段,冰川退缩地表裸露,丰富的冲洪积碎屑物源可能是风成沉积发育的主控因素;更早时段的风成沉积因LGM后气候转暖、冰川消融所致的侵蚀搬运作用而未能保存。③LGM以来风成沉积过程受区域及全球古气候环境共同控制,波动变化剧烈;其对30°N夏季太阳辐射、印度季风及西风变化信号的指示有所差异,但对YD等全球气候冷事件有较好记录,其沉积过程与高原面上其他区域既存在对全球古气候响应的同步性,又有其区域独特性。④流域内风成沉积的强烈堆积过程与全球气候变化并非简单对应关系,呈现出较复杂的响应模式。说明高山河谷环境的风成沉积除受大区域气候影响,还受许多局地环境因素控制,古气候环境的指示意义复杂。展开更多
文摘针对传统加权平均电流(weighted average current,WAC)控制策略未考虑数字控制延时使系统出现相位滞后而导致系统带宽减小、鲁棒性差的问题,提出了基于准比例谐振控制和超前补偿器结合的WAC控制策略。首先,引入电容电流反馈,抑制反向谐振峰;其次,在逆变桥传递函数处串联超前补偿器,提高系统的相位裕度;最后,应用准比例谐振控制器作为电流调节器,提高基频增益、降低系统的静态误差。经仿真验证,所提控制策略对弱电网具有良好的适应能力,并网电流谐波畸变率从1.84%降低到0.26%,增强了系统的鲁棒性、改善了并网电流的质量。
基金the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)(2019QZKK0602)the Open Foundation of MOE Key Laboratory of Western China's Environmental System,Lanzhou University and the Fundamental Research Funds for the Central Universities(lzujbky-2020-kb01)。
文摘Aeolian processes have been studied extensively at low elevations,but have been relatively little studied at high elevations.Aeolian sediments are widely distributed in the Yarlung Zangbo River basin,southern Tibetan Plateau,which is characterized by low pressure and low temperature.Here,we comprehensively analyzed the wind regime using data since 1980 from 11 meteorological stations in the study area,and examined the interaction between the near-surface wind and aeolian environment.The wind environment exhibited significant spatial and temporal variation,and mean wind speed has generally decreased on both annual and seasonal bases since 1980,at an average of 0.181 m/(s•10a).This decrease resulted from the reduced contribution of maximum wind speed,and depended strongly on variations of the frequency of sand-driving winds.The drift potential and related parameters also showed obvious spatial and temporal variation,with similar driving forces for the wind environment.The strength of the wind regime affected the formation and development of the aeolian geomorphological pattern,but with variation caused by local topography and sediment sources.The drift potential and resultant drift direction were two key parameters,as they quantify the dynamic conditions and depositional orientation of the aeolian sediments.Wind affected the spatial variation in sediment grain size,but the source material and complex topographic effects on the near-surface wind were the underlying causes for the grain size distribution of aeolian sands.These results will support efforts to control aeolian desertification in the basin and improve our understanding of aeolian processes in high-elevation environments.
基金financially supported by the National Natural Science Foundation of China (41301012,41271031,U1405231)the Natural Science Foundation of Fujian Province (2013J01153)
文摘Coastal dune is a common aeolian geomorphology in a sandy coast,which records the evolution process of the aeolian landscape system and reflects the complex interaction among land surface,atmosphere and ocean.Coast is a sensitive area to global climate change.Restricted by chronology,most previous researches in China focused only on the cause of formation of coastal dunes.In recent years,the development of optically stimulated luminescence （OSL） dating provides a good method and acts as a carrier for coastal dunes to paleoclimate and paleoenvironmental studies.In this study,we selected an aeolian dune at the Anshan archaeological site,Fujian,China as the research object based on field observations.For determining their sedimentary stages and the primary influencing factors,we used the OSL dating method to construct a chronological framework for the aeolian dune.In addition,the sizes of grains were analyzed for identifying factors influencing the winter monsoon during the Medieval Warm Period （MWP） and the Little Ice Age （LIA） in this area.The results showed that the deposition of the aeolian dune was closely related to variations in the winter monsoon intensity.The changes of the winter monsoon were similar to the tendency of the East Asian winter monsoon,although there were several sub-fluctuations.From an overall perspective,the winter monsoon was strengthened during the MWP （1050–1300） .The results of a power spectrum analysis showed that the intensity of the East Asian winter monsoon is correlated with sunspot activity.
文摘雅江流域风成沉积广泛发育,其气候指示意义及年代的界定尚不够清晰。从雅江全流域视角出发,全面分析了不同区域风成沉积的发育机制及模式,同时对风成沉积年代数据归一化处理,并与全球气候对比研究。结果表明:①流域内风成沉积有盛行风场发育模式和局地风场发育模式,不同模式对环境的指示意义不同。②雅江流域风成沉积多堆积于末次盛冰期(LGM)以后,且主要发育于晚冰期(15 ka BP)以来的不同时段,冰川退缩地表裸露,丰富的冲洪积碎屑物源可能是风成沉积发育的主控因素;更早时段的风成沉积因LGM后气候转暖、冰川消融所致的侵蚀搬运作用而未能保存。③LGM以来风成沉积过程受区域及全球古气候环境共同控制,波动变化剧烈;其对30°N夏季太阳辐射、印度季风及西风变化信号的指示有所差异,但对YD等全球气候冷事件有较好记录,其沉积过程与高原面上其他区域既存在对全球古气候响应的同步性,又有其区域独特性。④流域内风成沉积的强烈堆积过程与全球气候变化并非简单对应关系,呈现出较复杂的响应模式。说明高山河谷环境的风成沉积除受大区域气候影响,还受许多局地环境因素控制,古气候环境的指示意义复杂。
