Stagnating yield and declining input use efficiency in irrigated wheat of the Indo-Gangetic Plain (IGP) coupled with diminishing availability of water for agriculture is a major concern of food security in South Asia....Stagnating yield and declining input use efficiency in irrigated wheat of the Indo-Gangetic Plain (IGP) coupled with diminishing availability of water for agriculture is a major concern of food security in South Asia. The objective of our study was to establish an understanding of how wheat yield and input use efficiency can be improved and how land leveling and crop establishment practices can be modified to be more efficient in water use through layering of precision-conservation crop management techniques. The “precision land leveling with raised bed” planting can be used to improve crop yield, water and nutrient use efficiency over the existing “traditional land leveling with flat” planting practices. We conducted a field experiment during 2002-2004 at Modipuram, India to quantify the benefits of alternate land leveling (precision land leveling) and crop establishment (furrow irrigated raised bed planting) techniques alone or in combination (layering precision-conservation) in terms of crop yield, water savings, and nutrient use efficiency of wheat production in IGP. The wheat yield was about 16.6% higher with nearly 50% less irrigation water with layering precision land leveling and raised bed planting compared to traditional practices (traditional land leveling with flat planting). The agronomic (AE) and uptake efficiency (UE) of N, P and K were significantly improved under precision land leveling with raised bed planting technique compared to other practices.展开更多
针对如何减少三电平LCL并网逆变器电能损耗的问题,提出一种基于事件触发条件的有限控制集模型预测控制(finite control set-model predictive control,FCS-MPC)策略。首先,建立三电平LCL型并网逆变器并网电流预测模型。然后,根据控制目...针对如何减少三电平LCL并网逆变器电能损耗的问题,提出一种基于事件触发条件的有限控制集模型预测控制(finite control set-model predictive control,FCS-MPC)策略。首先,建立三电平LCL型并网逆变器并网电流预测模型。然后,根据控制目标构造FCS-MPC代价函数,并且根据系统的输入-状态稳定原理和事件触发控制的思想设计并网电流误差的事件触发条件和阈值,以减少逆变器稳定运行时的冗余开关操作,提高能量变换效率。MATLAB/Simulink仿真实验与硬件在环实验结果表明,所提出的控制策略能够保证并网逆变器稳定工作时输出电流质量前提下有效降低开关频率,设计的硬件在环实验系统可以被应用于电气工程及其自动化专业学生课堂与实验教学。展开更多
Environmentally Extended Input-Output(EEIO)tables have become a powerful element in supporting information-based environmental and economic policies.National-and provincial-level 10 tables are currently published by t...Environmentally Extended Input-Output(EEIO)tables have become a powerful element in supporting information-based environmental and economic policies.National-and provincial-level 10 tables are currently published by the National Bureau of Statistics of the People's Republic of China according to well-defined conventions.However,county-level 10tables are not provided as a rule by official statistics organizations.This paper conducts an overview of compiling EEIO tables for environmental and resources accounting at the county level and then answers several questions:First,what kind of data should be prepared for the compilation of county-level EEIO tables?Second,how can we set up comprehensive EEIO tables at the county level?Third,regarding the survey methods and the indirect modeling,which one should be chosen to build EEIO tables at the county level?Finally,what policy questions could such a table answer?EEIO tables at the county level can be used to predict the economic impacts of environmental policies and to perform trend and scenario analysis.展开更多
新能源中压直流汇集系统中的DC/DC变换器需要具备较大容量,而高频DC/DC变换器容量很难做大,因此需要多个模块并联,成本较高。此外,光伏发电的端口电压波动性大,通常需要两级变换器进行级联,导致系统效率降低。为此,该文研究一种适用于...新能源中压直流汇集系统中的DC/DC变换器需要具备较大容量,而高频DC/DC变换器容量很难做大,因此需要多个模块并联,成本较高。此外,光伏发电的端口电压波动性大,通常需要两级变换器进行级联,导致系统效率降低。为此,该文研究一种适用于新能源中压直流汇集的大容量宽范围输入DC/DC变换器,提出的高中频混频调制方法使得电流波形近似呈断续的梯形波,可显著减小开关器件的电流应力,还使得变压器工作在500Hz的中频,从而更易于设计和制造出较大的容量。此外,变换器的输入电压范围可接近两倍,因此对于大型光伏电站可直接将其连接至光伏阵列,只用一级变换器即可实现最大功率点跟踪(maximum power point tracking,MPPT)和升压功能,系统损耗得到减小。该文分析该变换器的工作原理,讨论参数设计,通过PLECS仿真软件进行仿真验证,并搭建300~500V/±3000V、额定功率7.2kW的原理样机进行实验验证。展开更多
文摘Stagnating yield and declining input use efficiency in irrigated wheat of the Indo-Gangetic Plain (IGP) coupled with diminishing availability of water for agriculture is a major concern of food security in South Asia. The objective of our study was to establish an understanding of how wheat yield and input use efficiency can be improved and how land leveling and crop establishment practices can be modified to be more efficient in water use through layering of precision-conservation crop management techniques. The “precision land leveling with raised bed” planting can be used to improve crop yield, water and nutrient use efficiency over the existing “traditional land leveling with flat” planting practices. We conducted a field experiment during 2002-2004 at Modipuram, India to quantify the benefits of alternate land leveling (precision land leveling) and crop establishment (furrow irrigated raised bed planting) techniques alone or in combination (layering precision-conservation) in terms of crop yield, water savings, and nutrient use efficiency of wheat production in IGP. The wheat yield was about 16.6% higher with nearly 50% less irrigation water with layering precision land leveling and raised bed planting compared to traditional practices (traditional land leveling with flat planting). The agronomic (AE) and uptake efficiency (UE) of N, P and K were significantly improved under precision land leveling with raised bed planting technique compared to other practices.
文摘针对如何减少三电平LCL并网逆变器电能损耗的问题,提出一种基于事件触发条件的有限控制集模型预测控制(finite control set-model predictive control,FCS-MPC)策略。首先,建立三电平LCL型并网逆变器并网电流预测模型。然后,根据控制目标构造FCS-MPC代价函数,并且根据系统的输入-状态稳定原理和事件触发控制的思想设计并网电流误差的事件触发条件和阈值,以减少逆变器稳定运行时的冗余开关操作,提高能量变换效率。MATLAB/Simulink仿真实验与硬件在环实验结果表明,所提出的控制策略能够保证并网逆变器稳定工作时输出电流质量前提下有效降低开关频率,设计的硬件在环实验系统可以被应用于电气工程及其自动化专业学生课堂与实验教学。
基金supported by the Key Project of the Chinese Academy of Sciences[grant number KZZD-EW-08]the Exploratory Forefront Project for the Strategic Science Plan in IGSNRR,CAS
文摘Environmentally Extended Input-Output(EEIO)tables have become a powerful element in supporting information-based environmental and economic policies.National-and provincial-level 10 tables are currently published by the National Bureau of Statistics of the People's Republic of China according to well-defined conventions.However,county-level 10tables are not provided as a rule by official statistics organizations.This paper conducts an overview of compiling EEIO tables for environmental and resources accounting at the county level and then answers several questions:First,what kind of data should be prepared for the compilation of county-level EEIO tables?Second,how can we set up comprehensive EEIO tables at the county level?Third,regarding the survey methods and the indirect modeling,which one should be chosen to build EEIO tables at the county level?Finally,what policy questions could such a table answer?EEIO tables at the county level can be used to predict the economic impacts of environmental policies and to perform trend and scenario analysis.
文摘新能源中压直流汇集系统中的DC/DC变换器需要具备较大容量,而高频DC/DC变换器容量很难做大,因此需要多个模块并联,成本较高。此外,光伏发电的端口电压波动性大,通常需要两级变换器进行级联,导致系统效率降低。为此,该文研究一种适用于新能源中压直流汇集的大容量宽范围输入DC/DC变换器,提出的高中频混频调制方法使得电流波形近似呈断续的梯形波,可显著减小开关器件的电流应力,还使得变压器工作在500Hz的中频,从而更易于设计和制造出较大的容量。此外,变换器的输入电压范围可接近两倍,因此对于大型光伏电站可直接将其连接至光伏阵列,只用一级变换器即可实现最大功率点跟踪(maximum power point tracking,MPPT)和升压功能,系统损耗得到减小。该文分析该变换器的工作原理,讨论参数设计,通过PLECS仿真软件进行仿真验证,并搭建300~500V/±3000V、额定功率7.2kW的原理样机进行实验验证。
