The existing power management schemes for interlinked AC-DC microgrids have several operational drawbacks.Some of the existing control schemes are designed with the main objective of sharing power among the interlinke...The existing power management schemes for interlinked AC-DC microgrids have several operational drawbacks.Some of the existing control schemes are designed with the main objective of sharing power among the interlinked microgrids based on their loading conditions,while other schemes regulate the voltage of the interlinked microgrids without considering the specific loading conditions.However,the existing schemes cannot achieve both objectives efficiently.To address these issues,an autonomous power management scheme is proposed,which explicitly considers the specific loading condition of the DC microgrid before importing power from the interlinked AC microgrid.This strategy enables voltage regulation in the DC microgrid,and also reduces the number of converters in operation.The proposed scheme is fully autonomous while it retains the plug-nplay features for generators and tie-converters.The performance of the proposed control scheme has been validated under different operating scenarios.The results demonstrate the effectiveness of the proposed scheme in managing the power deficit in the DC microgrid efficiently and autonomously while maintaining the better voltage regulation in the DC microgrid.展开更多
In May 1983,the governor of Hebei province,Zhang Shuguang,and the governor of the US state of Iowa,Terry Branstad,signed an agreemen t to establish friendly relations between the two areas in the state capital,Des Moi...In May 1983,the governor of Hebei province,Zhang Shuguang,and the governor of the US state of Iowa,Terry Branstad,signed an agreemen t to establish friendly relations between the two areas in the state capital,Des Moines.Two years later,in May 1985,Xi Jinping,secretary of the Zhengding County Committee of the Communist Party of China in Hebei.展开更多
Bidirectional interlinking converter(BIC)is the core equipment in a hybrid AC/DC microgrid connected between AC and DC sub-grids.However,the variety of control modes and flexible bidirectional power flow complicate th...Bidirectional interlinking converter(BIC)is the core equipment in a hybrid AC/DC microgrid connected between AC and DC sub-grids.However,the variety of control modes and flexible bidirectional power flow complicate the influence of AC faults on BIC itself and on DC sub-grid,which potentially threaten both converter safety and system reliability.This study first investigates AC fault influence on the BIC and DC bus voltage under different BIC control modes and different pre-fault operation states,by developing a mathematical model and equivalent sequence network.Second,based on the analysis results,a general accommodative current limiting strategy is proposed for BIC without limitations to specific mode or operation condition.Current amplitude is predicted and constrained according to the critical requirements to protect the BIC and relieving the AC fault influence on the DC bus voltage.Compared with conventional methods,potential current limit failure and distortions under asymmetric faults can also be avoided.Finally,experiments verify feasibility of the proposed method.展开更多
Linked Data is known as one of the best solutions for multisource and heterogeneous web data integration and discovery in this era of Big Data.However,data interlinking,which is the most valuable contribution of Linke...Linked Data is known as one of the best solutions for multisource and heterogeneous web data integration and discovery in this era of Big Data.However,data interlinking,which is the most valuable contribution of Linked Data,remains incomplete and inaccurate.This study proposes a multidimensional and quantitative interlinking approach for Linked Data in the geospatial domain.According to the characteristics and roles of geospatial data in data discovery,eight elementary data characteristics are adopted as data interlinking types.These elementary characteristics are further combined to form compound and overall data interlinking types.Each data interlinking type possesses one specific predicate to indicate the actual relationship of Linked Data and uses data similarity to represent the correlation degree quantitatively.Therefore,geospatial data interlinking can be expressed by a directed edge associated with a relation predicate and a similarity value.The approach transforms existing simple and qualitative geospatial data interlinking into complete and quantitative interlinking and promotes the establishment of high-quality and trusted Linked Geospatial Data.The approach is applied to build data intra-links in the Chinese National Earth System Scientific Data Sharing Network(NSTI-GEO)and data-links in NSTI-GEO with the Chinese Meteorological Data Network and National Population and Health Scientific Data Sharing Platform.展开更多
Better flexibility and controllability have been introduced into distribution system with the development of new loads and resources.As a consequence,the connotations and tools for evaluating the planning solution nee...Better flexibility and controllability have been introduced into distribution system with the development of new loads and resources.As a consequence,the connotations and tools for evaluating the planning solution need to be further enriched.This paper proposes a fast algorithm to quantify steady-state voltages and load profiles in distribution system by simulating the manipulation control process of controllable resources,taking the efficiency and ease of use into account.In this method,a complex distribution system is decoupled into several simple parts according to the ports of the DC interlink.Then,to achieve the qualified voltages and load profiles,the manipulation details of controllable resources are simulated following a certain control sequence in each part.Finally,the analysis results of each part are matched and filtered to obtain a complete evaluation.Five types of the most commonly controllable resources are considered in this method.The effectiveness of the proposed method is demonstrated through a case study based on field data from an actual distribution system.展开更多
A bipolar hybrid microgrid is a new topology which benefits from the advantages of both alternating current(AC)and direct current(DC)microgrids.Interlinking AC/DC converter is the key of this topology which has the fo...A bipolar hybrid microgrid is a new topology which benefits from the advantages of both alternating current(AC)and direct current(DC)microgrids.Interlinking AC/DC converter is the key of this topology which has the following characteristics:being able to provide two equal pole voltages in DC side;complying with the standards of current quality at AC side;being able to control active and reactive power independently in AC side,and transmitting bidirectional power.In this paper,two categories of power converters including single-stage and two-stage converters are proposed for this topology.A new cost-effective control strategy is added to the control of general grid-connected converter for each interlinking converter,and the control of autonomous DC-link pole voltage for both candidates is achieved.Detailed simulations based on the designed control strategies are conducted to validate the function of control strategies under the operation conditions of different DC sides.The performances of two selected interlinking converters with balanced and unbalanced DC loads are analyzed.Suggested power quality of microgrid and total harmonic distortion(THD)analysis are demonstrated in grid-tied and islanded modes.Eventually,semiconductor power loss simulations based on a closed-loop thermal network simulation are conducted.Thereby,the mutual effects of power loss and initial junction temperature are investigated.展开更多
In the eld of satellite constellations,an important requirement is often represented by the possibility to exchange data among the satellites or exploit mutual visibility to carry out measurements on the parameters of...In the eld of satellite constellations,an important requirement is often represented by the possibility to exchange data among the satellites or exploit mutual visibility to carry out measurements on the parameters of the Earth's atmosphere.Therefore,recursive and routing algorithms are usually implemented to evaluate inter-satellite visibility intervals.However,to design the con guration of the constellation,it is important to consider the orbital conditions that guarantee the mutual visibility between couples of satellites.Thus,in this study,a geometric analysis was performed to identify the optimal inter-satellite visibility conditions,expressed in terms of the di erence in the true anomaly between satellites characterized by di erent orbital con gurations.This approach allows a handy constellation design,without performing a numerical analysis.It is particularly useful in the case of a high number of satellites,when numerical techniques require signi cant computational e ort.Therefore,it is possible to considerably simplify the design of a constellation in which the mutual visibility between couples of satellites is always guaranteed.This type of constellation,usually referred to as satellite chain,can be exploited in several network services and remote sensing systems devoted to enhancing the knowledge of atmospheric parameters.展开更多
文摘The existing power management schemes for interlinked AC-DC microgrids have several operational drawbacks.Some of the existing control schemes are designed with the main objective of sharing power among the interlinked microgrids based on their loading conditions,while other schemes regulate the voltage of the interlinked microgrids without considering the specific loading conditions.However,the existing schemes cannot achieve both objectives efficiently.To address these issues,an autonomous power management scheme is proposed,which explicitly considers the specific loading condition of the DC microgrid before importing power from the interlinked AC microgrid.This strategy enables voltage regulation in the DC microgrid,and also reduces the number of converters in operation.The proposed scheme is fully autonomous while it retains the plug-nplay features for generators and tie-converters.The performance of the proposed control scheme has been validated under different operating scenarios.The results demonstrate the effectiveness of the proposed scheme in managing the power deficit in the DC microgrid efficiently and autonomously while maintaining the better voltage regulation in the DC microgrid.
文摘In May 1983,the governor of Hebei province,Zhang Shuguang,and the governor of the US state of Iowa,Terry Branstad,signed an agreemen t to establish friendly relations between the two areas in the state capital,Des Moines.Two years later,in May 1985,Xi Jinping,secretary of the Zhengding County Committee of the Communist Party of China in Hebei.
文摘Bidirectional interlinking converter(BIC)is the core equipment in a hybrid AC/DC microgrid connected between AC and DC sub-grids.However,the variety of control modes and flexible bidirectional power flow complicate the influence of AC faults on BIC itself and on DC sub-grid,which potentially threaten both converter safety and system reliability.This study first investigates AC fault influence on the BIC and DC bus voltage under different BIC control modes and different pre-fault operation states,by developing a mathematical model and equivalent sequence network.Second,based on the analysis results,a general accommodative current limiting strategy is proposed for BIC without limitations to specific mode or operation condition.Current amplitude is predicted and constrained according to the critical requirements to protect the BIC and relieving the AC fault influence on the DC bus voltage.Compared with conventional methods,potential current limit failure and distortions under asymmetric faults can also be avoided.Finally,experiments verify feasibility of the proposed method.
基金Thiswork was supported by the National Natural Science Foundation of China[grant number 41371381],[grant number 41431177]Natural Science Research Program of Jiangsu[grant number 14KJA170001]+4 种基金National Special Program on Basic Works for Science and Technology of China[grant number 2013FY110900]National Key Technology Innovation Project for Water Pollution Control and Remediation[grant number 2013ZX07103006]National Basic Research Program of China[grant number 2015CB954102]GuiZhou Welfare and Basic Geological Research Program of China[grant number 201423]China Scholarship Council[grant number 201504910358].
文摘Linked Data is known as one of the best solutions for multisource and heterogeneous web data integration and discovery in this era of Big Data.However,data interlinking,which is the most valuable contribution of Linked Data,remains incomplete and inaccurate.This study proposes a multidimensional and quantitative interlinking approach for Linked Data in the geospatial domain.According to the characteristics and roles of geospatial data in data discovery,eight elementary data characteristics are adopted as data interlinking types.These elementary characteristics are further combined to form compound and overall data interlinking types.Each data interlinking type possesses one specific predicate to indicate the actual relationship of Linked Data and uses data similarity to represent the correlation degree quantitatively.Therefore,geospatial data interlinking can be expressed by a directed edge associated with a relation predicate and a similarity value.The approach transforms existing simple and qualitative geospatial data interlinking into complete and quantitative interlinking and promotes the establishment of high-quality and trusted Linked Geospatial Data.The approach is applied to build data intra-links in the Chinese National Earth System Scientific Data Sharing Network(NSTI-GEO)and data-links in NSTI-GEO with the Chinese Meteorological Data Network and National Population and Health Scientific Data Sharing Platform.
基金supported by National Key Research and Development Program(No.2017YFB0903300)National Natural Science Foundation of China(No.51777105).
文摘Better flexibility and controllability have been introduced into distribution system with the development of new loads and resources.As a consequence,the connotations and tools for evaluating the planning solution need to be further enriched.This paper proposes a fast algorithm to quantify steady-state voltages and load profiles in distribution system by simulating the manipulation control process of controllable resources,taking the efficiency and ease of use into account.In this method,a complex distribution system is decoupled into several simple parts according to the ports of the DC interlink.Then,to achieve the qualified voltages and load profiles,the manipulation details of controllable resources are simulated following a certain control sequence in each part.Finally,the analysis results of each part are matched and filtered to obtain a complete evaluation.Five types of the most commonly controllable resources are considered in this method.The effectiveness of the proposed method is demonstrated through a case study based on field data from an actual distribution system.
文摘A bipolar hybrid microgrid is a new topology which benefits from the advantages of both alternating current(AC)and direct current(DC)microgrids.Interlinking AC/DC converter is the key of this topology which has the following characteristics:being able to provide two equal pole voltages in DC side;complying with the standards of current quality at AC side;being able to control active and reactive power independently in AC side,and transmitting bidirectional power.In this paper,two categories of power converters including single-stage and two-stage converters are proposed for this topology.A new cost-effective control strategy is added to the control of general grid-connected converter for each interlinking converter,and the control of autonomous DC-link pole voltage for both candidates is achieved.Detailed simulations based on the designed control strategies are conducted to validate the function of control strategies under the operation conditions of different DC sides.The performances of two selected interlinking converters with balanced and unbalanced DC loads are analyzed.Suggested power quality of microgrid and total harmonic distortion(THD)analysis are demonstrated in grid-tied and islanded modes.Eventually,semiconductor power loss simulations based on a closed-loop thermal network simulation are conducted.Thereby,the mutual effects of power loss and initial junction temperature are investigated.
基金M.C.was supported by INdAM(Istituto Nazionale di Alta Matematica)via F46C18000040005 grant“HER-MES Technological Path nder-HTP”.
文摘In the eld of satellite constellations,an important requirement is often represented by the possibility to exchange data among the satellites or exploit mutual visibility to carry out measurements on the parameters of the Earth's atmosphere.Therefore,recursive and routing algorithms are usually implemented to evaluate inter-satellite visibility intervals.However,to design the con guration of the constellation,it is important to consider the orbital conditions that guarantee the mutual visibility between couples of satellites.Thus,in this study,a geometric analysis was performed to identify the optimal inter-satellite visibility conditions,expressed in terms of the di erence in the true anomaly between satellites characterized by di erent orbital con gurations.This approach allows a handy constellation design,without performing a numerical analysis.It is particularly useful in the case of a high number of satellites,when numerical techniques require signi cant computational e ort.Therefore,it is possible to considerably simplify the design of a constellation in which the mutual visibility between couples of satellites is always guaranteed.This type of constellation,usually referred to as satellite chain,can be exploited in several network services and remote sensing systems devoted to enhancing the knowledge of atmospheric parameters.
