The equilibrium between dc bus voltage and ac bus frequency(Udc-f equilibrium)is the algorithm core of unified control strategies for ac-dc interlinking converters(ILCs),because the equilibrium implements certain mech...The equilibrium between dc bus voltage and ac bus frequency(Udc-f equilibrium)is the algorithm core of unified control strategies for ac-dc interlinking converters(ILCs),because the equilibrium implements certain mechanism.However,what the mechanism is has not been explicitly explored,which hinders further studies on unified control.This paper reveals that the state-space model of a Udc-f equilibrium controlled ILC is highly similar to that of a shaft-to-shaft machines system.Hence a detailed mechanism is dis-covered and named“virtual shaft-to-shaft machine(VSSM)”mechanism.A significant feature of VSSM mechanism is self-synchro-nization without current sampling or ac voltage sampling.展开更多
The stability problem arising from the DC-link voltage outer loop and current inner loop control in weak-grid-tied interlinking voltage-source converters(VSC)system has been extensively investigated.However,the differ...The stability problem arising from the DC-link voltage outer loop and current inner loop control in weak-grid-tied interlinking voltage-source converters(VSC)system has been extensively investigated.However,the different impacts on system stability caused by these controller parameters have not been well solved.A three-port hybrid AC/DC admittance-based model for VSC taking into account AC-and DC-side dynamics is developed for revealing the mechanism intuitively on the formation of the positive and negative feedback effects in the DC-link voltage control loop.Subsequently,the stability characteristics of the voltage outer loop and current inner loop controller parameters on VSC are analyzed.Compared to adjusting the voltage outer loop controller parameters which has significant effort on the dynamic regulation characteristics,it is more sensitive on system stability by the parameter change of the current inner loop controller.Theoretical results,along with experimental verification,are provided to validate the analysis.展开更多
Phase-shift(PS)dual-active-bridge(DAB)interlinking converters(ILCs)exhibit considerable potential in linking DC buses.DC ILC control research is focused on addressing three issues,namely modular series-parallel connec...Phase-shift(PS)dual-active-bridge(DAB)interlinking converters(ILCs)exhibit considerable potential in linking DC buses.DC ILC control research is focused on addressing three issues,namely modular series-parallel connection,control adaptability in various microgrid-operation modes,and microgrid stability with constant power loads.However,PS DAB converters operating with open-loop control cannot maintain bus voltage when load changes.Based on the open-loop controlled resonant converters which are called DC transformers(DCXs),this study proposes a closed-loop de-transformer(CL-DCX)control method for DAB ILCs.In conventional control techniques,specialized control loops are used for addressing each control issue.It is hard to combine these loops to address all three control issues simultaneously.By contrast,the CL-DCX control method is simple and can address all three control issues simultaneously.The proposed CL-DCX control method is conducive for implementation in independent microgrids and may benefit medium-voltage applications because of its versatility and simplicity.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
基金supported in part by the National Natural Science Foundation of China under Grants 51877117 and 52007096the International Joint Mission On Climate Change and Carbon Neutralitythe Major Science and Technology Innovation Project of Jiangsu Province of China under Grant BE2022038.
文摘The equilibrium between dc bus voltage and ac bus frequency(Udc-f equilibrium)is the algorithm core of unified control strategies for ac-dc interlinking converters(ILCs),because the equilibrium implements certain mechanism.However,what the mechanism is has not been explicitly explored,which hinders further studies on unified control.This paper reveals that the state-space model of a Udc-f equilibrium controlled ILC is highly similar to that of a shaft-to-shaft machines system.Hence a detailed mechanism is dis-covered and named“virtual shaft-to-shaft machine(VSSM)”mechanism.A significant feature of VSSM mechanism is self-synchro-nization without current sampling or ac voltage sampling.
基金supported by the National Natural Science Foundation of China(No.52177184)the Shanghai Municipality on Natural Science Fund(No.21ZR1425300).
文摘The stability problem arising from the DC-link voltage outer loop and current inner loop control in weak-grid-tied interlinking voltage-source converters(VSC)system has been extensively investigated.However,the different impacts on system stability caused by these controller parameters have not been well solved.A three-port hybrid AC/DC admittance-based model for VSC taking into account AC-and DC-side dynamics is developed for revealing the mechanism intuitively on the formation of the positive and negative feedback effects in the DC-link voltage control loop.Subsequently,the stability characteristics of the voltage outer loop and current inner loop controller parameters on VSC are analyzed.Compared to adjusting the voltage outer loop controller parameters which has significant effort on the dynamic regulation characteristics,it is more sensitive on system stability by the parameter change of the current inner loop controller.Theoretical results,along with experimental verification,are provided to validate the analysis.
基金supported in part by the National Natural Science Foundation of China(52007096 and 51877117)in part by the Delta Power Electronics Research and Education Development Program(DREM2019005).
文摘Phase-shift(PS)dual-active-bridge(DAB)interlinking converters(ILCs)exhibit considerable potential in linking DC buses.DC ILC control research is focused on addressing three issues,namely modular series-parallel connection,control adaptability in various microgrid-operation modes,and microgrid stability with constant power loads.However,PS DAB converters operating with open-loop control cannot maintain bus voltage when load changes.Based on the open-loop controlled resonant converters which are called DC transformers(DCXs),this study proposes a closed-loop de-transformer(CL-DCX)control method for DAB ILCs.In conventional control techniques,specialized control loops are used for addressing each control issue.It is hard to combine these loops to address all three control issues simultaneously.By contrast,the CL-DCX control method is simple and can address all three control issues simultaneously.The proposed CL-DCX control method is conducive for implementation in independent microgrids and may benefit medium-voltage applications because of its versatility and simplicity.
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.
