To enhance power flow regulation in scenarios involving large-scale renewable energy transmission via high-voltage direct current(HVDC)links and multi-infeed DC systems in load-center regions,this paper proposes a hyb...To enhance power flow regulation in scenarios involving large-scale renewable energy transmission via high-voltage direct current(HVDC)links and multi-infeed DC systems in load-center regions,this paper proposes a hybrid modular multilevel converter–capacitor-commutated line-commutated converter(MMC-CLCC)HVDC transmission system and its corresponding control strategy.First,the system topology is constructed,and a submodule configuration method for the MMC—combining full-bridge submodules(FBSMs)and half-bridge submodules(HBSMs)—is proposed to enable direct power flow reversal.Second,a hierarchical control strategy is introduced,includingMMCvoltage control,CLCC current control,and a coordinationmechanism,along with the derivation of the hybrid system’s power flow reversal characteristics.Third,leveraging the CLCC’s fast current regulation and theMMC’s negative voltage control capability,a coordinated power flow reversal control strategy is developed.Finally,an 800 kV MMC-CLCC hybrid HVDC system is modeled in PSCAD/EMTDC to validate the power flow reversal performance under a high proportion of full-bridge submodule configuration.Results demonstrate that the proposed control strategy enables rapid(1-s transition)and smooth switching of bidirectional power flow without modifying the structure of primary equipment:the transient fluctuation ofDC voltage from the rated value(UdcN)to themaximumreverse voltage(-kUdcN)is less than 5%;the DC current strictly follows the preset characteristic curve with a deviation of≤3%;the active power reverses continuously,and the system maintains stable operation throughout the reversal process.展开更多
In recent years, against a background of an environmental problem and resource problem, the introduction of RES （renewable energy source） such as wind power generation and PV （photovoltaic generation）, EV （electr...In recent years, against a background of an environmental problem and resource problem, the introduction of RES （renewable energy source） such as wind power generation and PV （photovoltaic generation）, EV （electric vehicle）, and PHEV （Plug-in hybrid electric vehicle） has been expanding. However, various problems have an ongoing discussion. When the production of electricity by RESs exceeds the power consumption, it is possible to cause a steep variation of point voltage and a deviation from a proper voltage range in a distribution system to which RESs are interconnected. When EVs and PHEVs have spread to the distribution system, a new peak power-demand and a steep voltage drop might occur in the midnight charging time zone in case the electricity charges are low. in this paper, the authors analyze the effects on the distribution system under widespread PVs, EVs, and PHEVs. In addition, the authors propose an improvement plan and analyze about the influence and contribution.展开更多
The optimization process of embedded, or DG （distributed generation） is a very complex task, and it should be evaluated and compared by means of multi-criteria methods of analysis. The classical method for selection...The optimization process of embedded, or DG （distributed generation） is a very complex task, and it should be evaluated and compared by means of multi-criteria methods of analysis. The classical method for selection is usually based only on a single criterion analysis, and it is defined by thermal or economic aspects. The problem of optimal dispatch of DG is typical example of optimization, because it differs from the classical problem of generation dispatch in the power system, due to the specific criteria related to the DG interconnection. The most important goals are to maximize the renewable production and to minimize the total cost, while satisfying additional constraints related to the operation of a distribution network. As there are many DGs in a distribution network, it is very complicated to decide the optimal DG outputs to satisfy all the criteria and constraints imposed by the distribution network. Another problem is the lack of the dispatcher control over DGs, and very often, the only available action is to switch on or off the generator. Finally, network operator and DG owner perspective are often opposed regarding appropriate control action in the network. In this paper, a multicriteria decision support based on AHP （analytical hierarchical processes） method is proposed for the choice of the dispatching action. The method is illustrated on the choice of the DG to be switched off in the case or reverse power flow.展开更多
Space plays a critical role in Romance of the Three Kingdoms.This paper examines the construction of feminine space in the fiction by applying the theory of gendered space and using methods such as induction,compariso...Space plays a critical role in Romance of the Three Kingdoms.This paper examines the construction of feminine space in the fiction by applying the theory of gendered space and using methods such as induction,comparison,and mutual corroboration of literature and history.The feminine space in the fiction was constructed on the basis of“gender segregation.”The female characters mainly stayed at the“backyard”of homesteads,and were rarely seen in external spaces,leaving space power in the hands of men.However,thanks to certain special opportunities,status,or class,women could acquire some knowledge and abilities not available to them in the space.Under such circumstances,they had the chance to reverse the space power.The fiction presents the richness and complexity of feminine space and circumstances in the late Han Dynasty.展开更多
Dogs exhibit close similarities to humans in terms of metabolic,physiological,and anatomical characteristics,and thus are ideal genetic and clinical models to study human diseases.Gene target technology is a powerful ...Dogs exhibit close similarities to humans in terms of metabolic,physiological,and anatomical characteristics,and thus are ideal genetic and clinical models to study human diseases.Gene target technology is a powerful tool to create new strains of animals with favorable trails.However,gene-target dogs were not developed for a long time due to their unique species-specific reproductive characteristics which limited their applications,especially in the field of biomedical research.Recently.展开更多
Power reversal control strategies for different types of hybrid line-commutated-converter(LCC)/modular multi-level converter(MMC)based high-voltage direct-current(HVDC)systems have been proposed with the consideration...Power reversal control strategies for different types of hybrid line-commutated-converter(LCC)/modular multi-level converter(MMC)based high-voltage direct-current(HVDC)systems have been proposed with the consideration of system configurations and MMC’s topologies.The studies show that the full-bridge(FB)MMC gives better performance than half-bridge(HB)MMCs in terms of power reversal in hybrid LCC/MMC systems.The modulation method employed in this paper can achieve a smooth online polarity reversal for hybrid LCC/FB-MMC HVDC systems.Additional DC switches and/or discharging resistors may be needed to reverse the DC polarity of LCC/HB-MMC HVDC systems.Based on the proposed strate-gies,the power reversal processes of the studied systems can be accomplished within several seconds.The speed can be changed according to system operation requirements.The effectiveness of the proposed control strategies has been verified through simulations conducted in PSCAD/EMTDC.展开更多
Using p~＋-type crystalline Si with n~＋-type nanocrystalline Si（nc-Si） and n~＋-type crystalline Si with p~＋-type nc-Si mosaic structures as electrodes,a type of power diode was prepared with epitaxial technique a...Using p~＋-type crystalline Si with n~＋-type nanocrystalline Si（nc-Si） and n~＋-type crystalline Si with p~＋-type nc-Si mosaic structures as electrodes,a type of power diode was prepared with epitaxial technique and plasmaenhanced chemical vapor deposition（PECVD） method.Firstly,the basic p~＋-n^--n~＋-type Si diode was fabricated by epitaxially growing p~＋- and n~＋-type layers on two sides of a lightly doped n^--type Si wafer respectively.Secondly,heavily phosphorus-doped Si film was deposited with PECVD on the lithography mask etched p~＋-type Si side of the basic device to form a component with mosaic anode.Thirdly,heavily boron-doped Si film was deposited on the etched n~＋-type Si side of the second device to form a diode with mosaic anode and mosaic cathode.The images of high resolution transmission electronic microscope and patterns of X-ray diffraction reveal nanocrystallization in the phosphorus- and boron-deposited films.Electrical measurements such as capacitancevoltage relation,current-voltage feature and reverse recovery waveform were carried out to clarify the performance of prepared devices.The important roles of（n^-）Si/（p~＋）nc-Si and（n^-）Si/（n~＋）nc-Si junctions in the static and dynamic conduction processes in operating diodes were investigated.The performance of mosaic devices was compared to that of a basic one.展开更多
基金supported by Science and Technology Project of the headquarters of the State Grid Corporation of China(No.5500-202324492A-3-2-ZN).
文摘To enhance power flow regulation in scenarios involving large-scale renewable energy transmission via high-voltage direct current(HVDC)links and multi-infeed DC systems in load-center regions,this paper proposes a hybrid modular multilevel converter–capacitor-commutated line-commutated converter(MMC-CLCC)HVDC transmission system and its corresponding control strategy.First,the system topology is constructed,and a submodule configuration method for the MMC—combining full-bridge submodules(FBSMs)and half-bridge submodules(HBSMs)—is proposed to enable direct power flow reversal.Second,a hierarchical control strategy is introduced,includingMMCvoltage control,CLCC current control,and a coordinationmechanism,along with the derivation of the hybrid system’s power flow reversal characteristics.Third,leveraging the CLCC’s fast current regulation and theMMC’s negative voltage control capability,a coordinated power flow reversal control strategy is developed.Finally,an 800 kV MMC-CLCC hybrid HVDC system is modeled in PSCAD/EMTDC to validate the power flow reversal performance under a high proportion of full-bridge submodule configuration.Results demonstrate that the proposed control strategy enables rapid(1-s transition)and smooth switching of bidirectional power flow without modifying the structure of primary equipment:the transient fluctuation ofDC voltage from the rated value(UdcN)to themaximumreverse voltage(-kUdcN)is less than 5%;the DC current strictly follows the preset characteristic curve with a deviation of≤3%;the active power reverses continuously,and the system maintains stable operation throughout the reversal process.
文摘In recent years, against a background of an environmental problem and resource problem, the introduction of RES （renewable energy source） such as wind power generation and PV （photovoltaic generation）, EV （electric vehicle）, and PHEV （Plug-in hybrid electric vehicle） has been expanding. However, various problems have an ongoing discussion. When the production of electricity by RESs exceeds the power consumption, it is possible to cause a steep variation of point voltage and a deviation from a proper voltage range in a distribution system to which RESs are interconnected. When EVs and PHEVs have spread to the distribution system, a new peak power-demand and a steep voltage drop might occur in the midnight charging time zone in case the electricity charges are low. in this paper, the authors analyze the effects on the distribution system under widespread PVs, EVs, and PHEVs. In addition, the authors propose an improvement plan and analyze about the influence and contribution.
文摘The optimization process of embedded, or DG （distributed generation） is a very complex task, and it should be evaluated and compared by means of multi-criteria methods of analysis. The classical method for selection is usually based only on a single criterion analysis, and it is defined by thermal or economic aspects. The problem of optimal dispatch of DG is typical example of optimization, because it differs from the classical problem of generation dispatch in the power system, due to the specific criteria related to the DG interconnection. The most important goals are to maximize the renewable production and to minimize the total cost, while satisfying additional constraints related to the operation of a distribution network. As there are many DGs in a distribution network, it is very complicated to decide the optimal DG outputs to satisfy all the criteria and constraints imposed by the distribution network. Another problem is the lack of the dispatcher control over DGs, and very often, the only available action is to switch on or off the generator. Finally, network operator and DG owner perspective are often opposed regarding appropriate control action in the network. In this paper, a multicriteria decision support based on AHP （analytical hierarchical processes） method is proposed for the choice of the dispatching action. The method is illustrated on the choice of the DG to be switched off in the case or reverse power flow.
基金funded by Sichuan Center for Zhuge Liang Studies(21ZGL03).
文摘Space plays a critical role in Romance of the Three Kingdoms.This paper examines the construction of feminine space in the fiction by applying the theory of gendered space and using methods such as induction,comparison,and mutual corroboration of literature and history.The feminine space in the fiction was constructed on the basis of“gender segregation.”The female characters mainly stayed at the“backyard”of homesteads,and were rarely seen in external spaces,leaving space power in the hands of men.However,thanks to certain special opportunities,status,or class,women could acquire some knowledge and abilities not available to them in the space.Under such circumstances,they had the chance to reverse the space power.The fiction presents the richness and complexity of feminine space and circumstances in the late Han Dynasty.
文摘Dogs exhibit close similarities to humans in terms of metabolic,physiological,and anatomical characteristics,and thus are ideal genetic and clinical models to study human diseases.Gene target technology is a powerful tool to create new strains of animals with favorable trails.However,gene-target dogs were not developed for a long time due to their unique species-specific reproductive characteristics which limited their applications,especially in the field of biomedical research.Recently.
基金This work was supported by Science and Technology Project of the State Grid Corporation of China,“HVDC Systems/Grids for Transnational Interconnections”,project number:SGTYHT/16-JS-198.
文摘Power reversal control strategies for different types of hybrid line-commutated-converter(LCC)/modular multi-level converter(MMC)based high-voltage direct-current(HVDC)systems have been proposed with the consideration of system configurations and MMC’s topologies.The studies show that the full-bridge(FB)MMC gives better performance than half-bridge(HB)MMCs in terms of power reversal in hybrid LCC/MMC systems.The modulation method employed in this paper can achieve a smooth online polarity reversal for hybrid LCC/FB-MMC HVDC systems.Additional DC switches and/or discharging resistors may be needed to reverse the DC polarity of LCC/HB-MMC HVDC systems.Based on the proposed strate-gies,the power reversal processes of the studied systems can be accomplished within several seconds.The speed can be changed according to system operation requirements.The effectiveness of the proposed control strategies has been verified through simulations conducted in PSCAD/EMTDC.
基金supported by the National Natural Science Foundation of China(No.61274006)
文摘Using p~＋-type crystalline Si with n~＋-type nanocrystalline Si（nc-Si） and n~＋-type crystalline Si with p~＋-type nc-Si mosaic structures as electrodes,a type of power diode was prepared with epitaxial technique and plasmaenhanced chemical vapor deposition（PECVD） method.Firstly,the basic p~＋-n^--n~＋-type Si diode was fabricated by epitaxially growing p~＋- and n~＋-type layers on two sides of a lightly doped n^--type Si wafer respectively.Secondly,heavily phosphorus-doped Si film was deposited with PECVD on the lithography mask etched p~＋-type Si side of the basic device to form a component with mosaic anode.Thirdly,heavily boron-doped Si film was deposited on the etched n~＋-type Si side of the second device to form a diode with mosaic anode and mosaic cathode.The images of high resolution transmission electronic microscope and patterns of X-ray diffraction reveal nanocrystallization in the phosphorus- and boron-deposited films.Electrical measurements such as capacitancevoltage relation,current-voltage feature and reverse recovery waveform were carried out to clarify the performance of prepared devices.The important roles of（n^-）Si/（p~＋）nc-Si and（n^-）Si/（n~＋）nc-Si junctions in the static and dynamic conduction processes in operating diodes were investigated.The performance of mosaic devices was compared to that of a basic one.
