The principle of single to single phase matrix electric power conversioin is further studied and the conversioin switch function is introduced into conventional rectifier inverter, thus a general character of the t...The principle of single to single phase matrix electric power conversioin is further studied and the conversioin switch function is introduced into conventional rectifier inverter, thus a general character of the two conversion techniques is discovered. It is characteristic of the switch functiion to follow mains voltage distortion and mains frequency drift. By utilizing the merit, unidirectional switch duty rations of the inverter follow the variation of DC link voltage automatically, thus the size of DC link electrolytic capacitor can be reduced considerably, bringing about improved mains side power factor. Corresponding topologies and theoretical and theoretical derivations are given, and so are the simulation results, based on which it is confirmed that the single to single phase matrix conversion technique is potentially useful in large scale production, and the introduction of switch function can yield good economic returns.展开更多
Electric power conversion system （EPCS）, which consists of a generator and power converter, is one of the most important subsystems in a direct-drive wind turbine （DD-WT）. However, this component accounts for the ...Electric power conversion system （EPCS）, which consists of a generator and power converter, is one of the most important subsystems in a direct-drive wind turbine （DD-WT）. However, this component accounts for the most failures （approximately 60% of the total number） in the entire DD-WT system according to statistical data. To improve the reliability of EPCSs and reduce the operation and maintenance cost of DD-WTs, numerous researchers have studied condition monitoring （CM） and fault diagnostics （FD）. Numerous CM and FD techniques, which have respective advantages and disadvantages, have emerged. This paper provides an overview of the CM, FD, and operation control of EPCSs in DD-WTs under faults. After introducing the functional principle and structure of EPCS, this survey discusses the common failures in wind generators and power converters; briefly reviewed CM and FD methods and operation control of these generators and power converters under faults; and discussed the grid voltage faults related to EPCSs in DD-WTs. These theories and their related technical concepts are systematically discussed. Finally, predicted development trends are presented. The paper provides a valuable reference for developing service quality evaluation methods and fault operation control systems to achieve high-performance and high-intelligence DD-WTs.展开更多
Mesophilic and thermophilic anaerobic fermentation performance of waste activated sludge(WAS)pretreated by enzymes catalysis associated with microbial community shifts were investigated.WAS disintegration was boosted ...Mesophilic and thermophilic anaerobic fermentation performance of waste activated sludge(WAS)pretreated by enzymes catalysis associated with microbial community shifts were investigated.WAS disintegration was boosted considerably by enzymolysis with 8750 mg/L of soluble COD release within 180 min.Mesophilic anaerobic fermentation(MAF)produced nearly equal VFA accumulation with over 3200 mg COD/L compared with that of thermophilic fermentation(TAF).Bacterial community consortia showed great shifting differences in dynamics of main T⁃RFs between MAF and TAF.Moreover,MAF was conducive to form intermediate bacterial community evenness compared to TAF,which preserved a robust function of VFA production.The enzymes catalysis prompted bio⁃energy(electricity)recovery potential of WAS organics via anaerobic fermentation(MAF/TAF)with evaluating electricity conversion efficiency of 0.75-0.82 kW·h/kg VSS(3.9 times higher than control test).Finally,this study proposed some novel thinking on future WAS treatment/management towards energy recovery coupled with energy⁃sufficient wastewater treatment by co⁃locating WAS anaerobic fermentation,MFC plant with wastewater treatment plant(s).展开更多
Based on decreasing the flexibility of the power grid through the integration of large-scale renewable energy,a multi-energy storage system architectural model and its coor-dination operational strategy with the same ...Based on decreasing the flexibility of the power grid through the integration of large-scale renewable energy,a multi-energy storage system architectural model and its coor-dination operational strategy with the same flexibility as in the pumped storage power station and battery energy storage system(BESS)are studied.According to the new energy fluctuation characteristics and the different peak valley parameters in the power grid,this paper proposes a electricity heat hydrogen multi-energy storage system(EHH-MESS)and its coordination and optimization operational model to reduce the curtailment of wind power and photovoltaic(PV)to the power grid and improve the flexibility of the power grid.Finally,this paper studied the simulation model of an energy storage optimization control strategy after the multi-energy storage system is connected to the distribution networks,and analyzed three operational modes of the multi-energy storage system.The simulation results show that the EHH-MESS proposed in this paper has a better power grid regulation flexibility and economy,and can be used to replace the battery energy storage system based on MATLAB.展开更多
Constant current power transmission is considered a good choice for subsea observatories due to its high resistance to shunt faults. A constant current subsea observatory is planned to be constructed in the East China...Constant current power transmission is considered a good choice for subsea observatories due to its high resistance to shunt faults. A constant current subsea observatory is planned to be constructed in the East China Sea. We discuss a constant current subsea observatory system used for scientific experiments. The power system and its heat dissipation system are carefully designed. The power conversion method is challenging due to the use of constant current power, which is considerably different from traditional power systems. Thus, we adopt power compensation circuits in the conversion system to obtain a constant 48-V output for science users. A power management system that performs overvoltage protection and real-time monitoring and control of junction box is discussed. An innovative heat dissipation structure of a junction box is designed in consideration of a sealed working environment to extend the useful life of the junction box. Simulations and experiments reveal that the system has high efficiency and stability, especially in long-term applications.展开更多
Selective reduction of CO_(2) into liquid products such as ethanol through electrochemical catalysis is promising in storing renewable energy in more deliverable chemicals and balancing the carbon footprint in the env...Selective reduction of CO_(2) into liquid products such as ethanol through electrochemical catalysis is promising in storing renewable energy in more deliverable chemicals and balancing the carbon footprint in the environment.However,the lack of efficient catalysts for electrochemical CO_(2) reduction reaction(eCO_(2)RR)makes the promise challenging because the formation of C2+alcohols requires coupling reactions between the shallow reduction intermediates and deep reduction intermediates that are usually difficult to form on uniform catalyst surfaces simultaneously with appropriate transient kinetics.Herein,we report a new strategy for synthesizing bimetallic nanostructures with high densities of interfaced Ag/Cu boundaries,which facilitate the coupling reaction of the high‐oxidation‐number intermediates(CO)formed on the Ag surface and the low‐oxidation‐number intermediates(CHx)formed on the Cu surface.The synthesis relies on the electrochemical reduction of bilayered nanoplates made of silver thiolate and copper thiolate,resulting in Ag/Cu nanostructures exposing Ag surface,Cu surface,and the Ag/Cu interfaced boundaries.Balancing the accessible surface areas of the Ag surface,Cu surface,and Ag/Cu boundaries is beneficial for maximizing the activity and selectivity of eCO_(2)RR towards ethanol production.Faradaic efficiency of forming ethanol has been observed as high as about 50%using the Ag/Cu nanostructure catalyst with molar ratio nAg:nCu of 1:1.Moreover,the promoted coupling reaction at the Ag/Cu boundaries and surface modification with thiolate anions significantly suppress the undesirable hydrogen evolution reaction,particularly at high cathodic potentials,maintaining high energy efficiency for eCO_(2)RR.展开更多
文摘The principle of single to single phase matrix electric power conversioin is further studied and the conversioin switch function is introduced into conventional rectifier inverter, thus a general character of the two conversion techniques is discovered. It is characteristic of the switch functiion to follow mains voltage distortion and mains frequency drift. By utilizing the merit, unidirectional switch duty rations of the inverter follow the variation of DC link voltage automatically, thus the size of DC link electrolytic capacitor can be reduced considerably, bringing about improved mains side power factor. Corresponding topologies and theoretical and theoretical derivations are given, and so are the simulation results, based on which it is confirmed that the single to single phase matrix conversion technique is potentially useful in large scale production, and the introduction of switch function can yield good economic returns.
基金This work was supported by the National Key R＆D Program of China （Grant No. 2016YFF0203400）. The program focuses on studies on service quality monitoring and maintenance quality control technology for large wind turbines. The project leader is Professor Shoudao Huang. The authors are also grateful to the National Natural Science Foundation of China （Grant No. 51377050） for the financial support.
文摘Electric power conversion system （EPCS）, which consists of a generator and power converter, is one of the most important subsystems in a direct-drive wind turbine （DD-WT）. However, this component accounts for the most failures （approximately 60% of the total number） in the entire DD-WT system according to statistical data. To improve the reliability of EPCSs and reduce the operation and maintenance cost of DD-WTs, numerous researchers have studied condition monitoring （CM） and fault diagnostics （FD）. Numerous CM and FD techniques, which have respective advantages and disadvantages, have emerged. This paper provides an overview of the CM, FD, and operation control of EPCSs in DD-WTs under faults. After introducing the functional principle and structure of EPCS, this survey discusses the common failures in wind generators and power converters; briefly reviewed CM and FD methods and operation control of these generators and power converters under faults; and discussed the grid voltage faults related to EPCSs in DD-WTs. These theories and their related technical concepts are systematically discussed. Finally, predicted development trends are presented. The paper provides a valuable reference for developing service quality evaluation methods and fault operation control systems to achieve high-performance and high-intelligence DD-WTs.
基金Sponsored by the Scientific Research Funds of Huaqiao University(Grant No.605-50Y18055).
文摘Mesophilic and thermophilic anaerobic fermentation performance of waste activated sludge(WAS)pretreated by enzymes catalysis associated with microbial community shifts were investigated.WAS disintegration was boosted considerably by enzymolysis with 8750 mg/L of soluble COD release within 180 min.Mesophilic anaerobic fermentation(MAF)produced nearly equal VFA accumulation with over 3200 mg COD/L compared with that of thermophilic fermentation(TAF).Bacterial community consortia showed great shifting differences in dynamics of main T⁃RFs between MAF and TAF.Moreover,MAF was conducive to form intermediate bacterial community evenness compared to TAF,which preserved a robust function of VFA production.The enzymes catalysis prompted bio⁃energy(electricity)recovery potential of WAS organics via anaerobic fermentation(MAF/TAF)with evaluating electricity conversion efficiency of 0.75-0.82 kW·h/kg VSS(3.9 times higher than control test).Finally,this study proposed some novel thinking on future WAS treatment/management towards energy recovery coupled with energy⁃sufficient wastewater treatment by co⁃locating WAS anaerobic fermentation,MFC plant with wastewater treatment plant(s).
基金This project was supported by National Key Research and Development Plan(2017YFB0902100).
文摘Based on decreasing the flexibility of the power grid through the integration of large-scale renewable energy,a multi-energy storage system architectural model and its coor-dination operational strategy with the same flexibility as in the pumped storage power station and battery energy storage system(BESS)are studied.According to the new energy fluctuation characteristics and the different peak valley parameters in the power grid,this paper proposes a electricity heat hydrogen multi-energy storage system(EHH-MESS)and its coordination and optimization operational model to reduce the curtailment of wind power and photovoltaic(PV)to the power grid and improve the flexibility of the power grid.Finally,this paper studied the simulation model of an energy storage optimization control strategy after the multi-energy storage system is connected to the distribution networks,and analyzed three operational modes of the multi-energy storage system.The simulation results show that the EHH-MESS proposed in this paper has a better power grid regulation flexibility and economy,and can be used to replace the battery energy storage system based on MATLAB.
基金Project supported by the National Natural Science Foundation of China(No.41676089),the Natural Science Foundation of Zhejiang Province,China(No.LY18E090003)the Fundamental Research Funds for the Central Universities,China(No.2018QNA4005)。
文摘Constant current power transmission is considered a good choice for subsea observatories due to its high resistance to shunt faults. A constant current subsea observatory is planned to be constructed in the East China Sea. We discuss a constant current subsea observatory system used for scientific experiments. The power system and its heat dissipation system are carefully designed. The power conversion method is challenging due to the use of constant current power, which is considerably different from traditional power systems. Thus, we adopt power compensation circuits in the conversion system to obtain a constant 48-V output for science users. A power management system that performs overvoltage protection and real-time monitoring and control of junction box is discussed. An innovative heat dissipation structure of a junction box is designed in consideration of a sealed working environment to extend the useful life of the junction box. Simulations and experiments reveal that the system has high efficiency and stability, especially in long-term applications.
文摘Selective reduction of CO_(2) into liquid products such as ethanol through electrochemical catalysis is promising in storing renewable energy in more deliverable chemicals and balancing the carbon footprint in the environment.However,the lack of efficient catalysts for electrochemical CO_(2) reduction reaction(eCO_(2)RR)makes the promise challenging because the formation of C2+alcohols requires coupling reactions between the shallow reduction intermediates and deep reduction intermediates that are usually difficult to form on uniform catalyst surfaces simultaneously with appropriate transient kinetics.Herein,we report a new strategy for synthesizing bimetallic nanostructures with high densities of interfaced Ag/Cu boundaries,which facilitate the coupling reaction of the high‐oxidation‐number intermediates(CO)formed on the Ag surface and the low‐oxidation‐number intermediates(CHx)formed on the Cu surface.The synthesis relies on the electrochemical reduction of bilayered nanoplates made of silver thiolate and copper thiolate,resulting in Ag/Cu nanostructures exposing Ag surface,Cu surface,and the Ag/Cu interfaced boundaries.Balancing the accessible surface areas of the Ag surface,Cu surface,and Ag/Cu boundaries is beneficial for maximizing the activity and selectivity of eCO_(2)RR towards ethanol production.Faradaic efficiency of forming ethanol has been observed as high as about 50%using the Ag/Cu nanostructure catalyst with molar ratio nAg:nCu of 1:1.Moreover,the promoted coupling reaction at the Ag/Cu boundaries and surface modification with thiolate anions significantly suppress the undesirable hydrogen evolution reaction,particularly at high cathodic potentials,maintaining high energy efficiency for eCO_(2)RR.
