Cost-effective and stable electrocatalysts with ultra-high current densities for electrochemical oxygen evolution reaction(OER)are critical to the energy crisis and environmental pollution.Herein,we report a superaero...Cost-effective and stable electrocatalysts with ultra-high current densities for electrochemical oxygen evolution reaction(OER)are critical to the energy crisis and environmental pollution.Herein,we report a superaerophobic three dimensional(3D)heterostructured nanowrinkles of bimetallic selenides consisting of crystalline NiSe2 and NiFe2Se4 grown on NiFe alloy(NiSe2/NiFe2Se4@NiFe)prepared by a thermal selenization procedure.In this unique 3D heterostructure,numerous nanowrinkles of NiSe2/NiFe2Se4 hybrid with a thickness of ~100 nm are grown on NiFe alloy in a uniform manner.Profiting by the large active surface area and high electronic conductivity,the superaerophobic NiSe2/NiFe2Se4@NiFe heterostructure exhibits excellent electrocatalytic activity and durability towards OER in alkaline media,outputting the low potentials of 1.53 and 1.54 V to achieve ultra-high current densities of 500 and 1000 mA cm^−2,respectively,which is among the most active Ni/Fe-based selenides,and even superior to the benchmark Ir/C catalyst.The in-situ derived FeOOH and NiOOH species from NiSe2/NiFe2Se4@NiFe are deemed to be efficient active sites for OER.展开更多
Developing high-performing oxygen evolution reaction(OER)electrocatalysts under high-current operation conditions is critical for future commercial applications of alkaline water electrolysis for clean energy generati...Developing high-performing oxygen evolution reaction(OER)electrocatalysts under high-current operation conditions is critical for future commercial applications of alkaline water electrolysis for clean energy generation.Herein,we prepared a three-dimensional(3D)bimetallic oxyhydroxide hybrid grown on a Ni foam(NiFeOOH/NF)prepared by immersing Ni foam(NF)into Fe(NO_(3))_(3) solution.In this unique 3D structure,the NiFeOOH/NF hybrid was composed of crystalline Ni(OH)_(2) and amorphous FeOOH evenly grown on the NF surface.As a bimetallic oxyhydroxide electrocatalyst,the NiFeOOH/NF hybrid exhibited excellent catalytic activity,surpassing not only the other reported Ni–Fe based electrocatalysts,but also the commercial Ir/C catalyst.In situ electrochemical Raman spectroscopy demonstrated the active FeOOH and NiOOH phases involved in the OER process.Profiting from the synergy of Fe and Ni catalytic sites,the NiFeOOH/NF hybrid delivered an outstanding OER performance under challenging industrial conditions in a 10.0 mol·L^(-1) KOH electrolyte at 80℃,requiring potentials as small as 1.47 and 1.51 V to achieve the super-high catalytic current densities of 100 and 500mA∙cm^(-2),respectively.展开更多
The large current generated by starting directly of super large capacity and high voltage induction motor would have a huge impact on the grid as well as the motor itself.The variation of the power factor and electrom...The large current generated by starting directly of super large capacity and high voltage induction motor would have a huge impact on the grid as well as the motor itself.The variation of the power factor and electromagnetic torque during direct start of motors with different capacity and voltage levels are obtained.Aiming at the problem that the secondary impact of auto-transformer starter is too large and the cost of magnetic control starter is too high,the auto-transformer and magnetic control soft start method of super large capacity and high voltage motor is proposed and the basic working principle is analyzed.The calculation formula of cost for magnetic control soft starter and auto-transformer and magnetic control soft starter is deduced,and specific examples are analyzed and compared.It is concluded that the choice of auto-transformer with appropriate tapping ratio can greatly reduce the cost of auto-transformer and magnetic control soft starter compared with the other one.Finally,the simulation and experiment results show that the start method can effectively avoid secondary current impact and constrain the motor starting current to less than 2.5 times the rated current.展开更多
At present, sudden load changes and terminal voltage fluctuations are two primary problems in the uninterrupted phase-separation passing (UPP) system. To further enhance the reliability of the UPP system and compensat...At present, sudden load changes and terminal voltage fluctuations are two primary problems in the uninterrupted phase-separation passing (UPP) system. To further enhance the reliability of the UPP system and compensate for the voltage sag at the end of the traction power supply network caused by the suddenly connection of locomotive to the power grid, a multi-function uninterrupted phase-separation passing system (MUPPS) and its control strategy are proposed. It has the advantages of linear load change and improving power supply reliability. First, the topology and working principles of a MUPPS are studied;secondly, the current variation characteristics of the bridge arm when the power is continuously supplied by MUPPS during the phase-separation passing are analyzed. Then, the characteristics of a MUPPS to provide reactive power and stabilize the terminal voltage of the traction arm are analyzed. Then, the power transmission characteristics of a MUPPS under emergency working conditions are analyzed. The control strategy for the two conditions is proposed. Finally, simulation analysis and small capacity experiments are conducted. The theoretical analysis and test confirm the correctness and effectiveness of the MUPPS.展开更多
High-voltage withstand tests are essential for electric equipment like power transformers,electric cable lines,gas insulated switchgears etc.The partial discharge(PD)measurement for such equipment under applied high v...High-voltage withstand tests are essential for electric equipment like power transformers,electric cable lines,gas insulated switchgears etc.The partial discharge(PD)measurement for such equipment under applied high voltage is also required at the same time.Pulse Width Modulation(PWM)-based variable frequency power supply(VFPS)finds wide applications in the series resonance high-voltage testing circuits.However,the steep rising and falling voltage edges in the PWM process will produce large amount of partial discharge interference in a wide spectrum range,which will confuse the real partial discharge signal of the device and lead to the wrong estimation of the insulation status.This paper proposes a new VFPS based on the highefficiency linear power amplifier without PD interference.The topology and principle of the VFPS are given and discussed.A prototype rated at 232 V/35 A was designed and constructed to verify the feasibility of the proposed VFPS.Physical experiments were carried out on the prototype.展开更多
To achieve economical compensation for the huge-capacity negative sequence currents generated by high-speed railway load, an electromagnetic hybrid compensation system(EHCS) and control strategy is proposed.The EHCS i...To achieve economical compensation for the huge-capacity negative sequence currents generated by high-speed railway load, an electromagnetic hybrid compensation system(EHCS) and control strategy is proposed.The EHCS is made up of a small-capacity railway static power conditioner(RPC) and a large-capacity magnetic static var compensator(MSVC). Compared with traditional compensation methods, the EHCS makes full use of the SVC’s advantages of economy and reliability and of RPC’s advantages of technical capability and flexibility. Based on the idea of injecting a negative sequence, the compensation principle of the EHCS is analyzed in detail. Then the minimum installation capacity of an EHCS is theoretically deduced. Furthermore, a constraint optimization compensation strategy that meets national standards, which reduces compensation capacity further, is proposed. An experimental platform based on a digital signal processor(DSP) and a programmable logic controller(PLC) is built to verify the analysis. Simulated and experimental results are given to demonstrate the effectiveness and feasibility of the proposed method.展开更多
This paper presents a multi-objective Pareto optimal method for allocation of fault current limiters based on an immune algorithm, which takes into account two objectives of the cost and fault current mitigation effec...This paper presents a multi-objective Pareto optimal method for allocation of fault current limiters based on an immune algorithm, which takes into account two objectives of the cost and fault current mitigation effect. A sensitivity factor calculation method based on the rate of fault current mitigation is proposed to reduce the search space and improve the efficiency of the algorithm.In this approach, the objective functions related to the cost and fault current mitigation effect are established. A modified inversion operator based on equal cost is proposed to converge to global optimal solutions more effectively. The proposed algorithm is tested on the IEEE39-bus system, and obtains the Pareto optimal solutions,from which the user can select the most suitable solutions according to the preferences and relative importance of the objective functions. Simulation results are used to verify the proposed method.展开更多
Background Patients with chronic pancreatitis often have irreversible pancreatic insufficiency before a clinical diagnosis.Pancreatic cancer is a fatal malignant tumor in the advanced stages.Patients having high risk ...Background Patients with chronic pancreatitis often have irreversible pancreatic insufficiency before a clinical diagnosis.Pancreatic cancer is a fatal malignant tumor in the advanced stages.Patients having high risk of pancreatic diseases must be screened early to obtain better outcomes using new imaging modalities.Therefore,this study aimed to investigate the reproducibility of tomoelastography measurements for assessing pancreatic stiffness and fluidity and the variance among healthy volunteers.Methods Forty-seven healthy volunteers were prospectively enrolled and underwent two tomoelastography examinations at a mean interval of 7 days.Two radiologists blindly and independently measured the pancreatic stiffness and fluidity at the first examination to determine the reproducibility between readers.One radiologist measured the adjacent pancreatic slice at the first examination to determine the reproducibility among slices and measured the pancreas at the second examination to determine short-termrepeatability.The stiffness and fluidity of the pancreatic head,body,and tail were compared to determine anatomical differences.The pancreatic stiffness and fluidity were compared based on sex,age,and body mass index(BMI).Results Bland–Altman analyses(all P>0.05)and intraclass correlation coefficients(all>0.9)indicated near perfect reproducibility among readers,slices,and examinations at short intervals.Neither stiffness(P=0.477)nor fluidity(P=0.368)differed among the pancreatic anatomical regions.The mean pancreatic stiffness was 1.45±0.09 m/s;the mean pancreatic fluidity was 0.83±0.06 rad.Stiffness and fluidity did not differ by sex,age,or BMI.Conclusion Tomoelastography is a promising and reproducible tool for assessing pancreatic stiffness and fluidity in healthy volunteers.展开更多
The large current generated by a direct start of the super-large-capacity high-voltage induction motor would have a huge impact on the power grid as well as the motor itself.Traditional soft starters have the shortcom...The large current generated by a direct start of the super-large-capacity high-voltage induction motor would have a huge impact on the power grid as well as the motor itself.Traditional soft starters have the shortcomings of discontinuous adjustment,voltage sags,sudden torque mutation,secondary current impact and high cost.To resolve this issue,the authors propose a novel coupled autotransformer and magnetic-control(CATMC)soft-start method.The structure of the new CATMC soft starter combines the functions of the autotransformer and magnetic control reactor via an innovative electric and magnetic circuit design.In this study,the authors analyse the magnetic circuit structure and working principles of the CATMC soft starter.Then,to validate its principle and performance,the authors conduct a simulation study using ANSYS software and design and test an 18 MW/10 kV CATMC soft starter prototype.The simulation results demonstrate that the CATMC soft starter effectively avoids secondary current impact and constrains the motor starting current to<2.5 times the rated current.The public connection point bus voltage also meets the voltage sag requirement of the IEEE standard and reduces the impact on the power grid.展开更多
With the continuous expansion of power grid capacity,the problem of short-circuit current exceeding the standard is becoming increasingly serious.Fault current limiter is a promising solution and is gradually becoming...With the continuous expansion of power grid capacity,the problem of short-circuit current exceeding the standard is becoming increasingly serious.Fault current limiter is a promising solution and is gradually becoming a research hotspot.In this study,fault current limiters are classified into four categories.And saturated-core fault current limiters are emphatically introduced,including its working principle and comparison with the other three categories.Saturated core fault current limiters are divided into four branches according to the ways leading the core saturated.A comprehensive review of the research activities and emerging technologies of saturated-core fault current limiters for AC power systems is presented in this study.The working principle and typical structure of DC-biased-,permanent-magnet-,superconducting-and hybrid-type saturated-core fault current limiters are introduced.The advantages and disadvantages of four types of saturated core fault current limiters are compared in detail from the aspects of current-limiting performance,iron core size and DC magnetomotive force.Real grid application examples of some types of devices are presented,as well as new progress in the techniques,are covered and discussed in detail.One may find the content of this study helpful as a detailed literature review or as practical technical guidance.展开更多
基金financially supported by the National Natural Science Foundation of China(21922811,51702284,and 21878270)Zhejiang Provincial Natural Science Foundation of China(LR19B060002)the Startup Foundation for Hundred-Talent Program of Zhejiang University.
文摘Cost-effective and stable electrocatalysts with ultra-high current densities for electrochemical oxygen evolution reaction(OER)are critical to the energy crisis and environmental pollution.Herein,we report a superaerophobic three dimensional(3D)heterostructured nanowrinkles of bimetallic selenides consisting of crystalline NiSe2 and NiFe2Se4 grown on NiFe alloy(NiSe2/NiFe2Se4@NiFe)prepared by a thermal selenization procedure.In this unique 3D heterostructure,numerous nanowrinkles of NiSe2/NiFe2Se4 hybrid with a thickness of ~100 nm are grown on NiFe alloy in a uniform manner.Profiting by the large active surface area and high electronic conductivity,the superaerophobic NiSe2/NiFe2Se4@NiFe heterostructure exhibits excellent electrocatalytic activity and durability towards OER in alkaline media,outputting the low potentials of 1.53 and 1.54 V to achieve ultra-high current densities of 500 and 1000 mA cm^−2,respectively,which is among the most active Ni/Fe-based selenides,and even superior to the benchmark Ir/C catalyst.The in-situ derived FeOOH and NiOOH species from NiSe2/NiFe2Se4@NiFe are deemed to be efficient active sites for OER.
基金Y.Hou expresses appreciation for the assistance of the National Natural Science Foundation of China(21922811,21878270,and 21961160742)the Zhejiang Provincial Natural Science Foundation of China(LR19B060002)+2 种基金the Fundamental Research Funds for the Central Universities(2020XZZX002-09)the Leading Innovative and Entrepreneur Team Introduction Program of Zhejiang(2019R01006)the Startup Foundation for Hundred-Talent Program of Zhejiang University.K.Ostrikov acknowledges partial assistance from the Australian Research Council.
文摘Developing high-performing oxygen evolution reaction(OER)electrocatalysts under high-current operation conditions is critical for future commercial applications of alkaline water electrolysis for clean energy generation.Herein,we prepared a three-dimensional(3D)bimetallic oxyhydroxide hybrid grown on a Ni foam(NiFeOOH/NF)prepared by immersing Ni foam(NF)into Fe(NO_(3))_(3) solution.In this unique 3D structure,the NiFeOOH/NF hybrid was composed of crystalline Ni(OH)_(2) and amorphous FeOOH evenly grown on the NF surface.As a bimetallic oxyhydroxide electrocatalyst,the NiFeOOH/NF hybrid exhibited excellent catalytic activity,surpassing not only the other reported Ni–Fe based electrocatalysts,but also the commercial Ir/C catalyst.In situ electrochemical Raman spectroscopy demonstrated the active FeOOH and NiOOH phases involved in the OER process.Profiting from the synergy of Fe and Ni catalytic sites,the NiFeOOH/NF hybrid delivered an outstanding OER performance under challenging industrial conditions in a 10.0 mol·L^(-1) KOH electrolyte at 80℃,requiring potentials as small as 1.47 and 1.51 V to achieve the super-high catalytic current densities of 100 and 500mA∙cm^(-2),respectively.
基金This work was supported in part by the National Key Research and Development Program of China under Grant 2017YFB0902904,in part by the Natural Science Foundation of Hubei Province under Grant 2016CFB448,and in part by the Shenzhen City Science and Technology Innovation Plan under Grant JCYJ20170306170937861,and in part by Wuhan City Science and Technology Program under Grant 2016070204020165.
文摘The large current generated by starting directly of super large capacity and high voltage induction motor would have a huge impact on the grid as well as the motor itself.The variation of the power factor and electromagnetic torque during direct start of motors with different capacity and voltage levels are obtained.Aiming at the problem that the secondary impact of auto-transformer starter is too large and the cost of magnetic control starter is too high,the auto-transformer and magnetic control soft start method of super large capacity and high voltage motor is proposed and the basic working principle is analyzed.The calculation formula of cost for magnetic control soft starter and auto-transformer and magnetic control soft starter is deduced,and specific examples are analyzed and compared.It is concluded that the choice of auto-transformer with appropriate tapping ratio can greatly reduce the cost of auto-transformer and magnetic control soft starter compared with the other one.Finally,the simulation and experiment results show that the start method can effectively avoid secondary current impact and constrain the motor starting current to less than 2.5 times the rated current.
基金the National Natural ScienceFoundation of China (U216620752207182)China Postdoctoral ScienceFoundation (2023M732690).
文摘At present, sudden load changes and terminal voltage fluctuations are two primary problems in the uninterrupted phase-separation passing (UPP) system. To further enhance the reliability of the UPP system and compensate for the voltage sag at the end of the traction power supply network caused by the suddenly connection of locomotive to the power grid, a multi-function uninterrupted phase-separation passing system (MUPPS) and its control strategy are proposed. It has the advantages of linear load change and improving power supply reliability. First, the topology and working principles of a MUPPS are studied;secondly, the current variation characteristics of the bridge arm when the power is continuously supplied by MUPPS during the phase-separation passing are analyzed. Then, the characteristics of a MUPPS to provide reactive power and stabilize the terminal voltage of the traction arm are analyzed. Then, the power transmission characteristics of a MUPPS under emergency working conditions are analyzed. The control strategy for the two conditions is proposed. Finally, simulation analysis and small capacity experiments are conducted. The theoretical analysis and test confirm the correctness and effectiveness of the MUPPS.
基金National Natural Science Foundation of China,Grant/Award Number:51907144Fundamental Research Funds for the Central Universities,Grant/Award Number:2042019kf0004。
文摘High-voltage withstand tests are essential for electric equipment like power transformers,electric cable lines,gas insulated switchgears etc.The partial discharge(PD)measurement for such equipment under applied high voltage is also required at the same time.Pulse Width Modulation(PWM)-based variable frequency power supply(VFPS)finds wide applications in the series resonance high-voltage testing circuits.However,the steep rising and falling voltage edges in the PWM process will produce large amount of partial discharge interference in a wide spectrum range,which will confuse the real partial discharge signal of the device and lead to the wrong estimation of the insulation status.This paper proposes a new VFPS based on the highefficiency linear power amplifier without PD interference.The topology and principle of the VFPS are given and discussed.A prototype rated at 232 V/35 A was designed and constructed to verify the feasibility of the proposed VFPS.Physical experiments were carried out on the prototype.
基金supported by National Key Technology Support Program(No.2013BAA02B00)National Natural Science Foundation of China(No.50807041)+3 种基金Asia Pacific Economic Cooperation FundHubei province science and technology support program(No.2014BAA013)the Fundamental Research Funds for the Central Universities(No.2042014kf0233)the Fundamental Research Funds for the Central Universities(No.2014207020202)
文摘To achieve economical compensation for the huge-capacity negative sequence currents generated by high-speed railway load, an electromagnetic hybrid compensation system(EHCS) and control strategy is proposed.The EHCS is made up of a small-capacity railway static power conditioner(RPC) and a large-capacity magnetic static var compensator(MSVC). Compared with traditional compensation methods, the EHCS makes full use of the SVC’s advantages of economy and reliability and of RPC’s advantages of technical capability and flexibility. Based on the idea of injecting a negative sequence, the compensation principle of the EHCS is analyzed in detail. Then the minimum installation capacity of an EHCS is theoretically deduced. Furthermore, a constraint optimization compensation strategy that meets national standards, which reduces compensation capacity further, is proposed. An experimental platform based on a digital signal processor(DSP) and a programmable logic controller(PLC) is built to verify the analysis. Simulated and experimental results are given to demonstrate the effectiveness and feasibility of the proposed method.
基金supported by National Natural Science Foundation of China(No.50807041)
文摘This paper presents a multi-objective Pareto optimal method for allocation of fault current limiters based on an immune algorithm, which takes into account two objectives of the cost and fault current mitigation effect. A sensitivity factor calculation method based on the rate of fault current mitigation is proposed to reduce the search space and improve the efficiency of the algorithm.In this approach, the objective functions related to the cost and fault current mitigation effect are established. A modified inversion operator based on equal cost is proposed to converge to global optimal solutions more effectively. The proposed algorithm is tested on the IEEE39-bus system, and obtains the Pareto optimal solutions,from which the user can select the most suitable solutions according to the preferences and relative importance of the objective functions. Simulation results are used to verify the proposed method.
基金supported by the National Natural Science foundation of China[grant number 81801761 to Y.L.].
文摘Background Patients with chronic pancreatitis often have irreversible pancreatic insufficiency before a clinical diagnosis.Pancreatic cancer is a fatal malignant tumor in the advanced stages.Patients having high risk of pancreatic diseases must be screened early to obtain better outcomes using new imaging modalities.Therefore,this study aimed to investigate the reproducibility of tomoelastography measurements for assessing pancreatic stiffness and fluidity and the variance among healthy volunteers.Methods Forty-seven healthy volunteers were prospectively enrolled and underwent two tomoelastography examinations at a mean interval of 7 days.Two radiologists blindly and independently measured the pancreatic stiffness and fluidity at the first examination to determine the reproducibility between readers.One radiologist measured the adjacent pancreatic slice at the first examination to determine the reproducibility among slices and measured the pancreas at the second examination to determine short-termrepeatability.The stiffness and fluidity of the pancreatic head,body,and tail were compared to determine anatomical differences.The pancreatic stiffness and fluidity were compared based on sex,age,and body mass index(BMI).Results Bland–Altman analyses(all P>0.05)and intraclass correlation coefficients(all>0.9)indicated near perfect reproducibility among readers,slices,and examinations at short intervals.Neither stiffness(P=0.477)nor fluidity(P=0.368)differed among the pancreatic anatomical regions.The mean pancreatic stiffness was 1.45±0.09 m/s;the mean pancreatic fluidity was 0.83±0.06 rad.Stiffness and fluidity did not differ by sex,age,or BMI.Conclusion Tomoelastography is a promising and reproducible tool for assessing pancreatic stiffness and fluidity in healthy volunteers.
基金This work was supported in part by the National Key Research and Development Program of China under Grant no.2017YFB0902904in part by the Natural Science Foundation of Hubei Province under Grant no.2016CFB448+1 种基金in part by the Shenzhen City Science and Technology Innovation Plan under Grant no.JCYJ20170306170937861in part by Wuhan City Science and Technology Program under Grant no.2016070204020165.
文摘The large current generated by a direct start of the super-large-capacity high-voltage induction motor would have a huge impact on the power grid as well as the motor itself.Traditional soft starters have the shortcomings of discontinuous adjustment,voltage sags,sudden torque mutation,secondary current impact and high cost.To resolve this issue,the authors propose a novel coupled autotransformer and magnetic-control(CATMC)soft-start method.The structure of the new CATMC soft starter combines the functions of the autotransformer and magnetic control reactor via an innovative electric and magnetic circuit design.In this study,the authors analyse the magnetic circuit structure and working principles of the CATMC soft starter.Then,to validate its principle and performance,the authors conduct a simulation study using ANSYS software and design and test an 18 MW/10 kV CATMC soft starter prototype.The simulation results demonstrate that the CATMC soft starter effectively avoids secondary current impact and constrains the motor starting current to<2.5 times the rated current.The public connection point bus voltage also meets the voltage sag requirement of the IEEE standard and reduces the impact on the power grid.
基金This work was supported in part by the Open Project of the State Rail Transit Technology Research Centre under Grant NEEC-2017-A04in part by the Open Fund of Cascade Hydropower Station Operation and Control in Hubei Province under Grant no.2017KJX02in part by the Shenzhen City Science and Technology Innovation Plan under Grant JCYJ20170306170937861。
文摘With the continuous expansion of power grid capacity,the problem of short-circuit current exceeding the standard is becoming increasingly serious.Fault current limiter is a promising solution and is gradually becoming a research hotspot.In this study,fault current limiters are classified into four categories.And saturated-core fault current limiters are emphatically introduced,including its working principle and comparison with the other three categories.Saturated core fault current limiters are divided into four branches according to the ways leading the core saturated.A comprehensive review of the research activities and emerging technologies of saturated-core fault current limiters for AC power systems is presented in this study.The working principle and typical structure of DC-biased-,permanent-magnet-,superconducting-and hybrid-type saturated-core fault current limiters are introduced.The advantages and disadvantages of four types of saturated core fault current limiters are compared in detail from the aspects of current-limiting performance,iron core size and DC magnetomotive force.Real grid application examples of some types of devices are presented,as well as new progress in the techniques,are covered and discussed in detail.One may find the content of this study helpful as a detailed literature review or as practical technical guidance.
