Natural gas methane and hydrates are a chemical compound of water molecules formed under low temperature and high pressure. The decomposition of 1 m^3 of natural gas hydrates can release about 0.8 m^3 of water and 164...Natural gas methane and hydrates are a chemical compound of water molecules formed under low temperature and high pressure. The decomposition of 1 m^3 of natural gas hydrates can release about 0.8 m^3 of water and 164 m3 of natural gas. Thus, natural gas hydrates are characterized by their high-energy density and huge resource potential. It is estimated that the world＇s total natural gas hydrates resource amount is equivalent to twice the total carbon amount of the global proven conventional fuels and can meet the human energy requirement in the future for 1000 years. They are thus the first choice to replace conventional energy of petroleum and coal.展开更多
A systematic approach to the design of the conducted electromagnetic interference （EMI） filter of high-density plasma cutting power supply has been developed. Converter components have been accurately modeled, with ...A systematic approach to the design of the conducted electromagnetic interference （EMI） filter of high-density plasma cutting power supply has been developed. Converter components have been accurately modeled, with parasitic elements extracted to reveal their impacts on the EMI noises. Circuit simulations have been used to analyze and minimize the EMI noises. Conducted EMI noise measurement and filter design of this power supply have been achieved which successfully satisfy the FCC class B limits in the frequency range from 150 kHz to 30 MHz. The analyses and experimental results show that the designed filter guarantees that the required attenuation will be achieved.展开更多
Under the inflammable or explosive environment, the direct measurement methods by opening up the explo- sion-proof shell of electrical installations were not adopted. So, it＇s impossible to have a quantitative analys...Under the inflammable or explosive environment, the direct measurement methods by opening up the explo- sion-proof shell of electrical installations were not adopted. So, it＇s impossible to have a quantitative analysis on the limit of conducted disturbance for electrical fast transient burst （EFT/B） in such dangerous environments. Transient conducted coupling model, which using EFT/B as its excitation source, can be built based on circuit and electromagnetic field theory. Furthermore, numerical analysis was performed. The results indicate that the capacitive coupling voltage is the same polarity as EFT/B, and is the main disturbance form of conducted coupling in mines. The inductive coupling voltage is reversed polarity with the ca- pacitive coupling voltage, and both peaks appear only in the rising time of EFT/B, which increase with the rising of load resistance. Moreover, the cable coupling voltage on the side of disturbance source is higher than the one on the other side in tunnel. To reduce the common resistance can suppress the resistive coupling disturbance.展开更多
This paper presents the design of a controller for the measurement and reduction of conducted Electro Magnetic Interference (EMI) caused in the power electronic circuits. The conducted EMI is also separating the Commo...This paper presents the design of a controller for the measurement and reduction of conducted Electro Magnetic Interference (EMI) caused in the power electronic circuits. The conducted EMI is also separating the Common Mode (CM) and Differential Mode (DM) simultaneously using Line Impedance Stabilization Network (LISN). EMI is mitigated by the fuzzy controller. By comparing common mode voltage with the standard reference value, the generated error can be minimized by using fuzzy controller. Fuzzy controller is varying the PWM signal of the power electronic switching devices for reducing the electromagnetic interference. In this paper, comparison of PI and fuzzy controller of the open loop and closed loop models are implemented using MATLAB<sup>®</sup></sup> SIMULINK for measurement and reduction of the EMI level;and also simulation results of the PI controller and fuzzy controller analysis are presented in this paper. The fuzzy controller is provided to achieve the EMI level of the inverter within the standard limit.展开更多
Recently,Software-Defined Radio(SDR)has gained great popularity owing to its attractive merits,such as flexible signals configuration in multiple channels.However,commercial SDR equipment also has large spurious emiss...Recently,Software-Defined Radio(SDR)has gained great popularity owing to its attractive merits,such as flexible signals configuration in multiple channels.However,commercial SDR equipment also has large spurious emissions in the Transmitting(Tx)channel.This paper presents a cascaded model for the Conducted Emission(CE)properties of a general SDR platform,which captures all the key components with high precision.Based on a deeper understanding of the CE properties,a mitigation method is proposed for suppressing the spurious emissions of an SDR Tx channel.This method is based on an efficient vector signal cancellation scheme,in which multiple SDR channels are adopted to suppress the second-and third-order harmonic signals simultaneously.A hardware prototype with dual SDR channels is built and measured for verification.Experimental results show that the suppression level of the third-order harmonic signal is 24 dB on average in the frequency range of 100 MHz to 3000 MHz.The theoretic limit of the suppression level is related to the magnitude and phase errors,and the suppression level may be further improved by calibrating each SDR channel.展开更多
Conducted electromagnetic interference (EMI) from a 7.5kVA DC/DC high power converter is investigated to agree with EN class A. Here in some passive methods of suppressing conducted EM Noise, such as mixed-mode (MM) E...Conducted electromagnetic interference (EMI) from a 7.5kVA DC/DC high power converter is investigated to agree with EN class A. Here in some passive methods of suppressing conducted EM Noise, such as mixed-mode (MM) EMI filters, snubbing circuits and other means, are used. Based on measurement, the sources of noise are detected with the characteristics analyzed in detail. The MM EMI filters is valuable means with which low-frequency part and some of the high frequency part of conducted EM Noise can be efficiently reduced. How to lay out the MM filters on both sides of the converter is outlined in detail. In addition, multiple grounding and RDC snubbing circuits are employed to improve the performance in high frequency. The experimental results confirm the methods adopted.展开更多
InIn accordance with the regulations as stipulated in Circularon Some Relevant Issues in Levying Tariff and ImportTaxes on Printed Matters Conducted in HongKong andMacao(Promulgated by Decree No.9 of Tariff Regulation...InIn accordance with the regulations as stipulated in Circularon Some Relevant Issues in Levying Tariff and ImportTaxes on Printed Matters Conducted in HongKong andMacao(Promulgated by Decree No.9 of Tariff Regulation Com-mission in 1997), the regulations regarding import duties as stipu-lated in Circular on Measures for Strict Control over Printing inHongKong and Macao, submitted by State Economic Commis-sion, State Planning Commission and Ministry of Finance andapproved by the State Council in its Decree No. 141 in 1985, shallcease to be effective as of July 1, 1997.The Customs, as of July 1, shall levy tariff and import taxesin line with the legal tax rate on inland printed matters conductedin HongKong and Macao. All former pertinent provisions shallbe null and void at the same time.展开更多
Conducted Energy Weapons (CEWs), such as those manufactured by TASER International Inc., are seeing increased use by law enforcement agencies as a less lethal force option;but, at the same time, these weapons are also...Conducted Energy Weapons (CEWs), such as those manufactured by TASER International Inc., are seeing increased use by law enforcement agencies as a less lethal force option;but, at the same time, these weapons are also seeing an increased level of concern in terms of their safety of use. In order to enable consistent evaluation of CEW performance, a systematic protocol for testing the electrical output of such weapons is required. In this paper, we propose a test specification for CEWs, designed to calculate the key performance and electrical safety parameters. The weapon is fired into a specified load, and current or voltage data are acquired, from which a set of electrical parameters are calculated and recorded. The protocol is based on experience of testing 6000 CEWs in the labs affiliated with the authors. This test protocol is designed to enable systematic testing, evaluation and research on CEW’s, including identification of weapons which are out of specification, determination of changes in weapon characteristics over time, and evaluation of weapons post-incident. Based on the proposed test protocol, we evaluate and report on electrical output produced by 208 X26TM and128 M26TM TASER? weapons. Results are shown in terms of proposed summary parameters and in terms of manufacturer’s performance specifications.展开更多
The service module of Chang’e 5-T1 has been conducting an in-orbit demonstration for the Chang’e-5 mission since it was left in space.The service module departed Earth-Moon L2 point finishing its extended L2 point f...The service module of Chang’e 5-T1 has been conducting an in-orbit demonstration for the Chang’e-5 mission since it was left in space.The service module departed Earth-Moon L2 point finishing its extended L2 point fly-by tests on January 4and entered a 127-minute circumlunar round orbit on January 13 with an altitude of 200km and inclined angle of 43.7degrees after three braking actions at perilune on January 11,12 and 13.During the L2 point fly-by,the cameras on-展开更多
This paper presents a new approach for modeling of the conducted electromagnetic interference(EMI) prediction for widely used converter systems.Coupling paths and mechanism of differential mode(DM) interference and co...This paper presents a new approach for modeling of the conducted electromagnetic interference(EMI) prediction for widely used converter systems.Coupling paths and mechanism of differential mode(DM) interference and common mode(CM) interference have been analyzed.Models to predict the high-frequency noise of PWM converter system are created.A direct calculation method in frequency domain is proposed for the deduction of frequency spectrum.A method is given for obtaining the parasitic parameters and topological structure of the model.An experimental investigation of the conducted emission from an actual high-power rectifier system is described.The validity of the models is confirmed by comparison to laboratory measurements.展开更多
The characteristics of conducted disturbances via current transformer(CT)caused by switch operations in 1000 kV UHV substations are studied in this paper.Since the broadband circuit models might have limitations on th...The characteristics of conducted disturbances via current transformer(CT)caused by switch operations in 1000 kV UHV substations are studied in this paper.Since the broadband circuit models might have limitations on the stability and accuracy for CT conducted disturbance simulation,a frequencydomain simulation method without circuit synthesis is proposed based on VFTC spectrum and CT transfer characteristics.To improve VFTC simulation accuracy,both the bushing radiation loss and frequency-dependent earth impedance are taken into consideration.Transfer characteristics of three types of windings for the 1000 kV GIS CT are ingeniously measured from a combination of fast and slow impulse tests.Through conducted disturbances simulations in UHV Wuhu substation,bushing radiation loss is found to have a suppression effect on the highfrequency response but the effect of frequency-dependent earth impedance can be ignored.As a result,the maximum amplitude of 84.5 A for the conducted disturbance is obtained,thus a fast damped oscillatory wave immunity test with no lower than Level 4 from IEC standard is suggested to test the anti-interference performance of the secondary equipment in UHV substation.展开更多
Focusing on the state-of-the-art conducted EMI prediction, this paper presents a noise source lumped circuit modeling and identification method, an EMI modeling method based on multiple slope approximation of switchin...Focusing on the state-of-the-art conducted EMI prediction, this paper presents a noise source lumped circuit modeling and identification method, an EMI modeling method based on multiple slope approximation of switching transitions, and dou-ble Fourier integral method modeling PWM conversion units to achieve an accurate modeling of EMI noise source. Meanwhile, a new sensitivity analysis method, a general coupling model for steel ground loops, and a partial element equivalent circuit method are proposed to identify and characterize conducted EMI coupling paths. The EMI noise and propagation modeling provide an accurate prediction of conducted EMI in the entire frequency range (0―10 MHz) with good practicability and generality. Finally a new measurement approach is presented to identify the surface current of large dimensional metal shell. The proposed analytical modeling methodology is verified by experimental results.展开更多
Modular multilevel converters(MMCs)have been widely used owing to their superior performance.However,the rapid switching of power electronics devices causes serious electromagnetic interference(EMI).There are a large ...Modular multilevel converters(MMCs)have been widely used owing to their superior performance.However,the rapid switching of power electronics devices causes serious electromagnetic interference(EMI).There are a large number of obvious EMI peaks in the frequency spectrum of the carrier phase-shifted constant-switching-frequency pulse-width modulation(CSFPWM).Spreading the EMI across a wider frequency range can help to reduce the EMI peaks.In this study,we designed a uniform distribution(UD)spread-spectrum modulation technology using the principle of uniform switching frequency distribution and minimum switching loss for MMC.Its feasibility is verified by theoretical derivation and simulation.Then,the effectiveness of UDPWM in reducing the EMI is verified in experiments with a prototype MMC testbed in the lab.Compared with traditional CSFPWM,UDPWM can reduce conducted EMI by 10-20 dB.Also,compared with random PWM(RPWM),UDPWM can improve efficiency and reduce total harmonic distortion(THD)of output voltage and current in MMC.展开更多
Copper manufactured by laser powder bed fusion(LPBF)process typically exhibits poor strength-ductility coordination,and the addition of strengthening phases is an effective way to address this issue.To explore the eff...Copper manufactured by laser powder bed fusion(LPBF)process typically exhibits poor strength-ductility coordination,and the addition of strengthening phases is an effective way to address this issue.To explore the effects of strengthening phases on Cu,Cu-carbon nanotubes(CNTs)composites were prepared using LPBF technique with Cu-CNTs mixed powder as the matrix.The formability,microstructure,mechanical properties,electrical conductivity,and thermal properties were studied.The result shows that the prepared composites have high relative density.The addition of CNTs results in inhomogeneous equiaxed grains at the edges of the molten pool and columnar grains at the center.Compared with pure copper,the overall mechanical properties of the composite are improved:tensile strength increases by 52.8%and elongation increases by 146.4%;the electrical and thermal properties are also enhanced:thermal conductivity increases by 10.8%and electrical conductivity increases by 12.7%.展开更多
The display image of a PC can be reconstructed by using the conducted emission on the PC＇s network cable. The relevant signals which be used to reconstruct the original image are coupling from the radiation of the sw...The display image of a PC can be reconstructed by using the conducted emission on the PC＇s network cable. The relevant signals which be used to reconstruct the original image are coupling from the radiation of the switching of red, green, blue （RGB） signals in PC. These pertinent signals are partly contained in the frequency region higher than 30 MHz in the conducted emission. From these findings, the near-field coupling principle from PC to the network cable is analyzed firstly. And then, a multi-conductor transmission model for the RGB signals which transmit in the network cable is proposed. In addition, the maximum safe distance is estimated by using this model. In order to check the validity of the estimating distance, the eavesdropping experiment is carried out to reconstruct the original display image. The results demonstrate that the blurred display image can be retrieved at the place of 29.5 m.展开更多
During his first year as an entrepreneur,Han Bicheng washed his hair roughly three times a day-more than 800 times in a single year.He and his team had to repeatedly apply conductive gel to their scalps to capture the...During his first year as an entrepreneur,Han Bicheng washed his hair roughly three times a day-more than 800 times in a single year.He and his team had to repeatedly apply conductive gel to their scalps to capture the clean electroencephalogram signals needed for their experiments,a routine that kept them in a near-constant cycle of shampooing.展开更多
Proton exchange membrane(PEM)is an integral component in fuel cells which enables proton transport for efficient energy conversion.Sulfonated Polyether Ether Ketone(SPEEK)has emerged as a cost-effective option with no...Proton exchange membrane(PEM)is an integral component in fuel cells which enables proton transport for efficient energy conversion.Sulfonated Polyether Ether Ketone(SPEEK)has emerged as a cost-effective option with non-fluorinated aromatic backbones for Proton Exchange Membrane Fuel Cell(PEMFC)applications,even though it exhibits lower proton conductivity compared to Nafion.This work aims to study the influence of Sulfonated Chitosan(SCS)concentrations on proton conductivity of SPEEK-based PEM at room temperature.SPEEK was synthesized using a sulfonation process with concentrated sulfuric acid at room temperature.SCS was synthesized via reflux of CS and 1.2 M H2SO4 with a ratio of 1:35(w/v)at 90℃ for 30 min.The composite membranes of SPEEK-SCS were formed with four different SCS concentrations,using the solution castingmethod,andDimethyl Sulfoxide(DMSO)was used as a solvent.The composite membranes synthesized include pure SPEEK(S0),SPEEK with 1%SCS(S1),SPEEK with 2%SCS(S2),and SPEEK with 3%SCS(S3).Fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),water uptake,degree of swelling,Ionic exchange capacity(IEC)with Electrochemical impedance spectroscopy(EIS)were used to characterize the composite membranes in terms of composition,crystallinity,water absorption,dimensional changes,number of exchangeable ions in membranes,and proton conductivity,respectively.Notably,S3 had the highest water uptake and the lowest degree of swelling.S2 had the highest proton conductivity among the SPEEK-SCS composite membranes at room temperature with 3.44×10^(−2) Scm^(-1).展开更多
In this study,multilayer lamination welding was employed to prepare graphene/copper(Gr/Cu)composite billets from graphene-coated copper foils,followed by multi-pass cold drawing to produce Φ1 mm Gr/Cu composite wires...In this study,multilayer lamination welding was employed to prepare graphene/copper(Gr/Cu)composite billets from graphene-coated copper foils,followed by multi-pass cold drawing to produce Φ1 mm Gr/Cu composite wires.Microstructure and property analyses in both the cold-drawn and annealed states show that the incorporation of graphene significantly improves the ductility and electrical conductivity of the copper wire.After annealing at 350℃ for 30 minutes,the composite wire demonstrates a tensile strength of 270 MPa and an electrical conductivity of 102.74%IACS,both superior to those of pure copper wire under identical conditions.At 150℃,the electrical conductivity of the annealed composite wire reaches 72.60%IACS,notably higher than the 68.19%IACS of pure copper.The results suggest that graphene is uniformly distributed within the composite wire,with minimal impact on conductivity,while effectively refining the copper grain structure to enhance ductility.Moreover,graphene suppresses copper lattice vibrations at elevated temperatures,reducing the rate of conductivity degradation.展开更多
文摘Natural gas methane and hydrates are a chemical compound of water molecules formed under low temperature and high pressure. The decomposition of 1 m^3 of natural gas hydrates can release about 0.8 m^3 of water and 164 m3 of natural gas. Thus, natural gas hydrates are characterized by their high-energy density and huge resource potential. It is estimated that the world＇s total natural gas hydrates resource amount is equivalent to twice the total carbon amount of the global proven conventional fuels and can meet the human energy requirement in the future for 1000 years. They are thus the first choice to replace conventional energy of petroleum and coal.
基金National Natural Science Foundation of China (No. 50477009)
文摘A systematic approach to the design of the conducted electromagnetic interference （EMI） filter of high-density plasma cutting power supply has been developed. Converter components have been accurately modeled, with parasitic elements extracted to reveal their impacts on the EMI noises. Circuit simulations have been used to analyze and minimize the EMI noises. Conducted EMI noise measurement and filter design of this power supply have been achieved which successfully satisfy the FCC class B limits in the frequency range from 150 kHz to 30 MHz. The analyses and experimental results show that the designed filter guarantees that the required attenuation will be achieved.
基金Supported by the National Natural Science Foundation of China （50674093） the Project of Fujian Provincial Education Department （JA11098）
文摘Under the inflammable or explosive environment, the direct measurement methods by opening up the explo- sion-proof shell of electrical installations were not adopted. So, it＇s impossible to have a quantitative analysis on the limit of conducted disturbance for electrical fast transient burst （EFT/B） in such dangerous environments. Transient conducted coupling model, which using EFT/B as its excitation source, can be built based on circuit and electromagnetic field theory. Furthermore, numerical analysis was performed. The results indicate that the capacitive coupling voltage is the same polarity as EFT/B, and is the main disturbance form of conducted coupling in mines. The inductive coupling voltage is reversed polarity with the ca- pacitive coupling voltage, and both peaks appear only in the rising time of EFT/B, which increase with the rising of load resistance. Moreover, the cable coupling voltage on the side of disturbance source is higher than the one on the other side in tunnel. To reduce the common resistance can suppress the resistive coupling disturbance.
文摘This paper presents the design of a controller for the measurement and reduction of conducted Electro Magnetic Interference (EMI) caused in the power electronic circuits. The conducted EMI is also separating the Common Mode (CM) and Differential Mode (DM) simultaneously using Line Impedance Stabilization Network (LISN). EMI is mitigated by the fuzzy controller. By comparing common mode voltage with the standard reference value, the generated error can be minimized by using fuzzy controller. Fuzzy controller is varying the PWM signal of the power electronic switching devices for reducing the electromagnetic interference. In this paper, comparison of PI and fuzzy controller of the open loop and closed loop models are implemented using MATLAB<sup>®</sup></sup> SIMULINK for measurement and reduction of the EMI level;and also simulation results of the PI controller and fuzzy controller analysis are presented in this paper. The fuzzy controller is provided to achieve the EMI level of the inverter within the standard limit.
基金supported by the National Natural Science Foundation of China(Nos.U2141230 and 61971018).
文摘Recently,Software-Defined Radio(SDR)has gained great popularity owing to its attractive merits,such as flexible signals configuration in multiple channels.However,commercial SDR equipment also has large spurious emissions in the Transmitting(Tx)channel.This paper presents a cascaded model for the Conducted Emission(CE)properties of a general SDR platform,which captures all the key components with high precision.Based on a deeper understanding of the CE properties,a mitigation method is proposed for suppressing the spurious emissions of an SDR Tx channel.This method is based on an efficient vector signal cancellation scheme,in which multiple SDR channels are adopted to suppress the second-and third-order harmonic signals simultaneously.A hardware prototype with dual SDR channels is built and measured for verification.Experimental results show that the suppression level of the third-order harmonic signal is 24 dB on average in the frequency range of 100 MHz to 3000 MHz.The theoretic limit of the suppression level is related to the magnitude and phase errors,and the suppression level may be further improved by calibrating each SDR channel.
文摘Conducted electromagnetic interference (EMI) from a 7.5kVA DC/DC high power converter is investigated to agree with EN class A. Here in some passive methods of suppressing conducted EM Noise, such as mixed-mode (MM) EMI filters, snubbing circuits and other means, are used. Based on measurement, the sources of noise are detected with the characteristics analyzed in detail. The MM EMI filters is valuable means with which low-frequency part and some of the high frequency part of conducted EM Noise can be efficiently reduced. How to lay out the MM filters on both sides of the converter is outlined in detail. In addition, multiple grounding and RDC snubbing circuits are employed to improve the performance in high frequency. The experimental results confirm the methods adopted.
文摘InIn accordance with the regulations as stipulated in Circularon Some Relevant Issues in Levying Tariff and ImportTaxes on Printed Matters Conducted in HongKong andMacao(Promulgated by Decree No.9 of Tariff Regulation Com-mission in 1997), the regulations regarding import duties as stipu-lated in Circular on Measures for Strict Control over Printing inHongKong and Macao, submitted by State Economic Commis-sion, State Planning Commission and Ministry of Finance andapproved by the State Council in its Decree No. 141 in 1985, shallcease to be effective as of July 1, 1997.The Customs, as of July 1, shall levy tariff and import taxesin line with the legal tax rate on inland printed matters conductedin HongKong and Macao. All former pertinent provisions shallbe null and void at the same time.
文摘Conducted Energy Weapons (CEWs), such as those manufactured by TASER International Inc., are seeing increased use by law enforcement agencies as a less lethal force option;but, at the same time, these weapons are also seeing an increased level of concern in terms of their safety of use. In order to enable consistent evaluation of CEW performance, a systematic protocol for testing the electrical output of such weapons is required. In this paper, we propose a test specification for CEWs, designed to calculate the key performance and electrical safety parameters. The weapon is fired into a specified load, and current or voltage data are acquired, from which a set of electrical parameters are calculated and recorded. The protocol is based on experience of testing 6000 CEWs in the labs affiliated with the authors. This test protocol is designed to enable systematic testing, evaluation and research on CEW’s, including identification of weapons which are out of specification, determination of changes in weapon characteristics over time, and evaluation of weapons post-incident. Based on the proposed test protocol, we evaluate and report on electrical output produced by 208 X26TM and128 M26TM TASER? weapons. Results are shown in terms of proposed summary parameters and in terms of manufacturer’s performance specifications.
文摘The service module of Chang’e 5-T1 has been conducting an in-orbit demonstration for the Chang’e-5 mission since it was left in space.The service module departed Earth-Moon L2 point finishing its extended L2 point fly-by tests on January 4and entered a 127-minute circumlunar round orbit on January 13 with an altitude of 200km and inclined angle of 43.7degrees after three braking actions at perilune on January 11,12 and 13.During the L2 point fly-by,the cameras on-
基金supported by the National Natural Science Foundation of China (Grant No. 50977063)Key Science and Technology Supporting Project of Tianjin (Grant No. 09ZCKFGX01800)
文摘This paper presents a new approach for modeling of the conducted electromagnetic interference(EMI) prediction for widely used converter systems.Coupling paths and mechanism of differential mode(DM) interference and common mode(CM) interference have been analyzed.Models to predict the high-frequency noise of PWM converter system are created.A direct calculation method in frequency domain is proposed for the deduction of frequency spectrum.A method is given for obtaining the parasitic parameters and topological structure of the model.An experimental investigation of the conducted emission from an actual high-power rectifier system is described.The validity of the models is confirmed by comparison to laboratory measurements.
基金supported by the National Natural Science Foundation of China(51977199).
文摘The characteristics of conducted disturbances via current transformer(CT)caused by switch operations in 1000 kV UHV substations are studied in this paper.Since the broadband circuit models might have limitations on the stability and accuracy for CT conducted disturbance simulation,a frequencydomain simulation method without circuit synthesis is proposed based on VFTC spectrum and CT transfer characteristics.To improve VFTC simulation accuracy,both the bushing radiation loss and frequency-dependent earth impedance are taken into consideration.Transfer characteristics of three types of windings for the 1000 kV GIS CT are ingeniously measured from a combination of fast and slow impulse tests.Through conducted disturbances simulations in UHV Wuhu substation,bushing radiation loss is found to have a suppression effect on the highfrequency response but the effect of frequency-dependent earth impedance can be ignored.As a result,the maximum amplitude of 84.5 A for the conducted disturbance is obtained,thus a fast damped oscillatory wave immunity test with no lower than Level 4 from IEC standard is suggested to test the anti-interference performance of the secondary equipment in UHV substation.
基金Supported by the National Natural Science Foundation of China (Grant No. 50721063)
文摘Focusing on the state-of-the-art conducted EMI prediction, this paper presents a noise source lumped circuit modeling and identification method, an EMI modeling method based on multiple slope approximation of switching transitions, and dou-ble Fourier integral method modeling PWM conversion units to achieve an accurate modeling of EMI noise source. Meanwhile, a new sensitivity analysis method, a general coupling model for steel ground loops, and a partial element equivalent circuit method are proposed to identify and characterize conducted EMI coupling paths. The EMI noise and propagation modeling provide an accurate prediction of conducted EMI in the entire frequency range (0―10 MHz) with good practicability and generality. Finally a new measurement approach is presented to identify the surface current of large dimensional metal shell. The proposed analytical modeling methodology is verified by experimental results.
基金Supported by the National Natural Science Fundation of China(U1866211)。
文摘Modular multilevel converters(MMCs)have been widely used owing to their superior performance.However,the rapid switching of power electronics devices causes serious electromagnetic interference(EMI).There are a large number of obvious EMI peaks in the frequency spectrum of the carrier phase-shifted constant-switching-frequency pulse-width modulation(CSFPWM).Spreading the EMI across a wider frequency range can help to reduce the EMI peaks.In this study,we designed a uniform distribution(UD)spread-spectrum modulation technology using the principle of uniform switching frequency distribution and minimum switching loss for MMC.Its feasibility is verified by theoretical derivation and simulation.Then,the effectiveness of UDPWM in reducing the EMI is verified in experiments with a prototype MMC testbed in the lab.Compared with traditional CSFPWM,UDPWM can reduce conducted EMI by 10-20 dB.Also,compared with random PWM(RPWM),UDPWM can improve efficiency and reduce total harmonic distortion(THD)of output voltage and current in MMC.
基金National Key Research and Development Program of China(2023YFB4606400)Supported by Longmen Laboratory Frontier Exploration Topics(LMQYTSKT003)。
文摘Copper manufactured by laser powder bed fusion(LPBF)process typically exhibits poor strength-ductility coordination,and the addition of strengthening phases is an effective way to address this issue.To explore the effects of strengthening phases on Cu,Cu-carbon nanotubes(CNTs)composites were prepared using LPBF technique with Cu-CNTs mixed powder as the matrix.The formability,microstructure,mechanical properties,electrical conductivity,and thermal properties were studied.The result shows that the prepared composites have high relative density.The addition of CNTs results in inhomogeneous equiaxed grains at the edges of the molten pool and columnar grains at the center.Compared with pure copper,the overall mechanical properties of the composite are improved:tensile strength increases by 52.8%and elongation increases by 146.4%;the electrical and thermal properties are also enhanced:thermal conductivity increases by 10.8%and electrical conductivity increases by 12.7%.
基金supported by the National Natural Science Foundation of China (61072136, 61171051)
文摘The display image of a PC can be reconstructed by using the conducted emission on the PC＇s network cable. The relevant signals which be used to reconstruct the original image are coupling from the radiation of the switching of red, green, blue （RGB） signals in PC. These pertinent signals are partly contained in the frequency region higher than 30 MHz in the conducted emission. From these findings, the near-field coupling principle from PC to the network cable is analyzed firstly. And then, a multi-conductor transmission model for the RGB signals which transmit in the network cable is proposed. In addition, the maximum safe distance is estimated by using this model. In order to check the validity of the estimating distance, the eavesdropping experiment is carried out to reconstruct the original display image. The results demonstrate that the blurred display image can be retrieved at the place of 29.5 m.
文摘During his first year as an entrepreneur,Han Bicheng washed his hair roughly three times a day-more than 800 times in a single year.He and his team had to repeatedly apply conductive gel to their scalps to capture the clean electroencephalogram signals needed for their experiments,a routine that kept them in a near-constant cycle of shampooing.
文摘Proton exchange membrane(PEM)is an integral component in fuel cells which enables proton transport for efficient energy conversion.Sulfonated Polyether Ether Ketone(SPEEK)has emerged as a cost-effective option with non-fluorinated aromatic backbones for Proton Exchange Membrane Fuel Cell(PEMFC)applications,even though it exhibits lower proton conductivity compared to Nafion.This work aims to study the influence of Sulfonated Chitosan(SCS)concentrations on proton conductivity of SPEEK-based PEM at room temperature.SPEEK was synthesized using a sulfonation process with concentrated sulfuric acid at room temperature.SCS was synthesized via reflux of CS and 1.2 M H2SO4 with a ratio of 1:35(w/v)at 90℃ for 30 min.The composite membranes of SPEEK-SCS were formed with four different SCS concentrations,using the solution castingmethod,andDimethyl Sulfoxide(DMSO)was used as a solvent.The composite membranes synthesized include pure SPEEK(S0),SPEEK with 1%SCS(S1),SPEEK with 2%SCS(S2),and SPEEK with 3%SCS(S3).Fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),water uptake,degree of swelling,Ionic exchange capacity(IEC)with Electrochemical impedance spectroscopy(EIS)were used to characterize the composite membranes in terms of composition,crystallinity,water absorption,dimensional changes,number of exchangeable ions in membranes,and proton conductivity,respectively.Notably,S3 had the highest water uptake and the lowest degree of swelling.S2 had the highest proton conductivity among the SPEEK-SCS composite membranes at room temperature with 3.44×10^(−2) Scm^(-1).
基金Funded by Hunan Provincial Natural Science Foundation(No.2023JJ40074)Hunan Provincial Education Department Excellent Youth Project(No.21B0757)Hunan Provincial Engineering Technology Center(No.2022TP2036)。
文摘In this study,multilayer lamination welding was employed to prepare graphene/copper(Gr/Cu)composite billets from graphene-coated copper foils,followed by multi-pass cold drawing to produce Φ1 mm Gr/Cu composite wires.Microstructure and property analyses in both the cold-drawn and annealed states show that the incorporation of graphene significantly improves the ductility and electrical conductivity of the copper wire.After annealing at 350℃ for 30 minutes,the composite wire demonstrates a tensile strength of 270 MPa and an electrical conductivity of 102.74%IACS,both superior to those of pure copper wire under identical conditions.At 150℃,the electrical conductivity of the annealed composite wire reaches 72.60%IACS,notably higher than the 68.19%IACS of pure copper.The results suggest that graphene is uniformly distributed within the composite wire,with minimal impact on conductivity,while effectively refining the copper grain structure to enhance ductility.Moreover,graphene suppresses copper lattice vibrations at elevated temperatures,reducing the rate of conductivity degradation.
