For demonstrating a multiterminal voltage-source converter(VSC)-based high-voltage DC(HVDC)(VSCHVDC) project, this study puts forward a technical route for calculating the power flow in a 500-kV VSC-HVDC power grid in...For demonstrating a multiterminal voltage-source converter(VSC)-based high-voltage DC(HVDC)(VSCHVDC) project, this study puts forward a technical route for calculating the power flow in a 500-kV VSC-HVDC power grid in comparison with that of an AC power grid. The Jacobian matrix used in the power-flow calculation was deduced through methods such as Newton–Laphson iteration and Taylor series expansion. Further, the operation effect of powerflow calculation on a true bipolar VSC-HVDC power grid was analyzed briefly. The elements of the Jacobian matrix corresponding to VSC were studied under the mode of droop control and the control strategy of VSC-HVDC power grid was analyzed in detail. The power-flow calculation model for VSC-HVDC power grid of the master–slave control mode was simplified using the PQ decomposition method of the power-flow calculation of an AC power grid. Moreover, a four-terminal model of the Zhangbei VSC-HVDC demonstration project was established and tested on MATLAB. The simulation results under two kinds of operating conditions were analyzed and compared to the results of BPA; the deviation between the power-flow results was studied. The results show that the proposed calculation method can provide a feasible support for calculating the power flow in VSC-HVDC grids.展开更多
The Cu-Ti-Si alloys containing in-situ formed Ti5Si3 are prepared. In order to clarify the Ti5Si3 formation processes and its microstructure characteristics, the as-cast and deeply etched Cu-Ti-Si alloys with differen...The Cu-Ti-Si alloys containing in-situ formed Ti5Si3 are prepared. In order to clarify the Ti5Si3 formation processes and its microstructure characteristics, the as-cast and deeply etched Cu-Ti-Si alloys with different compositions and cooling rates were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). It is found that the eutectic Ti5Si3 phases in Cu-Ti-Si alloys are rod-like with hexagonal cross section which tend to intertwine with each other to form a firm skeleton like a bird nest structure which can make the alloys keep their original shape even after etching off the Cu matrix. In addition, there is Cu in the center of many Ti5Si3 rods, resulting in a core-shell structure. With the increase of the cooling rate, Ti5Si3 distributes more uniformly, and the diameter of Ti5Si3 significantly decreases, with a minimum size of less than 100 nm, while the aspect ratio of Ti5Si3 increases.展开更多
Considering the complex coupling of multiple energies and the varying load forecasting errors for an integrated energy system(IES),this study proposes a dynamic time-scale scheduling strategy based on long short-term ...Considering the complex coupling of multiple energies and the varying load forecasting errors for an integrated energy system(IES),this study proposes a dynamic time-scale scheduling strategy based on long short-term memory(LSTM)and multiple load forecasting errors.This strategy dynamically selects a hybrid timescale which is suitable for a variety of energies for each month.This is obtained by combining the mean absolute percentage error(MAPE)curve of the load forecasting with the error restriction requirements of the dispatcher.Based on the day-ahead scheduling plan,the output of the partial equipment is selectively adjusted at each time-scale to realize multi-energy collaborative optimization and gives full play to the comprehensive advantages of the IES.This is achieved by considering the differences in the response speed for each piece of equipment within the intra-day scheduling.This study uses the IES as an example,and it dynamically determines the time scale of the energy monthly.In addition,this investigation presents a detailed analysis of the output plan of the key equipment to demonstrate the necessity and the advantages of the strategy.展开更多
Axial compression tests were conducted on AZ31 B magnesium and A6063 aluminum thin-walled square tubes with varied lengths and induced features at different compression rates. In compression, the magnesium tubes exhib...Axial compression tests were conducted on AZ31 B magnesium and A6063 aluminum thin-walled square tubes with varied lengths and induced features at different compression rates. In compression, the magnesium tubes exhibited a "local buckling and fracture" mode, with three fracture patterns, i.e."horizontal","double-oblique", and "spiral" fractures. In general, the magnesium tube showed an inferior crashworthiness to the aluminum square tube. In addition, the effects of L/W ratio, strain rate and induced features on the crashworthiness of thin-walled square tubes were investigated. With an increase in the L/W ratio(L and W represent the tube length and width, respectively) from 1 to 4, the maximal force and global specific energy absorption decreased in a power-law trend for the magnesium tubes,while they remained approximately constant for the aluminum tubes. Furthermore, as the compression rate increased from 5×10-5 to 10 m/s, the primary crashworthiness parameters of the magnesium tubes increased in an approximately exponential manner,while for the aluminum tubes,they changed slightly. Finally,the involved induced features were proven to be not an effective method to improve the specific energy absorption of magnesium tubes, thus, more trigger types,locations,and sizes will be evaluated in future to improve the energy-absorption ability.展开更多
Owing to safety issue and low energy density of liquid lithium-ion batteries(LIBs),all-solid-state lithium metal batteries(ASLMBs)with unique all-solid-state electrolytes(SEs)have attracted wide attentions.This arises...Owing to safety issue and low energy density of liquid lithium-ion batteries(LIBs),all-solid-state lithium metal batteries(ASLMBs)with unique all-solid-state electrolytes(SEs)have attracted wide attentions.This arises mainly from the advantages of the SEs in the suppression of lithium dendrite growth,long cycle life,and broad working temperature range,showing huge potential applications in electronic devices,electric vehicles,smart grids,and biomedical devices.However,SEs suffer from low lithiumion conductivity and low mechanical integrity,slowing down the development of practical ASLMBs.Nanostructure engineering is of great efficiency in tuning the structure and composition of the SEs with improved lithium-ion conductivity and mechanical integrity.Among various available technologies for nanostructure engineering,electrospinning is a promising technique because of its simple operation,cost-effectiveness,and efficient integration with different components.In this review,we will first give a simple description of the electrospinning process.Then,the use of electrospinning technique in the synthesis of various SEs is summarized,for example,organic nanofibrous matrix,organic/inorganic nanofibrous matrix,and inorganic nanofibrous matrix combined with other components.The current development of the advanced architectures of SEs through electrospinning technology is also presented to provide references and ideas for designing high-performance ASLMBs.Finally,an outlook and further challenges in the preparation of advanced SEs for ASLMBs through electrospinning engineering are given.展开更多
Based on seawater immersion,drying-wetting cycles,carbonation and drying-wetting cycles for coral aggregate sea-water concrete(CASC)with different strength grades,the effect of carbonation and drying-wetting cycles on...Based on seawater immersion,drying-wetting cycles,carbonation and drying-wetting cycles for coral aggregate sea-water concrete(CASC)with different strength grades,the effect of carbonation and drying-wetting cycles on chloride diffusion be-havior of CASC is studied.The results show that the free surface chloride concentration(Cs),free chloride diffusion coefficient(Df)and time-dependent index(m)of CASC in the drying-wetting cycles is obviously higher than that in seawater immersion.The Df and m of CASC of carbonation and drying-wetting cycles is higher than that in the drying-wetting cycles.Carbonation increases the Df and m of CASC,which is against CASC to resist chloride corrosion.The corrosion possibility of CASC structures in different ex-posed areas is as follows:splash zone(carbonation and drying-wetting cycles)>tidal zone(drying-wetting cycles)>underwater zone(seawater immersion).Besides,the chloride diffusion rate of C65-CASC is 17.8%-63.4%higher than that of C65-ordinary aggre-gate concrete(OAC)in seawater immersion(underwater zone).Therefore,anti-corrosion measures should be adopted to improve the service life of CASC structure in the oceanic environment.展开更多
To thoroughly study the extinguishing effect of a high-pressure water mist fire extinguishing system when a transformer fire occurs,a 3D experimental model of a transformer is established in this work by employing Fir...To thoroughly study the extinguishing effect of a high-pressure water mist fire extinguishing system when a transformer fire occurs,a 3D experimental model of a transformer is established in this work by employing Fire Dynamics Simulator(FDS)software.More specifically,by setting different parameters,the process of the highpressure water mist fire extinguishing system with the presence of both diverse ambient temperatures and water mist sprinkler laying conditions is simulated.In addition,the fire extinguishing effect of the employed high-pressure water mist system with the implementation of different strategies is systematically analyzed.The extracted results show that a fire source farther away fromthe centerline leads to a lower local temperature distribution.In addition,as the ambient temperature increases,the temperature above the fire source decreases,while the temperature and the concentrationof theupperflue gas layer bothdecrease.Interestingly,after thehigh-pressurewatermist sprinkler begins to operate,both the temperature distribution above the fire source and the concentration of the flue gas decrease,which indicates that the high-pressure water mist system plays the role of cooling and dust removal.By comparing various sprinkler laying methods,it is found that the lower sprinkler height has a better effect on the temperature above the fire source,the temperature of the upper flue gas layer,and the concentration of the flue gas.Moreover,when the sprinkler is spread over thewhole transformer,the cooling effect on both the temperature above the fire source and the temperature of the upper flue gas layer is good,whereas the change in the concentration of the flue gas above the fire source is not obvious compared to the case where the sprinkler is not fully spread.展开更多
In order to study the extinguishing performance of high-pressure-water-mist-based systems on the fires originating from power transformers the PyroSim software is used.Different particle velocities and flow rates are ...In order to study the extinguishing performance of high-pressure-water-mist-based systems on the fires originating from power transformers the PyroSim software is used.Different particle velocities and flow rates are considered.The evolution laws of temperature around transformer,flue gas concentration and upper layer temperature of flue gas are analyzed under different boundary conditions.It is shown that the higher the particle velocity is,the lower the smoke concentration is,the better the cooling effect on the upper layer temperature of flue gas layer is,the larger the flow rate is and the better the cooling effect is.展开更多
Capacitor voltage transformer (CVT), which is with simple structure, convenient maintenance, functional diversity and high impact pressure strength, is widely used. And its capacitance and dielectric loss Angle measur...Capacitor voltage transformer (CVT), which is with simple structure, convenient maintenance, functional diversity and high impact pressure strength, is widely used. And its capacitance and dielectric loss Angle measurement is an important test on testing the insulation of the equipment. This paper is mainly to introduce and discuss one of the CVT test methods——the “self excitation method”, combined with the actual situation encountered in the work, sums up and expounds the maintenance of CVT and preventive test of influence factors.展开更多
Fault diagnosis is an important application of the power grids monitoring system. Under the situation of continuous development of smart grid, it brings new challenges to the fault diagnosis technology. A fault diagno...Fault diagnosis is an important application of the power grids monitoring system. Under the situation of continuous development of smart grid, it brings new challenges to the fault diagnosis technology. A fault diagnosis expert system based on model driven approach is proposed in this paper. And the corresponding fault modeling technology based on Fault Logic Description Language (FLDL) is described step by step. Practices show that this system could meet the requirements of processing fault alarm information rapidly and reliably by operator.展开更多
The oil-pressboard insulation is a typical composite insulation system widely used in the design and manufactory of large power apparatus. The implement of oil-pressboard insulation may lead to surface electrification...The oil-pressboard insulation is a typical composite insulation system widely used in the design and manufactory of large power apparatus. The implement of oil-pressboard insulation may lead to surface electrification and discharge at the interface under certain condition. It is of significant importance to take an insight into the phenomenon occurring at the interface. Through experiment, the pressboard is found as a porous material. The interface changes abruptly from bulk pressboard to the bulk oil as a result of the porous structure. A new model is proposed which divides the interface into bulk oil region, transition region, and bulk pressboard region. The width of the transition region is decided according to the microtome figure. The effective permittivity of the transition region is calculated using a new model based on fractal theory. The model is validated and compared with previous calculation model. The effect of the existence of transition region on the electric field distribution is discussed.展开更多
At present the detecting of ultra high voltage direct current (UHVDC) earth electrode frequently uses manual inspection. This method can't get the real-time operational data of the earth electrodes, and meanwhile,...At present the detecting of ultra high voltage direct current (UHVDC) earth electrode frequently uses manual inspection. This method can't get the real-time operational data of the earth electrodes, and meanwhile, the labor cost is very high. In order to satisfy the security needs of UHVDC, this paper designs an on-line monitoring system for UHVDC earth electrode. By 3G wireless communication-technologies, the system can monitor remotely many kinds of data such as the value of the grounding current, water level of the observation well, soil temperature and humidity near the earth electrode, the micro-climate around the earth electrode site, video data, etc. Through analyzing the datum, the system has broad prospect on fault detection and life evaluation of the UHVDC earth electrode.展开更多
Poloidal field（PF） converters provide controlled DC voltage and current to PF coils. The many harmonics generated by the PF converter flow into the power grid and seriously affect power systems and electric equipmen...Poloidal field（PF） converters provide controlled DC voltage and current to PF coils. The many harmonics generated by the PF converter flow into the power grid and seriously affect power systems and electric equipment. Due to the complexity of the system, the traditional integral operation in Fourier analysis is complicated and inaccurate. This paper presents a piecewise method to calculate the harmonics of the ITER PF converter. The relationship between the grid input current and the DC output current of the ITER PF converter is deduced. The grid current is decomposed into the sum of some simple functions. By calculating simple function harmonics based on the piecewise method, the harmonics of the PF converter under different operation modes are obtained.In order to examine the validity of the method, a simulation model is established based on Matlab/Simulink and a relevant experiment is implemented in the ITER PF integration test platform.Comparative results are given. The calculated results are found to be consistent with simulation and experiment. The piecewise method is proved correct and valid for calculating the system harmonics.展开更多
The purpose of this paper is to investigate charging strategies for integrated electrolytic capacitorless onboard chargers(OBC)in electric vehicles(EVs).An integrated OBC shares power converters and inductance with th...The purpose of this paper is to investigate charging strategies for integrated electrolytic capacitorless onboard chargers(OBC)in electric vehicles(EVs).An integrated OBC shares power converters and inductance with the traction system.An electrolytic capacitor is avoided in DC link of this integrated OBC.Thus,volume is reduced and reliability is improved for the power conversion system.In this paper,a charging strategy is proposed for this integrated system with uncontrolled rectification,where active switches are kept off in the power inverter on machine side.Consequently,a virtual DC-link voltage is with a half-wave shape.An extended phase-shift(EPS)operation is proposed for high-frequency DC/DC converters with this charging strategy,respectively.By designing a dedicated modulation and control strategy,sinusoidal charging power and the satisfied grid current are achieved for the system.Both theoretical analysis of operation modes and experimental verification with laboratory prototypes have been presented for the proposed charging strategy.展开更多
This paper proposes an optimal day-ahead opti-mization schedule for gas-electric integrated energy system(IES)considering the bi-directional energy flow.The hourly topology of electric power system(EPS),natural gas sy...This paper proposes an optimal day-ahead opti-mization schedule for gas-electric integrated energy system(IES)considering the bi-directional energy flow.The hourly topology of electric power system(EPS),natural gas system(NGS),energy hubs(EH)integrated power to gas(P2G)unit,are modeled to minimize the day-ahead operation cost of IES.Then,a second-order cone programming(SOCP)method is utilized to solve the optimization problem,which is actually a mixed integer nonconvex and nonlinear programming issue.Besides,cutting planes are added to ensure the exactness of the global optimal solution.Finally,simulation results demonstrate that the proposed optimization schedule can provide a safe,effective and economical day-ahead scheduling scheme for gas-electric IES.展开更多
Accurate fault area localization is a challenging problem in resonant grounding systems(RGSs).Accordingly,this paper proposes a novel two-stage localization method for single-phase earth faults in RGSs.Firstly,a fault...Accurate fault area localization is a challenging problem in resonant grounding systems(RGSs).Accordingly,this paper proposes a novel two-stage localization method for single-phase earth faults in RGSs.Firstly,a faulty feeder identification algorithm based on a Bayesian classifier is proposed.Three characteristic parameters of the RGS(the energy ratio,impedance factor,and energy spectrum entropy)are calculated based on the zero-sequence current(ZSC)of each feeder using wavelet packet transformations.Then,the values of three parameters are sent to a pre-trained Bayesian classifier to recognize the exact fault mode.With this result,the faulty feeder can be finally identified.To find the exact fault area on the faulty feeder,a localization method based on the similarity comparison of dominant frequency-band waveforms is proposed in an RGS equipped with feeder terminal units(FTUs).The FTUs can provide the information on the ZSC at their locations.Through wavelet-packet transformation,ZSC dominant frequency-band waveforms can be obtained at all FTU points.Similarities of the waveforms of characteristics at all FTU points are calculated and compared.The neighboring FTU points with the maximum diversity are the faulty sections finally determined.The proposed method exhibits higher accuracy in both faulty feeder identification and fault area localization compared to the previous methods.Finally,the effectiveness of the proposed method is validated by comparing simulation and experimental results.展开更多
This paper proposes a new method for power transmission risk assessment considering historical failure statistics of transmission systems and operation failure risks of system components.Component failure risks are in...This paper proposes a new method for power transmission risk assessment considering historical failure statistics of transmission systems and operation failure risks of system components.Component failure risks are integrated into the new method based on operational condition assessment of components using the support vector data description(SVDD)approach.The traditional outage probability model of transmission lines has been modified to build a new framework for power transmission system risk assessment.The proposed SVDD approach can provide a suitable mechanism to map component assessment grades to failure risks based on probabilistic behaviors of power system failures.Under the new method,both up-todate component failure risks and traditional system risk indices can be processed with the proposed outage model.As a result,component failure probabilities are not only related to historical statistic data but also operational data of components,and derived risk indices can reflect current operational conditions of components.In simulation studies,the SVDD approach is employed to evaluate component conditions and link such conditions to failure rates using up-to-date component operational data,including both on-line and off-line data of components.The IEEE 24-bus RTS-1979 system is used to demonstrate that component operational conditions can greatly affect the overall transmission system failure risks.展开更多
Along with the improvement of electrical equipment reliability,people’s unsafe behaviors and human errors have become one of main sources of risks in power systems.However,there is no comprehensive study on human fac...Along with the improvement of electrical equipment reliability,people’s unsafe behaviors and human errors have become one of main sources of risks in power systems.However,there is no comprehensive study on human factors and human reliability analysis in power systems.In allusion to this situation,this paper attempts to analyze the impact of human factors on power system reliability.First,this paper introduces current situation of human factors in power systems and the latest research progress in this field.Several analysis methods are proposed according to specified situations,and these methods are verified by some power system practical cases.On this base,this paper illustrates how human factors affect power system operation reliability from 2 typical aspects:imperfect maintenance caused by human errors,and impact of human factors on emergency dispatch operation and power system cascading failure.Finally,based on information decision and action in crew(IDAC),a novel dispatcher training evaluation simulation system(DTESS)is established,which can incorporate all influencing factors.Once fully developed,DTESS can be used to simulate dispatchers’response when encountering an initial event,and improve power system dispatching reliability.展开更多
As the structures of multiple branch lines(MBLs)will be widely applied in the future flexible DC distribution network,there is a urgent need for improving system reliability by tackling the frequent non-permanent pole...As the structures of multiple branch lines(MBLs)will be widely applied in the future flexible DC distribution network,there is a urgent need for improving system reliability by tackling the frequent non-permanent pole-to-pole(P-P)fault on distribution lines.A novel fault restoration strategy based on local information is proposed to solve this issue.The strategy firstly splits a double-ended power supply network into two single-ended power supply networks through the timing difference characteristics of a hybrid direct current circuit breaker(HDCCB)entering the recloser.Then,a method based on the characteristic of the transient energy of fault current is proposed to screen the faulty branch line in each single-ended power supply network.Also,a four-terminal flexible DC distribution network with MBLs is constructed on PSCAD to demonstrate the efficacy of the proposed strategy.Various factors such as noise,fault location,and DC arc equivalent resistance are considered in the simulation model for testing.Test results prove that the proposed strategy for fault restoration is effective,and features high performance and scalability.展开更多
Voltage source converter based high-voltage direct current(VSC-HVDC)transmission technology has been extensively employed in power systems with a high penetration of renewable energy resources.However,connecting a vol...Voltage source converter based high-voltage direct current(VSC-HVDC)transmission technology has been extensively employed in power systems with a high penetration of renewable energy resources.However,connecting a voltage source converter(VSC)to an AC weak grid may cause the converter system to become unstable.In this paper,a phase-shift phaselocked loop(PS-PLL)is proposed wherein a back electromotive force(BEMF)observer is added to the conventional phaselocked loop(PLL).The BEMF observer is used to observe the voltage of the infinite grid in the stationaryαβframe,which avoids the problem of inaccurate observations of the grid voltage in the dq frame that are caused by the output phase angle errors of the PLL.The VSC using the PS-PLL can operate as if it is facing a strong grid,thus enhancing the stability of the VSC-HVDC system.The proposed PS-PLL only needs to be properly modified on the basis of a traditional PLL,which makes it easy to implement.In addition,because it is difficult to obtain the exact impedance of the grid,the influence of shortcircuit ratio(SCR)estimation errors on the performance of the PS-PLL is also studied.The effectiveness of the proposed PSPLL is verified by the small-signal stability analysis and timedomain simulation.展开更多
基金supported by the State Grid Corporation of China Headquarter technology project (52010118000K)
文摘For demonstrating a multiterminal voltage-source converter(VSC)-based high-voltage DC(HVDC)(VSCHVDC) project, this study puts forward a technical route for calculating the power flow in a 500-kV VSC-HVDC power grid in comparison with that of an AC power grid. The Jacobian matrix used in the power-flow calculation was deduced through methods such as Newton–Laphson iteration and Taylor series expansion. Further, the operation effect of powerflow calculation on a true bipolar VSC-HVDC power grid was analyzed briefly. The elements of the Jacobian matrix corresponding to VSC were studied under the mode of droop control and the control strategy of VSC-HVDC power grid was analyzed in detail. The power-flow calculation model for VSC-HVDC power grid of the master–slave control mode was simplified using the PQ decomposition method of the power-flow calculation of an AC power grid. Moreover, a four-terminal model of the Zhangbei VSC-HVDC demonstration project was established and tested on MATLAB. The simulation results under two kinds of operating conditions were analyzed and compared to the results of BPA; the deviation between the power-flow results was studied. The results show that the proposed calculation method can provide a feasible support for calculating the power flow in VSC-HVDC grids.
基金This work was financially supported by the Natural Science Foundation of Hebei Province of China(Grant No.E2019502057)the Fundamental Research Funds for the Central Universities,China(Grant No.2018MS120).
文摘The Cu-Ti-Si alloys containing in-situ formed Ti5Si3 are prepared. In order to clarify the Ti5Si3 formation processes and its microstructure characteristics, the as-cast and deeply etched Cu-Ti-Si alloys with different compositions and cooling rates were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). It is found that the eutectic Ti5Si3 phases in Cu-Ti-Si alloys are rod-like with hexagonal cross section which tend to intertwine with each other to form a firm skeleton like a bird nest structure which can make the alloys keep their original shape even after etching off the Cu matrix. In addition, there is Cu in the center of many Ti5Si3 rods, resulting in a core-shell structure. With the increase of the cooling rate, Ti5Si3 distributes more uniformly, and the diameter of Ti5Si3 significantly decreases, with a minimum size of less than 100 nm, while the aspect ratio of Ti5Si3 increases.
基金supported by the Fundamental Research Funds for the Central Universities(No.2017MS093)
文摘Considering the complex coupling of multiple energies and the varying load forecasting errors for an integrated energy system(IES),this study proposes a dynamic time-scale scheduling strategy based on long short-term memory(LSTM)and multiple load forecasting errors.This strategy dynamically selects a hybrid timescale which is suitable for a variety of energies for each month.This is obtained by combining the mean absolute percentage error(MAPE)curve of the load forecasting with the error restriction requirements of the dispatcher.Based on the day-ahead scheduling plan,the output of the partial equipment is selectively adjusted at each time-scale to realize multi-energy collaborative optimization and gives full play to the comprehensive advantages of the IES.This is achieved by considering the differences in the response speed for each piece of equipment within the intra-day scheduling.This study uses the IES as an example,and it dynamically determines the time scale of the energy monthly.In addition,this investigation presents a detailed analysis of the output plan of the key equipment to demonstrate the necessity and the advantages of the strategy.
基金Project(2017JBM041)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(51505024)supported by the National Natural Science Foundation of ChinaProject supported by the Foundation of Zhejiang Key Laboratory of Automobile Safety Technology of China
文摘Axial compression tests were conducted on AZ31 B magnesium and A6063 aluminum thin-walled square tubes with varied lengths and induced features at different compression rates. In compression, the magnesium tubes exhibited a "local buckling and fracture" mode, with three fracture patterns, i.e."horizontal","double-oblique", and "spiral" fractures. In general, the magnesium tube showed an inferior crashworthiness to the aluminum square tube. In addition, the effects of L/W ratio, strain rate and induced features on the crashworthiness of thin-walled square tubes were investigated. With an increase in the L/W ratio(L and W represent the tube length and width, respectively) from 1 to 4, the maximal force and global specific energy absorption decreased in a power-law trend for the magnesium tubes,while they remained approximately constant for the aluminum tubes. Furthermore, as the compression rate increased from 5×10-5 to 10 m/s, the primary crashworthiness parameters of the magnesium tubes increased in an approximately exponential manner,while for the aluminum tubes,they changed slightly. Finally,the involved induced features were proven to be not an effective method to improve the specific energy absorption of magnesium tubes, thus, more trigger types,locations,and sizes will be evaluated in future to improve the energy-absorption ability.
基金financially supported by the National Key Research and Development Project of China for Demonstration of Integrated Utilization of Solid Waste in Distinctive Convergent Areas of Southeast Light Industry Building Materials(2019YFC1904500)the National Natural Science Foundation of China(Grant No.81770222)+4 种基金the Social Development Industry University Research Cooperation Project from the Department of Science and Technology in Fujian(2018Y4002)support by the Award Program for Fujian Minjiang Scholar Professorshipsupport from the Australian Research Grants Council(DP130104648)support from the NSERC Discovery Grant(NSERC RGPIN-2020-04463)McGill Start-Up Grant。
文摘Owing to safety issue and low energy density of liquid lithium-ion batteries(LIBs),all-solid-state lithium metal batteries(ASLMBs)with unique all-solid-state electrolytes(SEs)have attracted wide attentions.This arises mainly from the advantages of the SEs in the suppression of lithium dendrite growth,long cycle life,and broad working temperature range,showing huge potential applications in electronic devices,electric vehicles,smart grids,and biomedical devices.However,SEs suffer from low lithiumion conductivity and low mechanical integrity,slowing down the development of practical ASLMBs.Nanostructure engineering is of great efficiency in tuning the structure and composition of the SEs with improved lithium-ion conductivity and mechanical integrity.Among various available technologies for nanostructure engineering,electrospinning is a promising technique because of its simple operation,cost-effectiveness,and efficient integration with different components.In this review,we will first give a simple description of the electrospinning process.Then,the use of electrospinning technique in the synthesis of various SEs is summarized,for example,organic nanofibrous matrix,organic/inorganic nanofibrous matrix,and inorganic nanofibrous matrix combined with other components.The current development of the advanced architectures of SEs through electrospinning technology is also presented to provide references and ideas for designing high-performance ASLMBs.Finally,an outlook and further challenges in the preparation of advanced SEs for ASLMBs through electrospinning engineering are given.
基金sup-ports from the National Natural Science Foundation of China(Nos.11832013 and 51878350)the Fundamental Research Funds for the Central Universities(No.B210202023)+5 种基金the Young Scientific and Technological Talents to Support Project of Jiangsu Association for Science and Technology(No.027)the Water Conservancy Science and Technology Project of Jiangsu Province(No.2020017)the Postdoctoral Research Funding Program of Ji-angsu Province(No.2021K133B)the Ningbo Science and Technology Innovation Project(No.2020Z040)the Nantong Science and Technology Plan Project(No.JC 2020120)the Open Research Fund of Changjiang River Research Institute of Changjiang Water Resources Com-mittee(No.CKWV2021879/KY).
文摘Based on seawater immersion,drying-wetting cycles,carbonation and drying-wetting cycles for coral aggregate sea-water concrete(CASC)with different strength grades,the effect of carbonation and drying-wetting cycles on chloride diffusion be-havior of CASC is studied.The results show that the free surface chloride concentration(Cs),free chloride diffusion coefficient(Df)and time-dependent index(m)of CASC in the drying-wetting cycles is obviously higher than that in seawater immersion.The Df and m of CASC of carbonation and drying-wetting cycles is higher than that in the drying-wetting cycles.Carbonation increases the Df and m of CASC,which is against CASC to resist chloride corrosion.The corrosion possibility of CASC structures in different ex-posed areas is as follows:splash zone(carbonation and drying-wetting cycles)>tidal zone(drying-wetting cycles)>underwater zone(seawater immersion).Besides,the chloride diffusion rate of C65-CASC is 17.8%-63.4%higher than that of C65-ordinary aggre-gate concrete(OAC)in seawater immersion(underwater zone).Therefore,anti-corrosion measures should be adopted to improve the service life of CASC structure in the oceanic environment.
基金supported by Science and Technology Projects Funded by State Grid Corporation of China (5200202024105A0000).
文摘To thoroughly study the extinguishing effect of a high-pressure water mist fire extinguishing system when a transformer fire occurs,a 3D experimental model of a transformer is established in this work by employing Fire Dynamics Simulator(FDS)software.More specifically,by setting different parameters,the process of the highpressure water mist fire extinguishing system with the presence of both diverse ambient temperatures and water mist sprinkler laying conditions is simulated.In addition,the fire extinguishing effect of the employed high-pressure water mist system with the implementation of different strategies is systematically analyzed.The extracted results show that a fire source farther away fromthe centerline leads to a lower local temperature distribution.In addition,as the ambient temperature increases,the temperature above the fire source decreases,while the temperature and the concentrationof theupperflue gas layer bothdecrease.Interestingly,after thehigh-pressurewatermist sprinkler begins to operate,both the temperature distribution above the fire source and the concentration of the flue gas decrease,which indicates that the high-pressure water mist system plays the role of cooling and dust removal.By comparing various sprinkler laying methods,it is found that the lower sprinkler height has a better effect on the temperature above the fire source,the temperature of the upper flue gas layer,and the concentration of the flue gas.Moreover,when the sprinkler is spread over thewhole transformer,the cooling effect on both the temperature above the fire source and the temperature of the upper flue gas layer is good,whereas the change in the concentration of the flue gas above the fire source is not obvious compared to the case where the sprinkler is not fully spread.
基金This work was supported by Science and Technology Project Funded by State Grid Henan Electric Power Company(521702200004)Henan Province Key R&D and Promotion Special(Technology Research)Project(212102210016)Opening Fund of State Key Laboratory of Fire Science(SKLFS)under Grant No.HZ2021-KF11.
文摘In order to study the extinguishing performance of high-pressure-water-mist-based systems on the fires originating from power transformers the PyroSim software is used.Different particle velocities and flow rates are considered.The evolution laws of temperature around transformer,flue gas concentration and upper layer temperature of flue gas are analyzed under different boundary conditions.It is shown that the higher the particle velocity is,the lower the smoke concentration is,the better the cooling effect on the upper layer temperature of flue gas layer is,the larger the flow rate is and the better the cooling effect is.
文摘Capacitor voltage transformer (CVT), which is with simple structure, convenient maintenance, functional diversity and high impact pressure strength, is widely used. And its capacitance and dielectric loss Angle measurement is an important test on testing the insulation of the equipment. This paper is mainly to introduce and discuss one of the CVT test methods——the “self excitation method”, combined with the actual situation encountered in the work, sums up and expounds the maintenance of CVT and preventive test of influence factors.
文摘Fault diagnosis is an important application of the power grids monitoring system. Under the situation of continuous development of smart grid, it brings new challenges to the fault diagnosis technology. A fault diagnosis expert system based on model driven approach is proposed in this paper. And the corresponding fault modeling technology based on Fault Logic Description Language (FLDL) is described step by step. Practices show that this system could meet the requirements of processing fault alarm information rapidly and reliably by operator.
基金Project(2009CB724504)supported by the National Basic Research Program of China
文摘The oil-pressboard insulation is a typical composite insulation system widely used in the design and manufactory of large power apparatus. The implement of oil-pressboard insulation may lead to surface electrification and discharge at the interface under certain condition. It is of significant importance to take an insight into the phenomenon occurring at the interface. Through experiment, the pressboard is found as a porous material. The interface changes abruptly from bulk pressboard to the bulk oil as a result of the porous structure. A new model is proposed which divides the interface into bulk oil region, transition region, and bulk pressboard region. The width of the transition region is decided according to the microtome figure. The effective permittivity of the transition region is calculated using a new model based on fractal theory. The model is validated and compared with previous calculation model. The effect of the existence of transition region on the electric field distribution is discussed.
文摘At present the detecting of ultra high voltage direct current (UHVDC) earth electrode frequently uses manual inspection. This method can't get the real-time operational data of the earth electrodes, and meanwhile, the labor cost is very high. In order to satisfy the security needs of UHVDC, this paper designs an on-line monitoring system for UHVDC earth electrode. By 3G wireless communication-technologies, the system can monitor remotely many kinds of data such as the value of the grounding current, water level of the observation well, soil temperature and humidity near the earth electrode, the micro-climate around the earth electrode site, video data, etc. Through analyzing the datum, the system has broad prospect on fault detection and life evaluation of the UHVDC earth electrode.
文摘Poloidal field（PF） converters provide controlled DC voltage and current to PF coils. The many harmonics generated by the PF converter flow into the power grid and seriously affect power systems and electric equipment. Due to the complexity of the system, the traditional integral operation in Fourier analysis is complicated and inaccurate. This paper presents a piecewise method to calculate the harmonics of the ITER PF converter. The relationship between the grid input current and the DC output current of the ITER PF converter is deduced. The grid current is decomposed into the sum of some simple functions. By calculating simple function harmonics based on the piecewise method, the harmonics of the PF converter under different operation modes are obtained.In order to examine the validity of the method, a simulation model is established based on Matlab/Simulink and a relevant experiment is implemented in the ITER PF integration test platform.Comparative results are given. The calculated results are found to be consistent with simulation and experiment. The piecewise method is proved correct and valid for calculating the system harmonics.
文摘The purpose of this paper is to investigate charging strategies for integrated electrolytic capacitorless onboard chargers(OBC)in electric vehicles(EVs).An integrated OBC shares power converters and inductance with the traction system.An electrolytic capacitor is avoided in DC link of this integrated OBC.Thus,volume is reduced and reliability is improved for the power conversion system.In this paper,a charging strategy is proposed for this integrated system with uncontrolled rectification,where active switches are kept off in the power inverter on machine side.Consequently,a virtual DC-link voltage is with a half-wave shape.An extended phase-shift(EPS)operation is proposed for high-frequency DC/DC converters with this charging strategy,respectively.By designing a dedicated modulation and control strategy,sinusoidal charging power and the satisfied grid current are achieved for the system.Both theoretical analysis of operation modes and experimental verification with laboratory prototypes have been presented for the proposed charging strategy.
基金This work was supported in part by the National Natural Science Foundation of China under Grants 61673161 and 51807134and in part by the program of fundamental research of the Siberian Branch of Russian Academy of Sciences and carried out within the framework of the research project III.17.3.1,Reg.No.AAAA-A17-117030310442-8.
文摘This paper proposes an optimal day-ahead opti-mization schedule for gas-electric integrated energy system(IES)considering the bi-directional energy flow.The hourly topology of electric power system(EPS),natural gas system(NGS),energy hubs(EH)integrated power to gas(P2G)unit,are modeled to minimize the day-ahead operation cost of IES.Then,a second-order cone programming(SOCP)method is utilized to solve the optimization problem,which is actually a mixed integer nonconvex and nonlinear programming issue.Besides,cutting planes are added to ensure the exactness of the global optimal solution.Finally,simulation results demonstrate that the proposed optimization schedule can provide a safe,effective and economical day-ahead scheduling scheme for gas-electric IES.
文摘Accurate fault area localization is a challenging problem in resonant grounding systems(RGSs).Accordingly,this paper proposes a novel two-stage localization method for single-phase earth faults in RGSs.Firstly,a faulty feeder identification algorithm based on a Bayesian classifier is proposed.Three characteristic parameters of the RGS(the energy ratio,impedance factor,and energy spectrum entropy)are calculated based on the zero-sequence current(ZSC)of each feeder using wavelet packet transformations.Then,the values of three parameters are sent to a pre-trained Bayesian classifier to recognize the exact fault mode.With this result,the faulty feeder can be finally identified.To find the exact fault area on the faulty feeder,a localization method based on the similarity comparison of dominant frequency-band waveforms is proposed in an RGS equipped with feeder terminal units(FTUs).The FTUs can provide the information on the ZSC at their locations.Through wavelet-packet transformation,ZSC dominant frequency-band waveforms can be obtained at all FTU points.Similarities of the waveforms of characteristics at all FTU points are calculated and compared.The neighboring FTU points with the maximum diversity are the faulty sections finally determined.The proposed method exhibits higher accuracy in both faulty feeder identification and fault area localization compared to the previous methods.Finally,the effectiveness of the proposed method is validated by comparing simulation and experimental results.
文摘This paper proposes a new method for power transmission risk assessment considering historical failure statistics of transmission systems and operation failure risks of system components.Component failure risks are integrated into the new method based on operational condition assessment of components using the support vector data description(SVDD)approach.The traditional outage probability model of transmission lines has been modified to build a new framework for power transmission system risk assessment.The proposed SVDD approach can provide a suitable mechanism to map component assessment grades to failure risks based on probabilistic behaviors of power system failures.Under the new method,both up-todate component failure risks and traditional system risk indices can be processed with the proposed outage model.As a result,component failure probabilities are not only related to historical statistic data but also operational data of components,and derived risk indices can reflect current operational conditions of components.In simulation studies,the SVDD approach is employed to evaluate component conditions and link such conditions to failure rates using up-to-date component operational data,including both on-line and off-line data of components.The IEEE 24-bus RTS-1979 system is used to demonstrate that component operational conditions can greatly affect the overall transmission system failure risks.
基金supported by the State Key Program of National Natural Science Foundation of China (No.51537010)Zhejiang Provincial Natural Science Foundation (No.LZ14E070001)
文摘Along with the improvement of electrical equipment reliability,people’s unsafe behaviors and human errors have become one of main sources of risks in power systems.However,there is no comprehensive study on human factors and human reliability analysis in power systems.In allusion to this situation,this paper attempts to analyze the impact of human factors on power system reliability.First,this paper introduces current situation of human factors in power systems and the latest research progress in this field.Several analysis methods are proposed according to specified situations,and these methods are verified by some power system practical cases.On this base,this paper illustrates how human factors affect power system operation reliability from 2 typical aspects:imperfect maintenance caused by human errors,and impact of human factors on emergency dispatch operation and power system cascading failure.Finally,based on information decision and action in crew(IDAC),a novel dispatcher training evaluation simulation system(DTESS)is established,which can incorporate all influencing factors.Once fully developed,DTESS can be used to simulate dispatchers’response when encountering an initial event,and improve power system dispatching reliability.
基金supported by the National Natural Science Foundation of China(No.51877174)。
文摘As the structures of multiple branch lines(MBLs)will be widely applied in the future flexible DC distribution network,there is a urgent need for improving system reliability by tackling the frequent non-permanent pole-to-pole(P-P)fault on distribution lines.A novel fault restoration strategy based on local information is proposed to solve this issue.The strategy firstly splits a double-ended power supply network into two single-ended power supply networks through the timing difference characteristics of a hybrid direct current circuit breaker(HDCCB)entering the recloser.Then,a method based on the characteristic of the transient energy of fault current is proposed to screen the faulty branch line in each single-ended power supply network.Also,a four-terminal flexible DC distribution network with MBLs is constructed on PSCAD to demonstrate the efficacy of the proposed strategy.Various factors such as noise,fault location,and DC arc equivalent resistance are considered in the simulation model for testing.Test results prove that the proposed strategy for fault restoration is effective,and features high performance and scalability.
基金supported by the National Natural Science Foundation of China(No.51677142)the National Key R&D Program of China(No.2016YFB0900600)。
文摘Voltage source converter based high-voltage direct current(VSC-HVDC)transmission technology has been extensively employed in power systems with a high penetration of renewable energy resources.However,connecting a voltage source converter(VSC)to an AC weak grid may cause the converter system to become unstable.In this paper,a phase-shift phaselocked loop(PS-PLL)is proposed wherein a back electromotive force(BEMF)observer is added to the conventional phaselocked loop(PLL).The BEMF observer is used to observe the voltage of the infinite grid in the stationaryαβframe,which avoids the problem of inaccurate observations of the grid voltage in the dq frame that are caused by the output phase angle errors of the PLL.The VSC using the PS-PLL can operate as if it is facing a strong grid,thus enhancing the stability of the VSC-HVDC system.The proposed PS-PLL only needs to be properly modified on the basis of a traditional PLL,which makes it easy to implement.In addition,because it is difficult to obtain the exact impedance of the grid,the influence of shortcircuit ratio(SCR)estimation errors on the performance of the PS-PLL is also studied.The effectiveness of the proposed PSPLL is verified by the small-signal stability analysis and timedomain simulation.
