In contemporary medium-voltage distribution networks heavily penetrated by distributed energy resources(DERs),the harmonic components injected by power-electronic interfacing converters,together with the inherently in...In contemporary medium-voltage distribution networks heavily penetrated by distributed energy resources(DERs),the harmonic components injected by power-electronic interfacing converters,together with the inherently intermittent output of renewable generation,distort the zero-sequence current and continuously reshape its frequency spectrum.As a result,single-line-to-ground(SLG)faults exhibit a pronounced,strongly non-stationary behaviour that varies with operating point,load mix and DER dispatch.Under such circumstances the performance of traditional rule-based algorithms—or methods that rely solely on steady-state frequency-domain indicators—degrades sharply,and they no longer satisfy the accuracy and universality required by practical protection systems.To overcome these shortcomings,the present study develops an SLG-fault identification scheme that transforms the zero-sequence currentwaveforminto two-dimensional image representations and processes themwith a convolutional neural network(CNN).First,the causes of sample-distribution imbalance are analysed in detail by considering different neutralgrounding configurations,fault-inception mechanisms and the statistical probability of fault occurrence on each phase.Building on these insights,a discriminator network incorporating a Convolutional Block Attention Module(CBAM)is designed to autonomously extract multi-layer spatial-spectral features,while Gradient-weighted Class Activation Mapping(Grad-CAM)is employed to visualise the contribution of every salient image region,thereby enhancing interpretability.A comprehensive simulation platform is subsequently established for a DER-rich distribution system encompassing several representative topologies,feeder lengths and DER penetration levels.Large numbers of realistic SLG-fault scenarios are generated—including noise and measurement uncertainty—and are used to train,validate and test the proposed model.Extensive simulation campaigns,corroborated by field measurements from an actual utility network,demonstrate that the proposed approach attains an SLG-fault identification accuracy approaching 100 percent and maintains robust performance under severe noise conditions,confirming its suitability for real-world engineering applications.展开更多
In order to increase the stability of the Mongolia power system, a single-phase automatic reclosing device (SPAR) was introduced on double-circuit power lines built with a size of 330 kV, operating on a voltage of 220...In order to increase the stability of the Mongolia power system, a single-phase automatic reclosing device (SPAR) was introduced on double-circuit power lines built with a size of 330 kV, operating on a voltage of 220 kV and a length of 250 km. These overhead power lines (L-213, L-214) connect the 220/110/35 kV “Songino” substation with the “Mandal” substation and form system networks. This paper presents the challenges encountered when implementing single-phase automatic reclosing (SPAR) devices and compares the changes in power system parameters before and after SPAR deployment for a long 220 kV line. Simulations and analyses were carried out using DIgSILENT PowerFactory software, focusing on rotor angle stability, and the overall impact on the power system during short-circuit faults. The evaluation also utilized measurement data from the Wide Area Monitoring System (WAMS) to compare system behavior pre- and post-implementation of SPAR. The findings reveal that SPAR significantly enhances system reliability and stability, effectively mitigating the risk of oscillations and stability loss triggered by short circuits. This improvement contributes to a more resilient power system, reducing the potential for disturbances caused by faults.展开更多
A novel white-light emitting single-phase phosphor La_3 Si_6 N_(11):Dy^(3+),exhibiting two emission peaks centering at 475 and 575 nm, was prepared via conventional solid-state reactions. The structure and morphology ...A novel white-light emitting single-phase phosphor La_3 Si_6 N_(11):Dy^(3+),exhibiting two emission peaks centering at 475 and 575 nm, was prepared via conventional solid-state reactions. The structure and morphology of La_3 Si_6 N_(11):Dy^(3+)/Tb^(3+) were investigated by X-ray diffraction(XRD) and scanning electron microscopy(SEM). The emission colors can be tuned from white to yellow-green through increasing the Tb^(3+) concentration in La_3 Si_6 N_(11):Dy^(3+),Tb^(3+), The mechanism of energy transfer(ET) from Dy^(3+) to Tb^(3+) is confirmed according to the excitation,emission spectra and decay lifetimes curve. The temperaturedependent luminescence measurements of La_(2.83)Si_6 N_(11):0.1 Dy^(3+),0.07 Tb^(3+) were also performed, and a good thermal stability is shown, suggesting superior properties for the application as white lightemitting diodes(w-LEDs) phosphor.展开更多
The microstructure,mechanical property,and in vitro biocorrosion behavior of as-cast single-phase biodegradable Mg-1.5Zn-0.6Zr alloy were investigated and compared with a commercial as-cast AZ91D alloy.The results sho...The microstructure,mechanical property,and in vitro biocorrosion behavior of as-cast single-phase biodegradable Mg-1.5Zn-0.6Zr alloy were investigated and compared with a commercial as-cast AZ91D alloy.The results show that the Mg-1.5Zn-0.6Zr alloy had a single-phase solid solution structure,with an average grain size of 34.7±13.1μm.The alloy exhibited ultimate tensile strength of 168±2.0 MPa,yield strength of 83±0.6 MPa,and elongation of 9.1±0.6%.Immersion tests and electrochemical measurements reveal that the alloy displayed lower biocorrosion rate and more uniform corrosion mode than AZ91D in Hank's solution.The elimination of intensive galvanic corrosion reactions and the formation of a much more compact and uniform corrosion film mainly account for the better biocorrosion properties of the Mg-1.5Zn-0.6Zr alloy than AZ91D.展开更多
This study focuses on the effects of rotational and welding speeds on the microstructure and hardness of joints in friction stir welded single-phase brass. Welds were achieved under low heat input conditions at rotati...This study focuses on the effects of rotational and welding speeds on the microstructure and hardness of joints in friction stir welded single-phase brass. Welds were achieved under low heat input conditions at rotational and welding speeds of 400-800 r/min and 100-300 mm/min, respectively. In order to characterize the obtained welds, optical microscopy and Vickers hardness measurements were taken on the weld cross sections. According to the obtained results, increasing the welding speed and/or decreasing the rotational speed caused the grain size of the stir zone to decrease and, hence, improved the average hardness of this region. These results are discussed with respect to the interplay between the welding parameters and the peak temperature in the weld thermal cycle.展开更多
A novel method for the preparation of single-phase ammonium dimolybdate with industrial ammonium molybdate was studied. Various in- fluential factors were evaluated in the paper, including reaction temperature, reacti...A novel method for the preparation of single-phase ammonium dimolybdate with industrial ammonium molybdate was studied. Various in- fluential factors were evaluated in the paper, including reaction temperature, reaction time, initial molybdenum concentration, initial NH_3 /Mo molar ratio, and stirring speed. Under the optimum experimental conditions, the crystallization rate of product is 85.23%. The X-ray diffraction (XRD) analysis and chemical analysis show that the product is single-phase ammonium dimolybdate, and no impurity phases exist. The scanning electronic microscope (SEM) image reveals uniform particle size, good particle dispersion, and no agglomeration between particles. Meanwhile, the final pH value of acidification was investigated. The total molybdenum recovery can reach up to 99.40%, and the main phases of acidification product are the same as those of raw material with the final pH value of 1.5. This determines that the acidification product can be used as a raw material to produce single-phase ammonium dimolybdate.展开更多
Complex dynamical phenomenon was studied in the single phase H-bridge inverter which was controlled by either a peak current or a valley current. The state functions and the discrete iterative map equations were estab...Complex dynamical phenomenon was studied in the single phase H-bridge inverter which was controlled by either a peak current or a valley current. The state functions and the discrete iterative map equations were established to analyze the dynamical phenomenon in the single phase H-bridge inverter. The dynamical characteristics of the single phase H- bridge inverter, such as time domain waveform diagram, bifurcation diagram, and folding map, were obtained by using the numerical calculation when the circuit parameters varied in specific range. Moreover, the simulation results were obtained by using the OrCAD-PSpice software to validate the numerical calculation. Both the numerical calculation and the circuit simulation show that the symmetrical dynamical phenomenon occurs in the single phase H-bridge inverter controlled by the peak current or the valley current.展开更多
Dynamic behavior of coalbed methane (CBM) flow will provide the theoretical basis to optimize production performance for a given well.A mathematical model is developed to simulate flowing pressures and pressure drops ...Dynamic behavior of coalbed methane (CBM) flow will provide the theoretical basis to optimize production performance for a given well.A mathematical model is developed to simulate flowing pressures and pressure drops of CBM column from well head to bottom hole.The measured parameters and independent variables of flow rates,flowing pressures and temperatures are involved in CBM producing process along the annulus.The developed relationships are validated against full-scale measured data in single-phase CBM wellbores.The proposed methodology can analyze the dynamic behavior in CBM reservoir and process of CBM flow with an overall accuracy of 2%.The calculating process of flowing pressures involves friction factor with variable Reynolds number and CBM temperature and compressibility factor with gravitational gradients.The results showed that the effect of flowing pressure on CBM column was more obvious than that on CBM and water column accompanied by an increase of dynamic water level.The ratios of flowing pressure on increment of CBM column to the whole column increased with the declined flow rates of water column.Bottom-hole pressure declined with the decreased flowing pressure of CBM column along the annulus.It will lead to the results of the increased pressure drop of CBM column and CBM flow rate in single-phase CBM wellbores.展开更多
Data centers are recognized as one of the most important aspects of the fourth industrial revolution since conventional data centers are inefficient and have dependency on high energy consumption,in which the cooling ...Data centers are recognized as one of the most important aspects of the fourth industrial revolution since conventional data centers are inefficient and have dependency on high energy consumption,in which the cooling is responsible for 40%of the usage.Therefore,this research proposes the immersion cooling method to solving the high energy consumption of data centers by cooling its component using two types of dielectric fluids.Four stages of experimentalmethods are used,such as fluid types,cooling effectiveness,optimization,and durability.Furthermore,benchmark software is used to measure the CPU maximum work with the temperature data performed for 24 h.The results of this study show that the immersion cooling reduces 13℃ lower temperature than the conventional cooling method which means it saves more energy consumption in the data center.The most optimum variable used to decrease the temperature is 1.5 lpm of flow rate and 800 rpm of fan rotation.Furthermore,the cooling performance of the dielectric fluids shows that the mineral oil(MO)is better than the virgin coconut oil(VCO).In durability experiment,there are no components damage after five months immersed in the fluid.展开更多
Outdoor power transformers are one of the most pervasive noise sources in power transmission and distribution systems.Accurate prediction of outdoor noise propagation plays a dominant role for the evaluation and contr...Outdoor power transformers are one of the most pervasive noise sources in power transmission and distribution systems.Accurate prediction of outdoor noise propagation plays a dominant role for the evaluation and control of noise relevant to the transformer stations.In this paper surface vibration tests are carried out on a scale model of a single-phase transformer tank wall at different excitation frequencies.The phase and amplitude of test data are found to be randomly distributed when the excitation frequency exceeds the seventh mode frequency,which allows the single-phase power transformer to be simplified as incoherent point sources.An outdoor-coherent model is subsequently developed and incorporated with the image source method to investigate noise propagation from single-phase power transformers,due to the occurrence of multiple reflections and diffractions in the propagation path of each point source.The proposed model is used to calculate the sound field of the power transformer group by exploiting the additional phase information.In comparison with the ISO9613 model and the boundary element method,it is found that the proposed coherent image source method leads to more accurate prediction results,and hence better performance for the prediction of the outdoor noise induced by single-phase power transformers.展开更多
The new 6-switch single-phase 5-level current-source inverter proposed in this paper was developed by properly simplifying the traditional 8-switch single-phase 5-level current-source inverter, and its operational pri...The new 6-switch single-phase 5-level current-source inverter proposed in this paper was developed by properly simplifying the traditional 8-switch single-phase 5-level current-source inverter, and its operational principle was analyzed. Just like the problem of voltage-unbalance between different levels existing in voltage-source multilevel inverters, a similar problem of current-unbalance between different levels whether for the 8-switch single-phase 5-level current-source inverter, or for the new 6-switch 5-level current-source inverter also exists. A simple current-balance control method via DC current feedback is presented here to implement the current-balance control between different levels. And to reduce the output current harmonics, PWM control technique was used. Simulation and experimental results showed that this new 6-switch topology operates correctly and that the balance-inductor can almost equally distribute the total DC current.展开更多
Single-phase Ba(Ti_(0.2)Zr_(0.2)Sn_(0.2)Hf_(0.2)Ce_(0.2))O_(3)(BTZSHC) high-entropy ceramics(HECs) with the perovskite structure were successfully prepared via the sol-gel method.The results reveal that the as-prepare...Single-phase Ba(Ti_(0.2)Zr_(0.2)Sn_(0.2)Hf_(0.2)Ce_(0.2))O_(3)(BTZSHC) high-entropy ceramics(HECs) with the perovskite structure were successfully prepared via the sol-gel method.The results reveal that the as-prepared ceramics exhibit a single cubic phase belonging to the Pm3 m space group.The high entropy is the driving force of the formation of single-phase ceramics.A larger entropy(ΔS_(mix)) and a negative enthalpy(ΔH_(mix)) are conducive to the formation of single-phase compounds.Herein,ΔS_(mix)=0.323 R mole-1andΔH_(mix)=43.88 kJ/mol.The sluggish-diffusion effect ensures the thermal stability of high-entropy systems.Dielectric measurements reveal that the as-prepared BTZSHC high-entropy ceramics are relaxor ferroelectrics,and the degree of relaxor(γ) is 1.9.The relaxor behavior of the as-prepared ceramics can be ascribed to the relaxation and thermal evolution of their polar units(PUs).The findings of this work provide a theoretical basis and technical support for the preparation of single-phase high-entropy ceramics.展开更多
To avoid stray current and maintain the benefit of no phase-split in the DC traction power supply system, an AC traction power supply system was proposed for the urban public transport such as metro and light rail tra...To avoid stray current and maintain the benefit of no phase-split in the DC traction power supply system, an AC traction power supply system was proposed for the urban public transport such as metro and light rail transit. The proposed system consists of a main substation （MSS） and cable traction network （CTN）. The MSS includes a single-phase main traction transformer and a negative-se- quence compensation device, while the CTN includes double-core cables, traction transformers, overhead catenary system, rails, etc. Several key techniques for the proposed system were put forward and discussed, which can be summarized as （1） the power supply principle, equivalent circuit and transmission ability of the CTN, the cable-catenary matching technique, and the selection of catenary voltage level; （2） the segmentation technology and status identification method for traction power supply network, distributed and centralized protection schemes, etc.; （3） a power supply scheme for single-line MSS and a power supply scheme of MSS shared by two or more lines. The proposed industrial frequency single-phase AC traction power supply system shows an excellent technical performance, good economy, and high reliability, hence provides a new alternative for metro and urban rail transit power supply systems.展开更多
According to the characteristics of single-phase circuits and demand of using active filter for real-time detecting harmonic and reactive currents, a detecting method based on Fryze＇s power definition is proposed. Th...According to the characteristics of single-phase circuits and demand of using active filter for real-time detecting harmonic and reactive currents, a detecting method based on Fryze＇s power definition is proposed. The results of theoretical analysis and simula- tion show that the proposed method is effective in realtime detecting of instantaneous harmonic and reactive currents in single-phase circuits. When only detecting the total reactive currents, this method does not need a phase-locked loop circuit, and it also can be used in some special applications to provide different compensations on the ground of different requirements of electric network. Compared with the other methods based on the theory of instantaneous reactive power, this method is simple and easy to realize.展开更多
A single-phase lattice Boltzmann model with modified surface tension is developed in this paper to solve the problem of high-density-ratio free surface flow.The computational efficiency and accuracy are both enhanced....A single-phase lattice Boltzmann model with modified surface tension is developed in this paper to solve the problem of high-density-ratio free surface flow.The computational efficiency and accuracy are both enhanced.The restriction to the relaxation factor （which needs to be smaller than 1） is circumvented by the new surface tension algebra,due to its rational physical nature compared with the treatment of Xing,Buther and Yang in their paper （Comp.Mater.Sci.,2007,39（2）：282-290）.The proposed stable surface tension scheme is applied to simulate the free deformation of a square droplet with surface tension effect and the process of a droplet impinging on a liquid film.The numerical solution for free deformation of a droplet agrees well with thermodynamic principles,and also achieves high accuracy in comparison with Xing,et al.＇s model.Three typical impinging modes are successfully obtained with the new scheme,and another particular mode found by Wang and Chen is also successfully simulated.The evolutions of liquid crown agree well with the power law related to time.展开更多
A series of tunable phosphors NaAlSiO_4：Ce^（3＋）,Sm^（3＋） were synthesized using a conventional high-temperature, solid-state method. Crystal structure, photoluminescence excitation, and emission spectra with flu...A series of tunable phosphors NaAlSiO_4：Ce^（3＋）,Sm^（3＋） were synthesized using a conventional high-temperature, solid-state method. Crystal structure, photoluminescence excitation, and emission spectra with fluorescence decay curves were investigated. Under UV excitation（325 nm）, NaAlSiO_4：Ce^（3＋）,Sm^（3＋） showed strong blue emission located at 444 nm and orange-reddish emission centered at 563, 601, 648 and 712 nm, stemming from the characteristic emission for 4f-5d transition of Ce^（3＋） and ~4G_（5/2）→~6H_J（J=5/2, 7/2, 9/2, 11/2） transition of Sm^（3＋）, respectively. In addition, we studied the detailed energy transfer process between Ce^（3＋） and Sm^（3＋） and found that it belonged to dipole-dipole resonance energy transfer. Furthermore, we noted that the white light emitting from the Ce^（3＋）, Sm^（3＋） co-doped phosphors with the color coordinate（x=0.313, y=0.283） could be observed under 325 nm excitation, which was close to the ideal white light（x=0.33, y=0.33）. The results indicated that this phosphor has a potential application as a single-phased alumino-silicate phosphor for ultraviolet white light-emitting diodes（UV-WLEDs）.展开更多
基金supported by the Science and Technology Program of China Southern Power Grid(031800KC23120003).
文摘In contemporary medium-voltage distribution networks heavily penetrated by distributed energy resources(DERs),the harmonic components injected by power-electronic interfacing converters,together with the inherently intermittent output of renewable generation,distort the zero-sequence current and continuously reshape its frequency spectrum.As a result,single-line-to-ground(SLG)faults exhibit a pronounced,strongly non-stationary behaviour that varies with operating point,load mix and DER dispatch.Under such circumstances the performance of traditional rule-based algorithms—or methods that rely solely on steady-state frequency-domain indicators—degrades sharply,and they no longer satisfy the accuracy and universality required by practical protection systems.To overcome these shortcomings,the present study develops an SLG-fault identification scheme that transforms the zero-sequence currentwaveforminto two-dimensional image representations and processes themwith a convolutional neural network(CNN).First,the causes of sample-distribution imbalance are analysed in detail by considering different neutralgrounding configurations,fault-inception mechanisms and the statistical probability of fault occurrence on each phase.Building on these insights,a discriminator network incorporating a Convolutional Block Attention Module(CBAM)is designed to autonomously extract multi-layer spatial-spectral features,while Gradient-weighted Class Activation Mapping(Grad-CAM)is employed to visualise the contribution of every salient image region,thereby enhancing interpretability.A comprehensive simulation platform is subsequently established for a DER-rich distribution system encompassing several representative topologies,feeder lengths and DER penetration levels.Large numbers of realistic SLG-fault scenarios are generated—including noise and measurement uncertainty—and are used to train,validate and test the proposed model.Extensive simulation campaigns,corroborated by field measurements from an actual utility network,demonstrate that the proposed approach attains an SLG-fault identification accuracy approaching 100 percent and maintains robust performance under severe noise conditions,confirming its suitability for real-world engineering applications.
文摘In order to increase the stability of the Mongolia power system, a single-phase automatic reclosing device (SPAR) was introduced on double-circuit power lines built with a size of 330 kV, operating on a voltage of 220 kV and a length of 250 km. These overhead power lines (L-213, L-214) connect the 220/110/35 kV “Songino” substation with the “Mandal” substation and form system networks. This paper presents the challenges encountered when implementing single-phase automatic reclosing (SPAR) devices and compares the changes in power system parameters before and after SPAR deployment for a long 220 kV line. Simulations and analyses were carried out using DIgSILENT PowerFactory software, focusing on rotor angle stability, and the overall impact on the power system during short-circuit faults. The evaluation also utilized measurement data from the Wide Area Monitoring System (WAMS) to compare system behavior pre- and post-implementation of SPAR. The findings reveal that SPAR significantly enhances system reliability and stability, effectively mitigating the risk of oscillations and stability loss triggered by short circuits. This improvement contributes to a more resilient power system, reducing the potential for disturbances caused by faults.
基金supported by the National Key Research and Development Plan(2017YFB0404300,2017YFB0404301)
文摘A novel white-light emitting single-phase phosphor La_3 Si_6 N_(11):Dy^(3+),exhibiting two emission peaks centering at 475 and 575 nm, was prepared via conventional solid-state reactions. The structure and morphology of La_3 Si_6 N_(11):Dy^(3+)/Tb^(3+) were investigated by X-ray diffraction(XRD) and scanning electron microscopy(SEM). The emission colors can be tuned from white to yellow-green through increasing the Tb^(3+) concentration in La_3 Si_6 N_(11):Dy^(3+),Tb^(3+), The mechanism of energy transfer(ET) from Dy^(3+) to Tb^(3+) is confirmed according to the excitation,emission spectra and decay lifetimes curve. The temperaturedependent luminescence measurements of La_(2.83)Si_6 N_(11):0.1 Dy^(3+),0.07 Tb^(3+) were also performed, and a good thermal stability is shown, suggesting superior properties for the application as white lightemitting diodes(w-LEDs) phosphor.
基金This project was supported by the National Natural Science Foundation of China(No.51174025)Specialized Research Fund for the Doctoral Program of Higher Education of China(No.20110006130004).
文摘The microstructure,mechanical property,and in vitro biocorrosion behavior of as-cast single-phase biodegradable Mg-1.5Zn-0.6Zr alloy were investigated and compared with a commercial as-cast AZ91D alloy.The results show that the Mg-1.5Zn-0.6Zr alloy had a single-phase solid solution structure,with an average grain size of 34.7±13.1μm.The alloy exhibited ultimate tensile strength of 168±2.0 MPa,yield strength of 83±0.6 MPa,and elongation of 9.1±0.6%.Immersion tests and electrochemical measurements reveal that the alloy displayed lower biocorrosion rate and more uniform corrosion mode than AZ91D in Hank's solution.The elimination of intensive galvanic corrosion reactions and the formation of a much more compact and uniform corrosion film mainly account for the better biocorrosion properties of the Mg-1.5Zn-0.6Zr alloy than AZ91D.
文摘This study focuses on the effects of rotational and welding speeds on the microstructure and hardness of joints in friction stir welded single-phase brass. Welds were achieved under low heat input conditions at rotational and welding speeds of 400-800 r/min and 100-300 mm/min, respectively. In order to characterize the obtained welds, optical microscopy and Vickers hardness measurements were taken on the weld cross sections. According to the obtained results, increasing the welding speed and/or decreasing the rotational speed caused the grain size of the stir zone to decrease and, hence, improved the average hardness of this region. These results are discussed with respect to the interplay between the welding parameters and the peak temperature in the weld thermal cycle.
基金supported by the National Natural Science Foundation of China(No.51072233)
文摘A novel method for the preparation of single-phase ammonium dimolybdate with industrial ammonium molybdate was studied. Various in- fluential factors were evaluated in the paper, including reaction temperature, reaction time, initial molybdenum concentration, initial NH_3 /Mo molar ratio, and stirring speed. Under the optimum experimental conditions, the crystallization rate of product is 85.23%. The X-ray diffraction (XRD) analysis and chemical analysis show that the product is single-phase ammonium dimolybdate, and no impurity phases exist. The scanning electronic microscope (SEM) image reveals uniform particle size, good particle dispersion, and no agglomeration between particles. Meanwhile, the final pH value of acidification was investigated. The total molybdenum recovery can reach up to 99.40%, and the main phases of acidification product are the same as those of raw material with the final pH value of 1.5. This determines that the acidification product can be used as a raw material to produce single-phase ammonium dimolybdate.
基金Project supported by the National Natural Science Foundation of China(Grant No.51107016)the National Basic Research Program of China(Grant No.2013CB035605)the Postdoctoral Science Research Developmental Foundation of Heilongjiang Province,China(Grant No.LHB-Q12086)
文摘Complex dynamical phenomenon was studied in the single phase H-bridge inverter which was controlled by either a peak current or a valley current. The state functions and the discrete iterative map equations were established to analyze the dynamical phenomenon in the single phase H-bridge inverter. The dynamical characteristics of the single phase H- bridge inverter, such as time domain waveform diagram, bifurcation diagram, and folding map, were obtained by using the numerical calculation when the circuit parameters varied in specific range. Moreover, the simulation results were obtained by using the OrCAD-PSpice software to validate the numerical calculation. Both the numerical calculation and the circuit simulation show that the symmetrical dynamical phenomenon occurs in the single phase H-bridge inverter controlled by the peak current or the valley current.
基金This work was financially supported by National Science and Technology Major Project of the Ministry of Science and Technology of China(2016ZX05065-001),Key Research Project of Shandong Province(2019GHY112029 and 2019GSF109090)and Higher Education Research and Development Project of Shandong Province(J17KA033).
文摘Dynamic behavior of coalbed methane (CBM) flow will provide the theoretical basis to optimize production performance for a given well.A mathematical model is developed to simulate flowing pressures and pressure drops of CBM column from well head to bottom hole.The measured parameters and independent variables of flow rates,flowing pressures and temperatures are involved in CBM producing process along the annulus.The developed relationships are validated against full-scale measured data in single-phase CBM wellbores.The proposed methodology can analyze the dynamic behavior in CBM reservoir and process of CBM flow with an overall accuracy of 2%.The calculating process of flowing pressures involves friction factor with variable Reynolds number and CBM temperature and compressibility factor with gravitational gradients.The results showed that the effect of flowing pressure on CBM column was more obvious than that on CBM and water column accompanied by an increase of dynamic water level.The ratios of flowing pressure on increment of CBM column to the whole column increased with the declined flow rates of water column.Bottom-hole pressure declined with the decreased flowing pressure of CBM column along the annulus.It will lead to the results of the increased pressure drop of CBM column and CBM flow rate in single-phase CBM wellbores.
基金This work is financially supported by the Ministry of Research and Technology of Indonesia(BRIN)in the project called“Penggunaan Immersion Cooling untukMeningkatkan Efisiensi Energi Data Center”.
文摘Data centers are recognized as one of the most important aspects of the fourth industrial revolution since conventional data centers are inefficient and have dependency on high energy consumption,in which the cooling is responsible for 40%of the usage.Therefore,this research proposes the immersion cooling method to solving the high energy consumption of data centers by cooling its component using two types of dielectric fluids.Four stages of experimentalmethods are used,such as fluid types,cooling effectiveness,optimization,and durability.Furthermore,benchmark software is used to measure the CPU maximum work with the temperature data performed for 24 h.The results of this study show that the immersion cooling reduces 13℃ lower temperature than the conventional cooling method which means it saves more energy consumption in the data center.The most optimum variable used to decrease the temperature is 1.5 lpm of flow rate and 800 rpm of fan rotation.Furthermore,the cooling performance of the dielectric fluids shows that the mineral oil(MO)is better than the virgin coconut oil(VCO).In durability experiment,there are no components damage after five months immersed in the fluid.
基金This work is funded by the Anhui Natural Science Foundation Project of China(under Grant KJ2016A201)the National Natural Science Foundation of China(under Grant 11774378).
文摘Outdoor power transformers are one of the most pervasive noise sources in power transmission and distribution systems.Accurate prediction of outdoor noise propagation plays a dominant role for the evaluation and control of noise relevant to the transformer stations.In this paper surface vibration tests are carried out on a scale model of a single-phase transformer tank wall at different excitation frequencies.The phase and amplitude of test data are found to be randomly distributed when the excitation frequency exceeds the seventh mode frequency,which allows the single-phase power transformer to be simplified as incoherent point sources.An outdoor-coherent model is subsequently developed and incorporated with the image source method to investigate noise propagation from single-phase power transformers,due to the occurrence of multiple reflections and diffractions in the propagation path of each point source.The proposed model is used to calculate the sound field of the power transformer group by exploiting the additional phase information.In comparison with the ISO9613 model and the boundary element method,it is found that the proposed coherent image source method leads to more accurate prediction results,and hence better performance for the prediction of the outdoor noise induced by single-phase power transformers.
基金Project (No. 50477033) supported by the National Natural ScienceFoundation of China
文摘The new 6-switch single-phase 5-level current-source inverter proposed in this paper was developed by properly simplifying the traditional 8-switch single-phase 5-level current-source inverter, and its operational principle was analyzed. Just like the problem of voltage-unbalance between different levels existing in voltage-source multilevel inverters, a similar problem of current-unbalance between different levels whether for the 8-switch single-phase 5-level current-source inverter, or for the new 6-switch 5-level current-source inverter also exists. A simple current-balance control method via DC current feedback is presented here to implement the current-balance control between different levels. And to reduce the output current harmonics, PWM control technique was used. Simulation and experimental results showed that this new 6-switch topology operates correctly and that the balance-inductor can almost equally distribute the total DC current.
基金financially supported by the National Natural Science Foundation of China (Nos.52102144,52172099)the Provincial Joint Fund of Shaanxi (No.2021JLM-28)+1 种基金the Natural Science Basic Research Plan in Shaanxi Province of China (No.2022JM-255)the Scientific Research Plan Projects of Shaanxi Education Department (No.19JK0525)。
文摘Single-phase Ba(Ti_(0.2)Zr_(0.2)Sn_(0.2)Hf_(0.2)Ce_(0.2))O_(3)(BTZSHC) high-entropy ceramics(HECs) with the perovskite structure were successfully prepared via the sol-gel method.The results reveal that the as-prepared ceramics exhibit a single cubic phase belonging to the Pm3 m space group.The high entropy is the driving force of the formation of single-phase ceramics.A larger entropy(ΔS_(mix)) and a negative enthalpy(ΔH_(mix)) are conducive to the formation of single-phase compounds.Herein,ΔS_(mix)=0.323 R mole-1andΔH_(mix)=43.88 kJ/mol.The sluggish-diffusion effect ensures the thermal stability of high-entropy systems.Dielectric measurements reveal that the as-prepared BTZSHC high-entropy ceramics are relaxor ferroelectrics,and the degree of relaxor(γ) is 1.9.The relaxor behavior of the as-prepared ceramics can be ascribed to the relaxation and thermal evolution of their polar units(PUs).The findings of this work provide a theoretical basis and technical support for the preparation of single-phase high-entropy ceramics.
文摘To avoid stray current and maintain the benefit of no phase-split in the DC traction power supply system, an AC traction power supply system was proposed for the urban public transport such as metro and light rail transit. The proposed system consists of a main substation （MSS） and cable traction network （CTN）. The MSS includes a single-phase main traction transformer and a negative-se- quence compensation device, while the CTN includes double-core cables, traction transformers, overhead catenary system, rails, etc. Several key techniques for the proposed system were put forward and discussed, which can be summarized as （1） the power supply principle, equivalent circuit and transmission ability of the CTN, the cable-catenary matching technique, and the selection of catenary voltage level; （2） the segmentation technology and status identification method for traction power supply network, distributed and centralized protection schemes, etc.; （3） a power supply scheme for single-line MSS and a power supply scheme of MSS shared by two or more lines. The proposed industrial frequency single-phase AC traction power supply system shows an excellent technical performance, good economy, and high reliability, hence provides a new alternative for metro and urban rail transit power supply systems.
文摘According to the characteristics of single-phase circuits and demand of using active filter for real-time detecting harmonic and reactive currents, a detecting method based on Fryze＇s power definition is proposed. The results of theoretical analysis and simula- tion show that the proposed method is effective in realtime detecting of instantaneous harmonic and reactive currents in single-phase circuits. When only detecting the total reactive currents, this method does not need a phase-locked loop circuit, and it also can be used in some special applications to provide different compensations on the ground of different requirements of electric network. Compared with the other methods based on the theory of instantaneous reactive power, this method is simple and easy to realize.
基金supported by the National Natural Science Foundation of China (Grant Nos.10625210,50609020 and 10902070)the Leading Academic Discipline Project of Shanghai Municipal Education Commission (Grant No.J50501)
文摘A single-phase lattice Boltzmann model with modified surface tension is developed in this paper to solve the problem of high-density-ratio free surface flow.The computational efficiency and accuracy are both enhanced.The restriction to the relaxation factor （which needs to be smaller than 1） is circumvented by the new surface tension algebra,due to its rational physical nature compared with the treatment of Xing,Buther and Yang in their paper （Comp.Mater.Sci.,2007,39（2）：282-290）.The proposed stable surface tension scheme is applied to simulate the free deformation of a square droplet with surface tension effect and the process of a droplet impinging on a liquid film.The numerical solution for free deformation of a droplet agrees well with thermodynamic principles,and also achieves high accuracy in comparison with Xing,et al.＇s model.Three typical impinging modes are successfully obtained with the new scheme,and another particular mode found by Wang and Chen is also successfully simulated.The evolutions of liquid crown agree well with the power law related to time.
基金supported by the National Natural Science Foundation of China(11464045)Autonomous Region Postgraduate Research Innovation Fund Project(XJGRI2016093)+1 种基金the subject of Xinjiang Normal University Key Laboratory(KWFG1605)the Introduction Program of High-Level Talents of Xinjiang Province
文摘A series of tunable phosphors NaAlSiO_4：Ce^（3＋）,Sm^（3＋） were synthesized using a conventional high-temperature, solid-state method. Crystal structure, photoluminescence excitation, and emission spectra with fluorescence decay curves were investigated. Under UV excitation（325 nm）, NaAlSiO_4：Ce^（3＋）,Sm^（3＋） showed strong blue emission located at 444 nm and orange-reddish emission centered at 563, 601, 648 and 712 nm, stemming from the characteristic emission for 4f-5d transition of Ce^（3＋） and ~4G_（5/2）→~6H_J（J=5/2, 7/2, 9/2, 11/2） transition of Sm^（3＋）, respectively. In addition, we studied the detailed energy transfer process between Ce^（3＋） and Sm^（3＋） and found that it belonged to dipole-dipole resonance energy transfer. Furthermore, we noted that the white light emitting from the Ce^（3＋）, Sm^（3＋） co-doped phosphors with the color coordinate（x=0.313, y=0.283） could be observed under 325 nm excitation, which was close to the ideal white light（x=0.33, y=0.33）. The results indicated that this phosphor has a potential application as a single-phased alumino-silicate phosphor for ultraviolet white light-emitting diodes（UV-WLEDs）.
