Plasma-activated water(PAW),as an extended form of cold atmospheric-pressure plasma,greatly expands the application of plasma-based technology.The biological effects of PAW are closely related to the aqueous reactive ...Plasma-activated water(PAW),as an extended form of cold atmospheric-pressure plasma,greatly expands the application of plasma-based technology.The biological effects of PAW are closely related to the aqueous reactive species,which can be regulated by the activation process.In this study,surface plasma-activated air(SAA)and a He+O_(2)plasma jet(Jet)were parallelly combined(the SAA+Jet combination)or sequentially combined(the SAA→Jet combination and the Jet→SAA combination)to prepare plasma-activated saline(PAS).The PAS activated by the combinations exhibited stronger bactericidal effects than that activated by the SAA or the Jet alone.The concentrations of H_(2)O_(2)and NO_(2)^(-)were higher in the PAS activated by the Jet→SAA combination,while ONOO^(-)concentrations were close in the three kinds of PAS and^(1)O_(2)concentrations were higher in the PAS activated by the SAA+Jet combination.The analysis of scavengers also demonstrated that H_(2)O_(2),^(1)O_(2),and ONOO^(-)in the PAS activated by the SAA+Jet combination,and^(1)O_(2)in the PAS activated by the Jet→SAA combination played critical roles in bactericidal effects.Further,the effective placement time of the three PAS varied,and the PAS activated by the Jet→SAA combination could also inactivate 2.6-log_(10)of MRSA cells after placement for more than 60 min.The regulation of reactive species in plasma-activated water via different combinations of plasma devices could improve the directional application of plasma-activated water in the biomedical field.展开更多
The most critical obstacle for four-wheel independently driven electric vehicles(4WID-EVs)is the driving range.Being the actuators of 4WID-EVs,motors account for its major power consumption.In this sense,by properly d...The most critical obstacle for four-wheel independently driven electric vehicles(4WID-EVs)is the driving range.Being the actuators of 4WID-EVs,motors account for its major power consumption.In this sense,by properly distributing torques to minimize the power consumption,the driving range of 4WID-EV can be effectively improved.This paper proposes a model predictive control(MPC)-based torque distribution scheme,which minimizes the power consumption of 4WID-EVs while guaranteeing its tracking performance of planar motions.By incorporating the motor model considering iron losses,the optimal torque distribution can be achieved without an additional torque controller.Also,for this reason,the proposed control scheme is computationally efficient,since the power consumption term to be optimized,which is expressed as the product of the motor voltages and currents,is much simpler than that derived from the efficiency map.With reasonable simplification and linearization,the MPC problem is converted to a quadratic programming problem,which can be solved efficiently.The simulation results in MATLAB and CarSim co-simulation environments demonstrate that the proposed scheme effectively reduces power consumption with guaranteed tracking performance.展开更多
Chattering phenomenon and singularity are still the main problems that hinder the practical application of sliding mode control. In this paper, a fixed time integral sliding mode controller is designed based on fixed ...Chattering phenomenon and singularity are still the main problems that hinder the practical application of sliding mode control. In this paper, a fixed time integral sliding mode controller is designed based on fixed time stability theory,which ensures precise convergence of the state variables of controlled system, and overcomes the drawback of convergence time growing unboundedly as the initial value increases in finite time controller. It makes the controlled system converge to the control objective within a fixed time bounded by a constant as the initial value grows, and convergence time can be changed by adjusting parameters of controllers properly. Compared with other fixed time controllers, the fixed time integral sliding mode controller proposed in this paper achieves chattering-free control, and integral expression is used to avoid singularity generated by derivation. Finally, the controller is used to stabilize four-order chaotic power system. The results demonstrate that the controller realizes the non-singular chattering-free control of chaotic oscillation in the power system and guarantees the fixed time convergence of state variables, which shows its higher superiority than other finite time controllers.展开更多
ZnO-Bi2O3-based varistor ceramics doped with Yb2O3 in the range from 0 to 0.4%(molar fraction) were obtained by a solid reaction route.The X-ray diffractometry(XRD) and scanning electron microscopy(SEM) were applied t...ZnO-Bi2O3-based varistor ceramics doped with Yb2O3 in the range from 0 to 0.4%(molar fraction) were obtained by a solid reaction route.The X-ray diffractometry(XRD) and scanning electron microscopy(SEM) were applied to characterize the phases and microstructure of the varistor ceramics,and a DC parameter instrument for varistor ceramics was applied to investigate their electrical properties and V-I characteristics.The XRD analysis of the samples shows that the ZnO phase,Bi2O3 phase,Zn7Sb2O12-type spinel phase and Zn2Bi3Sb3O14-type pyrochlore are present,and the Yb2O3 phases and Sb2O4 phases are found in varistor ceramics with increasing amounts of Yb2O3.The average size of ZnO grain firstly increases and then decreases with the increase of Yb2O3 content.The result also shows that the threshold voltage is between 656 V/mm and 1 232 V/mm,the nonlinear coefficient is in the range of 14.1-22.3,and the leakage current is between 0.60 μA and 19.6 μA.The 0.20% Yb2O3-added ZnO-Bi2O3-based varistor ceramics sintered at 900 °C have the best electrical characteristics.展开更多
In this paper,period-doubling bifurcation in a two-stage power factor correction converter is analyzed by using the method of incremental harmonic balance (IHB) and Floquet theory.A two-stage power factor correction c...In this paper,period-doubling bifurcation in a two-stage power factor correction converter is analyzed by using the method of incremental harmonic balance (IHB) and Floquet theory.A two-stage power factor correction converter typically employs a cascade configuration of a pre-regulator boost power factor correction converter with average current mode control to achieve a near unity power factor and a tightly regulated post-regulator DC-DC Buck converter with voltage feedback control to regulate the output voltage.Based on the assumption that the tightly regulated postregulator DC-DC Buck converter is represented as a constant power sink and some other assumptions,the simplified model of the two-stage power factor correction converter is derived and its approximate periodic solution is calculated by the method of IHB.And then,the stability of the system is investigated by using Floquet theory and the stable boundaries are presented on the selected parameter spaces.Finally,some experimental results are given to confirm the effectiveness of the theoretical analysis.展开更多
Serving as a promising alternative to liquid electrolyte in the application of portable and wearable devices,gel polymer electrolytes(GPEs)are expected to obtain more preferable properties rather than just be satisfie...Serving as a promising alternative to liquid electrolyte in the application of portable and wearable devices,gel polymer electrolytes(GPEs)are expected to obtain more preferable properties rather than just be satisfied with the merits of high safety and deformability.Here,an easy-operated method is employed to fabricate cross-linked composite polymer membranes used for GPEs assisted by UV irradiation,in which N-doped carbon quantum dots(N-CQDs)and TiO2are introduced as photocatalysts and additives to improve the performances of GPEs.Specifically,N-CQDs participate as a cross-linker to construct the inner porous structure,and TiO2nanoparticles serve as a stabilizer to improve the electrochemical stability of GPEs under high voltage(3.5 V).The excellent thermal and mechanical stability of the membrane fabricated in this work guarantee the safety of the supercapacitors(SCs).This GPE based SC not only exhibits prominent rate performance(105%capacitance retention at the current density of 40A g^(-1))and cyclic stability(85%at 1 A g^(-1)under 3.5 V after 20,000 cycles),but also displays remarkable energy density(42.88 Wh kg^(-1))with high power density(19.3 k W kg^(-1)).Moreover,the superior rate and cycling performances of the as-prepared GPE based flexible SCs under flat and bending state confirm the feasibility of its application in flexible energy storage devices.展开更多
In this paper, a computational model is constructed to investigate the phenomenon of the initial plasma formation and current transfer in the single-wire electrical explosion in a vacuum. The process of the single-wir...In this paper, a computational model is constructed to investigate the phenomenon of the initial plasma formation and current transfer in the single-wire electrical explosion in a vacuum. The process of the single-wire electrical explosion is divided into four stages. Stage Ⅰ: the wire is in solid state. Stage Ⅱ: the melting stage. Stage Ⅲ: the wire melts completely and the initial plasma forms. Stage IV: the core and corona expand separately. The thermodynamic calculation is applied before the wire melts completely in stages Ⅰ and Ⅱ. In stage Ⅲ, a one-dimensional magnetohydrodynamics model comes into play until the instant when the voltage collapse occurs. The temperature, density, and velocity, which are derived from the magnetohydrodynamics calculation, are averaged over the distribution area. The averaged parameters are taken as the initial conditions for stage Ⅳ in which a simplified magnetohydrodynamics model is applied. A wide-range semi-empirical equation of state, which is established based on the Thomas-Fermi-Kirzhnits model, is constructed to describe the phase transition from solid state to plasma state. The initial plasma formation and the phenomenon of current transfer in the electrical explosion of aluminum wire are investigated using the computational model. Experiments of electrical explosion of aluminum wires are carried out to verify this model. Simulation results are also compared with experimental results of the electrical explosion of copper wire.展开更多
This work is devoted to experimentally study the characteristics of discharge plasma in high power xenon flashlamps.In the experiments,plasma channel profiles are captured by using a high speed CCD camera,and the radi...This work is devoted to experimentally study the characteristics of discharge plasma in high power xenon flashlamps.In the experiments,plasma channel profiles are captured by using a high speed CCD camera,and the radiation energy of the flashlamp is obtained by a pyroelectric energy meter.Voltage and current curves are recorded to shed light on the plasma characteristics.With these diagnostic methods,typical factors influencing the evolution process of plasma channel are studied,including the external electric field and the pre-ionization.The electric potential distribution in the flashlamp influence the plasma channel characteristics the most significantly.The plasma channel pattern for the cases with grounded wires is different from that with ungrounded metal wires.When the wire is ungrounded,it is the coupling voltage between the metal wire and the flashlamp that influences the development of plasma channel.In terms of radiation efficiency,it is proven that there is an optimal interval within 200～300μs between the pre-ionization pulse and the main pulse.展开更多
Epoxy-based composites containing montmorillonite(MMT) modified by silylation reaction with γ-aminopropyltriethoxysilane(γ-APTES) and 3-(glycidyloxypropyl) trimethoxysilane(GPTMS) are successfully prepared.The effec...Epoxy-based composites containing montmorillonite(MMT) modified by silylation reaction with γ-aminopropyltriethoxysilane(γ-APTES) and 3-(glycidyloxypropyl) trimethoxysilane(GPTMS) are successfully prepared.The effects of filler loading and surface modification on the electrical and thermal properties of the epoxy/MMT composites are investigated. Compared with the pure epoxy resin, the epoxy/MMT composite, whether MMT is surface-treated or not, shows low dielectric permittivity, low dielectric loss, and enhanced dielectric strength. The MMT in the epoxy/MMT composite also influences the thermal properties of the composite by improving the thermal conductivity and stability.Surface functionalization of MMT not only conduces to the better dispersion of the nanoparticles, but also significantly affects the electric and thermal properties of the hybrid by influencing the interfaces between MMT and epoxy resin.Improved interfaces are good for enhancing the electric and thermal properties of nanocomposites. What is more, the MMT modified with GPTMS rather than γ-APTES is found to have greater influence on improving the interface between the MMT filler and polymer matrices, thus resulting in lower dielectric loss, lower electric conductivity, higher breakdown strength, lower thermal conductivity, and higher thermal stability.展开更多
The optimal allocation of integrated energy systemcapacity based on the heuristic algorithms can reduce economic costs and achieve maximum consumption of renewable energy,which has attracted many attentions.However,th...The optimal allocation of integrated energy systemcapacity based on the heuristic algorithms can reduce economic costs and achieve maximum consumption of renewable energy,which has attracted many attentions.However,the optimization results of heuristic algorithms are usually influenced by the choice of hyperparameters.To solve the above problem,the particle swarm algorithm is introduced to find the optimal hyperparameters of the heuristic algorithms.Firstly,an integrated energy system consisting of the photovoltaic,wind turbine,electrolysis cell,hydrogen storage tank,and energy storage is established.Meanwhile,the minimum economic cost,the maximum wind and PV power consumption rate,and the minimum load shortage rate are considered to be the objective functions.Then,a hybrid method combined the particle swarm combined with non-dominated sorting genetic algorithms-II is proposed to solve the optimal allocation problem.According to the optimal result,the economic cost is 6.3 million RMB,and the load shortage rate is 9.83%.Finally,four comparative experiments are conducted to verify the superiority-seeking ability of the proposed method.The comparative results indicate that the proposed method possesses a strongermerit-seeking ability,resulting in a solution satisfaction rate of 87.37%,which is higher than that of the unimproved non-dominated sorting genetic algorithms-II.展开更多
This paper demonstrated our discovery of the movement effect of BiFeO_3 nanoparticles in solution by strong electrical polarization. First, BiFeO_3 nanoparticles were prepared by ball milling and characterized by SEM....This paper demonstrated our discovery of the movement effect of BiFeO_3 nanoparticles in solution by strong electrical polarization. First, BiFeO_3 nanoparticles were prepared by ball milling and characterized by SEM. Then, the preparation of BiFeO_3 solution was finished. BiFeO_3 nanoparticles are found to move in solution due to electrical field. The movement velocity of BiFeO_3 nanoparticles, which is about 10 μm·s^-1 , is influenced and controlled by the applied electrical field. The concentration of BiFeO_3 solution and the nanoparticle sizes also have effects on its movement properties. The movement of BiFeO_3 nanoparticles in solution is induced by strong polarization, and BiFeO_3 nanoparticles have net negative electric charges because of the electrostatic force between BiFeO_3 nanoparticles and the negative ions in water resolver.展开更多
The spacer used in gas insulated switchgear(GIS)plays a vital role in its safe operation.The mismatch of mechanical properties between conductor and insulating material in spacers results in stress concentration at th...The spacer used in gas insulated switchgear(GIS)plays a vital role in its safe operation.The mismatch of mechanical properties between conductor and insulating material in spacers results in stress concentration at the interface between them.During a hydrostatic test,mechanical damages are often initiated from the interface.In this paper,the stress between aluminum conductors and epoxy resin is studied by using a simplified coaxial structure specimen.The measurement system and finite element simulation are used to explore the generation of stress and strain during curing and shrinkage.The real-time measurement of strain at the interface shows that the residual strain in the entire process is primarily generated during the cooling stage.Consequently,the temperature and stress/strain distribution at the interface during the cooling stage are further studied,and combined with experiments and simulations.The consistency between the finite element simulation and the experimental measurement results verifies the validity of the simulation method used.The results show that the maximum of the first principal stress generated during the cooling stage of the production process is concentrated on the upper and lower edges of the interface which is critical to the impact of the production quality of the spacer.展开更多
In order to further investigate the surface flashover mechanism in vacuum, the surface flashover and electric field distribution of multilayer organic insulation structure are studied and developed based on the previo...In order to further investigate the surface flashover mechanism in vacuum, the surface flashover and electric field distribution of multilayer organic insulation structure are studied and developed based on the previous studies. The samples of multilayer organic insulation structure are prepared by inserting multilayer organic composite material with different relative permittivity between the electrode and the dielectric. Two multilayer organic insulation structures are prepared in this study. One is the cylindrical samples, the other is 45° samples. The impulse (1.2/50 μs) and DC flashover voltages in vacuum are tested, and the electric field distributions of two insulation structures are analyzed by ANSYS. It is found that these two insulation structure could effectively improve the surface flashover performance in vacuum. The results indicate that the highest impulse first flashover voltage of cylindrical samples reaches 65 kV and increases by 25% under im- pulse voltage. The highest first flashover voltage of /c samples reaches 81 kV and increases by 32% under impulse voltage. The results of electric field simulation demonstrate that different mechanisms exist between 45° insulation structure and cylindrical structure.展开更多
This paper investigates the electronic relaxation of deep bulk trap and interface state in ZnO ceramics based on dielectric spectra measured in a wide range of temperature,frequency and bias,in addition to the steady ...This paper investigates the electronic relaxation of deep bulk trap and interface state in ZnO ceramics based on dielectric spectra measured in a wide range of temperature,frequency and bias,in addition to the steady state response.It discusses the nature of net current flowing over the barrier affected by interface state,and then obtains temperature-dependent barrier height by approximate calculation from steady I-V (current-voltage) characteristics.Additional conductance and capacitance arising from deep bulk trap relaxation are calculated based on the displacement of the cross point between deep bulk trap and Fermi level under small AC signal.From the resonances due to deep bulk trap relaxation on dielectric spectra,the activation energies are obtained as 0.22 eV and 0.35 eV,which are consistent with the electronic levels of the main defect interstitial Zn and vacancy oxygen in the depletion layer.Under moderate bias,another resonance due to interface relaxation is shown on the dielectric spectra.The DC-like conductance is also observed in high temperature region on dielectric spectra,and the activation energy is much smaller than the barrier height in steady state condition,which is attributed to the displacement current coming from the shallow bulk trap relaxation or other factors.展开更多
Effects of A-site non-stoichiometry on the structural and electrical properties of 0.96K0.5+xNa0.5+xNbO3- 0.04LiSbO3 lead-free piezoelectric ceramics were examined for 0 ≤ x ≤ 0.02. The piezoelectric coefficients ex...Effects of A-site non-stoichiometry on the structural and electrical properties of 0.96K0.5+xNa0.5+xNbO3- 0.04LiSbO3 lead-free piezoelectric ceramics were examined for 0 ≤ x ≤ 0.02. The piezoelectric coefficients exhibited a maximum, d33 = 187 pC/N at x = 0.0075, coinciding with the maximum of the grain size and the apparent density at x = 0.0075. The apparent density and the piezoelectric coefficients decreased with increasing x at higher x which was likely due to the crystal geometrical distortion of 0.96K0.5+xNa0.5+xNbO3-0.04LiSbO3. In addition, super-large grains were found and this may be due to liquid phase sintering. Excess (K++Na+) attracted a sum of space charges to keep the charge neutral, resulting in charge leakage during the course of ceramic polarization, influencing the piezoelectric and ferroelectric properties. These findings are of importance for guiding the design of K0.5Na0.5NbO3-based lead-free ceramics with enhanced electrical properties.展开更多
Oil-paper compound insulation has been widely used in power transformers for quite a long time because of its good performances. The insulation gradually degrades under combined thermal, electrical and chemical stress...Oil-paper compound insulation has been widely used in power transformers for quite a long time because of its good performances. The insulation gradually degrades under combined thermal, electrical and chemical stresses during routine operations, mainly because of space charges inside. This work investigated the space charge characteristics in oil-paper insulation under oil aging circumstance. New trans- former oil samples are thermally aged to obtain different aging states, and their physical and chemical properties are analyzed. New Kraft papers are dried in vacuum and fully immersed in these different aged oil samples, and three kinds of oil-paper samples are obtained. We use the pulsed electro-acoustic (PEA) method to measure space charge under both DC voltage-on and voltage-off conditions at room temperature. The effect of oil aging state on characteristics of space charge injection, accumulation, and decay is analyzed and discussed. The results show that comparing with the DC voltage-off condition, more charges are injected into samples at the interface of electrode and dielectric when DC voltage is on. When the oil-aged state gets worse, more charges are induced at both cathode and anode, more space charges are accumulated in the bulk, the area of negative charges is larger, and local electric field is distorted more seriously. Moreover, for the voltage-off condition, aged oil is good for space charge decay, and trapped positive space charges decay faster than trapped negative charges.展开更多
The influence of copper vapor on the low-voltage circuit breaker arcs is studied.Athree-dimensional (3-D) magnetohydrodynamics(MHD) model of arc motion under the effect ofexternal magnetic field is built up.By adoptin...The influence of copper vapor on the low-voltage circuit breaker arcs is studied.Athree-dimensional (3-D) magnetohydrodynamics(MHD) model of arc motion under the effect ofexternal magnetic field is built up.By adopting the commercial computational fluid dynamics(CFD) package FLUENT based on control-volume method,the above MHD model is solved.Forthe mediums of air-1% Cu and air-10% Cu,the distributions of stationary temperature,pressure,electrical potential and the arc motion processes are compared with those of a pure air arc.Thecopper vapor diffusion process in the arc chamber and the distribution of copper vapor massconcentration are also simulated.The results shows that the copper vapor has a cooling effecton the arc plasma and can decrease the stationary voltage as well.Moreover,the presence ofcopper vapor can decelerate the arc motion in the quenching chambers.The maximal coppervapor concentration locates behind the arc root because of the existence of a'double vortex'nearthe electrodes.展开更多
The world is witnessing increasing frequency of extreme events. The power system is the backbone critical infrastructure of our economy and is under treat of such events. The resilient power system is intended to cope...The world is witnessing increasing frequency of extreme events. The power system is the backbone critical infrastructure of our economy and is under treat of such events. The resilient power system is intended to cope with low probability, high risk extreme events including extreme natural disasters and man-made attacks. Realizing resilience in the power system has been an unprecedented mission. Equipped with today’s smart grid technologies, power system can be rendered more resilient by the strategies taken before, during and after a disruptive event erupts. Based on a thorough review of existing works, we present the most-investigated problems and solving measures according to their application stage. In the preparation stage, innovative planning frameworks considering disaster scenarios are discussed; after the event, the system can alter the topology and integrate resource allocation to alleviate load shedding. The characteristics of different disasters are investigated to facilitate enhancing resilience. The review provides a summary of resilience strategies in the power system and can shed light to future research and application.展开更多
This work deals with an experimental study of a Cu planar wire array(PWA)in air and water under the stored energy 300-1200 J.A single Cu wire is adopted as a controlled trial.Four configurations of PWA and a wire with...This work deals with an experimental study of a Cu planar wire array(PWA)in air and water under the stored energy 300-1200 J.A single Cu wire is adopted as a controlled trial.Four configurations of PWA and a wire with the same mass(cross-section area)but the different specific surface areas(15-223 cm^(2)g^(-1))are exploded.The transient process is analyzed using high-speed photography in combination with the results of optical emission and discharge.Discharge characteristics revealed that PWA always has a higher electric power peak,early but higher voltage peak,as well as faster vaporization and ionization process than the single-wire case.Two to three times stronger optical emission could be obtained when replacing the single-wire with PWA,indicating a higher energy-density state is reached.Phenomenologically,in both air and water,single-wire load tends to develop a transverse stratified structure,while PWA is dominated by the uneven energy deposition among wires.Finally,the synchronism and uniformity of the PWA explosion are discussed.展开更多
The thick insulation layer of 110 kV XLPE power cables will result in the gradient changing morphology with the radius due to crosslinking process and cooling of the XLPE insulation. In this paper, the morphology of c...The thick insulation layer of 110 kV XLPE power cables will result in the gradient changing morphology with the radius due to crosslinking process and cooling of the XLPE insulation. In this paper, the morphology of cross-linked polyethylene (XLPE) insulation of 110 kV cable and the uniforming effect of the heating process on it are researched by the differential scanning calorimetry (DSC) and X-ray diffraction(WAXD). The middle layer morphology structures of insulation produced by normal technology are of better uniform, while the crystallinity of the inner and outer layer of the insulation is lower than that of the middle one. The melting enthalpy ΔH_m of materials displays the difference of the crystal morphologies sensitively. The difference of crystallizing morphology in different layers of the high-voltage power cable insulation can be improved by heating process. But the uniforming of morphology of the insulation by heating process requires sufficient temperature and time. The effect of the on-line stress-relaxation equipment used widely by cable works now should be doubted. The test results of WAXD reveal that thermal stress changes the interplanar distances in the crystal region. So the radical stress in the insulation is tensile mainly.展开更多
基金supported by National Natural Science Foundation of China(No.51977174)。
文摘Plasma-activated water(PAW),as an extended form of cold atmospheric-pressure plasma,greatly expands the application of plasma-based technology.The biological effects of PAW are closely related to the aqueous reactive species,which can be regulated by the activation process.In this study,surface plasma-activated air(SAA)and a He+O_(2)plasma jet(Jet)were parallelly combined(the SAA+Jet combination)or sequentially combined(the SAA→Jet combination and the Jet→SAA combination)to prepare plasma-activated saline(PAS).The PAS activated by the combinations exhibited stronger bactericidal effects than that activated by the SAA or the Jet alone.The concentrations of H_(2)O_(2)and NO_(2)^(-)were higher in the PAS activated by the Jet→SAA combination,while ONOO^(-)concentrations were close in the three kinds of PAS and^(1)O_(2)concentrations were higher in the PAS activated by the SAA+Jet combination.The analysis of scavengers also demonstrated that H_(2)O_(2),^(1)O_(2),and ONOO^(-)in the PAS activated by the SAA+Jet combination,and^(1)O_(2)in the PAS activated by the Jet→SAA combination played critical roles in bactericidal effects.Further,the effective placement time of the three PAS varied,and the PAS activated by the Jet→SAA combination could also inactivate 2.6-log_(10)of MRSA cells after placement for more than 60 min.The regulation of reactive species in plasma-activated water via different combinations of plasma devices could improve the directional application of plasma-activated water in the biomedical field.
基金supported in part by National Natural Science Foundation of China(NSFC)under Project No.51737010.
文摘The most critical obstacle for four-wheel independently driven electric vehicles(4WID-EVs)is the driving range.Being the actuators of 4WID-EVs,motors account for its major power consumption.In this sense,by properly distributing torques to minimize the power consumption,the driving range of 4WID-EV can be effectively improved.This paper proposes a model predictive control(MPC)-based torque distribution scheme,which minimizes the power consumption of 4WID-EVs while guaranteeing its tracking performance of planar motions.By incorporating the motor model considering iron losses,the optimal torque distribution can be achieved without an additional torque controller.Also,for this reason,the proposed control scheme is computationally efficient,since the power consumption term to be optimized,which is expressed as the product of the motor voltages and currents,is much simpler than that derived from the efficiency map.With reasonable simplification and linearization,the MPC problem is converted to a quadratic programming problem,which can be solved efficiently.The simulation results in MATLAB and CarSim co-simulation environments demonstrate that the proposed scheme effectively reduces power consumption with guaranteed tracking performance.
基金Project supported by the Science Fund for Creative Research Groups of the National Natural Science Foundation of China(Grant No.51521065)
文摘Chattering phenomenon and singularity are still the main problems that hinder the practical application of sliding mode control. In this paper, a fixed time integral sliding mode controller is designed based on fixed time stability theory,which ensures precise convergence of the state variables of controlled system, and overcomes the drawback of convergence time growing unboundedly as the initial value increases in finite time controller. It makes the controlled system converge to the control objective within a fixed time bounded by a constant as the initial value grows, and convergence time can be changed by adjusting parameters of controllers properly. Compared with other fixed time controllers, the fixed time integral sliding mode controller proposed in this paper achieves chattering-free control, and integral expression is used to avoid singularity generated by derivation. Finally, the controller is used to stabilize four-order chaotic power system. The results demonstrate that the controller realizes the non-singular chattering-free control of chaotic oscillation in the power system and guarantees the fixed time convergence of state variables, which shows its higher superiority than other finite time controllers.
基金Project(BK2011243) supported by the Natural Science Foundation of Jiangsu Province,ChinaProject(2007DA10512711408) supported by the Visiting Scholarship of State Key Laboratory of Power Transmission Equipment & System Security and New Technology (Chongqing University),China+4 种基金Project(EIPE11204) supported by the State Key Laboratory of Electrical Insulation and Power Equipment,ChinaProject(KF201104) supported by the State Key Laboratory of New Ceramic and Fine Processing,ChinaProject(KFJJ201105) supported by the Opening Project of State Key Laboratory of Electronic Thin Films and Integrated Devices,ChinaProject(10KJD430002) supported by the Universities Natural Science Research Project of Jiangsu Province,ChinaProject(11JDG084) supported by the Research Foundation of Jiangsu University,China
文摘ZnO-Bi2O3-based varistor ceramics doped with Yb2O3 in the range from 0 to 0.4%(molar fraction) were obtained by a solid reaction route.The X-ray diffractometry(XRD) and scanning electron microscopy(SEM) were applied to characterize the phases and microstructure of the varistor ceramics,and a DC parameter instrument for varistor ceramics was applied to investigate their electrical properties and V-I characteristics.The XRD analysis of the samples shows that the ZnO phase,Bi2O3 phase,Zn7Sb2O12-type spinel phase and Zn2Bi3Sb3O14-type pyrochlore are present,and the Yb2O3 phases and Sb2O4 phases are found in varistor ceramics with increasing amounts of Yb2O3.The average size of ZnO grain firstly increases and then decreases with the increase of Yb2O3 content.The result also shows that the threshold voltage is between 656 V/mm and 1 232 V/mm,the nonlinear coefficient is in the range of 14.1-22.3,and the leakage current is between 0.60 μA and 19.6 μA.The 0.20% Yb2O3-added ZnO-Bi2O3-based varistor ceramics sintered at 900 °C have the best electrical characteristics.
基金supported by the National Natural Science Foundation of China (Grant No.51007068)the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No.20100201120028)+1 种基金the Fundamental Research Funds for the Central Universities of Chinathe State Key Laboratory of Electrical Insulation and Power Equipment of China (Grant No.EIPE10303)
文摘In this paper,period-doubling bifurcation in a two-stage power factor correction converter is analyzed by using the method of incremental harmonic balance (IHB) and Floquet theory.A two-stage power factor correction converter typically employs a cascade configuration of a pre-regulator boost power factor correction converter with average current mode control to achieve a near unity power factor and a tightly regulated post-regulator DC-DC Buck converter with voltage feedback control to regulate the output voltage.Based on the assumption that the tightly regulated postregulator DC-DC Buck converter is represented as a constant power sink and some other assumptions,the simplified model of the two-stage power factor correction converter is derived and its approximate periodic solution is calculated by the method of IHB.And then,the stability of the system is investigated by using Floquet theory and the stable boundaries are presented on the selected parameter spaces.Finally,some experimental results are given to confirm the effectiveness of the theoretical analysis.
基金funding supports from the Natural Science Basis Research Plan in Shaanxi Province of China(2019JLZ-10)the Independent Research Project of National Key Laboratory of Electrical Insulation and Power Equipment(EIPE19111)。
文摘Serving as a promising alternative to liquid electrolyte in the application of portable and wearable devices,gel polymer electrolytes(GPEs)are expected to obtain more preferable properties rather than just be satisfied with the merits of high safety and deformability.Here,an easy-operated method is employed to fabricate cross-linked composite polymer membranes used for GPEs assisted by UV irradiation,in which N-doped carbon quantum dots(N-CQDs)and TiO2are introduced as photocatalysts and additives to improve the performances of GPEs.Specifically,N-CQDs participate as a cross-linker to construct the inner porous structure,and TiO2nanoparticles serve as a stabilizer to improve the electrochemical stability of GPEs under high voltage(3.5 V).The excellent thermal and mechanical stability of the membrane fabricated in this work guarantee the safety of the supercapacitors(SCs).This GPE based SC not only exhibits prominent rate performance(105%capacitance retention at the current density of 40A g^(-1))and cyclic stability(85%at 1 A g^(-1)under 3.5 V after 20,000 cycles),but also displays remarkable energy density(42.88 Wh kg^(-1))with high power density(19.3 k W kg^(-1)).Moreover,the superior rate and cycling performances of the as-prepared GPE based flexible SCs under flat and bending state confirm the feasibility of its application in flexible energy storage devices.
基金Project supported by the National Science Foundation of China(Grant Nos.51322706,51237006,and 51325705)the Program for New Century Excellent Talents in University,China(Grant No.NCET-11-0428)the Fundamental Research Funds for the Central Universities,China
文摘In this paper, a computational model is constructed to investigate the phenomenon of the initial plasma formation and current transfer in the single-wire electrical explosion in a vacuum. The process of the single-wire electrical explosion is divided into four stages. Stage Ⅰ: the wire is in solid state. Stage Ⅱ: the melting stage. Stage Ⅲ: the wire melts completely and the initial plasma forms. Stage IV: the core and corona expand separately. The thermodynamic calculation is applied before the wire melts completely in stages Ⅰ and Ⅱ. In stage Ⅲ, a one-dimensional magnetohydrodynamics model comes into play until the instant when the voltage collapse occurs. The temperature, density, and velocity, which are derived from the magnetohydrodynamics calculation, are averaged over the distribution area. The averaged parameters are taken as the initial conditions for stage Ⅳ in which a simplified magnetohydrodynamics model is applied. A wide-range semi-empirical equation of state, which is established based on the Thomas-Fermi-Kirzhnits model, is constructed to describe the phase transition from solid state to plasma state. The initial plasma formation and the phenomenon of current transfer in the electrical explosion of aluminum wire are investigated using the computational model. Experiments of electrical explosion of aluminum wires are carried out to verify this model. Simulation results are also compared with experimental results of the electrical explosion of copper wire.
文摘This work is devoted to experimentally study the characteristics of discharge plasma in high power xenon flashlamps.In the experiments,plasma channel profiles are captured by using a high speed CCD camera,and the radiation energy of the flashlamp is obtained by a pyroelectric energy meter.Voltage and current curves are recorded to shed light on the plasma characteristics.With these diagnostic methods,typical factors influencing the evolution process of plasma channel are studied,including the external electric field and the pre-ionization.The electric potential distribution in the flashlamp influence the plasma channel characteristics the most significantly.The plasma channel pattern for the cases with grounded wires is different from that with ungrounded metal wires.When the wire is ungrounded,it is the coupling voltage between the metal wire and the flashlamp that influences the development of plasma channel.In terms of radiation efficiency,it is proven that there is an optimal interval within 200～300μs between the pre-ionization pulse and the main pulse.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.21806129,51872238,51407134,and 51521065)the China Postdoctoral Science Foundation(Grant No.2016M590619)+3 种基金the Natural Science Foundation of Shandong Province,China(Grant No.ZR2016EEQ28)the State Key Laboratory of Electrical Insulation and Power Equipment,China(Grant No.EIPE14107)the Fundamental Research Funds for the Central Universities,China(Grant No.3102018zy045)the Natural Science Basic Research Plan in Shaanxi Province,China(Grant No.2017JQ5116)
文摘Epoxy-based composites containing montmorillonite(MMT) modified by silylation reaction with γ-aminopropyltriethoxysilane(γ-APTES) and 3-(glycidyloxypropyl) trimethoxysilane(GPTMS) are successfully prepared.The effects of filler loading and surface modification on the electrical and thermal properties of the epoxy/MMT composites are investigated. Compared with the pure epoxy resin, the epoxy/MMT composite, whether MMT is surface-treated or not, shows low dielectric permittivity, low dielectric loss, and enhanced dielectric strength. The MMT in the epoxy/MMT composite also influences the thermal properties of the composite by improving the thermal conductivity and stability.Surface functionalization of MMT not only conduces to the better dispersion of the nanoparticles, but also significantly affects the electric and thermal properties of the hybrid by influencing the interfaces between MMT and epoxy resin.Improved interfaces are good for enhancing the electric and thermal properties of nanocomposites. What is more, the MMT modified with GPTMS rather than γ-APTES is found to have greater influence on improving the interface between the MMT filler and polymer matrices, thus resulting in lower dielectric loss, lower electric conductivity, higher breakdown strength, lower thermal conductivity, and higher thermal stability.
基金supported in part by the Natural Science Foundation of Shandong Province(ZR2021QE289)in part by State Key Laboratory of Electrical Insulation and Power Equipment(EIPE22201).
文摘The optimal allocation of integrated energy systemcapacity based on the heuristic algorithms can reduce economic costs and achieve maximum consumption of renewable energy,which has attracted many attentions.However,the optimization results of heuristic algorithms are usually influenced by the choice of hyperparameters.To solve the above problem,the particle swarm algorithm is introduced to find the optimal hyperparameters of the heuristic algorithms.Firstly,an integrated energy system consisting of the photovoltaic,wind turbine,electrolysis cell,hydrogen storage tank,and energy storage is established.Meanwhile,the minimum economic cost,the maximum wind and PV power consumption rate,and the minimum load shortage rate are considered to be the objective functions.Then,a hybrid method combined the particle swarm combined with non-dominated sorting genetic algorithms-II is proposed to solve the optimal allocation problem.According to the optimal result,the economic cost is 6.3 million RMB,and the load shortage rate is 9.83%.Finally,four comparative experiments are conducted to verify the superiority-seeking ability of the proposed method.The comparative results indicate that the proposed method possesses a strongermerit-seeking ability,resulting in a solution satisfaction rate of 87.37%,which is higher than that of the unimproved non-dominated sorting genetic algorithms-II.
基金supported by the National Natural Science Foundation of China(No.50807042)the Research Fund for the Doctoral Program of Higher Education of China(No.200806981043)+1 种基金the Fundamental Research Fund for the Central Universities(No.xjj2012088)the fund of StateKey Laboratory of Electrical Insulation and Power Equipment(Xi'an Jiaotong University No.EIPE12305)
文摘This paper demonstrated our discovery of the movement effect of BiFeO_3 nanoparticles in solution by strong electrical polarization. First, BiFeO_3 nanoparticles were prepared by ball milling and characterized by SEM. Then, the preparation of BiFeO_3 solution was finished. BiFeO_3 nanoparticles are found to move in solution due to electrical field. The movement velocity of BiFeO_3 nanoparticles, which is about 10 μm·s^-1 , is influenced and controlled by the applied electrical field. The concentration of BiFeO_3 solution and the nanoparticle sizes also have effects on its movement properties. The movement of BiFeO_3 nanoparticles in solution is induced by strong polarization, and BiFeO_3 nanoparticles have net negative electric charges because of the electrostatic force between BiFeO_3 nanoparticles and the negative ions in water resolver.
基金supported in part by the National Natural Science Foundation of China(No.51707155)China Postdoctoral Science Foundation(No.2020M673450)。
文摘The spacer used in gas insulated switchgear(GIS)plays a vital role in its safe operation.The mismatch of mechanical properties between conductor and insulating material in spacers results in stress concentration at the interface between them.During a hydrostatic test,mechanical damages are often initiated from the interface.In this paper,the stress between aluminum conductors and epoxy resin is studied by using a simplified coaxial structure specimen.The measurement system and finite element simulation are used to explore the generation of stress and strain during curing and shrinkage.The real-time measurement of strain at the interface shows that the residual strain in the entire process is primarily generated during the cooling stage.Consequently,the temperature and stress/strain distribution at the interface during the cooling stage are further studied,and combined with experiments and simulations.The consistency between the finite element simulation and the experimental measurement results verifies the validity of the simulation method used.The results show that the maximum of the first principal stress generated during the cooling stage of the production process is concentrated on the upper and lower edges of the interface which is critical to the impact of the production quality of the spacer.
基金Project supported by National Science Fund for Outstanding Young Scholars of China (50625721)National Basic Research Program of China (973 Program) (2011CB 209404)
文摘In order to further investigate the surface flashover mechanism in vacuum, the surface flashover and electric field distribution of multilayer organic insulation structure are studied and developed based on the previous studies. The samples of multilayer organic insulation structure are prepared by inserting multilayer organic composite material with different relative permittivity between the electrode and the dielectric. Two multilayer organic insulation structures are prepared in this study. One is the cylindrical samples, the other is 45° samples. The impulse (1.2/50 μs) and DC flashover voltages in vacuum are tested, and the electric field distributions of two insulation structures are analyzed by ANSYS. It is found that these two insulation structure could effectively improve the surface flashover performance in vacuum. The results indicate that the highest impulse first flashover voltage of cylindrical samples reaches 65 kV and increases by 25% under im- pulse voltage. The highest first flashover voltage of /c samples reaches 81 kV and increases by 32% under impulse voltage. The results of electric field simulation demonstrate that different mechanisms exist between 45° insulation structure and cylindrical structure.
基金supported by the National Outstanding Young Investigator Grant of China (Grant No. 50625721)the National Natural Science Foundation of China (Grant No. 50972118)
文摘This paper investigates the electronic relaxation of deep bulk trap and interface state in ZnO ceramics based on dielectric spectra measured in a wide range of temperature,frequency and bias,in addition to the steady state response.It discusses the nature of net current flowing over the barrier affected by interface state,and then obtains temperature-dependent barrier height by approximate calculation from steady I-V (current-voltage) characteristics.Additional conductance and capacitance arising from deep bulk trap relaxation are calculated based on the displacement of the cross point between deep bulk trap and Fermi level under small AC signal.From the resonances due to deep bulk trap relaxation on dielectric spectra,the activation energies are obtained as 0.22 eV and 0.35 eV,which are consistent with the electronic levels of the main defect interstitial Zn and vacancy oxygen in the depletion layer.Under moderate bias,another resonance due to interface relaxation is shown on the dielectric spectra.The DC-like conductance is also observed in high temperature region on dielectric spectra,and the activation energy is much smaller than the barrier height in steady state condition,which is attributed to the displacement current coming from the shallow bulk trap relaxation or other factors.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10804130 and 60871027)the Natural Science Foundation of Shaanxi Province of China (Grant No. 2009JQ1001)the Funds of the Key Laboratory of Electrical Insulation and Power Equipment (Grant No. EIPE10202)
文摘Effects of A-site non-stoichiometry on the structural and electrical properties of 0.96K0.5+xNa0.5+xNbO3- 0.04LiSbO3 lead-free piezoelectric ceramics were examined for 0 ≤ x ≤ 0.02. The piezoelectric coefficients exhibited a maximum, d33 = 187 pC/N at x = 0.0075, coinciding with the maximum of the grain size and the apparent density at x = 0.0075. The apparent density and the piezoelectric coefficients decreased with increasing x at higher x which was likely due to the crystal geometrical distortion of 0.96K0.5+xNa0.5+xNbO3-0.04LiSbO3. In addition, super-large grains were found and this may be due to liquid phase sintering. Excess (K++Na+) attracted a sum of space charges to keep the charge neutral, resulting in charge leakage during the course of ceramic polarization, influencing the piezoelectric and ferroelectric properties. These findings are of importance for guiding the design of K0.5Na0.5NbO3-based lead-free ceramics with enhanced electrical properties.
基金Project supported by China National Fund for Distinguished Young Scientists (51125029)National High-tech Research and Development Program of China (863 Program) (2007AA04Z411)
文摘Oil-paper compound insulation has been widely used in power transformers for quite a long time because of its good performances. The insulation gradually degrades under combined thermal, electrical and chemical stresses during routine operations, mainly because of space charges inside. This work investigated the space charge characteristics in oil-paper insulation under oil aging circumstance. New trans- former oil samples are thermally aged to obtain different aging states, and their physical and chemical properties are analyzed. New Kraft papers are dried in vacuum and fully immersed in these different aged oil samples, and three kinds of oil-paper samples are obtained. We use the pulsed electro-acoustic (PEA) method to measure space charge under both DC voltage-on and voltage-off conditions at room temperature. The effect of oil aging state on characteristics of space charge injection, accumulation, and decay is analyzed and discussed. The results show that comparing with the DC voltage-off condition, more charges are injected into samples at the interface of electrode and dielectric when DC voltage is on. When the oil-aged state gets worse, more charges are induced at both cathode and anode, more space charges are accumulated in the bulk, the area of negative charges is larger, and local electric field is distorted more seriously. Moreover, for the voltage-off condition, aged oil is good for space charge decay, and trapped positive space charges decay faster than trapped negative charges.
基金National Natural Science Foundation of China(Nos.5047702,50537050,50525722)Key Projects of Science and Technology Research of the Ministry of Education of China(No.10518)
文摘The influence of copper vapor on the low-voltage circuit breaker arcs is studied.Athree-dimensional (3-D) magnetohydrodynamics(MHD) model of arc motion under the effect ofexternal magnetic field is built up.By adopting the commercial computational fluid dynamics(CFD) package FLUENT based on control-volume method,the above MHD model is solved.Forthe mediums of air-1% Cu and air-10% Cu,the distributions of stationary temperature,pressure,electrical potential and the arc motion processes are compared with those of a pure air arc.Thecopper vapor diffusion process in the arc chamber and the distribution of copper vapor massconcentration are also simulated.The results shows that the copper vapor has a cooling effecton the arc plasma and can decrease the stationary voltage as well.Moreover,the presence ofcopper vapor can decelerate the arc motion in the quenching chambers.The maximal coppervapor concentration locates behind the arc root because of the existence of a'double vortex'nearthe electrodes.
基金funded by Science and Technology Project of State Grid,China(5202011600UG)the National Natural Science Foundation of China(51577147)
文摘The world is witnessing increasing frequency of extreme events. The power system is the backbone critical infrastructure of our economy and is under treat of such events. The resilient power system is intended to cope with low probability, high risk extreme events including extreme natural disasters and man-made attacks. Realizing resilience in the power system has been an unprecedented mission. Equipped with today’s smart grid technologies, power system can be rendered more resilient by the strategies taken before, during and after a disruptive event erupts. Based on a thorough review of existing works, we present the most-investigated problems and solving measures according to their application stage. In the preparation stage, innovative planning frameworks considering disaster scenarios are discussed; after the event, the system can alter the topology and integrate resource allocation to alleviate load shedding. The characteristics of different disasters are investigated to facilitate enhancing resilience. The review provides a summary of resilience strategies in the power system and can shed light to future research and application.
基金supported in part by National Natural Science Foundation of China(No.51907007)Natural Science Foundation of Beijing(No.3212034)+1 种基金State Key Laboratory of Electrical Insulation and Power Equipment(No.EIPE20204)State Key Laboratory of Advanced Electromagnetic Engineering and Technology(No.AEET 2019KF006)。
文摘This work deals with an experimental study of a Cu planar wire array(PWA)in air and water under the stored energy 300-1200 J.A single Cu wire is adopted as a controlled trial.Four configurations of PWA and a wire with the same mass(cross-section area)but the different specific surface areas(15-223 cm^(2)g^(-1))are exploded.The transient process is analyzed using high-speed photography in combination with the results of optical emission and discharge.Discharge characteristics revealed that PWA always has a higher electric power peak,early but higher voltage peak,as well as faster vaporization and ionization process than the single-wire case.Two to three times stronger optical emission could be obtained when replacing the single-wire with PWA,indicating a higher energy-density state is reached.Phenomenologically,in both air and water,single-wire load tends to develop a transverse stratified structure,while PWA is dominated by the uneven energy deposition among wires.Finally,the synchronism and uniformity of the PWA explosion are discussed.
文摘The thick insulation layer of 110 kV XLPE power cables will result in the gradient changing morphology with the radius due to crosslinking process and cooling of the XLPE insulation. In this paper, the morphology of cross-linked polyethylene (XLPE) insulation of 110 kV cable and the uniforming effect of the heating process on it are researched by the differential scanning calorimetry (DSC) and X-ray diffraction(WAXD). The middle layer morphology structures of insulation produced by normal technology are of better uniform, while the crystallinity of the inner and outer layer of the insulation is lower than that of the middle one. The melting enthalpy ΔH_m of materials displays the difference of the crystal morphologies sensitively. The difference of crystallizing morphology in different layers of the high-voltage power cable insulation can be improved by heating process. But the uniforming of morphology of the insulation by heating process requires sufficient temperature and time. The effect of the on-line stress-relaxation equipment used widely by cable works now should be doubted. The test results of WAXD reveal that thermal stress changes the interplanar distances in the crystal region. So the radical stress in the insulation is tensile mainly.
