For three phase four-wire active power filters （APFs）, several typical power theories and corresponding current reference generation strategies are induced, p-q, d-q, unify power factor （UPF） and instantaneous act...For three phase four-wire active power filters （APFs）, several typical power theories and corresponding current reference generation strategies are induced, p-q, d-q, unify power factor （UPF） and instantaneous active current （IAC） methods are analyzed and compared with each other. The interpretation of active and reactive currents in non-sinusoidal and unbalanced three-phase four-wire systems is given based on the generalized instantaneous reactive power theory. The performance and the characteristic are evaluated, and the application conditions of current reference generation strategies are concluded. Simulation results under different source voltages and loads verify the evaluation result.展开更多
Dual three-phase permanent-magnet synchronous machines(DTP-PMSM)connected with a single neutral point provide a loop for zero-sequence current(ZSC).This paper proposes a novel space vector pulse width modulation(SVPWM...Dual three-phase permanent-magnet synchronous machines(DTP-PMSM)connected with a single neutral point provide a loop for zero-sequence current(ZSC).This paper proposes a novel space vector pulse width modulation(SVPWM)strategy to suppress the ZSC.Five vectors are selected as basic voltage vectors in one switching period.The fundamental and harmonic planes and the zero-sequence plane are taken into consideration to synthesis the reference voltage vector.To suppress the ZSC,a non-zero zero-sequence voltage(ZSV)is generated to compensate the third harmonic back-EMF.Rather than triangular carrier modulation,the sawtooth carrier modulation strategy is used to generate asymmetric PWM signals.The modulation range is investigated to explore the variation of modulation range caused by considering the zero-sequence plane.With the proposed method,the ZSC can be considerably reduced.The simulated and experimental results are presented to validate the effectiveness of the proposed modulation strategy.展开更多
The new three-phase 5-level current-source inverter (CSI) proposed in this paper was developed by connecting three separate single-phase 5-level CSIs in series, and its operational principle was analyzed. There are tw...The new three-phase 5-level current-source inverter (CSI) proposed in this paper was developed by connecting three separate single-phase 5-level CSIs in series, and its operational principle was analyzed. There are two major problems existing in current-source multilevel inverters, one is the complex PWM control method (2-logic to 3-logic conversion), and the other is the problem of current-unbalance between different levels. A simple current-balance control method via DC current feedback is applied in each single-phase 5-level CSI cell to implement the current-balance control between different levels. And to reduce the output current harmonics, POD PWM control technique was used. Simulation and experimental results showed that this new three-phase 5-level CSI topology operates correctly.展开更多
Finite-control-set model predictive control(FCSMPC)has advantages of multi-objective optimization and easy implementation.To reduce the computational burden and switching frequency,this article proposed a simplified M...Finite-control-set model predictive control(FCSMPC)has advantages of multi-objective optimization and easy implementation.To reduce the computational burden and switching frequency,this article proposed a simplified MPC for dual three-phase permanent magnet synchronous motor(DTPPMSM).The novelty of this method is the decomposition of prediction function and the switching optimization algorithm.Based on the decomposition of prediction function,the current increment vector is obtained,which is employed to select the optimal voltage vector and calculate the duty cycle.Then,the computation burden can be reduced and the current tracking performance can be maintained.Additionally,the switching optimization algorithm was proposed to optimize the voltage vector action sequence,which results in lower switching frequency.Hence,this control strategy can not only reduce the computation burden and switching frequency,but also maintain the steady-state and dynamic performance.The simulation and experimental results are presented to verify the feasibility of the proposed strategy.展开更多
This work demonstrates experimentally the close relation between return currents from relativistic laser-driven target polarization and the quality of the relativistic laser–plasma interaction for laser-driven second...This work demonstrates experimentally the close relation between return currents from relativistic laser-driven target polarization and the quality of the relativistic laser–plasma interaction for laser-driven secondary sources,taking as an example ion acceleration by target normal sheath acceleration.The Pearson linear correlation of maximum return current amplitude and proton spectrum cutoff energy is found to be in the range from~0.70 to 0.94.kA-scale return currents rise in all interaction schemes where targets of any kind are charged by escaping laser-accelerated relativistic electrons.Their precise measurement is demonstrated using an inductive scheme that allows operation at high repetition rates.Thus,return currents can be used as a metrological online tool for the optimization of many laser-driven secondary sources and for diagnosing their stability.In particular,in two parametric studies of laser-driven ion acceleration,we carry out a noninvasive online measurement of return currents in a tape target system irradiated by the 1 PW VEGA-3 laser at Centro de Láseres Pulsados:first the size of the irradiated area is varied at best compression of the laser pulse;second,the pulse duration is varied by means of induced group delay dispersion at best focus.This work paves the way to the development of feedback systems that operate at the high repetition rates of PW-class lasers.展开更多
Accurate modeling of Earth's ionospheric F-region currents is essential for refining geomagnetic field models and understanding magnetosphere-ionosphere coupling.In this study,we develop averaged models to charact...Accurate modeling of Earth's ionospheric F-region currents is essential for refining geomagnetic field models and understanding magnetosphere-ionosphere coupling.In this study,we develop averaged models to characterize F-region currents using magnetic data from the MSS-1(Macao Science Satellite-1) and Swarm satellite missions.Our approach employs a toroidal field representation,utilizing spherical harmonics to capture spatial variations and Fourier series to represent temporal dynamics.Two models,Model-A and Model-B,derived from distinct datasets,are constructed to represent current patterns at altitudes of 450 km and 512 km,respectively.Our models successfully capture the primary spatial structures and seasonal variations of polar field-aligned currents.Additionally,they accurately reproduce the localized inter-hemispheric field-aligned currents observed in mid and low latitudes during solstices,particularly between 14:00 and 16:00 magnetic local times.These findings enhance our understanding of ionospheric F-region currents and contribute to more precise geomagnetic field modeling.展开更多
In this study, we examined variability of sun-related energies, auroral electrojet current, ring current, and magnetopause current during solar cycles 23 and 24. The study revealed a dependence of sun-related energies...In this study, we examined variability of sun-related energies, auroral electrojet current, ring current, and magnetopause current during solar cycles 23 and 24. The study revealed a dependence of sun-related energies to the Sun and Earth currents systems with solar activity from 1996 to 2019. A decrease in the correlation between sun-related energies and sunspot number was observed over solar cycles 23 and 24 (0.88 for the solar cycle 23 and 0.66 for the solar cycle 24), with a drop in the speed of magnetic disturbances in the solar wind. These results could be attributed to the decrease in Sun’s magnetic field toroidal component magnitude induced by a weak in sunspots number and solar flares during the solar cycle 24. A weak in the Earth currents systems (auroral electrojet current, ring current, and magnetopause current) is also observed. During the decrease in the Earth currents, several peaks are observed, indicating a nonlinear dependence in the Earth currents variation (ring current, auroral electrojet current, and magnetopause current) from solar cycle 23 to solar cycle 24. This could be attributed to the Corotating Interaction Regions (CIRs) observed during the declining phase of solar cycle 23 and the deep minimum preceding solar cycle 24.展开更多
To achieve high power rating and low current harmonics of motor drive,this paper develops a dual three-phase open-winding permanent magnet synchronous motor(DTP-OW-PMSM)drive with the DC-link voltage ratio of 2:1:1.Ba...To achieve high power rating and low current harmonics of motor drive,this paper develops a dual three-phase open-winding permanent magnet synchronous motor(DTP-OW-PMSM)drive with the DC-link voltage ratio of 2:1:1.Based on this topology,this paper proposes a DTP four-level space vector pulse width modulation(DTP-FL SVPWM)strategy.First,two identical three-phase four-level space vector diagrams are constructed and divided.Then,three adjacent vectors nearest to the reference vector in each diagram are selected for the vector synthesis to guarantee high modulation precision and low switching frequency.Furthermore,to avoid the modulation error caused by the voltage deviation,the proposed DTP-FL SVPWM strategy is further optimized through unified duty ratio compensation(UDRC).The effectiveness of the proposed strategy is verified through experiments.展开更多
In this paper,a control scheme based on current optimization is proposed for dual three-phase permanent-magnet synchronous motor(DTP-PMSM)drive to reduce the low-frequency temperature swing.The reduction of temperatur...In this paper,a control scheme based on current optimization is proposed for dual three-phase permanent-magnet synchronous motor(DTP-PMSM)drive to reduce the low-frequency temperature swing.The reduction of temperature swing can be equivalent to reducing maximum instantaneous phase copper loss in this paper.First,a two-level optimization aiming at minimizing maximum instantaneous phase copper loss at each electrical angle is proposed.Then,the optimization is transformed to a singlelevel optimization by introducing the auxiliary variable for easy solving.Considering that singleobjective optimization trades a great total copper loss for a small reduction of maximum phase copper loss,the optimization considering both instantaneous total copper loss and maximum phase copper loss is proposed,which has the same performance of temperature swing reduction but with lower total loss.In this way,the proposed control scheme can reduce maximum junction temperature by 11%.Both simulation and experimental results are presented to prove the effectiveness and superiority of the proposed control scheme for low-frequency temperature swing reduction.展开更多
A novel software implementation for current polarity detection and current compensation is presented. For a three-phase zero-voltage soft-switching （ZVS） PWM converter based on phase and amplitude control （PAC）, w...A novel software implementation for current polarity detection and current compensation is presented. For a three-phase zero-voltage soft-switching （ZVS） PWM converter based on phase and amplitude control （PAC）, when saw-tooth carriers with alternate positive and negative slopes are adopted, the positive or negative slopes are chosen according to the phase current polarity. Since polarity reversal causes current distortion, current at the instant of reversal should be compensated for. Based on the characteristic of unity power factor converter in rectification and regeneration modes, a software implementation for current polarity detection is proposed. Distortion of current zero-crossing caused by using saw-tooth carriers with alternate positive and negative slopes is analyzed, and the relevant compensation method is proposed. Experimental study with a 1.5 kW device shows that phase current has a small harmonic content and power factor is high both in rectification and regeneration modes.展开更多
The growing demand for efficient high-power switching power supplies has spurred interest in advanced topologies.The three-phase VIENNA converter stands out for its high power factor,simplified structure,and robust pe...The growing demand for efficient high-power switching power supplies has spurred interest in advanced topologies.The three-phase VIENNA converter stands out for its high power factor,simplified structure,and robust performance.Current research focuses on its operational principles,control strategies,and behavior under various load conditions.Key considerations include component selection,thermal management,and EMI/EMC optimization.This topology finds applications across renewable energy systems,industrial equipment,telecommunications,and electric vehicle charging infrastructures.Comparative analyses with alternative topologies and cost-benefit evaluations are also addressed.Future developments are expected to emphasize the integration of wide-bandgap devices and advancements in digital control techniques to further enhance efficiency and system performance.展开更多
Magnon spin currents in insulating magnets are useful for low-power spintronics. However, in magnets stacked by antiferromagnetic(AFM) exchange coupling, which have recently aroused significant interest for potential ...Magnon spin currents in insulating magnets are useful for low-power spintronics. However, in magnets stacked by antiferromagnetic(AFM) exchange coupling, which have recently aroused significant interest for potential applications in spintronics, Bose–Einstein distribution populates magnon states across all energies from opposite eigenmodes, and hence the magnon spin current is largely compensated. Contrary to this common observation,here, we show that magnets with X-type AFM stacking, where opposite magnetic sublattices form orthogonal intersecting chains, support giant magnon spin currents with minimal compensation. Our model Hamiltonian calculations predict magnetic chain locking of magnon spin currents in these X-type magnets, significantly reducing their compensation ratio. In addition, the one-dimensional nature of the chain-like magnetic sublattices enhances magnon spin conductivities surpassing those of two-dimensional ferromagnets and canonical altermagnets. Notably, uncompensated X-type magnets, such as odd-layer antiferromagnets and ferrimagnets, can exhibit magnon spin currents polarized opposite to those expected by their net magnetization. These unprecedented properties of X-type magnets, combined with their inherent advantages resulting from AFM coupling, offer a promising new path for low-power high-performance spintronics.展开更多
Since the beginning of the 20th century,alkaline electrolysis has been used as a proven method for producing hydrogen on a megawatt scale.The existence of parasitic shunt currents in alkaline water electrolysis,which ...Since the beginning of the 20th century,alkaline electrolysis has been used as a proven method for producing hydrogen on a megawatt scale.The existence of parasitic shunt currents in alkaline water electrolysis,which is utilized to produce clean hydrogen,is investigated in this work.Analysis has been done on a 20-cell stack.Steel end plates,bipolar plates,and an electrolyte concentration of 6 M potassium hydroxide are all included in the model.The Butler-Volmer kinetics equations are used to simulate the electrode surfaces.Ohmic losses are taken into consideration in both the electrode and electrolyte phases,although mass transport constraints in the gas phase are not.Using an auxiliary sweep to solve equations,the model maintains an isothermal condition at 85℃ while adjusting the average cell voltage between 1.3 and 1.8 V.The results show that lower shunt currents in the outlet channels as opposed to the intake channels are the result of the electrolyte’s lower effective conductivity in the upper channels,which is brought on by a lower volume fraction of the electrolyte.Additionally,it has been seen that the shunt currents intensify as the stack gets closer to the conclusion.Efficiency is calculated by dividing the maximum energy output(per unit of time)that a fuel cell operating under comparable conditions might produce by the electrical energy needed to generate that output inside the stack.At first,energy efficiency increases due to the rise in coulombic efficiency,peaking around 1400 mA.The subsequent decline after reaching 1400 mA is linked to an increase in stack voltage at elevated current levels.展开更多
Single shot all-optical switching of the magnetization by femtosecond laser pulses in rare-earth transition-metal ferrimagnetic materials is particularly promising for future ultrafast magnetic storage applications.Mo...Single shot all-optical switching of the magnetization by femtosecond laser pulses in rare-earth transition-metal ferrimagnetic materials is particularly promising for future ultrafast magnetic storage applications.Moreover,ultrafast lasergenerated spin currents appear to play an important role in the switching process.Here,we try to separately detect the spin current from Gd in a Co/Gd bilayer system using terahertz time-domain spectroscopy.To this aim,we use different capping,buffer and embedded layers in order to tune the spin-to-charge and spin-current propagation and identify currents from each of the layers.We attribute the observed THz emission in all layers to the transition metal demagnetization induced spin currents,and detect no contribution from the Gd demagnetization.We attribute this absence of Gd-induced THz signal to the potentially slow demagnetization of Gd,which shift the emission spectra to lower frequencies,below our detection capabilities.These results highlight the limitations in using materials suffering from the so-called critical slowdown for the optimization of spintronic THz emitters.展开更多
0 INTRODUCTION Microplastics are defined as small plastic debris(1μm-5 mm),which have complex properties of widerange densities(0.05-2.3 g/cm^3),diverse shapes(e.g.,beads,fibers,foam and pellets)and low degradability...0 INTRODUCTION Microplastics are defined as small plastic debris(1μm-5 mm),which have complex properties of widerange densities(0.05-2.3 g/cm^3),diverse shapes(e.g.,beads,fibers,foam and pellets)and low degradability(Harris,2020;Chubarenko et al.,2016).展开更多
In contrast to the concurrent mixer-settler,the interaction between the mixing and settling chambers have to be taken into account in the simulation of the countercurrent mixer-settler,and no work has been reported fo...In contrast to the concurrent mixer-settler,the interaction between the mixing and settling chambers have to be taken into account in the simulation of the countercurrent mixer-settler,and no work has been reported for this equipment.In this work,a three-phase flow model based on the Eulerian multiphase model,coupled with a sliding mesh model is proposed for a countercurrent mixer-settler.Based on this,the dispersed phase distribution,flow pattern,and pressure distribution are investigated,which can help to fill the gap in the operation mechanism.In addition,the velocity vector distribution at the phase port shows an intriguing phenomenon that two types of vectors with opposite directions are distributed on the left and right sides of the same plane,which indicates that the material exchange in the mixing and settling chambers is simultaneous.Analysis of this variation at this location by a fast Fourier transform(FFT)method reveals that it is mainly influenced by the mixing chamber and is consistent with the main period of the outlet flow fluctuations.Therefore,by monitoring the fluctuation of the outlet flow and then analyzing it by the FFT method,the state of the whole tank can be determined,which makes it promising for the design of control systems for countercurrent mixer-settlers.展开更多
The dual three-phase PMSM(DTP-PMSM)drives have received wide attention at high-power high-efficiency applications due to their merits of high output current ability and copper-loss-free field excitation.Meanwhile,the ...The dual three-phase PMSM(DTP-PMSM)drives have received wide attention at high-power high-efficiency applications due to their merits of high output current ability and copper-loss-free field excitation.Meanwhile,the DTPPMSM drive provides higher fault-tolerant capability for highreliability applications,e.g.,pumps and actuators in aircraft.For high-power drives with limited switching frequencies and highspeed drives with large fundamental frequencies,the ratio of switching frequency to fundamental frequency,i.e.,the carrier ratio,is usually below 15,which would significantly degrade the control performance.The purpose of this paper is to review the recent work on the modulation and control schemes for improving the operation performance of DTP-PMSM drives with low carrier ratios.Specifically,three categories of methods,i.e.,the space vector modulation based control,the model predictive control(MPC),and the optimized pulse pattern(OPP)based control are reviewed with principles and performance.In addition,brief discussions regarding the comparison and future trends are presented for low-carrier-ratio(LCR)modulation and control schemes of DTP-PMSM drives.展开更多
This paper focuses on a combination of three-phase VSI （voltage source inverter） with a predictive current control to provide an optimized system for three-phase inverters that control the load current. A FS-MPC （f...This paper focuses on a combination of three-phase VSI （voltage source inverter） with a predictive current control to provide an optimized system for three-phase inverters that control the load current. A FS-MPC （finite set-model predictive control） strategy for a three-phase VSI for RES （renewable energy systems） applications is implemented. The renewable energy systems model is used in this paper to investigate the system performance when power is supplied to resistive-inductive load. With three different cases, the evaluation of the system is done. Firstly, the robustness of control strategy under variable DC-Link is done in terms of the THD （total harmonic distortion）. Secondly, with one prediction step, the system performance is tested using different sampling time, and lastly, the dynamic response of the system with step change in the amplitude of the reference is investigated. The simulations and result analyses are carried out using Matlab/Simulink to test the effectiveness and robustness of FS-MPC for two-level VSI with AC filter for resistive-inductive load supplied by a renewable energy system.展开更多
Two Al2O3/Cu composites containing 0.24 wt.% Al2O3 and 0.60 wt.% Al2O3 separately are prepared by internal oxidation. Effects of sliding speed and pressure on the frictional characteristics of the composites and coppe...Two Al2O3/Cu composites containing 0.24 wt.% Al2O3 and 0.60 wt.% Al2O3 separately are prepared by internal oxidation. Effects of sliding speed and pressure on the frictional characteristics of the composites and copper against brass are investigated and compared. The changes in morphology of the sliding surface and subsurface are examined with scanning electron microscope （SEM） and energy dispersive X-ray spectrum （EDS）. The results show that the wear resistance of the Al2O3/Cu composites is superior to that of copper under the same conditions, Under a given electrical current, the wear rate of Al2O3/Cu composites decreases as the Al2O3-content increases, However, the wear rates of the Al2O3/Cu composites and copper increase as the sliding speed and pressure increase under dry sliding condition. The main wear mechanisms for Al2O3/Cu composites are of abrasion and adhesion; for copper, it is adhesion, although wear by oxidation and electrical erosion can also be observed as the speed and pressure rise.展开更多
文摘For three phase four-wire active power filters （APFs）, several typical power theories and corresponding current reference generation strategies are induced, p-q, d-q, unify power factor （UPF） and instantaneous active current （IAC） methods are analyzed and compared with each other. The interpretation of active and reactive currents in non-sinusoidal and unbalanced three-phase four-wire systems is given based on the generalized instantaneous reactive power theory. The performance and the characteristic are evaluated, and the application conditions of current reference generation strategies are concluded. Simulation results under different source voltages and loads verify the evaluation result.
基金supported in part by the National Natural Science Foundation of China under Grant 51977099。
文摘Dual three-phase permanent-magnet synchronous machines(DTP-PMSM)connected with a single neutral point provide a loop for zero-sequence current(ZSC).This paper proposes a novel space vector pulse width modulation(SVPWM)strategy to suppress the ZSC.Five vectors are selected as basic voltage vectors in one switching period.The fundamental and harmonic planes and the zero-sequence plane are taken into consideration to synthesis the reference voltage vector.To suppress the ZSC,a non-zero zero-sequence voltage(ZSV)is generated to compensate the third harmonic back-EMF.Rather than triangular carrier modulation,the sawtooth carrier modulation strategy is used to generate asymmetric PWM signals.The modulation range is investigated to explore the variation of modulation range caused by considering the zero-sequence plane.With the proposed method,the ZSC can be considerably reduced.The simulated and experimental results are presented to validate the effectiveness of the proposed modulation strategy.
基金Project (No. 50477033) supported by the National Natural Science Foundation of China
文摘The new three-phase 5-level current-source inverter (CSI) proposed in this paper was developed by connecting three separate single-phase 5-level CSIs in series, and its operational principle was analyzed. There are two major problems existing in current-source multilevel inverters, one is the complex PWM control method (2-logic to 3-logic conversion), and the other is the problem of current-unbalance between different levels. A simple current-balance control method via DC current feedback is applied in each single-phase 5-level CSI cell to implement the current-balance control between different levels. And to reduce the output current harmonics, POD PWM control technique was used. Simulation and experimental results showed that this new three-phase 5-level CSI topology operates correctly.
基金supported by the National Natural Science Foundation of China under Grant 5227705。
文摘Finite-control-set model predictive control(FCSMPC)has advantages of multi-objective optimization and easy implementation.To reduce the computational burden and switching frequency,this article proposed a simplified MPC for dual three-phase permanent magnet synchronous motor(DTPPMSM).The novelty of this method is the decomposition of prediction function and the switching optimization algorithm.Based on the decomposition of prediction function,the current increment vector is obtained,which is employed to select the optimal voltage vector and calculate the duty cycle.Then,the computation burden can be reduced and the current tracking performance can be maintained.Additionally,the switching optimization algorithm was proposed to optimize the voltage vector action sequence,which results in lower switching frequency.Hence,this control strategy can not only reduce the computation burden and switching frequency,but also maintain the steady-state and dynamic performance.The simulation and experimental results are presented to verify the feasibility of the proposed strategy.
基金funding from the European Union’s Horizon 2020 research and innovation program through the European IMPULSE project under Grant Agreement No.871161from LASERLAB-EUROPE V under Grant Agreement No.871124+6 种基金from the Grant Agency of the Czech Republic(Grant No.GM23-05027M)Grant No.PDC2021120933-I00 funded by MCIN/AEI/10.13039/501100011033by the European Union Next Generation EU/PRTRsupported by funding from the Ministerio de Ciencia,Innovación y Universidades in Spain through ICTS Equipment Grant No.EQC2018-005230-Pfrom Grant No.PID2021-125389O A-I00 funded by MCIN/AEI/10.13039/501100011033/FEDER,UEby“ERDF A Way of Making Europe”by the European Unionfrom grants of the Junta de Castilla y León with Grant Nos.CLP263P20 and CLP087U16。
文摘This work demonstrates experimentally the close relation between return currents from relativistic laser-driven target polarization and the quality of the relativistic laser–plasma interaction for laser-driven secondary sources,taking as an example ion acceleration by target normal sheath acceleration.The Pearson linear correlation of maximum return current amplitude and proton spectrum cutoff energy is found to be in the range from~0.70 to 0.94.kA-scale return currents rise in all interaction schemes where targets of any kind are charged by escaping laser-accelerated relativistic electrons.Their precise measurement is demonstrated using an inductive scheme that allows operation at high repetition rates.Thus,return currents can be used as a metrological online tool for the optimization of many laser-driven secondary sources and for diagnosing their stability.In particular,in two parametric studies of laser-driven ion acceleration,we carry out a noninvasive online measurement of return currents in a tape target system irradiated by the 1 PW VEGA-3 laser at Centro de Láseres Pulsados:first the size of the irradiated area is varied at best compression of the laser pulse;second,the pulse duration is varied by means of induced group delay dispersion at best focus.This work paves the way to the development of feedback systems that operate at the high repetition rates of PW-class lasers.
基金supported by the National Natural Science Foundation of China (42250101)the Macao Foundation. The computation made use of the high-performance computing resources at the center of the MSS data processing and analysis。
文摘Accurate modeling of Earth's ionospheric F-region currents is essential for refining geomagnetic field models and understanding magnetosphere-ionosphere coupling.In this study,we develop averaged models to characterize F-region currents using magnetic data from the MSS-1(Macao Science Satellite-1) and Swarm satellite missions.Our approach employs a toroidal field representation,utilizing spherical harmonics to capture spatial variations and Fourier series to represent temporal dynamics.Two models,Model-A and Model-B,derived from distinct datasets,are constructed to represent current patterns at altitudes of 450 km and 512 km,respectively.Our models successfully capture the primary spatial structures and seasonal variations of polar field-aligned currents.Additionally,they accurately reproduce the localized inter-hemispheric field-aligned currents observed in mid and low latitudes during solstices,particularly between 14:00 and 16:00 magnetic local times.These findings enhance our understanding of ionospheric F-region currents and contribute to more precise geomagnetic field modeling.
文摘In this study, we examined variability of sun-related energies, auroral electrojet current, ring current, and magnetopause current during solar cycles 23 and 24. The study revealed a dependence of sun-related energies to the Sun and Earth currents systems with solar activity from 1996 to 2019. A decrease in the correlation between sun-related energies and sunspot number was observed over solar cycles 23 and 24 (0.88 for the solar cycle 23 and 0.66 for the solar cycle 24), with a drop in the speed of magnetic disturbances in the solar wind. These results could be attributed to the decrease in Sun’s magnetic field toroidal component magnitude induced by a weak in sunspots number and solar flares during the solar cycle 24. A weak in the Earth currents systems (auroral electrojet current, ring current, and magnetopause current) is also observed. During the decrease in the Earth currents, several peaks are observed, indicating a nonlinear dependence in the Earth currents variation (ring current, auroral electrojet current, and magnetopause current) from solar cycle 23 to solar cycle 24. This could be attributed to the Corotating Interaction Regions (CIRs) observed during the declining phase of solar cycle 23 and the deep minimum preceding solar cycle 24.
基金supported in part by the National Natural Science Foundation of China under Grant 62303333in part by the Project of Hetao Shenzhen-Hong Kong Science and Technology Innovation Cooperation Zone under Grant HZQB-KCZYB-2020083.
文摘To achieve high power rating and low current harmonics of motor drive,this paper develops a dual three-phase open-winding permanent magnet synchronous motor(DTP-OW-PMSM)drive with the DC-link voltage ratio of 2:1:1.Based on this topology,this paper proposes a DTP four-level space vector pulse width modulation(DTP-FL SVPWM)strategy.First,two identical three-phase four-level space vector diagrams are constructed and divided.Then,three adjacent vectors nearest to the reference vector in each diagram are selected for the vector synthesis to guarantee high modulation precision and low switching frequency.Furthermore,to avoid the modulation error caused by the voltage deviation,the proposed DTP-FL SVPWM strategy is further optimized through unified duty ratio compensation(UDRC).The effectiveness of the proposed strategy is verified through experiments.
基金supported by the National Natural Science Foundation of China(No.62271109)。
文摘In this paper,a control scheme based on current optimization is proposed for dual three-phase permanent-magnet synchronous motor(DTP-PMSM)drive to reduce the low-frequency temperature swing.The reduction of temperature swing can be equivalent to reducing maximum instantaneous phase copper loss in this paper.First,a two-level optimization aiming at minimizing maximum instantaneous phase copper loss at each electrical angle is proposed.Then,the optimization is transformed to a singlelevel optimization by introducing the auxiliary variable for easy solving.Considering that singleobjective optimization trades a great total copper loss for a small reduction of maximum phase copper loss,the optimization considering both instantaneous total copper loss and maximum phase copper loss is proposed,which has the same performance of temperature swing reduction but with lower total loss.In this way,the proposed control scheme can reduce maximum junction temperature by 11%.Both simulation and experimental results are presented to prove the effectiveness and superiority of the proposed control scheme for low-frequency temperature swing reduction.
基金Project supported by Shanghai Leading Academic DisciplineProject (Grant No .T0103) ,and Shanghai Post Doctoral Scienti-fic Research (Grant No .05R214122)
文摘A novel software implementation for current polarity detection and current compensation is presented. For a three-phase zero-voltage soft-switching （ZVS） PWM converter based on phase and amplitude control （PAC）, when saw-tooth carriers with alternate positive and negative slopes are adopted, the positive or negative slopes are chosen according to the phase current polarity. Since polarity reversal causes current distortion, current at the instant of reversal should be compensated for. Based on the characteristic of unity power factor converter in rectification and regeneration modes, a software implementation for current polarity detection is proposed. Distortion of current zero-crossing caused by using saw-tooth carriers with alternate positive and negative slopes is analyzed, and the relevant compensation method is proposed. Experimental study with a 1.5 kW device shows that phase current has a small harmonic content and power factor is high both in rectification and regeneration modes.
文摘The growing demand for efficient high-power switching power supplies has spurred interest in advanced topologies.The three-phase VIENNA converter stands out for its high power factor,simplified structure,and robust performance.Current research focuses on its operational principles,control strategies,and behavior under various load conditions.Key considerations include component selection,thermal management,and EMI/EMC optimization.This topology finds applications across renewable energy systems,industrial equipment,telecommunications,and electric vehicle charging infrastructures.Comparative analyses with alternative topologies and cost-benefit evaluations are also addressed.Future developments are expected to emphasize the integration of wide-bandgap devices and advancements in digital control techniques to further enhance efficiency and system performance.
基金supported by the National Key R&D Program of China (Grant No.2022YFA1403203)the National Natural Science Funds for Distinguished Young Scholar (Grant No.52325105)+2 种基金the National Natural Science Foundation of China (Grant Nos.12274411,12241405,52250418,and12404185)the Basic Research Program of the Chinese Academy of Sciences (CAS) Based on Major Scientific Infrastructures (Grant No.JZHKYPT-2021-08)the CAS Project for Young Scientists in Basic Research (Grant No.YSBR-084)。
文摘Magnon spin currents in insulating magnets are useful for low-power spintronics. However, in magnets stacked by antiferromagnetic(AFM) exchange coupling, which have recently aroused significant interest for potential applications in spintronics, Bose–Einstein distribution populates magnon states across all energies from opposite eigenmodes, and hence the magnon spin current is largely compensated. Contrary to this common observation,here, we show that magnets with X-type AFM stacking, where opposite magnetic sublattices form orthogonal intersecting chains, support giant magnon spin currents with minimal compensation. Our model Hamiltonian calculations predict magnetic chain locking of magnon spin currents in these X-type magnets, significantly reducing their compensation ratio. In addition, the one-dimensional nature of the chain-like magnetic sublattices enhances magnon spin conductivities surpassing those of two-dimensional ferromagnets and canonical altermagnets. Notably, uncompensated X-type magnets, such as odd-layer antiferromagnets and ferrimagnets, can exhibit magnon spin currents polarized opposite to those expected by their net magnetization. These unprecedented properties of X-type magnets, combined with their inherent advantages resulting from AFM coupling, offer a promising new path for low-power high-performance spintronics.
文摘Since the beginning of the 20th century,alkaline electrolysis has been used as a proven method for producing hydrogen on a megawatt scale.The existence of parasitic shunt currents in alkaline water electrolysis,which is utilized to produce clean hydrogen,is investigated in this work.Analysis has been done on a 20-cell stack.Steel end plates,bipolar plates,and an electrolyte concentration of 6 M potassium hydroxide are all included in the model.The Butler-Volmer kinetics equations are used to simulate the electrode surfaces.Ohmic losses are taken into consideration in both the electrode and electrolyte phases,although mass transport constraints in the gas phase are not.Using an auxiliary sweep to solve equations,the model maintains an isothermal condition at 85℃ while adjusting the average cell voltage between 1.3 and 1.8 V.The results show that lower shunt currents in the outlet channels as opposed to the intake channels are the result of the electrolyte’s lower effective conductivity in the upper channels,which is brought on by a lower volume fraction of the electrolyte.Additionally,it has been seen that the shunt currents intensify as the stack gets closer to the conclusion.Efficiency is calculated by dividing the maximum energy output(per unit of time)that a fuel cell operating under comparable conditions might produce by the electrical energy needed to generate that output inside the stack.At first,energy efficiency increases due to the rise in coulombic efficiency,peaking around 1400 mA.The subsequent decline after reaching 1400 mA is linked to an increase in stack voltage at elevated current levels.
基金supported by the National Key Research and Development Program of China(Grant No.2023YFF0719200)the National Natural Science Foundation of China(Grant No.62105011)+3 种基金the French National Research Agency ANR through the UFO project(Grant No.ANR-20-CE090013)the SLAM project(Grant No.ANR-23-CE30-0047)the MAT-PULSE-Lorraine Universitéd’Excellence project(Grant No.ANR-15-IDEX-04-LUE)the France 2030 Government Grants PEPR Electronic EMCOM(Grant No.ANR-22-PEEL-0009)。
文摘Single shot all-optical switching of the magnetization by femtosecond laser pulses in rare-earth transition-metal ferrimagnetic materials is particularly promising for future ultrafast magnetic storage applications.Moreover,ultrafast lasergenerated spin currents appear to play an important role in the switching process.Here,we try to separately detect the spin current from Gd in a Co/Gd bilayer system using terahertz time-domain spectroscopy.To this aim,we use different capping,buffer and embedded layers in order to tune the spin-to-charge and spin-current propagation and identify currents from each of the layers.We attribute the observed THz emission in all layers to the transition metal demagnetization induced spin currents,and detect no contribution from the Gd demagnetization.We attribute this absence of Gd-induced THz signal to the potentially slow demagnetization of Gd,which shift the emission spectra to lower frequencies,below our detection capabilities.These results highlight the limitations in using materials suffering from the so-called critical slowdown for the optimization of spintronic THz emitters.
基金the National Natural Science Foundation of China(No.42277138)the National Key Research and Development Program of China(Nos.2024YFF0506803 and 2024YFC2815400)+2 种基金the Fundamental Research Funds for the Central Universities(Nos.202441003 and 202513032)the Shandong Province National-Level Leading Talent Supporting Project(No.2022GJJLJRC-15)the European Commission(Nos.HORIZON MSCA-2024-PF-01,101200637)。
文摘0 INTRODUCTION Microplastics are defined as small plastic debris(1μm-5 mm),which have complex properties of widerange densities(0.05-2.3 g/cm^3),diverse shapes(e.g.,beads,fibers,foam and pellets)and low degradability(Harris,2020;Chubarenko et al.,2016).
基金the National Natural Science Foundation of China(21978198)for financial support。
文摘In contrast to the concurrent mixer-settler,the interaction between the mixing and settling chambers have to be taken into account in the simulation of the countercurrent mixer-settler,and no work has been reported for this equipment.In this work,a three-phase flow model based on the Eulerian multiphase model,coupled with a sliding mesh model is proposed for a countercurrent mixer-settler.Based on this,the dispersed phase distribution,flow pattern,and pressure distribution are investigated,which can help to fill the gap in the operation mechanism.In addition,the velocity vector distribution at the phase port shows an intriguing phenomenon that two types of vectors with opposite directions are distributed on the left and right sides of the same plane,which indicates that the material exchange in the mixing and settling chambers is simultaneous.Analysis of this variation at this location by a fast Fourier transform(FFT)method reveals that it is mainly influenced by the mixing chamber and is consistent with the main period of the outlet flow fluctuations.Therefore,by monitoring the fluctuation of the outlet flow and then analyzing it by the FFT method,the state of the whole tank can be determined,which makes it promising for the design of control systems for countercurrent mixer-settlers.
基金supported by the National Key Research and Development Program of China under the grant of 2022YFB3403100。
文摘The dual three-phase PMSM(DTP-PMSM)drives have received wide attention at high-power high-efficiency applications due to their merits of high output current ability and copper-loss-free field excitation.Meanwhile,the DTPPMSM drive provides higher fault-tolerant capability for highreliability applications,e.g.,pumps and actuators in aircraft.For high-power drives with limited switching frequencies and highspeed drives with large fundamental frequencies,the ratio of switching frequency to fundamental frequency,i.e.,the carrier ratio,is usually below 15,which would significantly degrade the control performance.The purpose of this paper is to review the recent work on the modulation and control schemes for improving the operation performance of DTP-PMSM drives with low carrier ratios.Specifically,three categories of methods,i.e.,the space vector modulation based control,the model predictive control(MPC),and the optimized pulse pattern(OPP)based control are reviewed with principles and performance.In addition,brief discussions regarding the comparison and future trends are presented for low-carrier-ratio(LCR)modulation and control schemes of DTP-PMSM drives.
文摘This paper focuses on a combination of three-phase VSI （voltage source inverter） with a predictive current control to provide an optimized system for three-phase inverters that control the load current. A FS-MPC （finite set-model predictive control） strategy for a three-phase VSI for RES （renewable energy systems） applications is implemented. The renewable energy systems model is used in this paper to investigate the system performance when power is supplied to resistive-inductive load. With three different cases, the evaluation of the system is done. Firstly, the robustness of control strategy under variable DC-Link is done in terms of the THD （total harmonic distortion）. Secondly, with one prediction step, the system performance is tested using different sampling time, and lastly, the dynamic response of the system with step change in the amplitude of the reference is investigated. The simulations and result analyses are carried out using Matlab/Simulink to test the effectiveness and robustness of FS-MPC for two-level VSI with AC filter for resistive-inductive load supplied by a renewable energy system.
基金National Natural Science Foundation of China (50432020)Henan Innovation Project for University Prominent Re- search Talents (2007KYCX008)+3 种基金Henan Education Department Science and Technology Project (2007430004)Henan Plan Project for College Youth Backbone TeacherHenan University of Science and Technology Major Pre-research Foundation (2005ZD003)Henan University of Science and Technology Personnel Scientific Research Foundation (of023)
文摘Two Al2O3/Cu composites containing 0.24 wt.% Al2O3 and 0.60 wt.% Al2O3 separately are prepared by internal oxidation. Effects of sliding speed and pressure on the frictional characteristics of the composites and copper against brass are investigated and compared. The changes in morphology of the sliding surface and subsurface are examined with scanning electron microscope （SEM） and energy dispersive X-ray spectrum （EDS）. The results show that the wear resistance of the Al2O3/Cu composites is superior to that of copper under the same conditions, Under a given electrical current, the wear rate of Al2O3/Cu composites decreases as the Al2O3-content increases, However, the wear rates of the Al2O3/Cu composites and copper increase as the sliding speed and pressure increase under dry sliding condition. The main wear mechanisms for Al2O3/Cu composites are of abrasion and adhesion; for copper, it is adhesion, although wear by oxidation and electrical erosion can also be observed as the speed and pressure rise.
