Induction motor drive systems fed by cables are widely used in industrial applications. However, high-frequency switching of power devices will cause common-mode（CM） voltages during operation, leading to serious CM ...Induction motor drive systems fed by cables are widely used in industrial applications. However, high-frequency switching of power devices will cause common-mode（CM） voltages during operation, leading to serious CM currents in the motor drive systems. CM currents through the cables and motors in the drive systems can cause electromagnetic interference（EMI） with the surrounding electronic equipment and shorten the life of induction motors. Therefore, it is necessary to analyze the CM currents in motor drive systems. In this paper, high-frequency models of unshielded and shielded power cables are formulated. The frequency-dependent effects and mutual inductances of the cables are taken into account. The power cable parameters are extracted by the finite element method and validated by measurements. High-frequency models of induction motors and inverters are introduced from existing works. The CM currents at the motor and inverter terminals are obtained, and the influence of the cable length and cable type on the CM currents is analyzed. There is a good agreement between the experimental results and the CM currents predicted by the proposed models.展开更多
The common-mode current is an important indicator with transformerless photovoltaic inverters.However,up to now,there is not an accurate method to predict common-mode current in the inverter design process,resulting f...The common-mode current is an important indicator with transformerless photovoltaic inverters.However,up to now,there is not an accurate method to predict common-mode current in the inverter design process,resulting from inappropriate device selection or exceeded the expected common-mode current.In order to solve this problem,this paper proposes an accurate common-mode current prediction method based on graph theory for transformerless photovoltaic inverters.In this paper,the mathematic model of the common-mode current is derived using graph theory analysis method in the full-bridge topology,and it is used to predict common-mode current.The validity and correctness of the proposed prediction method are validated by simulation and experiment.The oscillation frequency and amplitude can be predicted by the proposed common-mode prediction method,whereas the traditional common-mode analysis method cannot.This paper provides a novel way to predict and analyze common-mode current in the transformerless photovoltaic inverters.展开更多
Insulation failure significantly contributes to the unpredictable shutdown of power equipment.Compared to the partial discharge and high-frequency(HF)injection methods,the HF common-mode(CM)leakage current method offe...Insulation failure significantly contributes to the unpredictable shutdown of power equipment.Compared to the partial discharge and high-frequency(HF)injection methods,the HF common-mode(CM)leakage current method offers a non-intrusive and highly sensitive alternative.However,the detection of HF CM currents is susceptible to interference from differential-mode(DM)currents,which exhibit high-amplitude and multifrequency components during normal operation.To address this challenge,this paper proposes a double-ring current sensor based on the principle of magnetic shielding for inverter-fed machine winding insulation monitoring.The inner ring harnesses the magnetic aggregation effect to isolate the DM current magnetic field,whereas the outer ring serves as the magnetic core of the Rogowski current sensor,enabling HF CM current monitoring.First,the magnetic field distributions of the CM and DM currents were analyzed.Then,a correlation between the sensor parameters and signal-to-noise ratio of the target HF CM current was established.Finally,an experimental study was conducted on a 3-kW PMSM for verification.The results indicate that the proposed double-ring HF CM sensor can effectively mitigate DM current interference.Compared to a single-ring sensor,a reduction of approximately 40%in the DM component was achieved,which significantly enhanced the precision of online insulation monitoring.展开更多
With the rapid integration of renewable energy sources,modern power systems are increasingly challenged by heightened volatility and uncertainty.Doubly-fed variable-speed pumped storage units(DFVS-PSUs)have emerged as...With the rapid integration of renewable energy sources,modern power systems are increasingly challenged by heightened volatility and uncertainty.Doubly-fed variable-speed pumped storage units(DFVS-PSUs)have emerged as promising technologies for mitigating grid oscillations and enhancing system flexibility.However,the excitation converters in DFVS-PSUs are prone to significant issues such as elevated common-mode voltage(CMV)and neutral-point voltage(NPV)fluctuations,which can lead to electromagnetic interference and degrade transient performance.To address these challenges,an optimized virtual space vector pulse width modulation(OVSVPWM)strategy is proposed,aiming to suppress CMV and NPV simultaneously through coordinated multi-objective control.Specifically,a dynamic feedback mechanism is introduced to adjust the balancing factor of basic vectors in the synthesized virtual small vector in real-time,achieving autonomous balancing of the NPV.To address the excessive switching actions introduced by the OVSVPWM strategy,a phase duty ratio-based sequence reconstruction method is adopted,which reduces the total number of switching actions to half of the original.A zero-level buffering scheme is employed to reconstruct the single-phase voltage-level output sequence,achieving peak CMV suppression down to udc/6.Simulation results demonstrate that the proposed strategy significantly improves electromagnetic compatibility and operational stability while maintaining high power quality.展开更多
Low-density short-duration pulsed current-assisted aging treatment was applied to the Ti-6Al-4V-0.5Mo-0.5Zr alloy subjected to different solution treatments.The results show that numerous α_(p) phases redissolve into...Low-density short-duration pulsed current-assisted aging treatment was applied to the Ti-6Al-4V-0.5Mo-0.5Zr alloy subjected to different solution treatments.The results show that numerous α_(p) phases redissolve into the new β phase during the pulsed current-assisted aging process,and then the newly formed β phase is mainly transformed into the β_(t) phase,with occasional transition to new α_(p) phase,leading to a remarkable grain refinement,especially for the lamellarαs phases.In comparison to conventional aging treatment,the pulsed current-assisted aging approach achieves a significant enhancement in strength without degrading ductility,yielding an excellent mechanical property combination:a yield strength of 932 MPa,a tensile strength of 1042 MPa,and an elongation of 12.2%.It is primarily ascribed to the increased fraction of β_(t) phases,the obvious grain refinement effect,and the slip block effect induced by the multiple-variantαs colonies distributed within β_(t) phases.展开更多
This article investigates the robust current tracking control problem of three-phase grid-connected inverters with LCL filter under external disturbance by a dynamic state feedback control method.First,this paper cons...This article investigates the robust current tracking control problem of three-phase grid-connected inverters with LCL filter under external disturbance by a dynamic state feedback control method.First,this paper constructs an internal model to learn the information of the states and input of the grid-connected inverter under steady state.Second,by utilizing the internal model principle,the paper turns the tracking control problem into the robust stabilization control problem based on some appropriate coordinate transformations.Then,The paper designs a dynamics state feedback control law to deal with this robust stabilization problem,and thus the solution of the robust current tracking control problem of three-phase grid-connected inverters can be obtained.This control method can ensure the asymptotic stability of the closedloop system.Finally,the paper illustrates the effectiveness of the proposed control approach through several groups of simulations,and compares it with the feedforward control method to verify the robustness of the proposed control method to uncertain parameters.展开更多
Machine stator winding insulation degradation is one of the main results of machine aging.It is non-negligible once this degradation process becomes asymmetric between phases.The traditional way to determine the insul...Machine stator winding insulation degradation is one of the main results of machine aging.It is non-negligible once this degradation process becomes asymmetric between phases.The traditional way to determine the insulation state of health is a partial discharge test.However,this method requires the system offline,which causes production loss and extra administrative burden.This paper presents an idea for better characterizing the insulation machine’s state of health using common-mode(CM)behavior in the machine-drive system.With the help of circuit decomposition methods and modeling tools,the CM quantities due to asymmetric aging show a unique characteristic that distinguishes itself from other differential-mode(DM)quantities in the equivalent circuit.It is shown effective to represent the asymmetric aging effect from the detection of system leakage current.This paper provides an analytical method to quantify this characteristic from mathematical approaches,and a proper approximation has been made on the CM equivalent model(CEM)such that the CM behavior is accurately characterized.The proposed method will serve the purpose of predicting machine abnormal behavior using the simple RLC circuit.Researchers can adapt this method to quantify and characterize the machine insulation state of health(SOH).展开更多
Energy density and safety are two crucial parameters when evaluating lithium-metal batteries(LMBs).Herein,we present an ultralight polymer-based current collector,incorporating flame-retardant materials,designed speci...Energy density and safety are two crucial parameters when evaluating lithium-metal batteries(LMBs).Herein,we present an ultralight polymer-based current collector,incorporating flame-retardant materials,designed specifically for thin lithium-metal anodes.Compared to the traditional copper current collector(8.96 mg cm^(-2),10μm thick),the polymer-based current collector(12μm thick)has a significantly lower areal density of 1.41 mg cm^(-2),i.e.,only one-sixth of the copper collector,thus enabling substantially higher energy densities.Accordingly,when employed in Li||NMC_(622)full-cells,the polymer-based current collector enables a specific energy of 449 Wh kg^(-1),representing a notable improvement of about14.5%compared to cells employing a classic copper current collector.The inclusion of Al(OH)_(3) as a flame retardant into the current collector suppresses flammability and,thereby,significantly improves the safety of the resulting LMBs.展开更多
With the advent of the big data era,modern statistics has enjoyed unprecedented development opportunities and also faced numerous new challenges.Traditional statistical computing methods are often limited by issues su...With the advent of the big data era,modern statistics has enjoyed unprecedented development opportunities and also faced numerous new challenges.Traditional statistical computing methods are often limited by issues such as computer memory capacity and distributed storage of data across different locations,and are unable to directly apply to large-scale data sets.Therefore,in the context of big data,designing efficient and theoretically guaranteed statistical learning and inference algorithms has become a key issue that the current field of statistics urgently needs to address.In this paper,the application status of statistical analysis methods in the big data environment was systematically reviewed,and its future development directions were analyzed to provide reference and support for the further development of theory and methods of the statistical analysis of big data.展开更多
The transient synchronization stability of grid-forming converters(GFMCs)is significantly challenged under grid voltage sags.Continuous efforts have been devoted to analyzing the GFMC transient stability,with limited ...The transient synchronization stability of grid-forming converters(GFMCs)is significantly challenged under grid voltage sags.Continuous efforts have been devoted to analyzing the GFMC transient stability,with limited attention paid to the impacts of control loop dynamics.However,the complex control dynamics,especially the interactions between the active/reactive power control loops and the current saturation process(CSP),are crucial for accurately describing the transient behavior and evaluating the stability.Thus,in this study,a new large-signal GFMC model is established,considering the reactive power control(RPC)with different kinds of controllers and the CSP simultaneously.It is revealed that GFMC does not switch to the current-limited mode immediately,and the dynamics of RPC further affect the transient behavior before the current limiting significantly.Hence,the complex control dynamics can alter the mode switching point of current saturation,thereby increasing the risk of loss of synchronization(LOS).Based on the above findings,comprehensive comparisons of typical RPC controllers are presented to facilitate practical engineering applications.A unified stability enhancement method is proposed for solving the problem of LOS.Finally,experiments validate the correctness of the analysis and the effectiveness of the proposed control strategy.展开更多
Lithium metal batteries(LMBs)are promising candidates for next-generation high-energy-density storage devices.However,an unstable lithium metal anode poses significant issues that critically compromise battery safety ...Lithium metal batteries(LMBs)are promising candidates for next-generation high-energy-density storage devices.However,an unstable lithium metal anode poses significant issues that critically compromise battery safety and cycle life,including lithium dendrite formation,solid electrolyte interphase degradation,dead lithium accumulation,and substantial volume fluctuations during cycling.These problems can be addressed by regulating lithium deposition and suppressing side reactions through the modification of copper current collectors using three classes of materials:metal and metal oxide,carbon,and polymer materials.This review comprehensively examines recent advances in the application of these materials as current collector coatings.Particularly,their distinct roles in the lithium deposition process are analyzed to understand how they mitigate the issues associated with the lithium metal anode.Furthermore,their inherent limitations are considered to inform future research directions.While each class of materials offers specific advantages,multifunctionality is required to effectively regulate lithium deposition.In prospect,a novel composite copper current collector design that integrates the merits of the aforementioned advanced materials is proposed.The insights from this review provide valuable guidance for the rational design of modified copper current collectors,which would significantly improve the safety and cycle life of LMBs and advance their commercialization.展开更多
When the converter bus voltage of a voltage source converter-based high voltage direct current(VSC-HVDC)system drops below a certain predetermined threshold,the system enters low-voltage ride-through(LVRT)mode to avoi...When the converter bus voltage of a voltage source converter-based high voltage direct current(VSC-HVDC)system drops below a certain predetermined threshold,the system enters low-voltage ride-through(LVRT)mode to avoid overcurrent and potential equipment failure,during which it operates as a controlled current source.The influence mechanism of LVRT control strategies on short-circuit current and overall system stability remains not yet fully and systematically investigated.First,this paper provides an overview of several LVRT strategies for VSC-HVDC systems and examines their effects on short-circuit current contribution.Next,it analyzes in detail the mechanisms through which active and reactive currents injected during LVRT impact system frequency stability,voltage stability,and synchronization stability.To address these interrelated issues,an optimized and comprehensive LVRT strategy incorporating short-circuit current constraints is proposed.The approach determines the active current ratio based on system frequency stability requirements and dynamically adjusts the active current recovery rate via phase control of the VSC-HVDC bus.The remaining capacity is allocated to reactive current support,thereby enhancing voltage and synchronization stability while maintaining sufficient short-circuit current margin and system frequency stability.Finally,simulations conducted on the PSS/E platform,using actual grid data from a selected cross-section system,validate convincingly the effectiveness of the proposed parameter optimization strategy for VSC-HVDC low-voltage ride-through.展开更多
Transcranial direct current stimulation(tDCS)is a non-invasive technique that modifies cortical excitability and induces neuroplasticity using low-intensity electrical currents.Nuclear medicine technologies like posit...Transcranial direct current stimulation(tDCS)is a non-invasive technique that modifies cortical excitability and induces neuroplasticity using low-intensity electrical currents.Nuclear medicine technologies like positron emission tomography(PET)and single-photon emission computed tomography(SPECT)can quantify cerebral metabolism and other dynamics.Evidence suggests that combining tDCS with these imaging methods enhances understanding and outcomes for neurological and psychiatric conditions.This review highlights how nuclear medicine can objectively characterize tDCS eff ects,map network modulation,and identify predictive biomarkers.PET and SPECT indicate changes in glucose metabolism and neurotransmitter activity post-tDCS,demonstrating their value in validation.While the co-application of these methodologies is still in conceptual stages,their integration may advance precision neuromodulation and inform rehabilitation strategies.展开更多
To elucidate the accelerated degradation mechanisms of metallic interconnects in operational solid oxide fuel cells,the oxidation behavior of FSS430 ferritic stainless steel under the coupling of simultaneous electric...To elucidate the accelerated degradation mechanisms of metallic interconnects in operational solid oxide fuel cells,the oxidation behavior of FSS430 ferritic stainless steel under the coupling of simultaneous electrical current and high-temperature exposure is investigated.Isothermal thermogravimetric analysis was employed to quantify oxidation kinetics,complemented by microstructural characterization using X-ray diffraction,scanning electron microscopy with energy-dispersive spectroscopy and transmission electron microscopy.Experimental results demonstrate that the applied current dramatically enhances oxidation rates,increasing specific mass gain from 0.25 mg/cm^(2)(0 A/cm^(2))to 5.20 mg/cm^(2)(0.2 A/cm^(2))and oxide scale thickness from 1.87 to 15.62μm after 200 h.This acceleration originates from current-induced electromigration forces that promote cationic transport through the oxide layer.The quantitative relationships between current density and oxidation parameters are established,enabling predictive modeling of interconnector degradation in solid oxide fuel cell(SOFC)systems.展开更多
Exercise produces a decrease in pain sensitivity via an effect called exercise-induced hypoalgesia(EIH).Transcranial direct current stimulation(tDCS),acting on similar analgesic mechanisms as EIH,represents a potentia...Exercise produces a decrease in pain sensitivity via an effect called exercise-induced hypoalgesia(EIH).Transcranial direct current stimulation(tDCS),acting on similar analgesic mechanisms as EIH,represents a potential complementary intervention that may amplify the effects of exercise on pain.This study aimed to explore if anodal tDCS could enhance the effect of exercise on pain compared to exercise alone.A total of 35 healthy participants aged 19–37 years completed a familiarisation session followed by two separate sessions where active and sham tDCS was applied in a randomised cross-over design.The familiarisation session involved familiarisation to the pain assessment and exercise tasks,while the subsequent tDCS sessions involved pain sensitivity assessment,exercise and either anodal tDCS or sham tDCS.tDCS doses were applied at 2 mA over the primary motor cortex for 10 min,with the reference electrode placed over the contralateral supraorbital area.The exercise task involved a sustained isometric grip strength contraction at 35%of maximal voluntary contraction(MVC)until volitional exhaustion.Pain sensitivity was evaluated as pressure pain threshold before tDCS,after tDCS,and after exercise.Across both tDCS conditions,pain threshold was higher after exercise when compared to pre-and post-tDCS measurement.This increase in pain threshold did not differ between active and sham tDCS conditions.Our findings suggest that the hypoalgesic effects of active anodal tDCS over the motor cortex prior to exercise are no greater than the effects of sham tDCS prior to exercise.展开更多
To address the issues of high costs and low component utilization caused by the independent configuration of hybrid DC circuit breakers(HCBs)and DC power flow controllers(DCPFCs)at each port in existing DC distributio...To address the issues of high costs and low component utilization caused by the independent configuration of hybrid DC circuit breakers(HCBs)and DC power flow controllers(DCPFCs)at each port in existing DC distribution networks,this paper adopts a component sharing mechanism to propose a composite multi-port hybrid DC circuit breaker(CM-HCB)with DC power flow and fault current limitation abilities,as well as reduced component costs.The proposed CM-HCB topology enables the sharing of the main breaker branch(MB)and the energy dissipation branch,while the load commutation switches(LCSs)in the main branch are reused as power flow control components,enabling flexible regulation of power flow in multiple lines.Meanwhile,by reconstructing the current path during the fault process,the proposed CM-HCB can utilize the internal coupled inductor to limit the current rise rate at the initial stage of the fault,significantly reducing the requirement for breaking current.A detailed study on the topological structure,steady-state power flow regulation mechanism,transient fault isolation mechanism,control strategy and characteristic analysis of the proposed CM-HCB is presented.Then,a Matlab/Simulink-based meshed three-terminal DC grid simulation platform with the proposed CM-HCB is built.The results indicate that the proposed CM-HCB can not only achieve flexible power flow control during steady-state operation,but also obtain current rise limitation and fault isolation abilities under short-circuit fault conditions,verifying its correctness and effectiveness.Finally,a comparative economic analysis is conducted between the proposed CM-HCB and the other two existing solutions,confirming that its component sharing mechanism can significantly reduce the number of components,lower system costs,and improve component utilization.展开更多
Virtor(VSG)technology is widely investigated and applied for dual synchronous generatoubly-fed induction generators(DFIGs)to provide virtual inertia.However,under grid faults,the conventional VSG-based DFIG faces chal...Virtor(VSG)technology is widely investigated and applied for dual synchronous generatoubly-fed induction generators(DFIGs)to provide virtual inertia.However,under grid faults,the conventional VSG-based DFIG faces challenges of transient overcurrent and instability.The critical limitation for grid-forming DFIGs to withstand serious grid faults is the rotor-side converter(RSC)’s inability to quickly generate proper rotor voltage to counteract transient electromotive force(EMF),which results in transient overcurrent and damage to the RSC.To fill this gap,this study introduces a novel low-voltage ride-through(LVRT)control strategy for the grid-forming DFIG under symmetrical grid fault conditions.To mitigate transient overcurrent,the core mechanism is to regulate the rotor flux linkage to align with the stator flux linkage in an optimal proportion.Under the proposed control strategy,both post-fault rotor current and required rotor voltage are constrained within operational limits.Moreover,fluctuations in electromagnetic torque are efficiently suppressed during grid disturbances.Consequently,the dynamic stability and power support capacity of the DFIG system remain intact throughout the transient process.Finally,simulation studies and experimental results are provided to verify the feasibility of the proposed approach.展开更多
Rectifiers with high efficiency and high power density are crucial to the stable and efficient power supply of 5G communication base stations,which deserves in-depth investigation.In general,there are two key problems...Rectifiers with high efficiency and high power density are crucial to the stable and efficient power supply of 5G communication base stations,which deserves in-depth investigation.In general,there are two key problems to be addressed:supporting both alternating current(AC)and direct current(DC)input,and minimizing the common-mode voltage as well as leakage current for safety reasons.In this paper,a hybrid five-level single-phase rectifier is proposed.A five-level topology is adopted in the upper arm,and a half-bridge diode topology is adopted in the lower arm.A dual closed-loop control strategy and a flying capacitor voltage regulation method are designed accordingly so that the compatibility of both AC and DC input is realized with low common voltage and small passive devices.Simulation and experimental results demonstrate the effectiveness and performance of the proposed rectifier.展开更多
The balanced operational amplifier including its merits and designing methods is discussed by comparing its performance to a conventional differential output amplifier when used in a single balanced stage. A balanced ...The balanced operational amplifier including its merits and designing methods is discussed by comparing its performance to a conventional differential output amplifier when used in a single balanced stage. A balanced OTA circuit design is also presented.展开更多
The multi-terminal direct current(DC)grid has extinctive superiorities over the traditional alternating current system in integrating large-scale renewable energy.Both the DC circuit breaker(DCCB)and the current flow ...The multi-terminal direct current(DC)grid has extinctive superiorities over the traditional alternating current system in integrating large-scale renewable energy.Both the DC circuit breaker(DCCB)and the current flow controller(CFC)are demanded to ensure the multiterminal DC grid to operates reliably and flexibly.However,since the CFC and the DCCB are all based on fully controlled semiconductor switches(e.g.,insulated gate bipolar transistor,integrated gate commutated thyristor,etc.),their separation configuration in the multiterminal DC grid will lead to unaffordable implementation costs and conduction power losses.To solve these problems,integrated equipment with both current flow control and fault isolation abilities is proposed,which shares the expensive and duplicated components of CFCs and DCCBs among adjacent lines.In addition,the complicated coordination control of CFCs and DCCBs can be avoided by adopting the integrated equipment in themultiterminal DC grid.In order to examine the current flow control and fault isolation abilities of the integrated equipment,the simulation model of a specific meshed four-terminal DC grid is constructed in the PSCAD/EMTDC software.Finally,the comparison between the integrated equipment and the separate solution is presented a specific result or conclusion needs to be added to the abstract.展开更多
基金Project supported by the National Natural Science Foundation of China(No.51577172)
文摘Induction motor drive systems fed by cables are widely used in industrial applications. However, high-frequency switching of power devices will cause common-mode（CM） voltages during operation, leading to serious CM currents in the motor drive systems. CM currents through the cables and motors in the drive systems can cause electromagnetic interference（EMI） with the surrounding electronic equipment and shorten the life of induction motors. Therefore, it is necessary to analyze the CM currents in motor drive systems. In this paper, high-frequency models of unshielded and shielded power cables are formulated. The frequency-dependent effects and mutual inductances of the cables are taken into account. The power cable parameters are extracted by the finite element method and validated by measurements. High-frequency models of induction motors and inverters are introduced from existing works. The CM currents at the motor and inverter terminals are obtained, and the influence of the cable length and cable type on the CM currents is analyzed. There is a good agreement between the experimental results and the CM currents predicted by the proposed models.
基金This work was supported by the National Natural Science Foundation of China under Grant 51577010the Fundamental Research Funds for the Central Universities under Grant 2017JBM054the Natural Science Foundation of Guangdong Province under Grant 1714060000016.
文摘The common-mode current is an important indicator with transformerless photovoltaic inverters.However,up to now,there is not an accurate method to predict common-mode current in the inverter design process,resulting from inappropriate device selection or exceeded the expected common-mode current.In order to solve this problem,this paper proposes an accurate common-mode current prediction method based on graph theory for transformerless photovoltaic inverters.In this paper,the mathematic model of the common-mode current is derived using graph theory analysis method in the full-bridge topology,and it is used to predict common-mode current.The validity and correctness of the proposed prediction method are validated by simulation and experiment.The oscillation frequency and amplitude can be predicted by the proposed common-mode prediction method,whereas the traditional common-mode analysis method cannot.This paper provides a novel way to predict and analyze common-mode current in the transformerless photovoltaic inverters.
基金supported in part by the National Natural Science Foundation of China under Grant 51907116in part sponsored by Natural Science Foundation of Shanghai 22ZR1425400sponsored by Shanghai Rising-Star Program 23QA1404000。
文摘Insulation failure significantly contributes to the unpredictable shutdown of power equipment.Compared to the partial discharge and high-frequency(HF)injection methods,the HF common-mode(CM)leakage current method offers a non-intrusive and highly sensitive alternative.However,the detection of HF CM currents is susceptible to interference from differential-mode(DM)currents,which exhibit high-amplitude and multifrequency components during normal operation.To address this challenge,this paper proposes a double-ring current sensor based on the principle of magnetic shielding for inverter-fed machine winding insulation monitoring.The inner ring harnesses the magnetic aggregation effect to isolate the DM current magnetic field,whereas the outer ring serves as the magnetic core of the Rogowski current sensor,enabling HF CM current monitoring.First,the magnetic field distributions of the CM and DM currents were analyzed.Then,a correlation between the sensor parameters and signal-to-noise ratio of the target HF CM current was established.Finally,an experimental study was conducted on a 3-kW PMSM for verification.The results indicate that the proposed double-ring HF CM sensor can effectively mitigate DM current interference.Compared to a single-ring sensor,a reduction of approximately 40%in the DM component was achieved,which significantly enhanced the precision of online insulation monitoring.
文摘With the rapid integration of renewable energy sources,modern power systems are increasingly challenged by heightened volatility and uncertainty.Doubly-fed variable-speed pumped storage units(DFVS-PSUs)have emerged as promising technologies for mitigating grid oscillations and enhancing system flexibility.However,the excitation converters in DFVS-PSUs are prone to significant issues such as elevated common-mode voltage(CMV)and neutral-point voltage(NPV)fluctuations,which can lead to electromagnetic interference and degrade transient performance.To address these challenges,an optimized virtual space vector pulse width modulation(OVSVPWM)strategy is proposed,aiming to suppress CMV and NPV simultaneously through coordinated multi-objective control.Specifically,a dynamic feedback mechanism is introduced to adjust the balancing factor of basic vectors in the synthesized virtual small vector in real-time,achieving autonomous balancing of the NPV.To address the excessive switching actions introduced by the OVSVPWM strategy,a phase duty ratio-based sequence reconstruction method is adopted,which reduces the total number of switching actions to half of the original.A zero-level buffering scheme is employed to reconstruct the single-phase voltage-level output sequence,achieving peak CMV suppression down to udc/6.Simulation results demonstrate that the proposed strategy significantly improves electromagnetic compatibility and operational stability while maintaining high power quality.
基金National Key Research and Development Program of China(2021YFB3700801)。
文摘Low-density short-duration pulsed current-assisted aging treatment was applied to the Ti-6Al-4V-0.5Mo-0.5Zr alloy subjected to different solution treatments.The results show that numerous α_(p) phases redissolve into the new β phase during the pulsed current-assisted aging process,and then the newly formed β phase is mainly transformed into the β_(t) phase,with occasional transition to new α_(p) phase,leading to a remarkable grain refinement,especially for the lamellarαs phases.In comparison to conventional aging treatment,the pulsed current-assisted aging approach achieves a significant enhancement in strength without degrading ductility,yielding an excellent mechanical property combination:a yield strength of 932 MPa,a tensile strength of 1042 MPa,and an elongation of 12.2%.It is primarily ascribed to the increased fraction of β_(t) phases,the obvious grain refinement effect,and the slip block effect induced by the multiple-variantαs colonies distributed within β_(t) phases.
基金Supported by the Fundamental Research Funds for the Central Universities(2024ZYGXZR047)the National Natural Science Foundation of China(62373156)the Guangdong Basic and Applied Basic Research Foundation(2024A1515011736)。
文摘This article investigates the robust current tracking control problem of three-phase grid-connected inverters with LCL filter under external disturbance by a dynamic state feedback control method.First,this paper constructs an internal model to learn the information of the states and input of the grid-connected inverter under steady state.Second,by utilizing the internal model principle,the paper turns the tracking control problem into the robust stabilization control problem based on some appropriate coordinate transformations.Then,The paper designs a dynamics state feedback control law to deal with this robust stabilization problem,and thus the solution of the robust current tracking control problem of three-phase grid-connected inverters can be obtained.This control method can ensure the asymptotic stability of the closedloop system.Finally,the paper illustrates the effectiveness of the proposed control approach through several groups of simulations,and compares it with the feedforward control method to verify the robustness of the proposed control method to uncertain parameters.
文摘Machine stator winding insulation degradation is one of the main results of machine aging.It is non-negligible once this degradation process becomes asymmetric between phases.The traditional way to determine the insulation state of health is a partial discharge test.However,this method requires the system offline,which causes production loss and extra administrative burden.This paper presents an idea for better characterizing the insulation machine’s state of health using common-mode(CM)behavior in the machine-drive system.With the help of circuit decomposition methods and modeling tools,the CM quantities due to asymmetric aging show a unique characteristic that distinguishes itself from other differential-mode(DM)quantities in the equivalent circuit.It is shown effective to represent the asymmetric aging effect from the detection of system leakage current.This paper provides an analytical method to quantify this characteristic from mathematical approaches,and a proper approximation has been made on the CM equivalent model(CEM)such that the CM behavior is accurately characterized.The proposed method will serve the purpose of predicting machine abnormal behavior using the simple RLC circuit.Researchers can adapt this method to quantify and characterize the machine insulation state of health(SOH).
基金financial support from the Helmholtz Association and the German Federal Ministry of Education and Research(BMBF)within the ExcellBattUlm project(03XP0257D)the HighSafe-3 project(03XP0568A)。
文摘Energy density and safety are two crucial parameters when evaluating lithium-metal batteries(LMBs).Herein,we present an ultralight polymer-based current collector,incorporating flame-retardant materials,designed specifically for thin lithium-metal anodes.Compared to the traditional copper current collector(8.96 mg cm^(-2),10μm thick),the polymer-based current collector(12μm thick)has a significantly lower areal density of 1.41 mg cm^(-2),i.e.,only one-sixth of the copper collector,thus enabling substantially higher energy densities.Accordingly,when employed in Li||NMC_(622)full-cells,the polymer-based current collector enables a specific energy of 449 Wh kg^(-1),representing a notable improvement of about14.5%compared to cells employing a classic copper current collector.The inclusion of Al(OH)_(3) as a flame retardant into the current collector suppresses flammability and,thereby,significantly improves the safety of the resulting LMBs.
文摘With the advent of the big data era,modern statistics has enjoyed unprecedented development opportunities and also faced numerous new challenges.Traditional statistical computing methods are often limited by issues such as computer memory capacity and distributed storage of data across different locations,and are unable to directly apply to large-scale data sets.Therefore,in the context of big data,designing efficient and theoretically guaranteed statistical learning and inference algorithms has become a key issue that the current field of statistics urgently needs to address.In this paper,the application status of statistical analysis methods in the big data environment was systematically reviewed,and its future development directions were analyzed to provide reference and support for the further development of theory and methods of the statistical analysis of big data.
基金supported by the National Natural Science Foundation of China under Grant 52277184 and Grant 52277183.
文摘The transient synchronization stability of grid-forming converters(GFMCs)is significantly challenged under grid voltage sags.Continuous efforts have been devoted to analyzing the GFMC transient stability,with limited attention paid to the impacts of control loop dynamics.However,the complex control dynamics,especially the interactions between the active/reactive power control loops and the current saturation process(CSP),are crucial for accurately describing the transient behavior and evaluating the stability.Thus,in this study,a new large-signal GFMC model is established,considering the reactive power control(RPC)with different kinds of controllers and the CSP simultaneously.It is revealed that GFMC does not switch to the current-limited mode immediately,and the dynamics of RPC further affect the transient behavior before the current limiting significantly.Hence,the complex control dynamics can alter the mode switching point of current saturation,thereby increasing the risk of loss of synchronization(LOS).Based on the above findings,comprehensive comparisons of typical RPC controllers are presented to facilitate practical engineering applications.A unified stability enhancement method is proposed for solving the problem of LOS.Finally,experiments validate the correctness of the analysis and the effectiveness of the proposed control strategy.
基金supported by the National Natural Science Foundation of China(grant numbers 52071225,22179143,and 22002176)the European Union’s Horizon Europe research and innovation program Electron Beam Emergent Additive Manufacturing(EBEAM)(grant number 101087143)+2 种基金a Norway Grant through the National Science Centre(project number 2019/34/H/ST8/00547)the National Key R&D Program of China(grant number 2021YFB3800300)the Jiangsu Funding Program for Excellent Postdoctoral Talent。
文摘Lithium metal batteries(LMBs)are promising candidates for next-generation high-energy-density storage devices.However,an unstable lithium metal anode poses significant issues that critically compromise battery safety and cycle life,including lithium dendrite formation,solid electrolyte interphase degradation,dead lithium accumulation,and substantial volume fluctuations during cycling.These problems can be addressed by regulating lithium deposition and suppressing side reactions through the modification of copper current collectors using three classes of materials:metal and metal oxide,carbon,and polymer materials.This review comprehensively examines recent advances in the application of these materials as current collector coatings.Particularly,their distinct roles in the lithium deposition process are analyzed to understand how they mitigate the issues associated with the lithium metal anode.Furthermore,their inherent limitations are considered to inform future research directions.While each class of materials offers specific advantages,multifunctionality is required to effectively regulate lithium deposition.In prospect,a novel composite copper current collector design that integrates the merits of the aforementioned advanced materials is proposed.The insights from this review provide valuable guidance for the rational design of modified copper current collectors,which would significantly improve the safety and cycle life of LMBs and advance their commercialization.
基金funded by State Grid Corporation of China,grant number DQ30DK24001L。
文摘When the converter bus voltage of a voltage source converter-based high voltage direct current(VSC-HVDC)system drops below a certain predetermined threshold,the system enters low-voltage ride-through(LVRT)mode to avoid overcurrent and potential equipment failure,during which it operates as a controlled current source.The influence mechanism of LVRT control strategies on short-circuit current and overall system stability remains not yet fully and systematically investigated.First,this paper provides an overview of several LVRT strategies for VSC-HVDC systems and examines their effects on short-circuit current contribution.Next,it analyzes in detail the mechanisms through which active and reactive currents injected during LVRT impact system frequency stability,voltage stability,and synchronization stability.To address these interrelated issues,an optimized and comprehensive LVRT strategy incorporating short-circuit current constraints is proposed.The approach determines the active current ratio based on system frequency stability requirements and dynamically adjusts the active current recovery rate via phase control of the VSC-HVDC bus.The remaining capacity is allocated to reactive current support,thereby enhancing voltage and synchronization stability while maintaining sufficient short-circuit current margin and system frequency stability.Finally,simulations conducted on the PSS/E platform,using actual grid data from a selected cross-section system,validate convincingly the effectiveness of the proposed parameter optimization strategy for VSC-HVDC low-voltage ride-through.
文摘Transcranial direct current stimulation(tDCS)is a non-invasive technique that modifies cortical excitability and induces neuroplasticity using low-intensity electrical currents.Nuclear medicine technologies like positron emission tomography(PET)and single-photon emission computed tomography(SPECT)can quantify cerebral metabolism and other dynamics.Evidence suggests that combining tDCS with these imaging methods enhances understanding and outcomes for neurological and psychiatric conditions.This review highlights how nuclear medicine can objectively characterize tDCS eff ects,map network modulation,and identify predictive biomarkers.PET and SPECT indicate changes in glucose metabolism and neurotransmitter activity post-tDCS,demonstrating their value in validation.While the co-application of these methodologies is still in conceptual stages,their integration may advance precision neuromodulation and inform rehabilitation strategies.
基金supported by Natural Science Foundation of Wuhan(2024040701010051)Natural Science Foundation of Hubei(2023AFB111)and National Natural Science Foundation of China(52401108).
文摘To elucidate the accelerated degradation mechanisms of metallic interconnects in operational solid oxide fuel cells,the oxidation behavior of FSS430 ferritic stainless steel under the coupling of simultaneous electrical current and high-temperature exposure is investigated.Isothermal thermogravimetric analysis was employed to quantify oxidation kinetics,complemented by microstructural characterization using X-ray diffraction,scanning electron microscopy with energy-dispersive spectroscopy and transmission electron microscopy.Experimental results demonstrate that the applied current dramatically enhances oxidation rates,increasing specific mass gain from 0.25 mg/cm^(2)(0 A/cm^(2))to 5.20 mg/cm^(2)(0.2 A/cm^(2))and oxide scale thickness from 1.87 to 15.62μm after 200 h.This acceleration originates from current-induced electromigration forces that promote cationic transport through the oxide layer.The quantitative relationships between current density and oxidation parameters are established,enabling predictive modeling of interconnector degradation in solid oxide fuel cell(SOFC)systems.
文摘Exercise produces a decrease in pain sensitivity via an effect called exercise-induced hypoalgesia(EIH).Transcranial direct current stimulation(tDCS),acting on similar analgesic mechanisms as EIH,represents a potential complementary intervention that may amplify the effects of exercise on pain.This study aimed to explore if anodal tDCS could enhance the effect of exercise on pain compared to exercise alone.A total of 35 healthy participants aged 19–37 years completed a familiarisation session followed by two separate sessions where active and sham tDCS was applied in a randomised cross-over design.The familiarisation session involved familiarisation to the pain assessment and exercise tasks,while the subsequent tDCS sessions involved pain sensitivity assessment,exercise and either anodal tDCS or sham tDCS.tDCS doses were applied at 2 mA over the primary motor cortex for 10 min,with the reference electrode placed over the contralateral supraorbital area.The exercise task involved a sustained isometric grip strength contraction at 35%of maximal voluntary contraction(MVC)until volitional exhaustion.Pain sensitivity was evaluated as pressure pain threshold before tDCS,after tDCS,and after exercise.Across both tDCS conditions,pain threshold was higher after exercise when compared to pre-and post-tDCS measurement.This increase in pain threshold did not differ between active and sham tDCS conditions.Our findings suggest that the hypoalgesic effects of active anodal tDCS over the motor cortex prior to exercise are no greater than the effects of sham tDCS prior to exercise.
基金funded by Youth Talent Growth Project of Guizhou Provincial Department of Education(No.Qianjiaoji[2024]21)National Natural Science Foundation of China(No.62461008 and No.52507211)Guizhou Provincial Key Technology R&D Program(No.[2024]General 049).
文摘To address the issues of high costs and low component utilization caused by the independent configuration of hybrid DC circuit breakers(HCBs)and DC power flow controllers(DCPFCs)at each port in existing DC distribution networks,this paper adopts a component sharing mechanism to propose a composite multi-port hybrid DC circuit breaker(CM-HCB)with DC power flow and fault current limitation abilities,as well as reduced component costs.The proposed CM-HCB topology enables the sharing of the main breaker branch(MB)and the energy dissipation branch,while the load commutation switches(LCSs)in the main branch are reused as power flow control components,enabling flexible regulation of power flow in multiple lines.Meanwhile,by reconstructing the current path during the fault process,the proposed CM-HCB can utilize the internal coupled inductor to limit the current rise rate at the initial stage of the fault,significantly reducing the requirement for breaking current.A detailed study on the topological structure,steady-state power flow regulation mechanism,transient fault isolation mechanism,control strategy and characteristic analysis of the proposed CM-HCB is presented.Then,a Matlab/Simulink-based meshed three-terminal DC grid simulation platform with the proposed CM-HCB is built.The results indicate that the proposed CM-HCB can not only achieve flexible power flow control during steady-state operation,but also obtain current rise limitation and fault isolation abilities under short-circuit fault conditions,verifying its correctness and effectiveness.Finally,a comparative economic analysis is conducted between the proposed CM-HCB and the other two existing solutions,confirming that its component sharing mechanism can significantly reduce the number of components,lower system costs,and improve component utilization.
基金supported by the National Natural Science Foundation of China(No.52477195,No.U25B20204,No.52437009).
文摘Virtor(VSG)technology is widely investigated and applied for dual synchronous generatoubly-fed induction generators(DFIGs)to provide virtual inertia.However,under grid faults,the conventional VSG-based DFIG faces challenges of transient overcurrent and instability.The critical limitation for grid-forming DFIGs to withstand serious grid faults is the rotor-side converter(RSC)’s inability to quickly generate proper rotor voltage to counteract transient electromotive force(EMF),which results in transient overcurrent and damage to the RSC.To fill this gap,this study introduces a novel low-voltage ride-through(LVRT)control strategy for the grid-forming DFIG under symmetrical grid fault conditions.To mitigate transient overcurrent,the core mechanism is to regulate the rotor flux linkage to align with the stator flux linkage in an optimal proportion.Under the proposed control strategy,both post-fault rotor current and required rotor voltage are constrained within operational limits.Moreover,fluctuations in electromagnetic torque are efficiently suppressed during grid disturbances.Consequently,the dynamic stability and power support capacity of the DFIG system remain intact throughout the transient process.Finally,simulation studies and experimental results are provided to verify the feasibility of the proposed approach.
文摘Rectifiers with high efficiency and high power density are crucial to the stable and efficient power supply of 5G communication base stations,which deserves in-depth investigation.In general,there are two key problems to be addressed:supporting both alternating current(AC)and direct current(DC)input,and minimizing the common-mode voltage as well as leakage current for safety reasons.In this paper,a hybrid five-level single-phase rectifier is proposed.A five-level topology is adopted in the upper arm,and a half-bridge diode topology is adopted in the lower arm.A dual closed-loop control strategy and a flying capacitor voltage regulation method are designed accordingly so that the compatibility of both AC and DC input is realized with low common voltage and small passive devices.Simulation and experimental results demonstrate the effectiveness and performance of the proposed rectifier.
文摘The balanced operational amplifier including its merits and designing methods is discussed by comparing its performance to a conventional differential output amplifier when used in a single balanced stage. A balanced OTA circuit design is also presented.
基金supported in part by Natural Science Foundation of Jiangsu Province under Grant BK20230255Natural Science Foundation of Shandong Province under Grant ZR2023QE281.
文摘The multi-terminal direct current(DC)grid has extinctive superiorities over the traditional alternating current system in integrating large-scale renewable energy.Both the DC circuit breaker(DCCB)and the current flow controller(CFC)are demanded to ensure the multiterminal DC grid to operates reliably and flexibly.However,since the CFC and the DCCB are all based on fully controlled semiconductor switches(e.g.,insulated gate bipolar transistor,integrated gate commutated thyristor,etc.),their separation configuration in the multiterminal DC grid will lead to unaffordable implementation costs and conduction power losses.To solve these problems,integrated equipment with both current flow control and fault isolation abilities is proposed,which shares the expensive and duplicated components of CFCs and DCCBs among adjacent lines.In addition,the complicated coordination control of CFCs and DCCBs can be avoided by adopting the integrated equipment in themultiterminal DC grid.In order to examine the current flow control and fault isolation abilities of the integrated equipment,the simulation model of a specific meshed four-terminal DC grid is constructed in the PSCAD/EMTDC software.Finally,the comparison between the integrated equipment and the separate solution is presented a specific result or conclusion needs to be added to the abstract.
