As a new dynamic reactive power compensator,the grid-forming Static Var Generator(GF-SVG)can not only provide reactive power-voltage support,but also has inertial support capability.It has been experimentally deployed...As a new dynamic reactive power compensator,the grid-forming Static Var Generator(GF-SVG)can not only provide reactive power-voltage support,but also has inertial support capability.It has been experimentally deployed in many wind farms.However,studies have shown that when the three-phase short-circuit fault occurs in the wind farm,the transient overcurrent during the fault occurrence and fault clearance is suppressed,making it difficult for GF-SVG to use traditional fixed virtual impedance.Aiming at the problem,firstly,the influence of virtual reactance on control stability is analyzed using the GF-SVG’s current open-loop transfer function.Secondly,based on the existing current limitation strategies of GF-SVG,an adaptive virtual reactance current limitation strategy suitable for symmetrical faults of the power grid is proposed,which limits GF-SVG’s transient overcurrent during fault occurrence and fault clearance stage to the tolerance range of GF-SVG’s power devices.Based on the GF-SVG’s active power loop and reactive power loop small signal models,the availability of the proposed adaptive virtual reactance in suppressing the DC voltage drop of GF-SVG is analyzed,and shortening the transient overvoltage recovery time of the wind farm after the fault clearance is also discussed.Finally,electromagnetic simulation proves the effectiveness and correctness of the proposed adaptive current limitation method.展开更多
Due to the low impedance characteristic of the high voltage direct current(HVDC)grid,the fault current rises extremely fast after a DC-side fault occurs,and this phenomenon seriously endangers the safety of the HVDC g...Due to the low impedance characteristic of the high voltage direct current(HVDC)grid,the fault current rises extremely fast after a DC-side fault occurs,and this phenomenon seriously endangers the safety of the HVDC grid.In order to suppress the rising speed of the fault current and reduce the current interruption requirements of the main breaker(MB),a fault current limiting hybrid DC circuit breaker(FCL-HCB)has been proposed in this paper,and it has the capability of bidirectional fault current limiting and fault current interruption.After the occurrence of the overcurrent in the HVDC grid,the current limiting circuit(CLC)of FCL-HCB is put into operation immediately,and whether the protected line is cut off or resumed to normal operation is decided according to the fault detection result.Compared with the traditional hybrid DC circuit breaker(HCB),the required number of semiconductor switches and the peak value of fault current after fault occurs are greatly reduced by adopting the proposed device.Extensive simulations also verify the effectiveness of the proposed FCL-HCB.展开更多
A novel magnetic-controlled switcher type fault current limiter (FCL) based on the topology of the saturated iron core high temperature superconducting FCL is proposed. The magnetic field distribution of the FCL iron ...A novel magnetic-controlled switcher type fault current limiter (FCL) based on the topology of the saturated iron core high temperature superconducting FCL is proposed. The magnetic field distribution of the FCL iron core is analyzed by FEA software ANSYS. The current limiting characteristic is investigated by both 3-D field-circuit coupled simulation and Matlab. The experiments on the 220 V/50 A test model show that the FCL can limit the fault current swiftly and effectively,and the FCL has the advantages of simple and reliable structure, flexible control strategy. The simulation and experimental results prove that the theoretical expectation and current limiting performance is satisfactory for practical use.展开更多
In a DC grid with dedicated metallic return(DMR),the coupling effects among the positive pole,negative pole,and DMR conductors must be considered,which makes fault identification particularly difficult.In addition,the...In a DC grid with dedicated metallic return(DMR),the coupling effects among the positive pole,negative pole,and DMR conductors must be considered,which makes fault identification particularly difficult.In addition,the identification of high-impedance faults remains a major challenge for DC grid protection.To address these issues,this study proposes an adaptive single-end protection method for DC grid based on the transient mean value of the current limiting reactor(CLR)modal voltage.First,a fault analysis model of the DC grid with DMR is established using the Clarke transformation.The characteristics of CLR modal voltage are then clarified.A fault pole-selection method based on a novel modulus phase plane is next proposed.A threshold scaling factor based on the differential of DC bus voltage is then constructed to enhance the sensitivity and rapidity of the protection,which can adaptively modify the threshold according to the fault severity.Finally,a simulation model of a four-terminal DC grid with DMR is developed in PSCAD/EMTDC.The speed and reliability of the proposed protection method are verified by simulations and experiments.展开更多
DC series-parallel power flow controller(SP-PFC)is a highly efficient device to solve the problem of uncontrolled line current in the bipolar DC distribution system.However,its potential in fault current limiting is n...DC series-parallel power flow controller(SP-PFC)is a highly efficient device to solve the problem of uncontrolled line current in the bipolar DC distribution system.However,its potential in fault current limiting is not fully explored.In this paper,a self-adaptive action strategy(SAAS)and a parameter optimization method of SP-PFC in bipolar DC distribution systems are proposed.Firstly,the common-and different-mode(CDM)equivalent circuits of the bipolar DC distribution system with SP-PFC in different fault stages are established,which avoids the line coupling inductance.Based on this,the influence of different parameters and line coupling inductance on the fault current limiting capability are investigated.It is found that the SP-PFC has the best fault current limiting capability when the capacitance and inductance of filter are inversely proportional.To realize the adaptability of fault current limiting capability under different fault severities,the SAAS of SP-PFC is proposed.The validity of the CDM equivalent circuits and parameter optimization method,and the effectiveness of the SAAS are verified by simulations and experiments.展开更多
Fault current limiting is a critical technology to en sure the safe operation of modular multilevel converter based multi-terminal direct current(MMC-MTDC)grids.This paper proposes a fault severity classification base...Fault current limiting is a critical technology to en sure the safe operation of modular multilevel converter based multi-terminal direct current(MMC-MTDC)grids.This paper proposes a fault severity classification based coordination con trol strategy of fault current limiter(FCL)and MMC for adap tive fault current limiting.The proposed strategy reduces the in vestment in FCL,and keeps the bus voltages of non-faulty lines at reasonable values.Firstly,a rapid fault circuit parameter esti mation(FCPE)method using initial fault current information is proposed.With this method,the fault distance and fault transi tion resistance can be quickly estimated,which are used for a quantitative indication of the fault severity.Subsequently,the coordination control strategy of FCL and MMC is proposed,in which the FCL action is prioritized,while the control of MMC is complementary for current limiting.Based on the proposed strategy,fault severity phase planes(FSPPs)are constructed to assess fault severity and calculate the activation time of FCL and voltage regulation factor of MMC.Therefore,the FCL acti vation and MMC control are matched to the fault severity.The effectiveness and advantages of the proposed strategy are vali dated by the simulations in PSCAD/EMTDC.展开更多
Bidirectional interlinking converter(BIC)is the core equipment in a hybrid AC/DC microgrid connected between AC and DC sub-grids.However,the variety of control modes and flexible bidirectional power flow complicate th...Bidirectional interlinking converter(BIC)is the core equipment in a hybrid AC/DC microgrid connected between AC and DC sub-grids.However,the variety of control modes and flexible bidirectional power flow complicate the influence of AC faults on BIC itself and on DC sub-grid,which potentially threaten both converter safety and system reliability.This study first investigates AC fault influence on the BIC and DC bus voltage under different BIC control modes and different pre-fault operation states,by developing a mathematical model and equivalent sequence network.Second,based on the analysis results,a general accommodative current limiting strategy is proposed for BIC without limitations to specific mode or operation condition.Current amplitude is predicted and constrained according to the critical requirements to protect the BIC and relieving the AC fault influence on the DC bus voltage.Compared with conventional methods,potential current limit failure and distortions under asymmetric faults can also be avoided.Finally,experiments verify feasibility of the proposed method.展开更多
In order to overcome the problems of power flow control and fault current limiting in multi-terminal high voltage direct current(MTDC)grids,this paper proposes a modular multi-terminal DC power flow controller(MM-DCPF...In order to overcome the problems of power flow control and fault current limiting in multi-terminal high voltage direct current(MTDC)grids,this paper proposes a modular multi-terminal DC power flow controller(MM-DCPFC)with fault current limiting function.The topology structure,operation principle,and equivalent circuit of MM-DCPFC are introduced,and such a structure has the advantages of modularity and scalability.The power balance mechanism is studied and a hierarchical power balance control strategy is proposed.The results show that MM-DCPFC can achieve internal power exchange,which avoids the use of external power supply.The fault characteristics of MM-DCPFC are analyzed,fault current limiting and self-protection methods are proposed,and the factors affecting the current limiting capability are studied.The simulation models are established in PLECS,and the simulation results verify the effectiveness of MM-DCPFC in power flow control,fault current limiting,and scalability.In addition,a prototype is developed to validate the function and control method of MM-DCPFC.展开更多
In the voltage source converter based high-voltage direct current(VSC-HVDC)grids,fast and reliable protections are the key technologies.The traditional protection schemes are easily affected by fault resistance,line d...In the voltage source converter based high-voltage direct current(VSC-HVDC)grids,fast and reliable protections are the key technologies.The traditional protection schemes are easily affected by fault resistance,line distributed capacitance,etc.Meanwhile,the influence of fault current limiting strategy(FCLS)has not been fully considered.In this paper,the fault characteristics under FCLS and the feasibility of traditional travelling wave protections are analyzed.To improve the reliability and sensibility,a similarity comparison based pilot protection scheme is proposed,which focuses on the relationship between the fault characteristics and the state of the protected transmission line,with the establishment of a precise frequencydependent transmission line model.The criteria based on the similarity comparison calculated by cross-wavelet can identify the fault effectively.Meanwhile,the protection scheme can also endure the influence of error synchronization.Finally,the protection performance is verified in the PSCAD/EMTDC under different fault conditions.展开更多
The series voltage source converter(SVSC)is widely used in the power electronic equipment,such as series active power filter,dynamic voltage restorer,unified power flow controller and so on.However,while the SVSC is m...The series voltage source converter(SVSC)is widely used in the power electronic equipment,such as series active power filter,dynamic voltage restorer,unified power flow controller and so on.However,while the SVSC is more vulnerable to the impact of fault current,its applications are increasing,bringing huge challenges to the safe operation of the grid.In recent years,the topology and control strategy of the series voltage source converter with fault current limiting(SVSC-FCL)are a research hotspot.In this paper,it suggests classifying SVSC-FCL based SVSC into two groups:the control scheme optimization group and the existing topology improvement group.The research challenges and perspectives of the SVSC-FCL are introduced in detail.This paper aims to illustrate current research progress on SVSC-FCL and enrich the available pool of the multi-functional power electronic equipment.展开更多
The problem of reclosing current limiting in voltage source converter based high-voltage direct current(VSCHVDC)systems is becoming more and more serious.A soft reclosing scheme for DC permanent faults is presented in...The problem of reclosing current limiting in voltage source converter based high-voltage direct current(VSCHVDC)systems is becoming more and more serious.A soft reclosing scheme for DC permanent faults is presented in this paper.Because the converter voltages of stations at both terminals of the disconnected faulty line may be different,the choice of which terminal to reclose first will affect the reclosing overcurrent.A method for selecting the terminal to reclose first is investigated to achieve a minimum peak overcurrent during the reclosing process.In order to ensure that the hybrid DC circuit breaker(HDCCB)adapts to the needs of the reclosing process better,the traditional HDCCB is improved by adding a soft reclosing module(SRM).The energy dissipated in the arresters is significantly reduced when using the improved HDCCB.The improved HDCCB will be able to reclose multiple times safely and thus increase the possibility of successful reclosing.Moreover,the recovery time after the HDCCB is successfully reclosed is very short with the improved HDCCB and its control principles.Simulation results show that this proposed scheme is capable of limiting the reclosing overcurrent when the fault still exists.展开更多
With the level of short-circuit current of power systems growing increasingly higher,optimal allocation of current limiters has received considerable attention in recent years,especially in China.This paper analyzes t...With the level of short-circuit current of power systems growing increasingly higher,optimal allocation of current limiters has received considerable attention in recent years,especially in China.This paper analyzes two kinds of common used current limiters based on the increment of bus impedance matrix and proposes a multi-objective current limiters configuration model considering the investment of limiters,the level of short-circuit current,as well as the transient stability of power system.An innovative search space reduction technique based on sensitivity factor is introduced to choose better candidate locations for current limiters so as to avoid the curse of dimensionality.The elitist non-dominated sorting genetic algorithm II is used to search the Pareto-optimal solutions of the proposed model.In order to further improve optimization efficiency,master-slave parallel modification of NSGA-II program structure is implemented.The satisfactory case study results demonstrate the feasibility of the proposed multi-objective method in power system current limiters allocation associated with cost,security and stability.展开更多
The water dissociation mechanism on a bipolar membrane under the electrical field was investigated and characterized in terms of ionic transport and limiting current density. It is considered that the depletion layer ...The water dissociation mechanism on a bipolar membrane under the electrical field was investigated and characterized in terms of ionic transport and limiting current density. It is considered that the depletion layer exists at the junction of a bipolar membrane, which is coincided with the viewpoint of the most literatures, but we also consider that the thickness and conductivity of this layer is not only related with the increase of the applied voltage but also with the limiting current density. Below the limiting current density, the thickness of the depletion layer keeps a constant and the conductivity decreases with the increase of the applied voltage; while above the limiting current density, the depletion thickness will increase with the increase of the applied voltage and the conductivity keeps a very low constant. Based on the data reported in the literatures and independent determinations, the limiting current density was calculated and the experimental curves Ⅰ-Ⅴ in the two directions were com展开更多
Rotating disk electrode systems are widely used to study the kinetics of electrocatalytic reactions that may suffer from insufficient mass transfer of the reactants.Kinetic current density at certain overpotential cal...Rotating disk electrode systems are widely used to study the kinetics of electrocatalytic reactions that may suffer from insufficient mass transfer of the reactants.Kinetic current density at certain overpotential calculated by the Koutecky-Levich equation is commonly used as the metrics to evaluate the activity of electrocatalysts.However,it is frequently found that the diffusion limiting current density is not correctly identified in the literatures.Instead of kinetic current density,the measured current density normalized by diffusion limiting current density(j/jL)has also been frequently under circumstance where its validity is not justified.By taking oxygen reduction reaction/hydrogen oxidation reaction/hydrogen evolution reaction as examples,we demonstrate that identifying the actual diffusion limiting current density for the same reaction under otherwise identical conditions from the experimental data is essential to accurately deduce kinetic current density.Our analysis reveals that j/jLis a rough activity metric which can only be used to qualitatively compare the activity trend under conditions that the mass transfer conditions and the roughness factor of the electrode are exactly the same.In addition,if one wants to use j/jLto compare the intrinsic activity,the concentration overpotential should be eliminated.展开更多
The self-consistent differential equations, which describe a laminar-flow equilibrium state in a magnetically focused intense relativistic electron beam propagating inside a conducting waveguide, are presented. The ca...The self-consistent differential equations, which describe a laminar-flow equilibrium state in a magnetically focused intense relativistic electron beam propagating inside a conducting waveguide, are presented. The canonical angular momentum, Pe, defined under the conditions at the source, uniquely determines the possible solutions of these equations. By numerically solving these equations, the space-charge limited current and the externally applied magnetic field are obtained in a solid beam and a hollow beam in two cases of Pθ= 0 （magnetically shielded source） and Pθ= const. （immersed source） separately. It is shown that the hollow beam is more beneficial to the propagation of the intense relativistic beam through a drift tube than the solid beam.展开更多
The current-voltage（I-V） characteristics of cBN crystal sandwiched between two metallic electrodes are measured and found to be nonlinear. Over 20 samples are measured at room temperature with various electrodes, an...The current-voltage（I-V） characteristics of cBN crystal sandwiched between two metallic electrodes are measured and found to be nonlinear. Over 20 samples are measured at room temperature with various electrodes, and the resulting curves are all similar in shape. When a voltage of about 560V is applied to the cBN crystal, the emitted light is visible to the naked eye in a dark room. We explain these phenomena by the space charge limited current and the electronic transition between the X and Г valleys of the conduction band.展开更多
The GaInSn liquid metal current limiter based on the fluid pinch effect has broad application prospects due to its particular properties. However, the limited rated current and abil- ity of power dissipation are the c...The GaInSn liquid metal current limiter based on the fluid pinch effect has broad application prospects due to its particular properties. However, the limited rated current and abil- ity of power dissipation are the critical problems for its wide application. Firstly, the temperature distribution of the liquid metal current limiter （LMCL） was obtained by experiments with a rated current of 1 kA and the arc ignition phenomenon was observed with 1.5 kA, which indicates that the rated current is mainly limited by the arc rather than the high temperature compared to the traditional switchgears. Furthermore, an improved method is proposed by adding the paralleled pure resistance, impedance or another LMCL element to protect the setup from the fault energy concentration in the setup. The problem of a slower arc voltage increasing rate can be solved by adding a paralleled impedance with suitable parameters. Finally, the current limiting properties based on the improved method were investigated and the alternating oscillating current was found between two paralleled LMCL elements owing to their deviation of arc ignition in reality.展开更多
A high-voltage transverse pulsed nanosecond discharge with a slotted hollow cathode was found to be a source of high-energy （few kV） ribbon electron beams. Conditions for the formation and extinction of electron bea...A high-voltage transverse pulsed nanosecond discharge with a slotted hollow cathode was found to be a source of high-energy （few kV） ribbon electron beams. Conditions for the formation and extinction of electron beams were experimentally studied in discharges in helium at pressures of 1-100 Torr. It was found that interaction of fast electrons with a non-uniform electric field near the slotted cathode led to limitation of the magnitude of the discharge current. A physical model was developed to describe the discharge current self-limitation that was in satisfactory agreement with the experimental results. Some technical solutions that are expected to increase the upper current limits in transverse nanosecond discharge are discussed.展开更多
This paper presents a new type of fault current limiter (FCL) based on fast closing switch, which is composed of a capacitor bank and a reactor in series. The main control component is a fast closing switch connecte...This paper presents a new type of fault current limiter (FCL) based on fast closing switch, which is composed of a capacitor bank and a reactor in series. The main control component is a fast closing switch connected in parallel with the capacitors, which is driven by the electromagnetic repulsion force. It can response the order within 1 ms. When fault occurs, the switch closes and the capacitors are bypassed, and the fault current is limited by the reactor. Simulation analysis and experiment show that the electromagnetic repulsion force actuator can meet the demand of fast closing switch, it is feasible to develop the FCL with low cost and high reliability.展开更多
The liquid metal current limiter(LMCL)is regarded as a viable solution for reducing the fault current in a power grid.But demonstrating the liquid metal arc plasma self-pinching process of the resistive wall,and reduc...The liquid metal current limiter(LMCL)is regarded as a viable solution for reducing the fault current in a power grid.But demonstrating the liquid metal arc plasma self-pinching process of the resistive wall,and reducing the erosion of the LMCL are challenging,not only theoretically,but also practically.In this work,a novel LMCL is designed with a resistive wall that can be connected to the current-limiting circuit inside the cavity.Specifically,a novel fault current limiter(FCL)topology is put forward where the novel LMCL is combined with a fast switch and current-limiting reactor.Further,the liquid metal self-pinch effect is modeled mathematically in three dimensions,and the gas-liquid two-phase dynamic diagrams under different short-circuit currents are obtained by simulation.The simulation results indicate that with the increase of current,the time for the liquid metal-free surface to begin depressing is reduced,and the position of the depression also changes.Different kinds of bubbles formed by the depressions gradually extend,squeeze,and break.With the increase of current,the liquid metal takes less time to break,but breaks still occur at the edge of the channel,forming arc plasma.Finally,relevant experiments are conducted for the novel FCL topology.The arcing process and current transfer process are analyzed in particular.Comparisons of the peak arc voltage,arcing time,current limiting efficiency,and electrode erosion are presented.The results demonstrate that the arc voltage of the novel FCL topology is reduced by more than 4.5times and the arcing time is reduced by more than 12%.The erosions of the liquid metal and electrodes are reduced.Moreover,the current limiting efficiency of the novel FCL topology is improved by 1%–5%.This work lays a foundation for the topology and optimal design of the LMCL.展开更多
基金supported by the National Natural Science Foundation of China under Grant 52077030.
文摘As a new dynamic reactive power compensator,the grid-forming Static Var Generator(GF-SVG)can not only provide reactive power-voltage support,but also has inertial support capability.It has been experimentally deployed in many wind farms.However,studies have shown that when the three-phase short-circuit fault occurs in the wind farm,the transient overcurrent during the fault occurrence and fault clearance is suppressed,making it difficult for GF-SVG to use traditional fixed virtual impedance.Aiming at the problem,firstly,the influence of virtual reactance on control stability is analyzed using the GF-SVG’s current open-loop transfer function.Secondly,based on the existing current limitation strategies of GF-SVG,an adaptive virtual reactance current limitation strategy suitable for symmetrical faults of the power grid is proposed,which limits GF-SVG’s transient overcurrent during fault occurrence and fault clearance stage to the tolerance range of GF-SVG’s power devices.Based on the GF-SVG’s active power loop and reactive power loop small signal models,the availability of the proposed adaptive virtual reactance in suppressing the DC voltage drop of GF-SVG is analyzed,and shortening the transient overvoltage recovery time of the wind farm after the fault clearance is also discussed.Finally,electromagnetic simulation proves the effectiveness and correctness of the proposed adaptive current limitation method.
基金This project is funded by the Dongying Science Development Fund Project(DJ2021013).
文摘Due to the low impedance characteristic of the high voltage direct current(HVDC)grid,the fault current rises extremely fast after a DC-side fault occurs,and this phenomenon seriously endangers the safety of the HVDC grid.In order to suppress the rising speed of the fault current and reduce the current interruption requirements of the main breaker(MB),a fault current limiting hybrid DC circuit breaker(FCL-HCB)has been proposed in this paper,and it has the capability of bidirectional fault current limiting and fault current interruption.After the occurrence of the overcurrent in the HVDC grid,the current limiting circuit(CLC)of FCL-HCB is put into operation immediately,and whether the protected line is cut off or resumed to normal operation is decided according to the fault detection result.Compared with the traditional hybrid DC circuit breaker(HCB),the required number of semiconductor switches and the peak value of fault current after fault occurs are greatly reduced by adopting the proposed device.Extensive simulations also verify the effectiveness of the proposed FCL-HCB.
基金Major State Basic Research Development Program of China ( No.2005CB221505)Research Foundation for the Doctoral Programof Higher Education of China(No.20050248058)
文摘A novel magnetic-controlled switcher type fault current limiter (FCL) based on the topology of the saturated iron core high temperature superconducting FCL is proposed. The magnetic field distribution of the FCL iron core is analyzed by FEA software ANSYS. The current limiting characteristic is investigated by both 3-D field-circuit coupled simulation and Matlab. The experiments on the 220 V/50 A test model show that the FCL can limit the fault current swiftly and effectively,and the FCL has the advantages of simple and reliable structure, flexible control strategy. The simulation and experimental results prove that the theoretical expectation and current limiting performance is satisfactory for practical use.
基金supported in part by the Joint Funds of the National Natural Science Foundation of China(No.U22B6006)the National Natural Science Foundation of China(No.52207126)Natural Science Foundation of Sichuan Province(No.2023NSFSC0296).
文摘In a DC grid with dedicated metallic return(DMR),the coupling effects among the positive pole,negative pole,and DMR conductors must be considered,which makes fault identification particularly difficult.In addition,the identification of high-impedance faults remains a major challenge for DC grid protection.To address these issues,this study proposes an adaptive single-end protection method for DC grid based on the transient mean value of the current limiting reactor(CLR)modal voltage.First,a fault analysis model of the DC grid with DMR is established using the Clarke transformation.The characteristics of CLR modal voltage are then clarified.A fault pole-selection method based on a novel modulus phase plane is next proposed.A threshold scaling factor based on the differential of DC bus voltage is then constructed to enhance the sensitivity and rapidity of the protection,which can adaptively modify the threshold according to the fault severity.Finally,a simulation model of a four-terminal DC grid with DMR is developed in PSCAD/EMTDC.The speed and reliability of the proposed protection method are verified by simulations and experiments.
基金supported by the National Natural Science Foundation of China(No.52207126)the Natural Science Foundation of Sichuan Province(No.2023NSFSC0296)the Joint Funds of the National Natural Science Foundation of China(No.U22B6006).
文摘DC series-parallel power flow controller(SP-PFC)is a highly efficient device to solve the problem of uncontrolled line current in the bipolar DC distribution system.However,its potential in fault current limiting is not fully explored.In this paper,a self-adaptive action strategy(SAAS)and a parameter optimization method of SP-PFC in bipolar DC distribution systems are proposed.Firstly,the common-and different-mode(CDM)equivalent circuits of the bipolar DC distribution system with SP-PFC in different fault stages are established,which avoids the line coupling inductance.Based on this,the influence of different parameters and line coupling inductance on the fault current limiting capability are investigated.It is found that the SP-PFC has the best fault current limiting capability when the capacitance and inductance of filter are inversely proportional.To realize the adaptability of fault current limiting capability under different fault severities,the SAAS of SP-PFC is proposed.The validity of the CDM equivalent circuits and parameter optimization method,and the effectiveness of the SAAS are verified by simulations and experiments.
基金supported in part by the National Natural Science Foundation of China(No.52207126)the Natural Science Foundation of Sichuan Province(No.2024NSFSC0869)the Joint Funds of the National Natural Science Foundation of China(No.U22B6006).
文摘Fault current limiting is a critical technology to en sure the safe operation of modular multilevel converter based multi-terminal direct current(MMC-MTDC)grids.This paper proposes a fault severity classification based coordination con trol strategy of fault current limiter(FCL)and MMC for adap tive fault current limiting.The proposed strategy reduces the in vestment in FCL,and keeps the bus voltages of non-faulty lines at reasonable values.Firstly,a rapid fault circuit parameter esti mation(FCPE)method using initial fault current information is proposed.With this method,the fault distance and fault transi tion resistance can be quickly estimated,which are used for a quantitative indication of the fault severity.Subsequently,the coordination control strategy of FCL and MMC is proposed,in which the FCL action is prioritized,while the control of MMC is complementary for current limiting.Based on the proposed strategy,fault severity phase planes(FSPPs)are constructed to assess fault severity and calculate the activation time of FCL and voltage regulation factor of MMC.Therefore,the FCL acti vation and MMC control are matched to the fault severity.The effectiveness and advantages of the proposed strategy are vali dated by the simulations in PSCAD/EMTDC.
文摘Bidirectional interlinking converter(BIC)is the core equipment in a hybrid AC/DC microgrid connected between AC and DC sub-grids.However,the variety of control modes and flexible bidirectional power flow complicate the influence of AC faults on BIC itself and on DC sub-grid,which potentially threaten both converter safety and system reliability.This study first investigates AC fault influence on the BIC and DC bus voltage under different BIC control modes and different pre-fault operation states,by developing a mathematical model and equivalent sequence network.Second,based on the analysis results,a general accommodative current limiting strategy is proposed for BIC without limitations to specific mode or operation condition.Current amplitude is predicted and constrained according to the critical requirements to protect the BIC and relieving the AC fault influence on the DC bus voltage.Compared with conventional methods,potential current limit failure and distortions under asymmetric faults can also be avoided.Finally,experiments verify feasibility of the proposed method.
基金supported in part by National Key R&D Program of China(No.2018YFB0904600)National Natural Science Foundation of China(No.51807053)。
文摘In order to overcome the problems of power flow control and fault current limiting in multi-terminal high voltage direct current(MTDC)grids,this paper proposes a modular multi-terminal DC power flow controller(MM-DCPFC)with fault current limiting function.The topology structure,operation principle,and equivalent circuit of MM-DCPFC are introduced,and such a structure has the advantages of modularity and scalability.The power balance mechanism is studied and a hierarchical power balance control strategy is proposed.The results show that MM-DCPFC can achieve internal power exchange,which avoids the use of external power supply.The fault characteristics of MM-DCPFC are analyzed,fault current limiting and self-protection methods are proposed,and the factors affecting the current limiting capability are studied.The simulation models are established in PLECS,and the simulation results verify the effectiveness of MM-DCPFC in power flow control,fault current limiting,and scalability.In addition,a prototype is developed to validate the function and control method of MM-DCPFC.
基金supported by National Natural Science Foundation of ChinaState Grid Joint Fund for Smart Grid(No.U2066210)National Natural Science Foundation of China(No.52007003)。
文摘In the voltage source converter based high-voltage direct current(VSC-HVDC)grids,fast and reliable protections are the key technologies.The traditional protection schemes are easily affected by fault resistance,line distributed capacitance,etc.Meanwhile,the influence of fault current limiting strategy(FCLS)has not been fully considered.In this paper,the fault characteristics under FCLS and the feasibility of traditional travelling wave protections are analyzed.To improve the reliability and sensibility,a similarity comparison based pilot protection scheme is proposed,which focuses on the relationship between the fault characteristics and the state of the protected transmission line,with the establishment of a precise frequencydependent transmission line model.The criteria based on the similarity comparison calculated by cross-wavelet can identify the fault effectively.Meanwhile,the protection scheme can also endure the influence of error synchronization.Finally,the protection performance is verified in the PSCAD/EMTDC under different fault conditions.
基金Supported by National Natural Science Foundation of China 51707014in part by Scientific Research Fund of Hunan Provincial Education Department 17C0040+1 种基金in part by Key Laboratory of Renewable Energy Electric-Technology of Hunan Province 2017ZNDL005in part by Open Research Project of the State Key Laboratory of Industrial Control Technology(Zhejiang University)(ICT170316).
文摘The series voltage source converter(SVSC)is widely used in the power electronic equipment,such as series active power filter,dynamic voltage restorer,unified power flow controller and so on.However,while the SVSC is more vulnerable to the impact of fault current,its applications are increasing,bringing huge challenges to the safe operation of the grid.In recent years,the topology and control strategy of the series voltage source converter with fault current limiting(SVSC-FCL)are a research hotspot.In this paper,it suggests classifying SVSC-FCL based SVSC into two groups:the control scheme optimization group and the existing topology improvement group.The research challenges and perspectives of the SVSC-FCL are introduced in detail.This paper aims to illustrate current research progress on SVSC-FCL and enrich the available pool of the multi-functional power electronic equipment.
基金This work was supported by National Key R&D Program of China(No.2017YFB0902400).
文摘The problem of reclosing current limiting in voltage source converter based high-voltage direct current(VSCHVDC)systems is becoming more and more serious.A soft reclosing scheme for DC permanent faults is presented in this paper.Because the converter voltages of stations at both terminals of the disconnected faulty line may be different,the choice of which terminal to reclose first will affect the reclosing overcurrent.A method for selecting the terminal to reclose first is investigated to achieve a minimum peak overcurrent during the reclosing process.In order to ensure that the hybrid DC circuit breaker(HDCCB)adapts to the needs of the reclosing process better,the traditional HDCCB is improved by adding a soft reclosing module(SRM).The energy dissipated in the arresters is significantly reduced when using the improved HDCCB.The improved HDCCB will be able to reclose multiple times safely and thus increase the possibility of successful reclosing.Moreover,the recovery time after the HDCCB is successfully reclosed is very short with the improved HDCCB and its control principles.Simulation results show that this proposed scheme is capable of limiting the reclosing overcurrent when the fault still exists.
文摘With the level of short-circuit current of power systems growing increasingly higher,optimal allocation of current limiters has received considerable attention in recent years,especially in China.This paper analyzes two kinds of common used current limiters based on the increment of bus impedance matrix and proposes a multi-objective current limiters configuration model considering the investment of limiters,the level of short-circuit current,as well as the transient stability of power system.An innovative search space reduction technique based on sensitivity factor is introduced to choose better candidate locations for current limiters so as to avoid the curse of dimensionality.The elitist non-dominated sorting genetic algorithm II is used to search the Pareto-optimal solutions of the proposed model.In order to further improve optimization efficiency,master-slave parallel modification of NSGA-II program structure is implemented.The satisfactory case study results demonstrate the feasibility of the proposed multi-objective method in power system current limiters allocation associated with cost,security and stability.
基金National Natural Science Foundation of China(29976040),Natural Science Foundation of AnhuiProvince(99045431),Foundation of Environments and Resources of USTC and Youth Foundation of USTC.
文摘The water dissociation mechanism on a bipolar membrane under the electrical field was investigated and characterized in terms of ionic transport and limiting current density. It is considered that the depletion layer exists at the junction of a bipolar membrane, which is coincided with the viewpoint of the most literatures, but we also consider that the thickness and conductivity of this layer is not only related with the increase of the applied voltage but also with the limiting current density. Below the limiting current density, the thickness of the depletion layer keeps a constant and the conductivity decreases with the increase of the applied voltage; while above the limiting current density, the depletion thickness will increase with the increase of the applied voltage and the conductivity keeps a very low constant. Based on the data reported in the literatures and independent determinations, the limiting current density was calculated and the experimental curves Ⅰ-Ⅴ in the two directions were com
基金supported by the National Natural Science Foundation of China(No.91545124,No.21972131,and No.21832004)。
文摘Rotating disk electrode systems are widely used to study the kinetics of electrocatalytic reactions that may suffer from insufficient mass transfer of the reactants.Kinetic current density at certain overpotential calculated by the Koutecky-Levich equation is commonly used as the metrics to evaluate the activity of electrocatalysts.However,it is frequently found that the diffusion limiting current density is not correctly identified in the literatures.Instead of kinetic current density,the measured current density normalized by diffusion limiting current density(j/jL)has also been frequently under circumstance where its validity is not justified.By taking oxygen reduction reaction/hydrogen oxidation reaction/hydrogen evolution reaction as examples,we demonstrate that identifying the actual diffusion limiting current density for the same reaction under otherwise identical conditions from the experimental data is essential to accurately deduce kinetic current density.Our analysis reveals that j/jLis a rough activity metric which can only be used to qualitatively compare the activity trend under conditions that the mass transfer conditions and the roughness factor of the electrode are exactly the same.In addition,if one wants to use j/jLto compare the intrinsic activity,the concentration overpotential should be eliminated.
基金Project supported by the National Natural Science Foundation of China （Grant No 10476004）.
文摘The self-consistent differential equations, which describe a laminar-flow equilibrium state in a magnetically focused intense relativistic electron beam propagating inside a conducting waveguide, are presented. The canonical angular momentum, Pe, defined under the conditions at the source, uniquely determines the possible solutions of these equations. By numerically solving these equations, the space-charge limited current and the externally applied magnetic field are obtained in a solid beam and a hollow beam in two cases of Pθ= 0 （magnetically shielded source） and Pθ= const. （immersed source） separately. It is shown that the hollow beam is more beneficial to the propagation of the intense relativistic beam through a drift tube than the solid beam.
文摘The current-voltage（I-V） characteristics of cBN crystal sandwiched between two metallic electrodes are measured and found to be nonlinear. Over 20 samples are measured at room temperature with various electrodes, and the resulting curves are all similar in shape. When a voltage of about 560V is applied to the cBN crystal, the emitted light is visible to the naked eye in a dark room. We explain these phenomena by the space charge limited current and the electronic transition between the X and Г valleys of the conduction band.
基金supported by the Technology Project of State Grid(No.SGSNKYOOKJJS1501564)the National Key Basic Research Program of China(973 Program)(No.2015CB251005)
文摘The GaInSn liquid metal current limiter based on the fluid pinch effect has broad application prospects due to its particular properties. However, the limited rated current and abil- ity of power dissipation are the critical problems for its wide application. Firstly, the temperature distribution of the liquid metal current limiter （LMCL） was obtained by experiments with a rated current of 1 kA and the arc ignition phenomenon was observed with 1.5 kA, which indicates that the rated current is mainly limited by the arc rather than the high temperature compared to the traditional switchgears. Furthermore, an improved method is proposed by adding the paralleled pure resistance, impedance or another LMCL element to protect the setup from the fault energy concentration in the setup. The problem of a slower arc voltage increasing rate can be solved by adding a paralleled impedance with suitable parameters. Finally, the current limiting properties based on the improved method were investigated and the alternating oscillating current was found between two paralleled LMCL elements owing to their deviation of arc ignition in reality.
基金financially supported by the project part of the state assignment of the Ministry of Education and Science of Russia in scientific activities,project 3.1262.2014K
文摘A high-voltage transverse pulsed nanosecond discharge with a slotted hollow cathode was found to be a source of high-energy （few kV） ribbon electron beams. Conditions for the formation and extinction of electron beams were experimentally studied in discharges in helium at pressures of 1-100 Torr. It was found that interaction of fast electrons with a non-uniform electric field near the slotted cathode led to limitation of the magnitude of the discharge current. A physical model was developed to describe the discharge current self-limitation that was in satisfactory agreement with the experimental results. Some technical solutions that are expected to increase the upper current limits in transverse nanosecond discharge are discussed.
文摘This paper presents a new type of fault current limiter (FCL) based on fast closing switch, which is composed of a capacitor bank and a reactor in series. The main control component is a fast closing switch connected in parallel with the capacitors, which is driven by the electromagnetic repulsion force. It can response the order within 1 ms. When fault occurs, the switch closes and the capacitors are bypassed, and the fault current is limited by the reactor. Simulation analysis and experiment show that the electromagnetic repulsion force actuator can meet the demand of fast closing switch, it is feasible to develop the FCL with low cost and high reliability.
基金supported by National Natural Science Foundation of China(Nos.51777025,52177131)the Interdisciplinary Program of the Wuhan National High Magnetic Field Center(No.WHMFC202130)Huazhong University of Science and Technology。
文摘The liquid metal current limiter(LMCL)is regarded as a viable solution for reducing the fault current in a power grid.But demonstrating the liquid metal arc plasma self-pinching process of the resistive wall,and reducing the erosion of the LMCL are challenging,not only theoretically,but also practically.In this work,a novel LMCL is designed with a resistive wall that can be connected to the current-limiting circuit inside the cavity.Specifically,a novel fault current limiter(FCL)topology is put forward where the novel LMCL is combined with a fast switch and current-limiting reactor.Further,the liquid metal self-pinch effect is modeled mathematically in three dimensions,and the gas-liquid two-phase dynamic diagrams under different short-circuit currents are obtained by simulation.The simulation results indicate that with the increase of current,the time for the liquid metal-free surface to begin depressing is reduced,and the position of the depression also changes.Different kinds of bubbles formed by the depressions gradually extend,squeeze,and break.With the increase of current,the liquid metal takes less time to break,but breaks still occur at the edge of the channel,forming arc plasma.Finally,relevant experiments are conducted for the novel FCL topology.The arcing process and current transfer process are analyzed in particular.Comparisons of the peak arc voltage,arcing time,current limiting efficiency,and electrode erosion are presented.The results demonstrate that the arc voltage of the novel FCL topology is reduced by more than 4.5times and the arcing time is reduced by more than 12%.The erosions of the liquid metal and electrodes are reduced.Moreover,the current limiting efficiency of the novel FCL topology is improved by 1%–5%.This work lays a foundation for the topology and optimal design of the LMCL.
