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
In this paper,a comprehensive evaluation on the silicon/silicon carbide(Si/SiC)hybrid switch is performed through experimental tests in terms of both electrical performance and robustness under extreme stresses.Based ...In this paper,a comprehensive evaluation on the silicon/silicon carbide(Si/SiC)hybrid switch is performed through experimental tests in terms of both electrical performance and robustness under extreme stresses.Based on the optional turn-on and turn-off delay times under the efficiency control mode obtained from the double-pulse test(DPT),both nondestructive and destructive single-pulse avalanche tests are conducted on the Si/SiC hybrid switch as well as on the two discrete device branches inside the hybrid switch.In addition,the avalanche voltage,critical avalanche energy,and peak avalanche current,which intrinsically characterize the unclamped-inductive-switching(UIS)avalanche characteristics,are carefully examined.In this way,the physical factors dominating the UIS characteristics of the hybrid switch,thus limiting its single-pulse avalanche withstand capability,are specifically and comprehensively identified;the underlying physical mechanisms are analyzed and revealed in depth,and how the gate control sequence affects the UIS characteristics of the hybrid switch is extensively investigated.We additionally carry out short-circuit(SC)tests under the fault-under-load(FUL)condition and perform a parallel in-depth analysis to experimentally determine which branch dominates the SC withstand capability of the hybrid switch.Our experimental study indicates that,for both SC robustness and single-pulse avalanche capability,the limiting factor is a single device branch among the two parallel discrete devices,and the UIS behavior is sensitive to the variation of the gate turn-off delay time Toff_delay.The study conducted in this paper not only provides deep academic insights into the electrical performance and reliability of the Si/SiC hybrid switch,but also offers fundamental theoretical principles and technical evidence to support its more efficient and long-term reliable applications of the hybrid switch in the industrial fields.展开更多
In this article, an inter-turn short-circuit(ITSC) fault diagnosis and severity estimation method based on extended state observer(ESO) and convolutional neural network(CNN) is proposed for five-phase permanent magnet...In this article, an inter-turn short-circuit(ITSC) fault diagnosis and severity estimation method based on extended state observer(ESO) and convolutional neural network(CNN) is proposed for five-phase permanent magnet synchronous motor(PMSM) drives. The relationship between fault parameters and motor parameters is analyzed and the equivalent model of ITSC faults in the natural reference frame is accordingly derived. To achieve fault detection and location, the short-circuit turn ratio and short-circuit current are integrated as the fault diagnosis index. According to the model of the shortcircuit current, an ESO is designed for the estimation of the fault diagnosis index. Further, the sensitivity analysis among fault parameters is conducted to evaluate the short-circuit turn ratio and the short-circuit resistance. Subsequently, the postfault current, back electromotive force, electrical angular velocity, q1-axis current reference and the fault diagnosis index are selected as the input signals of CNN to estimate the short-circuit turn ratio. This approach not only resolves parameter coupling challenges but also provides a quantitative assessment of fault severity. Finally, simulations and experiments under different operating points validate the effectiveness of the proposed method.展开更多
Based on the phase space reconstruction of welding current in short-circuiting transfer arc welding under carbon dioxide, the approximate entropy of welding current and its standard deviation have been calculated and ...Based on the phase space reconstruction of welding current in short-circuiting transfer arc welding under carbon dioxide, the approximate entropy of welding current and its standard deviation have been calculated and analyzed at different welding speeds and different electrode extensions respectively. The experimental and calculated results show that at a certain arc voltage, wire feeding rate and gas flow rate, welding speed and electrode extension have significant effects not only on the approximate entropy of welding current, but also on the stability of welding process. Further analysis proves that when the welding speed and electrode extension are in an appropriate range respectively, the welding current approximate entropy attains maximum and its standard deviation minimum. Just under such circumstances, the welding process is in the most stable state.展开更多
In this paper a short-circuit computation(SCC) procedure for large-scale distribution systems with high penetration of distributed generators based on contemporary technologies is proposed. The procedure is suitable f...In this paper a short-circuit computation(SCC) procedure for large-scale distribution systems with high penetration of distributed generators based on contemporary technologies is proposed. The procedure is suitable for real-time calculations.Modeling of modern distributed generators differs from the modeling of traditional synchronous and induction generators.Hence, SCC procedures found on the presumption of distribution systems with only traditional generators are not suitable in nowadays systems. In the work presented in this paper, for computation of the state of the system with short-circuit, the improved backward/forward sweep(IBFS) procedure is used.Computation results show that the IBFS procedure is much more robust than previous SCC procedures, as it takes into account all distribution system elements, including modern distributed generators.展开更多
A novel 1200 V SiC super-junction(SJ)MOSFET with a partially widened pillar structure is proposed and investi-gated by using the two-dimensional numerical simulation tool.Based on the SiC SJ MOSFET structure,a partial...A novel 1200 V SiC super-junction(SJ)MOSFET with a partially widened pillar structure is proposed and investi-gated by using the two-dimensional numerical simulation tool.Based on the SiC SJ MOSFET structure,a partially widened P-region is added at the SJ pillar region to improve the short-circuit(SC)ability.After investigating the position and doping concentration of the widened P-region,an optimal structure is determined.From the simulation results,the SC withstand times(SCWTs)of the conventional trench MOSFET(CT-MOSFET),the SJ MOSFET,and the proposed structure at 800 V DC bus voltage are 15μs,17μs,and 24μs,respectively.The SCWTs of the proposed structure are increased by 60%and 41.2%in comparison with that of the other two structures.The main reason for the proposed structure with an enhanced SC capability is related to the effective suppression of saturation current at the high DC bias conditions by using a modu-lated P-pillar region.Meanwhile,a good Baliga's FOM(BV^(2)/R_(on))also can be achieved in the proposed structure due to the advantage of the SJ structure.In addition,the fabrication technology of the proposed structure is compatible with the standard epitaxy growth method used in the SJ MOSFET.As a result,the SJ structure with this feasible optimization skill presents an effect on improving the SC reliability of the SiC SJ MOSFET without the degeneration of the Baliga's FOM.展开更多
In gas metal arc welding(GMAW)process,the short-circuit transition was the most typical transition observed in molten metal droplets.This paper used orthogonal tests to explore the coupling effect law of welding proce...In gas metal arc welding(GMAW)process,the short-circuit transition was the most typical transition observed in molten metal droplets.This paper used orthogonal tests to explore the coupling effect law of welding process parameters on the quality of weld forming under short-circuit transition,the design of 3 factors and 3 levels of a total of 9 groups of orthogonal tests,welding current,welding voltage,welding speed as input parameters:effective area ratio,humps,actual linear power density,aspect ratio,Vickers hardness as output paramet-ers(response targets).Using range analysis and trend charts,we can visually depict the relationship between input parameters and a single output parameter,ultimately determining the optimal process parameters that impact the single output index.Then combined with gray the-ory to transform the three response targets into a single gray relational grade(GRG)for analysis,the optimal combination of the weld mor-phology parameters as follows:welding current 100 A,welding voltage 25 V,welding speed 30 cm/min.Finally,validation experiments were conducted,and the results showed that the error between the gray relational grade and the predicted value was 2.74%.It was observed that the effective area ratio of the response target significantly improved,validating the reliability of the orthogonal gray relational method.展开更多
Base on the arc phase and short-circuit phase and their relationship, the paper considers the changes of the extension of wire, the arc length, liquid bridge resistance and mass of liquid bridge, combines the improved...Base on the arc phase and short-circuit phase and their relationship, the paper considers the changes of the extension of wire, the arc length, liquid bridge resistance and mass of liquid bridge, combines the improved “mass-spring” model with the loop model of welding power system, puts forward the critical judgment condition of droplet transition, and establishes a more accurate dynamic model for describing the short-circuit transition process. The dynamic changes of short-circuit transfer frequency, welding current and voltage, contact droplet and residual droplet equivalent radius and droplet equivalent radius at different wire feeding speeds were calculated and analyzed, and compared with the experimental results. It shows that the fluctuation of droplet displacement, velocity and wire extension length at the optimal arc starting point is the smallest. The smaller the initial liquid bridge curvature radius is, the better the stability of short-circuit transfer is.展开更多
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.
基金supported in part by the Anhui Provincial Natural Science Foundation Youth Project(Category C)under Grant No.2508085QE184the Opening Project of Key Laboratory of Power Electronics and Motion Control of Anhui Higher Education Institutions under Grant No.PEMC24004+1 种基金the Anhui University of Technology Young Teachers Research Fund under Grant No.QZ202412the Scientific Research Startup Fund for Introduced Talents of Anhui University of Technology under Grant No.QD202340.
文摘In this paper,a comprehensive evaluation on the silicon/silicon carbide(Si/SiC)hybrid switch is performed through experimental tests in terms of both electrical performance and robustness under extreme stresses.Based on the optional turn-on and turn-off delay times under the efficiency control mode obtained from the double-pulse test(DPT),both nondestructive and destructive single-pulse avalanche tests are conducted on the Si/SiC hybrid switch as well as on the two discrete device branches inside the hybrid switch.In addition,the avalanche voltage,critical avalanche energy,and peak avalanche current,which intrinsically characterize the unclamped-inductive-switching(UIS)avalanche characteristics,are carefully examined.In this way,the physical factors dominating the UIS characteristics of the hybrid switch,thus limiting its single-pulse avalanche withstand capability,are specifically and comprehensively identified;the underlying physical mechanisms are analyzed and revealed in depth,and how the gate control sequence affects the UIS characteristics of the hybrid switch is extensively investigated.We additionally carry out short-circuit(SC)tests under the fault-under-load(FUL)condition and perform a parallel in-depth analysis to experimentally determine which branch dominates the SC withstand capability of the hybrid switch.Our experimental study indicates that,for both SC robustness and single-pulse avalanche capability,the limiting factor is a single device branch among the two parallel discrete devices,and the UIS behavior is sensitive to the variation of the gate turn-off delay time Toff_delay.The study conducted in this paper not only provides deep academic insights into the electrical performance and reliability of the Si/SiC hybrid switch,but also offers fundamental theoretical principles and technical evidence to support its more efficient and long-term reliable applications of the hybrid switch in the industrial fields.
基金supported in part by the National Natural Science Foundation of China under Grant 52307056in part by the Natural Science Foundation of Jiangsu Province under Grant BK20210475。
文摘In this article, an inter-turn short-circuit(ITSC) fault diagnosis and severity estimation method based on extended state observer(ESO) and convolutional neural network(CNN) is proposed for five-phase permanent magnet synchronous motor(PMSM) drives. The relationship between fault parameters and motor parameters is analyzed and the equivalent model of ITSC faults in the natural reference frame is accordingly derived. To achieve fault detection and location, the short-circuit turn ratio and short-circuit current are integrated as the fault diagnosis index. According to the model of the shortcircuit current, an ESO is designed for the estimation of the fault diagnosis index. Further, the sensitivity analysis among fault parameters is conducted to evaluate the short-circuit turn ratio and the short-circuit resistance. Subsequently, the postfault current, back electromotive force, electrical angular velocity, q1-axis current reference and the fault diagnosis index are selected as the input signals of CNN to estimate the short-circuit turn ratio. This approach not only resolves parameter coupling challenges but also provides a quantitative assessment of fault severity. Finally, simulations and experiments under different operating points validate the effectiveness of the proposed method.
基金Supported by Project of the National Natural Science Foundation of China(50375053,50575077)
文摘Based on the phase space reconstruction of welding current in short-circuiting transfer arc welding under carbon dioxide, the approximate entropy of welding current and its standard deviation have been calculated and analyzed at different welding speeds and different electrode extensions respectively. The experimental and calculated results show that at a certain arc voltage, wire feeding rate and gas flow rate, welding speed and electrode extension have significant effects not only on the approximate entropy of welding current, but also on the stability of welding process. Further analysis proves that when the welding speed and electrode extension are in an appropriate range respectively, the welding current approximate entropy attains maximum and its standard deviation minimum. Just under such circumstances, the welding process is in the most stable state.
文摘In this paper a short-circuit computation(SCC) procedure for large-scale distribution systems with high penetration of distributed generators based on contemporary technologies is proposed. The procedure is suitable for real-time calculations.Modeling of modern distributed generators differs from the modeling of traditional synchronous and induction generators.Hence, SCC procedures found on the presumption of distribution systems with only traditional generators are not suitable in nowadays systems. In the work presented in this paper, for computation of the state of the system with short-circuit, the improved backward/forward sweep(IBFS) procedure is used.Computation results show that the IBFS procedure is much more robust than previous SCC procedures, as it takes into account all distribution system elements, including modern distributed generators.
基金Project supported by the Key Research and Development Program of Guangdong Province,China(Grant No.2019B090917010).
文摘A novel 1200 V SiC super-junction(SJ)MOSFET with a partially widened pillar structure is proposed and investi-gated by using the two-dimensional numerical simulation tool.Based on the SiC SJ MOSFET structure,a partially widened P-region is added at the SJ pillar region to improve the short-circuit(SC)ability.After investigating the position and doping concentration of the widened P-region,an optimal structure is determined.From the simulation results,the SC withstand times(SCWTs)of the conventional trench MOSFET(CT-MOSFET),the SJ MOSFET,and the proposed structure at 800 V DC bus voltage are 15μs,17μs,and 24μs,respectively.The SCWTs of the proposed structure are increased by 60%and 41.2%in comparison with that of the other two structures.The main reason for the proposed structure with an enhanced SC capability is related to the effective suppression of saturation current at the high DC bias conditions by using a modu-lated P-pillar region.Meanwhile,a good Baliga's FOM(BV^(2)/R_(on))also can be achieved in the proposed structure due to the advantage of the SJ structure.In addition,the fabrication technology of the proposed structure is compatible with the standard epitaxy growth method used in the SJ MOSFET.As a result,the SJ structure with this feasible optimization skill presents an effect on improving the SC reliability of the SiC SJ MOSFET without the degeneration of the Baliga's FOM.
基金supported by Major Special Projects of Science and Technology in Fujian Province,(Grant No.2020HZ03018)Natural Science Foundation of Fujian Province(Grant No.2020J01873).
文摘In gas metal arc welding(GMAW)process,the short-circuit transition was the most typical transition observed in molten metal droplets.This paper used orthogonal tests to explore the coupling effect law of welding process parameters on the quality of weld forming under short-circuit transition,the design of 3 factors and 3 levels of a total of 9 groups of orthogonal tests,welding current,welding voltage,welding speed as input parameters:effective area ratio,humps,actual linear power density,aspect ratio,Vickers hardness as output paramet-ers(response targets).Using range analysis and trend charts,we can visually depict the relationship between input parameters and a single output parameter,ultimately determining the optimal process parameters that impact the single output index.Then combined with gray the-ory to transform the three response targets into a single gray relational grade(GRG)for analysis,the optimal combination of the weld mor-phology parameters as follows:welding current 100 A,welding voltage 25 V,welding speed 30 cm/min.Finally,validation experiments were conducted,and the results showed that the error between the gray relational grade and the predicted value was 2.74%.It was observed that the effective area ratio of the response target significantly improved,validating the reliability of the orthogonal gray relational method.
基金the Natural Science Foundation Project of Guizhou Province([2019]1069)Guizhou Province Cultivation Project([2017]5788-42)+1 种基金Guizhou Province Science and Technology Support Plan General Project([2022]051)Guizhou University Talent Introduction Plan((2017)28).
文摘Base on the arc phase and short-circuit phase and their relationship, the paper considers the changes of the extension of wire, the arc length, liquid bridge resistance and mass of liquid bridge, combines the improved “mass-spring” model with the loop model of welding power system, puts forward the critical judgment condition of droplet transition, and establishes a more accurate dynamic model for describing the short-circuit transition process. The dynamic changes of short-circuit transfer frequency, welding current and voltage, contact droplet and residual droplet equivalent radius and droplet equivalent radius at different wire feeding speeds were calculated and analyzed, and compared with the experimental results. It shows that the fluctuation of droplet displacement, velocity and wire extension length at the optimal arc starting point is the smallest. The smaller the initial liquid bridge curvature radius is, the better the stability of short-circuit transfer is.
