The comparison of domestic and foreign studies has been utilized to extensively employ junction termination extension(JTE)structures for power devices.However,achieving a gradual doping concentration change in the lat...The comparison of domestic and foreign studies has been utilized to extensively employ junction termination extension(JTE)structures for power devices.However,achieving a gradual doping concentration change in the lateral direction is difficult for SiC devices since the diffusion constants of the implanted aluminum ions in SiC are much less than silicon.Many previously reported studies adopted many new structures to solve this problem.Additionally,the JTE structure is strongly sensitive to the ion implantation dose.Thus,GA-JTE,double-zone etched JTE structures,and SM-JTE with modulation spacing were reported to overcome the above shortcomings of the JTE structure and effectively increase the breakdown voltage.They provided a theoretical basis for fabricating terminal structures of 4H-SiC PiN diodes.This paper summarized the effects of different terminal structures on the electrical properties of SiC devices at home and abroad.Presently,the continuous development and breakthrough of terminal technology have significantly improved the breakdown voltage and terminal efficiency of 4H-SiC PiN power diodes.展开更多
Silicon carbide(SiC)material features a wide bandgap and high critical breakdown field intensity.It also plays an important role in the high efficiency and miniaturization of power electronic equipment.It is an ideal ...Silicon carbide(SiC)material features a wide bandgap and high critical breakdown field intensity.It also plays an important role in the high efficiency and miniaturization of power electronic equipment.It is an ideal choice for new power electronic devices,especially in smart grids and high-speed trains.In the medium and high voltage fields,SiC devices with a blocking voltage of more than 6.5 kV will have a wide range of applications.In this paper,we study the influence of epitaxial material properties on the static characteristics of 6.5 kV SiC MOSFET.6.5 kV SiC MOSFETs with different channel lengths and JFET region widths are manufactured on three wafers and analyzed.The FN tunneling of gate oxide,HTGB and HTRB tests are performed and provide data support for the industrialization process for medium/high voltage SiC MOSFETs.展开更多
DC short-circuit faults pose a hazard to the operation of a modular multilevel converter(MMC)-based high voltage direct current(HVDC)system,necessitating reliable fault clearing solutions with rapid reaction.However,b...DC short-circuit faults pose a hazard to the operation of a modular multilevel converter(MMC)-based high voltage direct current(HVDC)system,necessitating reliable fault clearing solutions with rapid reaction.However,because the parasitic capacitances of the main equipment oscillate with the lumped inductances of the HVDC system,strong electromagnetic oscillations with multiple frequencies occur during clearance transients.These oscillations will disturb the HVDC system’s protection and control systems.Therefore,this paper focuses on the modeling of these oscillations.First,an equivalent circuit for the MMC-based HVDC system is proposed,taking into account the parasitic capacitances of the system’s major components,such as DC reactors,connecting cables,and DC circuit breakers(DCCBs).Second,four distinct oscillation stages are postulated based on action coordination of MMCs and DCCBs,and the associated analytical equations for the oscillation frequencies are derived.Third,a 200 kV MMC-based DC converter station is subjected to an 6ms/6kA pole-to-pole(PTP)short-circuit test.Electromagnetic oscillations have a frequency range of several kHz to several hundreds of kHz.The measured waveforms correspond well with simulated results,including the parasitic characteristics.Additionally,the relative errors between the simulated and measured frequencies are less than 5%.展开更多
Because of its controlled power factor and no commutation failure,current source converter(CSC)made up of reverse-blocking IGCTs(RB-IGCTs)offers broad application prospects in the field of HVDC system.Valve voltage an...Because of its controlled power factor and no commutation failure,current source converter(CSC)made up of reverse-blocking IGCTs(RB-IGCTs)offers broad application prospects in the field of HVDC system.Valve voltage and power operating range as the most important operating characteristics should be paid attention to but they are always contradictory.First,the relationship between valve voltage and modulation index is obtained.In particular,valve voltage of converter under the three typical modulation methods is compared,analyzed,and verified.Second,with the help of the independent control strategy and coordinated control strategy of both ends,power operating ranges of the three modulation methods are comprehensively analyzed and compared.Third,in order to solve power coupling at a low active power,the improved coordination control strategy at both ends in this paper is proposed and the relationships among active power,reactive power,DC current and phase angle difference are given in detail.Finally,a 500 kV/3 kA simulation system was built in PSCAD/EMTDC to obtain comparison results of the key operating characteristics of CSC under different modulation methods and the converter can realize unity power operation under random active power after adopting the improved coordinated control strategy,and DC current does not decrease to zero,verifying effectiveness of the coordinated control strategy.展开更多
This paper presents an isolated DC/AC/DC converter using a middle frequency transformer coupling two modular multilevel converters(MMC),suitable for interconnecting DC transmission lines of different voltage levels in...This paper presents an isolated DC/AC/DC converter using a middle frequency transformer coupling two modular multilevel converters(MMC),suitable for interconnecting DC transmission lines of different voltage levels in high voltage direct current(HVDC)system.The basic operational principle of the isolated module multilevel DC/DC converter(IMMDCC)is analyzed.The dynamic model of IMMDCC is studied in detail and the transient relationship between DC side and AC side of IMMDCC is revealed,which is physically straightforward for understanding the power transfer in IMMDCC.The control strategy in D-Q coordinate system is put forward,and the fault characteristic and corresponding protection method is analyzed.Finally,computer simulation using Matlab/Simulink is performed to verify the dynamic model and the proposed control strategy.The simulation results show good performances and the quick response ability of the proposed control strategy.展开更多
The direct‐current circuit breaker(DCCB)is the most ideal choice for DC fault isolation in DC grids.Despite a late start,China's research and development on the DCCB have made outstanding achievements.This articl...The direct‐current circuit breaker(DCCB)is the most ideal choice for DC fault isolation in DC grids.Despite a late start,China's research and development on the DCCB have made outstanding achievements.This article provides a brief glance of current China's DCCB development status.It begins by sorting out the technical route according to the topology of DCCB.Then it systematically summarises both mechanical and hybrid DCCBs with focussing on the aspects of topology structure and principle,key technology and characteristics,prototype development and application.It is apparent that Chinese scientists and engineers confronted the worldwide problem of large capacity DC breaking,and put forward a comprehensive solution which consists of an innovative topology structure based on coupled negative voltage circuit,breaking throughs on the key technologies such as highly controllable and reliable fault current commutation,millisecond‐level ultra‐fast and efficient electromagnetic repulsion mechanism,high tolerance and high stability power electronic switch,low residual voltage and fast response energy consumption device,etc.The article states that the world's first set of hybrid high‐voltage(HV)DCCB,and the first set of mechanical HV DCCB have been developed.These DCCBs will soon be deployed to the DC grids which have the highest voltage levels therefore require the strongest breaking capacity.These achievements are leading the world in the development and application of DCCB.The article also discusses the overall development trends of DCCB in the areas of new topologies,key techno-logical breakthroughs and application scenarios,etc.These discussions serve as references for DCCB's future technological advancement and its ever‐expanding applications.展开更多
High-frequency voltage oscillation occurs at the initial stage of DC short-circuit fault in the modular multilevel converter(MMC)-based high-voltage direct-current systems,which directly threatens the reliable operati...High-frequency voltage oscillation occurs at the initial stage of DC short-circuit fault in the modular multilevel converter(MMC)-based high-voltage direct-current systems,which directly threatens the reliable operation of the secondary equipment in DC circuit breakers(DCCBs).Therefore,this paper focusses on the voltage oscillation characteristic at DCCB terminals,considered the stray parameters of connecting lines,the parasitic parameters of main equipment and the impedance of grounding grid,established equivalent circuit models of MMC-HVDC converter station at the initial stage of pole-topole and pole-to-ground fault,and obtained the analytical formula for the voltage oscillation frequency.Then,the comparison with the DC short-circuit test data of�200 kV MMC-HVDC converter station verified the validity of the models and revealed the mechanism of voltage oscillation.Finally,the influence of the parameters of the converter station on the oscillation characteristics was discussed.It was proposed to install the DCCB at the MMC valve's terminal near the DC side,and the oscillation frequency is about 10–60 kHz,which is more than 5 times lower than that at the DC reactor's terminal near the DC pole bus,and the disturbance of oscillation to DCCB was alleviated.展开更多
The high current of hybrid DC circuit breaker(HCB)in the process of breaking generates strong transient magnetic field(MF),which may interfere with the normal operation of driver control units(DCUs).Therefore,the anal...The high current of hybrid DC circuit breaker(HCB)in the process of breaking generates strong transient magnetic field(MF),which may interfere with the normal operation of driver control units(DCUs).Therefore,the analysis for transient MF disturbance is of great significance.Due to the large space scale of HCB,with the large number of power electronic devices,the numerical calculation method has the disadvantages of large consumption of resources and slow calculation speed in solving the transient MF inside the HCB.In this study,the current generation mechanism of a 500 kV HCB is analysed,and the equivalent current path is obtained by considering the skin effect.Combined with the temporal and spatial distribution of transient current,the multi-process transient equivalent model of transient MF calculation is established,and the model has the advantages of high precision and high speed.Then,the breaking experiment of HCB is carried out,and the transient MF near the DCU is measured.The experiment results verify the validity of the model.Furthermore,the disturbance of transient MF at the DCU of the transfer branch during breaking 25 kA current is analysed.展开更多
The current interruption test based on an LC resonance circuit for hybrid DC circuit breakers(HVDC CBs)is widely employed to characterize the current interruption capability of CBs.In order to ensure a high-fidelity r...The current interruption test based on an LC resonance circuit for hybrid DC circuit breakers(HVDC CBs)is widely employed to characterize the current interruption capability of CBs.In order to ensure a high-fidelity replica of the fault current in a high voltage application,this paper first proposes an equivalent model of the test circuit,where not only parasitic resistances but also the threshold voltages and on-state resistances of various semiconductor devices are considered.Moreover,the analytical formula of the test current is derived by including the working principle of the HVDC CB.Secondly,the parameter extraction method,which combines finite element analysis and measurements by an impedance analyzer,is given in this paper.The extracted result implies that,in current interruption transients,equivalent resistances of 500 kV CB are as large as 535 mS,which have a significant influence on current waveforms.Thirdly,the 34 kV/25 kA current interruption test for the 500 kV CB is conducted.The measured results are proved to be consistent with the analytical results obtained from the proposed model,and the relative error is less than 2%.展开更多
To ensure their sound and continuous operation to the greatest extent,VSC-based DC girds have extremely stringent requirements for transmission line relay protection.In terms of guaranteeing their reliability,accurate...To ensure their sound and continuous operation to the greatest extent,VSC-based DC girds have extremely stringent requirements for transmission line relay protection.In terms of guaranteeing their reliability,accurate identification of lightning strikes on DC transmission lines is one of the urgent key problems to be solved.An effective ultra-high-speed identification scheme of lightning strikes suitable for the VSC-based DC grid is proposed in this paper.First,an 1-mode reverse voltage traveling wave(RVTW)is constructed applying the pole-mode transformation theory.Next,fault traveling wave propagation characteristics along the DC transmission line are analyzed in depth utilizing Peterson's law.Then,differences of time-frequency electromagnetic transient characteristics of 1-mode RVTWs between disturbances and faults caused by lightning strikes are distinguished in detail by means of the classical wavelet transformation multi-resolution analysis theory.Finally,extensive simulations are carried out to evaluate the performance of the proposed identification scheme,and by which its excellent rapidity,reliability and robustness are validated.Index Terms-Lightning-strike identification,Multi-resolution analysis,Relay protection,Traveling-wave protection,VsC-based DC grid,Wavelet transformation.展开更多
基金financially supported by the Scientific and Technology Project of State Grid Corporation of China,Research on Dry Etching Forming Technology of Silicon Carbide Device,Project No.5500-202158437A-0-0-00.
文摘The comparison of domestic and foreign studies has been utilized to extensively employ junction termination extension(JTE)structures for power devices.However,achieving a gradual doping concentration change in the lateral direction is difficult for SiC devices since the diffusion constants of the implanted aluminum ions in SiC are much less than silicon.Many previously reported studies adopted many new structures to solve this problem.Additionally,the JTE structure is strongly sensitive to the ion implantation dose.Thus,GA-JTE,double-zone etched JTE structures,and SM-JTE with modulation spacing were reported to overcome the above shortcomings of the JTE structure and effectively increase the breakdown voltage.They provided a theoretical basis for fabricating terminal structures of 4H-SiC PiN diodes.This paper summarized the effects of different terminal structures on the electrical properties of SiC devices at home and abroad.Presently,the continuous development and breakthrough of terminal technology have significantly improved the breakdown voltage and terminal efficiency of 4H-SiC PiN power diodes.
基金the support of the National Key Research and Development Program(Grant No.2016YFB0400500)the Science&Technology Program of the State Grid Corporation of China Co.,Ltd.“High voltage and high power SiC materials,devices and the application demonstration in power electronic transformers”.
文摘Silicon carbide(SiC)material features a wide bandgap and high critical breakdown field intensity.It also plays an important role in the high efficiency and miniaturization of power electronic equipment.It is an ideal choice for new power electronic devices,especially in smart grids and high-speed trains.In the medium and high voltage fields,SiC devices with a blocking voltage of more than 6.5 kV will have a wide range of applications.In this paper,we study the influence of epitaxial material properties on the static characteristics of 6.5 kV SiC MOSFET.6.5 kV SiC MOSFETs with different channel lengths and JFET region widths are manufactured on three wafers and analyzed.The FN tunneling of gate oxide,HTGB and HTRB tests are performed and provide data support for the industrialization process for medium/high voltage SiC MOSFETs.
基金supported by the National Key Research and Development Program of China(2021YFB2400602)。
文摘DC short-circuit faults pose a hazard to the operation of a modular multilevel converter(MMC)-based high voltage direct current(HVDC)system,necessitating reliable fault clearing solutions with rapid reaction.However,because the parasitic capacitances of the main equipment oscillate with the lumped inductances of the HVDC system,strong electromagnetic oscillations with multiple frequencies occur during clearance transients.These oscillations will disturb the HVDC system’s protection and control systems.Therefore,this paper focuses on the modeling of these oscillations.First,an equivalent circuit for the MMC-based HVDC system is proposed,taking into account the parasitic capacitances of the system’s major components,such as DC reactors,connecting cables,and DC circuit breakers(DCCBs).Second,four distinct oscillation stages are postulated based on action coordination of MMCs and DCCBs,and the associated analytical equations for the oscillation frequencies are derived.Third,a 200 kV MMC-based DC converter station is subjected to an 6ms/6kA pole-to-pole(PTP)short-circuit test.Electromagnetic oscillations have a frequency range of several kHz to several hundreds of kHz.The measured waveforms correspond well with simulated results,including the parasitic characteristics.Additionally,the relative errors between the simulated and measured frequencies are less than 5%.
基金supported in part by Science and Technology Project of State Grid Corporation of China.(5500202058059A0000).
文摘Because of its controlled power factor and no commutation failure,current source converter(CSC)made up of reverse-blocking IGCTs(RB-IGCTs)offers broad application prospects in the field of HVDC system.Valve voltage and power operating range as the most important operating characteristics should be paid attention to but they are always contradictory.First,the relationship between valve voltage and modulation index is obtained.In particular,valve voltage of converter under the three typical modulation methods is compared,analyzed,and verified.Second,with the help of the independent control strategy and coordinated control strategy of both ends,power operating ranges of the three modulation methods are comprehensively analyzed and compared.Third,in order to solve power coupling at a low active power,the improved coordination control strategy at both ends in this paper is proposed and the relationships among active power,reactive power,DC current and phase angle difference are given in detail.Finally,a 500 kV/3 kA simulation system was built in PSCAD/EMTDC to obtain comparison results of the key operating characteristics of CSC under different modulation methods and the converter can realize unity power operation under random active power after adopting the improved coordinated control strategy,and DC current does not decrease to zero,verifying effectiveness of the coordinated control strategy.
文摘This paper presents an isolated DC/AC/DC converter using a middle frequency transformer coupling two modular multilevel converters(MMC),suitable for interconnecting DC transmission lines of different voltage levels in high voltage direct current(HVDC)system.The basic operational principle of the isolated module multilevel DC/DC converter(IMMDCC)is analyzed.The dynamic model of IMMDCC is studied in detail and the transient relationship between DC side and AC side of IMMDCC is revealed,which is physically straightforward for understanding the power transfer in IMMDCC.The control strategy in D-Q coordinate system is put forward,and the fault characteristic and corresponding protection method is analyzed.Finally,computer simulation using Matlab/Simulink is performed to verify the dynamic model and the proposed control strategy.The simulation results show good performances and the quick response ability of the proposed control strategy.
基金Tsinghua UniversityHuazhong University of Science and Technology+2 种基金Xi'an Jiaotong UniversityGlobal Energy Interconnection Research Institute Co.,Ltd.NR Electric Co.,Ltd。
文摘The direct‐current circuit breaker(DCCB)is the most ideal choice for DC fault isolation in DC grids.Despite a late start,China's research and development on the DCCB have made outstanding achievements.This article provides a brief glance of current China's DCCB development status.It begins by sorting out the technical route according to the topology of DCCB.Then it systematically summarises both mechanical and hybrid DCCBs with focussing on the aspects of topology structure and principle,key technology and characteristics,prototype development and application.It is apparent that Chinese scientists and engineers confronted the worldwide problem of large capacity DC breaking,and put forward a comprehensive solution which consists of an innovative topology structure based on coupled negative voltage circuit,breaking throughs on the key technologies such as highly controllable and reliable fault current commutation,millisecond‐level ultra‐fast and efficient electromagnetic repulsion mechanism,high tolerance and high stability power electronic switch,low residual voltage and fast response energy consumption device,etc.The article states that the world's first set of hybrid high‐voltage(HV)DCCB,and the first set of mechanical HV DCCB have been developed.These DCCBs will soon be deployed to the DC grids which have the highest voltage levels therefore require the strongest breaking capacity.These achievements are leading the world in the development and application of DCCB.The article also discusses the overall development trends of DCCB in the areas of new topologies,key techno-logical breakthroughs and application scenarios,etc.These discussions serve as references for DCCB's future technological advancement and its ever‐expanding applications.
基金Science and Technology Project of State Grid Corporation of China,Grant/Award Number:520201190095。
文摘High-frequency voltage oscillation occurs at the initial stage of DC short-circuit fault in the modular multilevel converter(MMC)-based high-voltage direct-current systems,which directly threatens the reliable operation of the secondary equipment in DC circuit breakers(DCCBs).Therefore,this paper focusses on the voltage oscillation characteristic at DCCB terminals,considered the stray parameters of connecting lines,the parasitic parameters of main equipment and the impedance of grounding grid,established equivalent circuit models of MMC-HVDC converter station at the initial stage of pole-topole and pole-to-ground fault,and obtained the analytical formula for the voltage oscillation frequency.Then,the comparison with the DC short-circuit test data of�200 kV MMC-HVDC converter station verified the validity of the models and revealed the mechanism of voltage oscillation.Finally,the influence of the parameters of the converter station on the oscillation characteristics was discussed.It was proposed to install the DCCB at the MMC valve's terminal near the DC side,and the oscillation frequency is about 10–60 kHz,which is more than 5 times lower than that at the DC reactor's terminal near the DC pole bus,and the disturbance of oscillation to DCCB was alleviated.
基金State Grid Corporation of China,Grant/Award Number:520201190095。
文摘The high current of hybrid DC circuit breaker(HCB)in the process of breaking generates strong transient magnetic field(MF),which may interfere with the normal operation of driver control units(DCUs).Therefore,the analysis for transient MF disturbance is of great significance.Due to the large space scale of HCB,with the large number of power electronic devices,the numerical calculation method has the disadvantages of large consumption of resources and slow calculation speed in solving the transient MF inside the HCB.In this study,the current generation mechanism of a 500 kV HCB is analysed,and the equivalent current path is obtained by considering the skin effect.Combined with the temporal and spatial distribution of transient current,the multi-process transient equivalent model of transient MF calculation is established,and the model has the advantages of high precision and high speed.Then,the breaking experiment of HCB is carried out,and the transient MF near the DCU is measured.The experiment results verify the validity of the model.Furthermore,the disturbance of transient MF at the DCU of the transfer branch during breaking 25 kA current is analysed.
基金supported by Science and Technology Project of State Grid Corporation of China(No.520201190095).
文摘The current interruption test based on an LC resonance circuit for hybrid DC circuit breakers(HVDC CBs)is widely employed to characterize the current interruption capability of CBs.In order to ensure a high-fidelity replica of the fault current in a high voltage application,this paper first proposes an equivalent model of the test circuit,where not only parasitic resistances but also the threshold voltages and on-state resistances of various semiconductor devices are considered.Moreover,the analytical formula of the test current is derived by including the working principle of the HVDC CB.Secondly,the parameter extraction method,which combines finite element analysis and measurements by an impedance analyzer,is given in this paper.The extracted result implies that,in current interruption transients,equivalent resistances of 500 kV CB are as large as 535 mS,which have a significant influence on current waveforms.Thirdly,the 34 kV/25 kA current interruption test for the 500 kV CB is conducted.The measured results are proved to be consistent with the analytical results obtained from the proposed model,and the relative error is less than 2%.
基金supported by the National Natural Science Foundation of China(No.52277075)the State Key Laboratory of Advanced Power Transmission Technology(Grant No.GEIRI-SKL-2020-012).
文摘To ensure their sound and continuous operation to the greatest extent,VSC-based DC girds have extremely stringent requirements for transmission line relay protection.In terms of guaranteeing their reliability,accurate identification of lightning strikes on DC transmission lines is one of the urgent key problems to be solved.An effective ultra-high-speed identification scheme of lightning strikes suitable for the VSC-based DC grid is proposed in this paper.First,an 1-mode reverse voltage traveling wave(RVTW)is constructed applying the pole-mode transformation theory.Next,fault traveling wave propagation characteristics along the DC transmission line are analyzed in depth utilizing Peterson's law.Then,differences of time-frequency electromagnetic transient characteristics of 1-mode RVTWs between disturbances and faults caused by lightning strikes are distinguished in detail by means of the classical wavelet transformation multi-resolution analysis theory.Finally,extensive simulations are carried out to evaluate the performance of the proposed identification scheme,and by which its excellent rapidity,reliability and robustness are validated.Index Terms-Lightning-strike identification,Multi-resolution analysis,Relay protection,Traveling-wave protection,VsC-based DC grid,Wavelet transformation.