The series line-commutated converter(LCC)and modular multilevel converter(MMC)hybrid high-voltage direct current(HVDC)system provides a more economical and flexible alternative for ultra-HVDC(UHVDC)transmission,which ...The series line-commutated converter(LCC)and modular multilevel converter(MMC)hybrid high-voltage direct current(HVDC)system provides a more economical and flexible alternative for ultra-HVDC(UHVDC)transmission,which is the so-called Baihetan-Jiangsu HVDC(BJ-HVDC)project of China.In one LCC and two MMCs(1+2)operation mode,the sub-module(SM)capacitors suffer the most rigorous overvoltage induced by three-phase-to-ground fault at grid-side MMC and valve-side single-phase-to-ground fault in internal MMC.In order to suppress such huge overvoltage,this paper demonstrates a novel alternative by employing the MMC-based embedded battery energy storage system(MMC-BESS).Firstly,the inducements of SM overvoltage are analyzed.Then,coordinated with MMC-BESS,new fault ride-through(FRT)strategies are proposed to suppress the overvoltage and improve the FRT capability.Finally,several simulation scenarios are carried out on PSCAD/EMTDC.The overvoltage suppression is verified against auxiliary device used in the BJ-HVDC project in a monopolar BJ-HVDC system.Further,the proposed FRT strategies are validated in the southern Jiangsu power grid of China based on the planning data in the summer of 2025.Simulation results show that the MMC-BESS and proposed FRT strategies could effectively suppress the overvoltage and improve the FRT capability.展开更多
Symmetrical monopolar configuration is the prevailing scheme configuration for modular multilevel converter based high-voltage direct current(MMC-HVDC) links, in which severe DC overvoltage or overcurrent can be cause...Symmetrical monopolar configuration is the prevailing scheme configuration for modular multilevel converter based high-voltage direct current(MMC-HVDC) links, in which severe DC overvoltage or overcurrent can be caused by the DC faults. To deal with the possible asymmetry in the DC faults and the coupling effects of the DC lines, this paper analyzes the DC fault characteristics based on the phase-mode transformation. First, the DC grid is decomposed into the common-mode and the differential-mode networks. The equivalent models of the MMCs and DC lines in the two networks are derived, respectively. Then, based on the state matrices, a unified numerical calculation method for the fault voltages and currents at the DC side is proposed. Compared with the time-domain simulations performed on PSCAD/EMTDC, the accuracy of the proposed method is validated. Last, the system parameter analysis shows that the grounding parameters play an important role in reducing the severity of the pole-to-ground faults, whereas the coupling effects of the DC lines should be considered when calculating the DC fault currents associated with the pole-to-pole faults.展开更多
Current field calculation based on the resistance network method (RNM) and temperature field calculation based on the finite volume method (FVM) can be used to evaluate the performance of high-voltage direct-current(H...Current field calculation based on the resistance network method (RNM) and temperature field calculation based on the finite volume method (FVM) can be used to evaluate the performance of high-voltage direct-current(HVDC) grounding electrodes.The main idea of the two methods is to transform an electric and temperature field problems to equivalent circuit problems by dividing the 3D soil space near the grounding electrode into a suitable number of contiguous and non-overlapped cells.Each cell is represented as a central node connecting to the adjacent cells.The resistance network formed by connecting all the adjacent cells together can be solved to calculate the current field.Under the same conditions,the results calculated by the RNM are consistent with the result by CDEGS,a widely used software package for current distribution and electromagnetic field calculation.Based on the finite volume method,the temperature field results are also calculated using time domain simulation.展开更多
DC circuit breaker(DCCB)is one of the most promising solutions for handling DC fault in half-bridge modular multilevel converter(MMC)-based DC grid.Generally after fault isolation,DCCBs are required to have the abilit...DC circuit breaker(DCCB)is one of the most promising solutions for handling DC fault in half-bridge modular multilevel converter(MMC)-based DC grid.Generally after fault isolation,DCCBs are required to have the ability to quickly reclose so as to restore power transmission.However,the traditional simultaneous reclosing scheme may make the whole system suffer from secondary strikes such as overvoltage and overcurrent in the event of permanent faults.To solve this problem,many adaptive reclosing schemes have been proposed.Among them,the sequential reclosing scheme can achieve rapid recovery without laying any burden on the sampling and protection system.Unfortunately,secondary strikes under a reclosing failure still exist though they can be suppressed.Due to this,this paper illustrates that the overcurrent protection-based fault identification method is not able to identify the fault in time,and thus the secondary strikes are generated during the second tripping.Optimal configuration of DCCBs'parameters can reduce these adverse impacts but cannot avoid them.Based on this,an adaptive reclosing scheme is proposed.Permanent and temporary faults are recognised according to the voltage characteristics at the beginning of the fault line as soon as the arresters are conducted.Extensive simulations on a four-terminal DC grid in PSCAD/EMTDC show that the proposed method can eliminate the potential adverse impacts and is robust to fault resistance.展开更多
Hybrid circuit breakers(CBs)are the most promising technology to isolate DC faults in modular multilevel converter(MMC)‐based DC grids.However,they consist of expen-sive power electronic components that are sensitive...Hybrid circuit breakers(CBs)are the most promising technology to isolate DC faults in modular multilevel converter(MMC)‐based DC grids.However,they consist of expen-sive power electronic components that are sensitive to high overvoltage and overcurrent.This study proposes a hybrid high‐voltage DC circuit breaker with an energy absorption branch of a parallel arrester structure,and investigates the possibility of reducing the fault current and the switching overvoltage.First,the basic principle of an energy absorption branch with a parallel arrester structure is presented.Then,the simultaneous and sequential insertion strategies are illustrated.Second,each strategy and each structure are combined separately to analyse their respective characteristics in reducing the over-voltage,the fault current,the energy absorption and the fault clearance time.The sequential insertion strategy of the proposed energy absorption branch is proved to have the best performance.Finally,the trade‐offs between these four metrics are achieved through the non‐dominated sorting genetic algorithm II(NSGA‐II).A general method to determine the parameters of the proposed energy absorption branch from the Pareto front based on different preferences is provided.Simulations on PSCAD show that sequential insertion of the proposed energy absorption branch with the optimal pa-rameters is able to suppress the switching overvoltage and limit the fault current to a relatively low extent simultaneously.展开更多
文摘The series line-commutated converter(LCC)and modular multilevel converter(MMC)hybrid high-voltage direct current(HVDC)system provides a more economical and flexible alternative for ultra-HVDC(UHVDC)transmission,which is the so-called Baihetan-Jiangsu HVDC(BJ-HVDC)project of China.In one LCC and two MMCs(1+2)operation mode,the sub-module(SM)capacitors suffer the most rigorous overvoltage induced by three-phase-to-ground fault at grid-side MMC and valve-side single-phase-to-ground fault in internal MMC.In order to suppress such huge overvoltage,this paper demonstrates a novel alternative by employing the MMC-based embedded battery energy storage system(MMC-BESS).Firstly,the inducements of SM overvoltage are analyzed.Then,coordinated with MMC-BESS,new fault ride-through(FRT)strategies are proposed to suppress the overvoltage and improve the FRT capability.Finally,several simulation scenarios are carried out on PSCAD/EMTDC.The overvoltage suppression is verified against auxiliary device used in the BJ-HVDC project in a monopolar BJ-HVDC system.Further,the proposed FRT strategies are validated in the southern Jiangsu power grid of China based on the planning data in the summer of 2025.Simulation results show that the MMC-BESS and proposed FRT strategies could effectively suppress the overvoltage and improve the FRT capability.
文摘Symmetrical monopolar configuration is the prevailing scheme configuration for modular multilevel converter based high-voltage direct current(MMC-HVDC) links, in which severe DC overvoltage or overcurrent can be caused by the DC faults. To deal with the possible asymmetry in the DC faults and the coupling effects of the DC lines, this paper analyzes the DC fault characteristics based on the phase-mode transformation. First, the DC grid is decomposed into the common-mode and the differential-mode networks. The equivalent models of the MMCs and DC lines in the two networks are derived, respectively. Then, based on the state matrices, a unified numerical calculation method for the fault voltages and currents at the DC side is proposed. Compared with the time-domain simulations performed on PSCAD/EMTDC, the accuracy of the proposed method is validated. Last, the system parameter analysis shows that the grounding parameters play an important role in reducing the severity of the pole-to-ground faults, whereas the coupling effects of the DC lines should be considered when calculating the DC fault currents associated with the pole-to-pole faults.
文摘Current field calculation based on the resistance network method (RNM) and temperature field calculation based on the finite volume method (FVM) can be used to evaluate the performance of high-voltage direct-current(HVDC) grounding electrodes.The main idea of the two methods is to transform an electric and temperature field problems to equivalent circuit problems by dividing the 3D soil space near the grounding electrode into a suitable number of contiguous and non-overlapped cells.Each cell is represented as a central node connecting to the adjacent cells.The resistance network formed by connecting all the adjacent cells together can be solved to calculate the current field.Under the same conditions,the results calculated by the RNM are consistent with the result by CDEGS,a widely used software package for current distribution and electromagnetic field calculation.Based on the finite volume method,the temperature field results are also calculated using time domain simulation.
文摘DC circuit breaker(DCCB)is one of the most promising solutions for handling DC fault in half-bridge modular multilevel converter(MMC)-based DC grid.Generally after fault isolation,DCCBs are required to have the ability to quickly reclose so as to restore power transmission.However,the traditional simultaneous reclosing scheme may make the whole system suffer from secondary strikes such as overvoltage and overcurrent in the event of permanent faults.To solve this problem,many adaptive reclosing schemes have been proposed.Among them,the sequential reclosing scheme can achieve rapid recovery without laying any burden on the sampling and protection system.Unfortunately,secondary strikes under a reclosing failure still exist though they can be suppressed.Due to this,this paper illustrates that the overcurrent protection-based fault identification method is not able to identify the fault in time,and thus the secondary strikes are generated during the second tripping.Optimal configuration of DCCBs'parameters can reduce these adverse impacts but cannot avoid them.Based on this,an adaptive reclosing scheme is proposed.Permanent and temporary faults are recognised according to the voltage characteristics at the beginning of the fault line as soon as the arresters are conducted.Extensive simulations on a four-terminal DC grid in PSCAD/EMTDC show that the proposed method can eliminate the potential adverse impacts and is robust to fault resistance.
基金supported by‘The Fundamental Research Funds for the Central Universities’(2021QNA4014).
文摘Hybrid circuit breakers(CBs)are the most promising technology to isolate DC faults in modular multilevel converter(MMC)‐based DC grids.However,they consist of expen-sive power electronic components that are sensitive to high overvoltage and overcurrent.This study proposes a hybrid high‐voltage DC circuit breaker with an energy absorption branch of a parallel arrester structure,and investigates the possibility of reducing the fault current and the switching overvoltage.First,the basic principle of an energy absorption branch with a parallel arrester structure is presented.Then,the simultaneous and sequential insertion strategies are illustrated.Second,each strategy and each structure are combined separately to analyse their respective characteristics in reducing the over-voltage,the fault current,the energy absorption and the fault clearance time.The sequential insertion strategy of the proposed energy absorption branch is proved to have the best performance.Finally,the trade‐offs between these four metrics are achieved through the non‐dominated sorting genetic algorithm II(NSGA‐II).A general method to determine the parameters of the proposed energy absorption branch from the Pareto front based on different preferences is provided.Simulations on PSCAD show that sequential insertion of the proposed energy absorption branch with the optimal pa-rameters is able to suppress the switching overvoltage and limit the fault current to a relatively low extent simultaneously.
