As the structures of multiple branch lines(MBLs)will be widely applied in the future flexible DC distribution network,there is a urgent need for improving system reliability by tackling the frequent non-permanent pole...As the structures of multiple branch lines(MBLs)will be widely applied in the future flexible DC distribution network,there is a urgent need for improving system reliability by tackling the frequent non-permanent pole-to-pole(P-P)fault on distribution lines.A novel fault restoration strategy based on local information is proposed to solve this issue.The strategy firstly splits a double-ended power supply network into two single-ended power supply networks through the timing difference characteristics of a hybrid direct current circuit breaker(HDCCB)entering the recloser.Then,a method based on the characteristic of the transient energy of fault current is proposed to screen the faulty branch line in each single-ended power supply network.Also,a four-terminal flexible DC distribution network with MBLs is constructed on PSCAD to demonstrate the efficacy of the proposed strategy.Various factors such as noise,fault location,and DC arc equivalent resistance are considered in the simulation model for testing.Test results prove that the proposed strategy for fault restoration is effective,and features high performance and scalability.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
基金supported by the National Natural Science Foundation of China(No.51877174)。
文摘As the structures of multiple branch lines(MBLs)will be widely applied in the future flexible DC distribution network,there is a urgent need for improving system reliability by tackling the frequent non-permanent pole-to-pole(P-P)fault on distribution lines.A novel fault restoration strategy based on local information is proposed to solve this issue.The strategy firstly splits a double-ended power supply network into two single-ended power supply networks through the timing difference characteristics of a hybrid direct current circuit breaker(HDCCB)entering the recloser.Then,a method based on the characteristic of the transient energy of fault current is proposed to screen the faulty branch line in each single-ended power supply network.Also,a four-terminal flexible DC distribution network with MBLs is constructed on PSCAD to demonstrate the efficacy of the proposed strategy.Various factors such as noise,fault location,and DC arc equivalent resistance are considered in the simulation model for testing.Test results prove that the proposed strategy for fault restoration is effective,and features high performance and scalability.
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.
