Journal
IEEE ACCESS
Volume 9, Issue -, Pages 165219-165226Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/ACCESS.2021.3134248
Keywords
Voltage control; Circuit faults; Rectifiers; HVDC transmission; Inverters; Fault currents; Wind power generation; Fault protection; modular multilevel converter (MMC); HVDC transmission; symmetrical monopole; overvoltage; blocking diode
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Funding
- Japan Society for the Promotion of Science (JSPS) under KAKENHI Grant [18K04097, 21K04018]
- Grants-in-Aid for Scientific Research [18K04097, 21K04018] Funding Source: KAKEN
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This study proposes a novel protection method for symmetrical monopole HVDC systems, which introduces lower arm short protection and upper arm short protection modes as well as inserts blocking diodes to the DC terminal of the inverter to suppress overvoltage, achieving successful power transmission in the non-faulted pole during and after a DC fault.
It is known that the pole-to-ground fault in the symmetrical monopole HVDC transmission system causes overvoltage in the non-faulted pole. The overvoltage increases the required insulation level of the converters and transmission lines. To suppress the overvoltage, this paper proposes a protection method for symmetrical monopole HVDC systems. The proposed method introduces novel protection modes lower arm short protection and upper arm short protection to the modular multilevel converter (MMC) being composed of half-bridge (HB) submodules. In addition, blocking diodes are inserted to the DC terminal of the inverter. As a result, the method enables to clear the DC fault currents and to avoid the voltage increase in the non-faulted pole. Experimental results obtained by a 5.5-kW HB-MMC HVDC system demonstrate that the proposed protection method enables to suppress the voltage increase to 106 % of the rated voltage, while the conventional protection method caused overvoltage of 200 %. The proposed method is also effective to the multi-terminal HVDC systems. Even if a fault occurs in one of the transmission sections, the fault does not cause the overvoltage in the other non-faulted section. Therefore, the non-faulted section can continue the power transmission both during and after the DC fault.
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