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Title
Japanese: 
English:An overvoltage-less protection method for pole-to-ground faults in symmetrical monopole HVDC systems by half-bridge MMC 
Author
Japanese: 佐野 憲一朗, 中山 比呂.  
English: Kenichiro Sano, Hiro Nakayama.  
Language English 
Journal/Book name
Japanese: 
English:IEEE Energy Conversion Congress and Exposition (ECCE 2020) 
Volume, Number, Page        
Published date Oct. 2020 
Publisher
Japanese: 
English: 
Conference name
Japanese: 
English:IEEE Energy Conversion Congress and Exposition (ECCE 2020) 
Conference site
Japanese: 
English: 
Official URL https://ieeexplore.ieee.org/document/9236061
 
DOI https://doi.org/10.1109/ECCE44975.2020.9236061
Abstract The recent voltage-source converter based HVDC (VSC-HVDC) transmission systems apply a symmetrical monopole configuration with a modular multilevel converter (MMC) consisting of half-bridge submodules. Pole-to-ground faults in the symmetrical monopole system cause the voltage increase in the non-faulted pole. The overvoltage significantly increases the required insulation level of the transmission lines and converters. This paper proposes an overvoltage-less protection method for the pole-to-ground faults in the symmetrical monopole HVDC systems based on the half-bridge MMC. The proposed method combines the following two approaches. The MMC operating as a rectifier utilizes a short-mode protection instead of the conventional blocking protection. The MMC operating as an inverter is equipped with blocking diodes in its dc terminal. As a result, both the rectifier and the inverter immediately decrease the dc fault current, and avoid the overvoltage in the non-faulted pole. The simulation results verify that the proposed method can suppress the overvoltage of the non-faulted pole to 110% of the nominal voltage, whereas the conventional method reaches 210%.

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