Faults Analysis And Protection Strategy For MMC-HVDC System

Modular multilevel converter HVDC (MMC-HVDC) system hasgoodprospectsfor developmentdue to itstechnical advantages.Faults analysis andprotection strategyare importantto the reliable operation of MMC-HVDC. Atpresent, the research on faults and protection for MMC-HVDC is stillrelatively uncommon at home and abroad. So, this paper focuses on theresearch of faults and protection of MMC-HVDC.The main contents of thispaperare:Firstly, the basic theories of MMC-HVDC, includingtopology, operatingcharacteristics, modulation, capacitor voltage balancing control strategy,sub-module capacitor pre-charging technology,are analyzed,which providesome part of theoretical supportfor the faults analysis and protectionstrategyof MMC-HVDC.Secondly, the sub module fault,the line to ground fault, line break faultand line to line fault have been analyzed through theoretical and simulation.The operating characteristics of system with faults are presented.Thirdly, according to the fault performance,the detection methods arepresented. The protection strategiesareproposed based on the fault effects.At last,because of the uncontrollable of DC fault current, an improved MMCtopology using Clamp Double SubModule(CDSM)isintroduced. The principle ofDC short fault clearing isanalyzed and proved by simulation.