Fault Analysis And Protection Strategies On MMC-HVDC

With the development of power electronics technology and grid technology,the advantages of VSC-HVDC technology are more and more obvious in lots ofaspects, For example：power supply to the island or passive load，new energy grid，non-synchronous interconnection of the AC system and environmental protection.Modular multi-level converter (MMC),of which the circuit topology is simple withmodular characteristics，can be applied to systems of various power and voltagelevels and controled by PWM modulation technique flexibly. The MMC used in HighVoltage Direct Current transmission (HVDC) system, has opened up new areas of researchof the VSC-HVDC transmission. MMC-HVDC is a brand new technology ofVSC-HVDC，the research on it carried out late and mainly concentrated in thecontrol strategy at home and abroad，but the analysis of it’s fault characteristics isless.So this paper focuses on the MMC-HVDC Fault Analysis and Protection StrategyStudy of MMC-HVDC system. The specific content of this paper is as follows：（1）Technical background and research status of the MMC-HVDC areintroduced and the value of the MMC-HVDC is cleared；（2）Based on the analysis of circuit topology and operating principle，themodulation mode、the start up method and capacitor voltage control strategy ofMMC-HVDC system is designed according to the unique characteristics of theMMC；（3）Sub-module overcurrent protection、Sub-module redundancy protection andcirculating current suppression strategies are designed according to the uniquecharacteristics of the MMC.And, Sub-module redundancy protection and Circulatingcurrent suppression strategies are simulated；（4）The quivalent models of MMC-HVDC system under the typical DC faults（Including single-pole grounded fault、pole-to-pole fault and DC bus break fault）are established and analyzed deeply. And the fault performances of MMC-HVDCsystem are simulated，too. On this basis，the protection strategies are given andsimulated for each fault from the perspective of ensuring the system security；（5）The quivalent models of MMC-HVDC system under the typical AC faults（Including three-phase unbalanced fault、 single-phase grounded fault and phase-to-phase fault）are established and analyzed deeply. And the fault performancesof MMC-HVDC system are simulated，too. On this basis，the protection strategiesare given and simulated for each fault from the perspective of ensuring the systemsecurity.