Research on the VSC-HVDC System Using Modular Multilevel Converters Under Fault Condition

This paper researches the control method of the VSC -HVDC system based on modular multilevel converter(MMC) when the unbalanced fault of AC voltage occurred.Based on the mathematic model of the MMC system,considering the existence of zero-sequence path in the faulty system,the decoupled positive-negative-zero sequence controller is proposed.To maintain the transmission of the most active power,while ensure the faulty current meet the conditions of safely operation of the system,the active power control strategy under fault condition is proposed.By simulation software PSCAD/EMTDC,the effectiveness of the proposed controller and control strategy are testified.