Fast protection strategy for DC transmission lines of MMC-based MT-HVDC grid

Multi-terminal high voltage DC (MT-HVDC) grid has broad application prospects in connecting different energy sources, asynchronous interconnection of power grids, remote load power supply, and other fields. At present, the key technologies that affect the development of MT-HVDC transmission system include swift fault identification and location in the DC line and its rapid isolation. Traditional fault monitoring relies on line communication, which cannot guarantee the rapidity and reliability of protection; moreover, it may even cause device damage. A fault identification scheme based on a single-terminal transient is presented in this paper. This scheme calculates the line inductance by using the rise rate of fault current at the initial stage of the fault, and determines the occurrence of the fault by comparing the observed line inductance with the set value, which lays a foundation for calculating the location of the fault point using distance protection. A simulation model on the PSCAD/EMTDC platform is built; the simulation example verifies that the proposed scheme can identify faults under dissimilar conditions while maintaining a low error level on the premise of no communication lines so as to meet the protection requirements of the MT-HVDC grid.