Common Grounding Electrode Schemes for Multi-terminal MMC-based HVDC

In a multi-terminal MMC-HVDC(MMC-MTDC)system,if some converters are grounded,the voltages of the other converters can be specified through the DC power lines.In order to reduce the number of grounding electrodes and to lower the requirements of MMC-MTDCs in planning,design,operation and cost,we studied a common grounding strategy of the system through scanning the most severe overvoltage in some specified grounding schemes.Moreover,we established a 5-terminal MMC-HVDC system in PSCAD/EMTDC,and studied 4types of grounding schemes.The simulation results show that the overvoltage in converter stations is influenced by the common grounding electrode scheme,and the maximum overvoltage is closely related to station control strategies.When the maximum overvoltage and the number of grounding electrodes are taken into consideration,installing grounding electrodes in the master converter stations is the best common grounding scheme.