Mechanism Analysis of Fault Interaction Effects Between the Positive and Negative Poles in Bipolar MMC-HVDC Systems

Modular multilevel converter (MMC) based high-voltage direct current (HVDC) is an effective solution for achieving large-scale coordination, complementarity, and reliable transmission of renewable energy, and is an important application direction for future high-voltage and large-capacity DC transmission. However, at the DC side of the bipolar VSC-HVDC system, if the pole-to-ground fault occurs in one pole, it will not only lead to the rapid rise of fault current that may damage the power electronic devices, but also affect the operation of the other pole. Therefore, it is of great importance to investigate the characteristics of the pole-to-ground fault at DC side and the mechanism of fault interaction effects between two poles. In this paper, the operation principle of the MMC and the bipolar VSCHVDC system are introduced firstly. Then, the characteristics of the pole-to-ground fault are analysed and the interaction effects is studied. Finally, the fault characteristics and mechanism of interaction effects are verified by electromagnetic transient (EMT) simulations.