Analysis of MMC Grounding Fault on hybrid UHVDC systems

A multi-terminnal UHVDC project is under construction by China Southern Power Grid, which consists of one LCC-based sending end and two MMC-based receiving ends, rated at ±800kV. The receiving ends of each pole consist of two 400kV valve groups in series. In this paper, fault mechanisms and fault characteristics of MMC terminal grounding fault are studied. Analysis results show that single-phase grounding fault on high-end valve leads to severe overvoltage on sub-module. To solve this problem, protection schemes are discussed. The simulation results demonstrate the relevant analysis is precise.