DC Short Circuit Ride-through Strategy for a Full-Bridge MMC HVDC Transmission System

Modular multi-level converters (MMC) are considered a promising topology for HV applications like HVDC transmission systems. Such systems must be designed to provide high reliability against different types of faults. MMCs using Half-Bridge (HF) cells are well known for lacking the capability to block short circuits in the DC link. On the contrary, Full-Bridge (FB) cells can block the short circuit current in the DC link, they also enable the implementation of Fault Ride-through (FRT) functionalities, as the cells can generate bipolar voltages in this case. This paper presents a DC short circuit fault ride-through strategy for HVDC transmission system using an MMC topology with FB cells (FBMMC). Two modes of operation are possible during the fault. In the first one, the MMC can support the AC grid with reactive power, but will not transfer active power. In the second mode, the MMC can transfer active power during the fault.