Fast Pre-charge Strategy of a Modified MMC with Enhanced DC Fault Ride-through Capability

This paper proposes a modified topology of modular multilevel converter (MMC) to accelerate the DC fault ride-through speed. The modified topology mainly consists of a half bridge sub-module (HBSM) and a modified series double submodule (MSDSM). The difference between the series double submodule (SDSM) and the MSDSM is a damping resistance which is used to increase the capability of the energy dissipation when DC fault occurs. This improvement can disperse the energy to dissipate. Moreover, the selection of resistance is analyzed. In addition, an improved pre-charging strategy based on this modified topology is presented to shorten the start-up time of MMC. At the same time, the value of additional limiting resistance can be lowered because the damping resistances of the MSDSMs are more fully utilized. Simulation results demonstrate the validity of the proposed topology and pre-charging strategy.