Fault Ride-through Operation Using an MMC based 12-Pulse DAB in Platform-less DC Collection System for Offshore Wind Farms

The implementation of a series-connected high voltage DC (HVDC) collection system operating in voltage source mode holds potential for significantly reducing the installation costs associated with offshore wind farms (OWFs). The proposed configuration, as outlined in this study, involves an interfacing arrangement connecting the wind turbine-generator unit to the HVDC link. This interfacing arrangement comprises of three key components: a twelve-pulse converter, a high-frequency transformer, and a modular multi-level converter (MMC). The formation of the HVDC link is achieved through the series connected DC terminals of the MMCs, thereby eliminating the requirement of an expensive platform to place a low-frequency, bulky, voltage stepping-up transformer. The 12-pulse converters along with high frequency transformer, not only reduce the size and VA rating of the transformer but also provide galvanic isolation feature. Additionally, the inclusion of MMCs provides the system with the ability to withstand and continue operating during a short circuit fault in the HVDC line, ensuring fault ride-through capability.