Enhancing Fault Ride-Through and Voltage Support Capability for MMC-HVDC Integrated Offshore Wind Farms Based on Multi-Mode Matching

To cope with onshore AC faults in modular multilevel converter based high voltage direct current integrated offshore wind farms (OWF-MMC-HVDC), this paper proposes a multi-mode matching control (MMMC) approach. Mode I is active energy control. It is activated at high fault levels, when the reactive power output capability of the MMC is weak. Mode I uses the MMC sub-module energy to maximise the absorption of offshore surplus power to mitigate DC overvoltage problems. Mode II is dynamic reactive current optimization (DRO) control. It is activated at medium fault levels. It dynamically optimises the MMC active and reactive current command values within the permitted current margins. This simultaneously enables voltage support to the onshore grid and maximises offshore active power output, reducing offshore surplus power. Mode III is energy coordinated synchronous (ECS) control. It is activated under more mild faults. It allows simultaneous adjustment of the energy absorption rate of the wind farm-side MMC (WFMMC) and the grid-side MMC (GSMMC). This allows the energy margin of the MMCs to be utilised more fully to improve support to the onshore grid while maintaining fault ride-through capability. Finally the correctness and validity of the proposed method was verified by the PSCAD/EMTDC.