Dynamic Reactive Current Optimization Based Onshore AC Fault Ride-Through Strategy for MMC-HVDC Integrated Offshore Wind Farms

Onshore AC faults may cause the modular multilevel converter based high voltage direct current integrated offshore wind farms (MMC-HVDC-OWF) to develop surplus power and trigger overvoltage problems. This article proposes a dynamic reactive current optimization (DRO) strategy that combines MMC energy control capability with transient overload capability to achieve onshore AC fault ride-through (ACFRT). Firstly, the decoupling control mechanism and constraints of the active and reactive currents of the onshore gird-side MMC (GSMMC) are analyzed. Furthermore, a dynamic reactive current optimization based ACFRT strategy is proposed based on the current constraints and the energy control capability of MMCs. The main parameters of DRO are set according to the fault characteristic analysis results. Once a fault occurs, the proposed DRO based ACFRT strategy can control the offshore surplus power by controlling the MMC internal sub-module energy. The DRO strategy quickly optimizes the active and reactive power output commands of the GSMMC by collecting and comparing the local power signals. It enables to increase the onshore AC grid voltage and the transient active power output of the MMC-HVDC-OWF. Finally, The effectiveness of the proposed control strategy is verified through comprehensive case studies conducted on the PSCAD/EMTDC.