A review of system topologies, key operation and control technologies for offshore wind power transmission based on HVDC

Offshore wind farm (OWF) is considered as a perfect zero-carbon energy source for the future power system. However, the growing offshore distance and water depth of OWF make the OWF HVDC transmission technique a more promising solution than HVAC due to higher cost-efficiency and reliability. In this paper, the current situation of OWF-HVDC projects is introduced at first. Then, novel converter topologies with the higher power density and cost-efficiency are presented, including the hybrid modular multilevel converter (MMC), alternative arm converter (AAC), and diode rectifier (DR). Next, several OWF HVDC transmission system topologies are introduced, including terminal-hybrid, station-hybrid and all-DC delivered system. Furthermore, the key technologies for OWF HVDC operation and control are summarized, including grid-forming control strategy for offshore wind turbines, stability analysis method, corresponding stability enhancement measures and frequency support control strategies. Additionally, the fault ride-through and protection strategies for different fault locations have been presented. Finally, the main conclusions and prospects for OWF HVDC are summarized.