Abstract:

Offshore wind power represents a significant renewable energy source, with large-scale grid integration being a key development trend. This paper addresses the challenges of collecting distributed offshore wind energy and transmitting it to onshore grids, while mitigating the impacts of short-circuit faults in offshore transmission systems. A novel four-port flexible DC converter topology is proposed, featuring two input ports and two output ports. This topology interconnects multiple offshore wind farms via DC cables and delivers power to separate onshore grids. To enhance system reliability, a fault ride-through (FRT) control strategy is introduced to manage DC-side short-circuit faults. The topology employs modular multilevel converters (MMCs) at each port to regulate DC voltage, with a master-slave control scheme to stabilize AC bus voltage and power transmission. During DC-side faults, dynamic switching between master and slave converters ensures system stability while reducing fault currents. Furthermore, a communication-free strategy maintains power balance by curtailing offshore wind farm output. Simulation results on the PLECS platform validate the effectiveness of the proposed topology and control strategies.

Key words: renewable energy stations, flexible DC Converters, control design, short-circuit faults, fault ride-through