An Enhanced Series-Connected Offshore Wind Farm (SC-OWF) System Considering Fault Resiliency

The series-connected offshore wind farm (SC-OWF) is a promising offshore wind generation solution to mitigate the need of centralized offshore high-voltage/power converter stations. Predominantly, researchers have focused on the steady-state operation and control of SC-OWFs, without considering the system-level characteristics and ability to ride-through dc side and ac network faults. This paper proposes an enhanced system for SC-OWF applications with fault-resilient capability, where comprehensive circuit configuration and protection strategies are articulated to minimize the negative effects caused by various types of dc and ac faults. For the offshore wind farm architecture, a grouping scheme is adopted where a substation based on disconnectors and diodes is proposed to realize prompt fault bypass/isolation and protection functions in the event of offshore system faults. Additionally, an onshore fault-tolerant modular multilevel converter (MMC) with modified dc-system-oriented control is employed to enable smooth and secure operation under steady-state and fault conditions. The proposed SC-OWF system is quantitatively substantiated by time-domain simulations where four ac/dc fault cases are considered, and the results consolidate the feasibility of the proposed configuration and control, indicating fault resilience of the SC-OWF system. Additionally, size, weight and cost estimations of the proposed offshore substation are presented and compared to a conventional MMC offshore station, to further highlight the merits of the proposed solution.