Grounding Fault in Series-Connection-Based Offshore Wind Farms: Fault Clearance

In series-connection-based offshore wind farms (SC-OWFs), the huge platforms, transformers, and converters, which are used to convert the high-voltage alternating current to high-voltage direct current, can be eliminated. Therefore, the overall cost and losses can be reduced considerably. However, grounding fault is inevitable in SC-OWFs, and no one has studied this problem. In this research, the characteristic of grounding fault in SC-OWFs is examined. When grounding fault occurs in SC-OWFs, the dc current of the wind converters between the grounding and fault points increases rapidly, unlike in the traditional parallel ac and dc system. Topologies of the wind energy conversion systems and SC-OWF are proposed to cut off the fault current and isolate the faulty part from SC-OWF. On this basis, grounding fault detection, wind converter protection, and fault clearance strategies are developed. Simulation and experimental results show that the proposed topologies and methods for grounding fault in SC-OWF are feasible).