Collector System Topology Design for Offshore Wind Farm's Repowering and Expansion

After decades of operations, the first batches of offshore wind farms (OWF) are approaching the end of service lifetimes, while the demand for energy transformation is continuously pushing countries around the globe to construct larger OWFs. Therefore, the old OWF's repowering and scale-expansion becomes a possibly-feasible plan which deserves more researches. This paper firstly analyzes the potential benefits of combining the repowering and expansion parts in collector system topology design, which is followed by further analysis and mathematical verifications of economy and reliability advantages for applying cross-substation incorporation (CSI) to the collector system. To achieve the optimal topology design for OWF repowering and expansion, this paper also proposes a multi-layer optimization framework that consists of an offshore substation (OS) refinement layer, an OWF partition layer, and an intra-zone cable connection layer. The whole optimization concerns the wind turbine (WT) capacity deviation between the repowered part and the expanded part, and the final output is generated with the aim of achieving optimal economy and reliability. The proposed topology is tested and compared with traditional radial and ring topologies on a benchmark collector system, and the results verify the high performance in the economy (both short-term and long-term) and reliability.