Joint optimization of offshore DC and onshore AC electrical systems for large-scale offshore wind power clusters integration

• A comprehensive optimization methodology for integrating OWFC via DC transmission. • The joint optimization problem is decoupled. • The impacts are investigated rigorously from three aspects. • operation, stability, and economy. • A tri-level optimization strategy. With the scaling and deep-sea development of offshore wind power, offshore wind farm clusters (OWFC) integrate to multiple Point of Common Coupling (PCCs) in the onshore grid through DC transmission. The planning of OWFC integration is impacted by numerous factors arising from the offshore and onshore electrical systems interlinkage. This paper investigates the pivotal elements implicated in onshore and offshore systems interlinkage and elucidates the convoluted challenges inherent to the integration systems planning. A decoupled hierarchical optimization model is formulated to optimize the collection system in each wind farm, the transmission system between wind farms, and the onshore and offshore grid interconnection simultaneously. An engineering case that focuses on the OWFC of Jiangsu Province, China integrating to a modified IEEE 118 node system is discussed to illustrate the effectiveness of the proposed methodology. The case study shows that the proposed methodology not only minimizes the investment costs of offshore electrical systems but also decreases the expansion and operational costs of onshore grids. Furthermore, it augments the flexible regulation capacity for the grid-connection of OWFC, facilitating the efficient consumption of large-scale offshore wind power.