In the coming years, an extensive development of offshore wind energy will present a clear trend of clustering offshore wind farms (OWFs). Offshore grid is a novel concept proposed to address the problem of connecting OWFs and integrating large offshore wind energy into the regional onshore power system economically and reliably. Compared with traditional electrical systems in large OWFs, the connection of offshore grid demonstrates some new features. This paper presents a tri-level optimization strategy to optimize offshore grid planning while considering onshore network expansions simultaneously. The proposed strategy turns the optimization of these two complicated electrical networks into three nested optimization models: the ‘Point of common coupling (PCC) optimizer’, ‘Offshore substation (OS) optimizer’, and ‘Offshore grid optimizer’. An engineering case from the East China Sea is discussed to illustrate the effectiveness of the proposed methodology. The results show that offshore grid demonstrates better overall economic efficiency and less marine corridor consumption. In addition, the proposed methodology can make the integration of large OWFs more friendly to onshore networks.

未来几年，海上风能的广泛发展将呈现出明显的海上风电场集群化趋势。海上电网是一个新颖的概念，旨在解决连接 OWF 并将大型海上风能经济可靠地整合到区域陆上电力系统中的问题。与大型 OWF 中的传统电气系统相比，海上电网的连接展示了一些新的特点。本文提出了一种三级优化策略，可在同时考虑陆上网络扩展的同时优化海上电网规划。所提出的策略将这两个复杂电网的优化转换为三个嵌套优化模型：“公共耦合点 (PCC) 优化器”、“海上变电站 (OS) 优化器”和“海上电网优化器”。讨论了东海的一个工程案例，以说明所提出方法的有效性。结果表明，海上电网表现出更好的整体经济效益和更少的海上走廊消耗。此外，所提出的方法可以使大型 OWF 的集成对陆上网络更加友好。