Abstract The hybrid modular multilevel converter (HMMC) consisting of half- and full-bridge submodules (SMs), with DC fault ride-through capability, have become a promising candidate for offshore wind energy conversion system, especially all-DC output wind turbines. The topology of HMMC needs to be optimized for lower cost and higher reliability with active redundancy. This paper presents an optimization method for HMMC topology with cost and reliability objectives. The reliability is defined to be not only reliable under normal operation, but also able to ride through DC fault even with faulted SMs, which is different from the former model. Firstly, reliability and cost models with power loss, considering active redundancy configuration, are derived. Then, cost and reliability, with different numbers of original and redundant SMs, are quantified by taking a case study of 10-MW and 10-kV HMMC for offshore DC wind turbines. Finally, a multi-objective optimization approach that regards maximum reliability and minimum cost is proposed, and the optimal solution from Pareto-optimal set is selected according to fuzzy membership function, which determines the optimal topology for HMMC. The results show that reliability can be improve with redundant full-bridge SMs (FBSMs) but weakened with excessive half-bridge SMs (HBSMs). Furthermore, the incremental cost with a redundant FBSM is approximately 3 times that of HBSM. The optimal topology, 10 original SMs per arm (5 HBSMs and 5 FBSMs) with 1 redundant HBSM and 4 FBSMs, is validated by comparing with the results of former reliability model and single-objective optimization.

中文翻译：

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带混合子模块的海上直流风机模块化多电平换流器的成本和可靠性优化

摘要 由半桥和全桥子模块（SM）组成的混合模块化多电平转换器（HMMC）具有直流故障穿越能力，已成为海上风能转换系统特别是全直流输出风力涡轮机的有前途的候选者。HMMC 的拓扑结构需要通过主动冗余进行优化，以实现更低的成本和更高的可靠性。本文提出了一种具有成本和可靠性目标的 HMMC 拓扑优化方法。可靠性定义为不仅在正常运行情况下可靠，而且即使SM故障也能穿越直流故障，这与前一种模型不同。首先，推导出考虑有源冗余配置的带功率损耗的可靠性和成本模型。然后，成本和可靠性，具有不同数量的原始和冗余 SM，通过对海上直流风力涡轮机的 10 MW 和 10 kV HMMC 进行案例研究来量化。最后，提出了一种考虑最大可靠性和最小成本的多目标优化方法，根据模糊隶属度函数从帕累托最优集合中选择最优解，确定HMMC的最优拓扑结构。结果表明，冗余全桥 SM (FBSM) 可以提高可靠性，但过多的半桥 SM (HBSM) 会削弱可靠性。此外，冗余 FBSM 的增量成本约为 HBSM 的 3 倍。最优拓扑，每臂 10 个原始 SM（5 个 HBSM 和 5 个 FBSM），1 个冗余 HBSM 和 4 个 FBSM，通过与以前的可靠性模型和单目标优化的结果进行比较来验证。