Uninterruptable Hierarchical Distributed Coordinated Control Scheme of Islanded AC/DC Microgrid Clusters Under Grid-Forming Converter Faults

Grid-forming converter faults in islanded hybrid AC/DC microgrid clusters could lead to voltage and frequency instability risk in the subgrid, thus threatening system operating safety. To solve this issue, this paper has proposed an uninterruptable hierarchical distributed coordinated control scheme of islanded hybrid AC/DC microgrid clusters. Firstly, when grid-forming converter faults occur in a certain AC microgrid (ACMG), the interlinking converter connected with the faulty subgrid switches its control mode into grid-forming, providing stable voltage and frequency support for the faulty ACMG. Then, a two-layer coordinated control scheme is presented, where the first layer is designed for the remaining interlinking converters, and the second layer is designed for converters in normal subgrids and grid-following converters in abnormal ACMG together with its interlinking converter. By the control mode switch of the IC and the two-layer coordinated control scheme, accurate power sharing can quickly fill the power deficit in the faulty subgrid, and the voltage and frequency of the microgrid clusters can remain stable. Verification results indicate that with the proposed scheme, the islanded AC/DC microgrid clusters can operate uninterruptedly under different kinds of grid-forming converter faults.