Equivalent Active Distribution Networks Considering Grid Forming Converters

Converters connected to distribution networks play an increasingly important role in the generation mix. Especially grid forming converters providing inertia to the system are vital to handle critical events in a converter dominated system. Thus, converters need to be properly represented in grid models used for stability analysis. As opposed to detailed modeling, equivalent distribution network models allow comprehensive system stability studies without extensive knowledge of the distribution network and with acceptable computational efforts. Since converters are mostly connected to distribution networks, their dynamic response needs to be represented in the equivalent model of the corresponding active distribution network. Previous work elaborated that gray-box methods show satisfactory results when conventional grid following converters are considered. However, with the introduction of grid forming control, previous approaches fail to adequately capture the dynamic behavior. In this paper, a novel method based on voltage sensitivity clustering is proposed. It is applied on a distribution network containing grid forming converters, which then is used as part of a test system comprising a transmission and distribution network. Dynamic simulations performed with this system demonstrate that the novel approach is capable of reproducing the detailed network's dynamic behavior without neglecting the influence of grid forming converters.