A Voltage Sensitivity Based Equivalent for Active Distribution Networks Containing Grid Forming Converters

The evolution of load-dominated to active distribution networks with significant dispersed generation calls for accurate models of these networks in the context of system stability analysis. Embedding detailed distribution network models in a dynamic transmission system model is impracticable due to model complexity. Complexity-reduced equivalent dynamic models solve this obstacle. However, equivalent models that consider grid forming converters emulating inertia have not been addressed in research yet. To fill this gap, this work proposes a novel gray-box method for aggregating active distribution networks containing grid forming converters. The approach utilizes voltage sensitivities to represent the grid's strength at the grid forming converter's connection point. We compare the proposed method with an existing gray-box approach capable of creating equivalent models for networks dominated by conventional grid following converters. Both aggregation approaches are applied on an active distribution network model. Simulation results for different events of the detailed and both equivalent models are compared. The equivalent model aggregated with the proposed approach reproduces the detailed network's dynamic behavior adequately, while the existing approach fails to meet validation criteria. Hence, the proposed method provides an equivalent model that is capable of substituting detailed distribution network models in stability studies of renewable power systems.