Modeling approaches for considering active distribution grids in power system stability studies

This paper analyzes two different modeling approaches for the dynamic representation of active distribution grids regarding their applicability in power system stability studies. The first one is derived from a coherency-based aggregation method. It represents the distributed generation (DG) by equivalent generators in combination with a static load. The second modeling approach uses a linearized model for representing distribution grids and is named state-space model highlighting its inheriting nature. This approach is expanded by a new strategy considering explicit state limitations. It is shown that this limitation strategy significantly increases the accuracy of the state-space model. Both models are benchmarked against a detailed distribution grid model, and model accuracies are evaluated. The state-space model shows a higher accuracy for voltage dips smaller than 50 %, since all characteristic modes are preserved, and state limitations are represented in detail. For voltage dips above 50 %, the aggregated model may be applied to achieve higher accuracy.