Modeling Adequacy of Droop-Controlled Grid-Forming Converters for Transient Studies: Singular Perturbation Analysis

The converter-interfaced generation (CIGs) are expected to dominate the grid of the future. These CIGs will cohabit with a small percentage of synchronous generators (SGs) producing power from hydro, solar thermal or even nuclear resources. It appears that the literature lacks comprehensive modeling adequacy studies on such grids with SGs and CIGs. This paper takes the first step in that direction. To that end, a nonlinear averaged phasor model of the system with detailed model of the converters including grid-forming converters (GFCs) and their control is developed. Then a singular perturbation analysis based model reduction approach for such system is proposed. Based on the proposed method, two levels of reduced order models for the GFCs are derived. Finally, the adequacy of these reduced-order models are presented via time-domain simulations on two test system models using MATLAB/Simulink.