An Efficient Reduced-Order Model for Studying Synchronization Stability of Grid-Following Converters during Grid Faults

Renewable energy sources interfaced with the grid through power-electronic converters may lose stability and capability to perform as desired when exposed to severe grid faults. As a result of this, transient stability analysis and assessment are particularly important for power system studies. Usually, synchronization stability and transient stability analysis are performed by simulation studies containing a large amount of details, which makes this process highly time-consuming for large-scale systems. To circumvent this issue, a nonlinear second-order model is developed to capture the essential effects of the synchronization process of grid-tied converters during faults. Due to this low-order model, the stability assessment can be approached using phase-plane analysis with a low computational burden - more than 4000 times faster than the full-order switching model. The simplified model is verified against a detailed switching model and laboratory setup of the entire converter system indicating a high accuracy (>96%). Accordingly, the simplified reduced-order model can be used for accurate transient stability studies when a low availability of computational power is present, if large-scale systems are considered, or for detailed uncertainty and sensitivity analysis.