Comparative Analysis of Models for Inverter-Based Resources

With the increasing penetration of Inverter-Based Resources in modern power systems, system stability and power quality have emerged as critical issues. This complexity is primarily driven by the active control mechanisms present at both the source and the load side and is further compounded by the growing proliferation of Distributed Energy Resources across distribution networks. Consequently, identifying potential instabilities and resonance phenomena triggered by these dynamic interactions has become a priority. A highly effective method to evaluate these critical system conditions and assess small-signal stability is Impedance-Based Stability Analysis in the frequency domain. This thesis presents a rigorous comparative study and cross-validation between two of the leading simulation environments: MATLAB/Simulink and DIgSILENT PowerFactory. The project revolves around the implementation of a benchmark test grid, focusing on the detailed translation of a Grid-Following inverter and its control algorithms into the DIgSILENT Simulation Language. After validating the absolute dynamic equivalence of the models in the time domain, the system's stability is evaluated under critical weak grid conditions. The study highlights the analytical limitations of traditional decoupled sequence extraction methods which failed to predict the instability observed during Electromagnetic Transient simulations. To overcome this, a coupled Multi-Input Multi-Output methodology was developed. By explicitly accounting for the cross-sequence coupling driven by the Phase-Locked Loop, the custom Generalized Nyquist Criterion algorithm successfully predicted the instability. This analytical finding was fully corroborated by the native Impedance-Based Stability Analysis tool in DIgSILENT PowerFactory; when explicitly configured to include these sequence coupling effects, the native software accurately reproduced the theoretical predictions and successfully captured the onset of instability. Ultimately, this thesis establishes a clear comparative framework that not only highlights the operational discrepancies of the simulation tools but definitively proves that MIMO sequence modelling is strictly mandatory for the accurate stability assessment of modern IBRs in low-inertia grids.