Generalized Operational Short-Circuit Ratio for Grid Strength Assessment in Power Systems With High Renewable Penetration

The growing integration of converter-interfaced generators (CIGs) has caused small-signal stability issues driven by the converter control interaction of CIGs, especially in weak grids. Grid strength assessment is an important tool for fast identifying the stability issues. However, the existing techniques are ineffective in a multi-CIG system under actual operating conditions (MCIGS-AO). It is challenging for the small-signal stability analysis in a MCIGS-AO while considering different terminal voltages and power outputs for CIGs coupled with their different control parameters and configurations. The black-box converter modeling further increases the analysis complexity. This paper proposes a method for fast identifying the small-signal stability issues in a MCIGS-AO via grid strength assessment. First, we leverage the multiple-time scale analysis technique to study converter control dynamics with a focus on the stability issues mainly caused by converter phase-lock loops. Then, we transform a MCIGS-AO into a set of simple subsystems for the small-signal stability analysis. According to the analysis results, we propose the generalized operational short-circuit ratio (gOSCR) and critical gOSCR (i.e., CgOSCR) to assess grid strength in terms of the small-signal stability. With the gOSCR and CgOSCR, our method is proposed, and it is applicable even when converter details are unknown. The proposed method is validated on a modified IEEE 39-bus system and a practical power system with high wind generation.