Small-Signal Stability Assessment of Multi- Converter-Based-Renewable Systems With STATCOMs Based on Generalized Short-Circuit Ratio

The increasing integration of renewable resources (such as wind and solar) through grid-following converters is shifting the modern power system into a multi-converter-based- renewable (multi-CBR) system. In such a multi-CBR system, the dynamic interaction between CBRs and the power network may cause small-signal stability issues, especially under low short-circuit strength conditions. While static synchronous compensators (STATCOMs) are integrated into the multi-CBR system for providing voltage support, their dynamics also influence the small-signal stability. However, it has not been theoretically revealed how STATCOMs affect the small-signal stability, especially for low short-circuit strength systems. To fill this gap, this paper proposes a method to analyze small-signal stability of a multi-CBR system with STATCOMs based on grid strength analysis, wherein the grid strength is represented by short-circuit ratio (SCR) for a single-CBR system and generalized SCR (gSCR) for a multi-CBR system. Firstly, we analyze the relationship between small-signal stability and SCR in a single-CBR single-STATCOM system. Then, we study the relationship between the small-signal stability and gSCR in a multi-CBR system with STATCOMs. On this basis, a gSCR-based method is proposed for assessing the small-signal stability of a multi-CBR system with STATCOMs. The proposed method is validated through eigenvalue analysis, electromagnetic transient simulations and hardware-in-loop simulations.