Small-Signal Stability of Power Systems with a Mix of Synchronous Generators and Inverter-Based Resources

This paper focuses on the problem of small-signal instability due to the inverter-based resource (IBR) used to interface renewable energy sources (e.g., offshore wind farms) in a traditional power system with synchronous generators (SGs). A power system consisting of an IBR, SG, transmission line, and resistive inductive (RL) load was used to represent an aggregated system. The small-signal stability of the SG-IBR-RL system was investigated for varying levels of IBR penetration ($\eta$), followed by three case studies: i) a parameter sensitivity analysis, ii) a model adequacy analysis, and iii) a stability margin improvement study. The sensitivity analysis found that variations across the typical range of most parameters resulted in maximum stable $\eta$ changes of around 5%, with parameters such as the IBR PI controller gains, the load concentration, and the transmission line impedance having very strong effects on the permissible $\eta$. The model adequacy analysis showed that neglecting the SG stator dynamics led to a larger deviation from the “full” model compared to neglecting the transmission dynamics. Finally, the stability margin improvement study found that fast IBR controls coupled with slow SG controls resulted in permissible $\eta$ values 3% higher than the base case.