Impact of Inverter Controls in Small-Signal Stability of Power Systems Dominated by Inverter-Based Resources

Initiatives to decarbonize contemporary power systems will lead to power systems dominated by inverter-based resources (IBR). These IBRs are broadly classified into grid-following (GFL) and grid-forming (GFM) inverter control regimes. In this paper, a small-signal state-space model is formulated for a 100% IBR-dominated power system. This formulation is then used to perform stability analysis on the IEEE 9-bus system. The analysis thoroughly investigates the impacts of varying GFM inverter penetration on system stability. The paper also discusses the system behavior in the wake of varying shares of different GFL inverter control schemes. The cause of instability is ascertained by investigating the participation factor of each component. Moreover, the paper examines the effects of phase-locked loop (PLL) and power synchronization loop (PSL) parameters on determining the minimum GFM penetration necessary for ensuring stable system operation. It has been found that the inverter type with the highest capacity is not always the biggest contributor to instability. Also, increasing the proportional coefficient and decreasing the integral coefficient of the PLL of GFL inverters allow the system to be operated under lower GFM penetration. Similarly, increasing the moment of inertia or damping coefficient of the GFM inverter’s power synchronization loop has a similar effect. The conclusions and the underlying theoretical analysis are verified by time-domain simulations of electromagnetic transient (EMT) models in Matlab/Simulink.