Power System Transient Stability Studies with Droop-Controlled Grid-Forming Inverters

Transient stability performance of a bulk power system is of utmost significance to power system operators. Due to the rapid integration of inverter-based resources (IBRs) in the power grid, it is essential to ascertain their ability to stay in synchronism with system during severe transient events. Grid-forming (GFM) inverter control techniques have received increased attention in recent times. However, transient stability studies with grid forming inverters are not readily available and are pursued in this work. Studies are conducted for droop controlled GFM inverters with single loop voltage magnitude control and virtual impedance fault current limiting. Power angle curves and phase portraits are presented to analyze the behavior of this control approach. Next, transient stability simulations are conducted on the IEEE 39 bus system test case with generators replaced with IBRs. Results suggest that droop controlled GFM inverters with well-designed current limiting can preserve transient stability and potentially help improve the stability limit at higher inverter penetration levels.