for support, technical challenges related to stability include the following: ✔ The frequency sensitivity due to lower inertia and the large size of a contingency relative to the system size can easily lead to inadvertent GFL IBR tripping. The same can happen due to voltage stability issues since older distributed IBRs are particularly sensitive to voltage events. At high penetrations, this can cause rapid changes in available generation, making frequency control difficult and preventing effective load shedding. Enforcing ride-through standards on distributed IBRs (for example, adopting the IEEE 15472018 standard) may help address these issues. ✔ Control-driven stability issues can widely propagate through a small island system, with devastating effects. ✔ Protection coordination and sufficient short circuit current may also be challenging unless addressed with modern protection technologies that are smarter than simple overcurrent protection. Recent work evaluating the potential benefit of GFM control in batteries is showing a strong stabilizing influence table 1. Stability risks in various power systems. Frequency Stability Risks CE CE (Intact) TX (System Split) AU GB IR Occasional * Under intact conditions, a system is relatively immune to fast and severe frequency events. * Challenges tend to be weighted toward congestion management. Acute * Frequency control concerns can limit operation. * Periods of poor frequency containment occur during credible events. * Control of frequency following possible or planned system splits is difficult. Voltage and Angle Stability Risks IR HI CE GB TX AU Local * Electrical distances are limited. * Interface collapse and system separations are remote concerns. * Local voltage support issues are possible. Regional * Significant power imports and exports with dynamic constraints are an occasional factor. * Separation tends to be a high-impact, low-frequency event. Control Stability Risks IR CE GB Local * There are some locations (e.g., individual nodes and small areas) with low system strength and a risk of control interactions. Regional * There are entire regions of very high IBR penetration and little or no synchronous generation with ac transmission to other stronger areas. CE: Central Europe; TX: Texas; GB: Great Britain; AU: Australia; IR: Ireland; HI: Hawaii. november/december 2021 ieee power & energy magazine 25 Systemwide * An entire system has extended periods of very low or even zero synchronous short circuit contribution. AU HI TX Systemwide * A system has high power transfers across ac transmission interfaces, for which voltage instability and angular separation are a primary concern and often impose operating constraints. Chronic * A system often has a risk of substantial frequency control problems and a high RoCoF. HI