Weak Grid Test Case Development and Enhancement for High Penetration of Inverter-Based Resources

Inverter-based Resources (IBRs) are becoming a major generation resource in the modern bulk power system. Most of existing IBRs are legacy grid-following (GFL) inverters, which provide limited system inertia or system strength. As a result, weak grid (low system strength) becomes one of the major stability issues in power systems with high penetration of IBRs. This paper presents a weak grid test case that mimics the stability issue observed in the ERCOT large system stability studies especially in the IBR concentration area that is far away from load centers. Additionally, this paper tests various stability enhancements including STATCOM, Synchronous Condenser (SynCon), and the recently developed gird-forming (GFM) battery on the developed weak grid case. It clearly demonstrates that SynCons and GFM battery can effectively improve stability performance of the legacy GFL inverters under weak grid conditions. The developed test cases can serve as the benchmark cases for identifying mitigation plans and the future IBR weak grid research and study. The developed test cases including generic models are published in a google site that is available to the public [1].