A Classification for Synthetic Inertia Quantification Methods with Practical Recommendations

With ongoing advancements in grid-forming (GFM) technologies and inverter design, future power systems will likely operate with a mix of synthetic inertia, provided by inverter-based resources (IBRs) and large-scale loads, and synchronous inertia from traditional rotating machines such as synchronous condensers and conventional power plants. In this context, there is an essential need to quantify synthetic inertia to ensure its commercial viability as a service, add further certainty to GFM system interconnection and business cases of GFM projects, and their integration into emerging ancillary service market mechanisms. This paper presents a classification for synthetic inertia quantification methods, including large disturbance methods, RoCoF emulation methods, probing signal injection strategies, and conceptual approaches that may become practical in the future. The mathematical and implementation process for these synthetic inertia quantification methods are presented, as well as the issues and requirements. A rigorous comparison between different methods are presented considering accuracy, perturbation type, damping decoupling, as well as the issues with implementation and the complexity involved. Finally, practical recommendations and future research directions are presented along with industry specifications on equipment capable of providing synthetic inertial responses.