Impact of Inverter-Based Resources on Inertia Provision and RoCoF Limitation

The ongoing replacement of traditional power plants with Photovoltaic (PV), Wind Turbine (WT) and Battery Energy Storage System (BESS) power plants will lead to problems of inertia shortage in future power systems. Thus, the provision of Synthetic Inertia (SI) by Inverter-Based Resources (IBRs) will be crucial in order to deliver effective Rate of Change of Frequency (RoCoF) mitigation actions. The present paper presents a methodology to assess the impact of IBRs on the available inertia in future power systems. The study, carried out in partnership with Terna, the Italian transmission system operator, focuses on a critical market zone in the 2030 Italian scenario. First, the availability of inertia by synchronous generators and already-installed Synchronous Compensators (SCs) is assessed, along with the need of inertia (i.e., the inertia necessary to limit the zonal RoCoF at the limit value following a reference contingency). If the need is larger than the availability, the intervention of IBRs is considered to limit the RoCoF. In particular, a sensitivity analysis is carried out varying both the limit value of RoCoF and the overloading capability of IBRs inverters, showing that the predominant SI contribution will be delivered by BESSs. Regarding RoCoF containment, if the limit value is set at 2 Hz/s IBRs are able to make the gap negative over the whole year. On the other hand, if a more stressful condition is considered (i.e., limit value set at 1 Hz/s), the installation of additional SCs may become necessary to make the inertia gap negative for the whole year under whatever IBRs overloading capability scenario.