RoCoF Mitigation in the Italian Transmission Network: a Methodology for Inertia Optimization

The replacement of traditional Synchronous Generators (SGs) with inverter-based sources, like Photovoltaic (PV) units, Wind Turbine (WT) power plants and Battery Energy Storage Systems (BESSs), poses critical challenges for Transmission System Operators (TSOs), related to a reduction of the system inertia. In particular, the lack of inertia may lead to issues in containing the Rate of Change of Frequency (RoCoF) within the limits prescribed by grid codes. This paper proposes a methodology for estimating the need of additional inertia for the Italian transmission network in the future 2030 scenario. The methodology sets up an optimization problem able to find the best technological mix of Synthetic Inertia (SI) providing sources (PV, WT and BESS units) and of additional Synchronous Compensators (SCs) to be installed in the Italian scenario, able to limit the RoCoF of the Centre of Inertia (COI) of the Italian network within the prescribed range, while minimizing the economic costs related to inverters' control upgrade and SCs installation. The 2030 scenario is characterized thanks to the data provided by Terna S.p.A, the Italian TSO.