Evaluation of the Impact of Grid Forming Inverter Penetration on Frequency Transients in Systems with a High Percentage of Renewables

The increasing integration of inverter-based resources (IBRs) for renewable energy sources (RESs) generation into power systems has a significant impact on their frequency transient behaviour. This is due to the variability and partially non-programmability of RES power generation and the lack of rotating inertia due to the use of static converters. This research work aims to analyse how frequency transients are affected by the increasing share of generation from RES, e.g. photovoltaics (PV), in the total generation, focusing on the types of inverters used as an interface with the grid, Grid Following (GFL) or Grid Forming (GFM) inverters. A quantitative analysis of the impact on the frequency transient of different GFM percentages on total IBR generation is provided. The study shows that a share of 50% of GFM inverter allows a frequency transient with a similar Nadir and still a higher Rate of Change of Frequency (RoCoF) of a system with only synchronous generators (SGs). The frequency-supporting actions of these technologies will be evaluated considering the periods of overgeneration, characterised by the need to cut PV production, creating a reserve of available but untapped energy.