Short circuit analysis and voltage support needs in power systems with relevant share of inverter-based resources

The large-scale integration of Inverter-Based Resources (IBRs) in transmission networks introduces significant challenges for voltage regulation. This paper proposes a comprehensive methodology to evaluate the contribution of IBRs during fault conditions. The approach consists of two key steps: first, a quasi-analytical procedure is developed to calculate post-fault nodal voltages in networks with IBRs, avoiding the need for specialized power systems software and ensuring both accuracy and computational efficiency. Secondly, an optimization problem is designed to determine the optimal susceptance to be installed at network nodes, ensuring that local reactive power injection maintains nodal voltages within grid code requirements. The quasi-analytical method incorporates the specific Italian grid code requirements for IBR behaviour during faults. Results demonstrate that the proposed procedure achieves a maximum error of just 0.1 % compared to detailed simulations performed in DIgSILENT PowerFactory and highlight the inability of existing short-circuit calculation standards to accurately predict nodal voltages under the Italian grid code specifications. Furthermore, the optimization results are validated through simulations, confirming that the calculated susceptances effectively maintain nodal voltages within the prescribed limits. Overall, the proposed strategy provides an accurate modelling of IBR fault response in compliance with specific grid code requirements and an approach to determine the minimum reactive power support needed to maintain voltage during short-circuit events in networks with high IBR penetration. This procedure specifically addresses the limitations of general Short-Circuit (SC) standards for IBR modelling and offers a fast, practical tool for TSOs to evaluate voltage support needs in large transmission networks.