Enhancing system stability with GFM (E-)STATCOMS: a case study of the DK2 2020 incident in the Danish power system

Denmark's goal of carbon neutrality by 2050 requires a power system largely based on renewable energy, leading to the gradual replacement of synchronous machines with grid-following inverter-based resources. This transition reduces system strength, creating challenges for maintaining voltage and frequency stability. Grid-forming (GFM) control has emerged as one of the promising solutions to address the challenges. In 2023, the Danish TSO Energinet launched the “Deployment of Grid Forming Technology in the Danish Power System” project to evaluate commercial GFM products. Within this project, the GFM capabilities of different technologies were assessed through system-level EMT studies of the Danish grid. This paper presents a detailed study of an incident that happened in eastern Danish power grid (DK2) in 2020, where sequential faults caused a network split at 400 kV backbone, synchronous condenser (SynCon) tripping, and HVDC blocking. The incident is revisited by replacing the SynCon with either a GFM STATCOM or an E-STATCOM, evaluating their effectiveness in mitigating the instability. Comparative results indicate that both devices provide better voltage control compared with the SynCon, with the E-STATCOM demonstrating further improvements in damping capability. These findings underline the potential of GFM (E-)STATCOMs to ensure security and resilience in future renewable-dominated power systems.