Energinet

This paper presents a semi-automated approach for accelerating grid connection approval by streamlining grid code compliance testing of steady-state, dynamic (RMS) and electromagnetic transient (EMT) simulation models, utilising Energinet's Model Test Bench (MTB). As the integration of new generation sources intensifies, regulatory bodies demand rigorous model validation aligned with European and Danish grid codes. The MTB significantly reduces manual workload by automating the execution of comprehensive test suites in DIgSILENT PowerFactory for RMS models and PSCAD/EMTDC for EMT models, thereby minimising inconsistencies and improving reliability. Skilled grid connection engineers can efficiently leverage the MTB to perform grid code compliance assessments, meeting the requirements outlined in EU 2016/631 RfG, Danish Grid Codes, and Energinet's own RfG Appendix B for model criteria or even other regulations and requirements, if adjusted accordingly. The toolbox supports the aggregation of multiple generation assets into representative models and ensures robust documentation of modelling methodologies. This automation facilitates both Interim and Final Operational Notification processes, empowers stakeholders to demonstrate regulatory adherence, and enhances the transparency and effectiveness of grid integration procedures. The approach outlined contributes to a more adaptive and responsive power system, supporting the transition towards sustainable energy generation while maintaining grid security and operational standards.

Transmission system operators (TSOs) increasingly encounter small-signal instabilities (SSIs) when integrating converter-based resources into modern, converter-dominated power systems. Identifying and mitigating such instabilities is challenging due to complex converter interactions among multiple converters under a wide range of operating points (OPs). The challenge is particularly critical during the grid-connection process, where TSOs must validate stability before new converter-based resources are integrated into the system. Intellectual property rights (IPRs) further complicate the analysis by restricting TSOs' access to original equipment manufacturers (OEMs) and plant owners (POs) detailed models, which pose difficulty in coordinating studies and communicating analysis insights among multiple parties. Hence, methods that can address both the inherent complexity of SSIs and the IPR restrictions are needed. To address this challenge, this paper proposes a collaborative study framework between the TSO and OEMs/POs, which preserves OEM/PO IPRs while enabling an automated system-level smallsignal stability risk assessment and root cause identification across the OP space. The framework considers black-box OEM/PO state-space models, which are combined with the TSO's power system model using the component-connection method, enabling the eigenvalue-based stability analysis. The effectiveness of the study framework is demonstrated on a system with two gridfollowing wind-power plants (WPPs) and two parallel grid-forming high-voltage direct-current interconnections, where one WPP is undergoing grid-connection. Electromagnetic transient simulations validate the theoretical analysis of the framework.

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.

This paper investigates the application of Grid-Forming Battery Energy Storage Systems (GFM-BESS) to enhance power system stability, using large-scale simulations of a real incident in Denmark’s eastern transmission system (DK2). On August 6, 2020, DK2 experienced a sequence of transmission line faults that drastically reduced system strength, disconnected key assets such as HVDC link and synchronous condenser (SynCon), and posed a risk of system collapse. The event highlighted the need for faster and more flexible grid support. To evaluate the potential of GFM-BESS, detailed electromagnetic transient simulations with vendor-specific models replicated system topology, operational scenarios, and fault sequences. Two configurations were compared: the original setup with SynCons and a modified system including GFM-BESS. Results show that GFM-BESS stabilizes voltage and improves fault recovery more effectively than SynCons, even at smaller capacities. Its near-instantaneous reactive power response enables rapid voltage restoration and mitigates active and reactive power oscillations. Performance depends on installation site, GFM-BESS capacity, and control tuning, emphasizing the importance of strategic deployment. Overall, GFM-BESS demonstrates superior adaptability and resilience, offering a robust solution for the secure transition to converter-dominated power systems.

This paper demonstrates how Extended Dynamic Mode Decomposition (EDMD), grounded in Koopman operator theory, can effectively identify the main contributor(s) to oscillations in power grids. We use PMU data recorded from a real 0.15 Hz oscillation event in Denmark for post-event analysis. To this end, the EDMD algorithm processed only voltage and current phasors from nineteen PMUs at different voltage levels across the Danish grid. In such a blind-test setting with no supplementary system information, EDMD accurately pinpointed the location of the main contributor to the 0.2 Hz oscillation, consistent with the location of the problematic IBR plant later confirmed by Energinet, where the underlying cause was a control system issue. Conventional approaches, such as the dissipating energy flow (DEF) method used in the ISO-NE OSL tool did not clearly identify this plant. This joint validation with Energinet, reinforcing earlier studies using simulated IBR-dominated systems and real PMU data from ISO-NE, highlights the potential of EDMD-based post-event analysis for identifying major oscillation contributors and enabling targeted SSO mitigation.