How HVDC-WISE Is Making Power Grids More Resilient
April 28 began as a perfectly ordinary day. We had carefully prepared the webinar scheduled for that date and we had tested the webinar tool to anticipate potential issues. Nothing indicated that the unlikely was about to happen; at 12:33, the lights went out. Our initial suspicion of a local failure within the university quickly turned out to be wrong. People from nearby buildings poured into the streets, searching for cell phone signal or at least some information. Although we didn’t know for sure then, Portugal, Spain and parts of southern France had just experienced a massive blackout. Slightly stressed and with some luck, we managed to inform our colleagues involved in the webinar, and the webinar went ahead as planned—albeit with a few unexpected absences and corrective measures. The twist of fate: the webinar was about the resilience of power systems.
Blackouts significantly affect modern societies and are part of those unlikely but impactful events that are studied within the framework of resilience. The Iberian blackout is not an isolated case. For as long as power systems have existed on such a scale, regional or national collapses have happened somewhere in the world, on average, at least once a year. This is because,under certain adverse conditions a domino effect can be created by a combination of factors, usually triggered by a fault event that reveals some other undesirable conditions of which the system operator was unaware. The blackout of the Iberian power system was preceded by a series of events and actions that eventually turned into a cascading tripping of generators due to high voltages and the full separation of the Iberian peninsula from the Central European power system (see https://www.entsoe.eu/publications/blackout/28-april-2025-iberian-blackout/).
High Voltage Direct Current (HVDC) links allow electricity to be transmitted over long distances with minimal losses. They have controls that can be used extremely flexibly and that are designed to mitigate the impacts of disturbances to a power system. Indeed, the HVDC interconnector between Spain and France was the last line that tripped during the blackout. By connecting regions asynchronously, HVDC links can block the spread of disturbances from one area to another, helping contain failures before they escalate. Their high degree of controllability can help alleviate adverse system conditions, but without careful design, this same capability can also exacerbate instability.
The Horizon Europe and UKRI funded HVDC-WISE project is harnessing this potential to reshape how we plan and protect future power systems. A key focus, in Work Package 5 of the project, has been the development of advanced simulation tools for reliability- and resilience-oriented planning and operation of hybrid AC/DC grids. These tools go beyond traditional steady-state models, capturing the cascading effects of high-impact, low-probability (HILP) events and simulating recovery scenarios such as black or brown starts. They have the potential to enable assessments and quantifications of voltage, frequency and protection relay behaviour during extreme events like storms or equipment failures in planning or operational studies.
A reliability and resilience-oriented planning methodology has been proposed within the project, with a view to integrating resilience assessments into existing standard reliability-based grid planning approaches.Some early results in the project have demonstrated how HVDC links and a range of novel control and protection approaches can contain disruptions and enhance grid stability, acting as a firewall to large-scale cascading events. Together,these efforts provide a robust framework for designing future grids that are both renewable-ready and resilient to extreme events.
Researchers have also developed a dynamic criticality assessment framework to identify which AC and DC transmission components are most likely to initiate or propagate cascading failures in grids dominated by inverter-based resources (IBR), i.e. sources of power connected via power electronic converters. Using time-domain RMS simulations1, the framework can capture the complex interactions of voltage and frequency dynamics, controller behaviour, and protection relay operations during high-impact, low-probability events. It can be used to quantify metrics such as Expected Demand-Not-Served(EDNS) and Conditional Value-at-Risk (CVaR) of demand and several cascading-related metrics (e.g. speed and depth of cascading). The approach can help to identify key lines, power sources, loads or interconnections that have a disproportionate effect in propagation of a cascade of outages2. This potentially enables grid operators to prioritise reinforcement of the most vulnerable corridors, highlight the need for specific HVDC controls, or target the design and installation of defence measures such as under-voltage load shedding, tap-changer blocking or controlled system splitting, enhancing overall system resilience.
The project also explores converter control strategies.Grid-forming (GFM) controls have been found to outperform grid-following (GFL)in stabilising frequency and voltage, especially in systems with high renewable penetration. GFM converters actively support the grid during disturbances,while GFL converters tend to maintain their set points, offering limited support during cascading events.
Looking ahead, HVDC-WISE will end in one year. The project is applying its resilience and reliability methodologies across three large-scale use cases: one focused on mainland Europe, another on the GB grid, and a third examining the HVDC grid that connects the GB to continental Europe.These applications will inform a forthcoming set of recommendations on standardisation and best practices for integrating resilient planning into future grid development.
The expected outcomes of the work include the enhancement of existing simulation and planning tools through the integration of additional models tailored for hybrid AC/DC grid architectures. By testing and simplifying these tools and models, the project team hopes to enhance the capabilities of industry professionals to understand and use them. This will help decision-makers choose investment strategies that strike the right balance between reliability, resilience, and cost across different system configurations.
As the energy transition accelerates and society’s expectations for reliable, resilient low carbon electricity supply increase,this work becomes ever more critical. It’s about making sure future grids can handle the unexpected—keeping the lights on, the trains running, and the world moving forward.
[1] S. Hashemi, M. Asprou, L. Hadjidemetriou and M. Panteli, "Quantifyingand Mitigating Cascading Impacts in
HVDC-Interconnected Power Grids," in IEEE Access, doi:10.1109/ACCESS.2025.3603695
[2] Hashemi, S., Panteli, M., Gordon, S., MacIver, C., &Bell, K. (2025). Cascading-aware Criticality Assessment of
Transmission Corridors in IBR-dominated Systems-preprint.Powertech 2025, Kiel, Germany.
Zenodo. https://doi.org/10.5281/zenodo.15261434
