HVDC-WISE and the future of grid codes

As Europe’s energy system undergoes a rapid transformation, the infrastructure that supports it must evolve – not only in terms of technology, but also in the rules that govern how it operates. 

These rules, known as grid codes and regulatory frameworks, are the backbone of the power system. They define how assets connect to the grid, how they behave during faults and how they interact with electricity markets. Yet, as hybrid AC/DC grids and multi-terminal HVDC networks become more prevalent, the existing codes are increasingly out of step with the realities of modern transmission systems.

The HVDC-WISE project, funded by Horizon Europe and UKRI, is addressing this challenge head-on. Its work spans planning tools, technical innovations and regulatory insights, all aimed at supporting the integration of HVDC into Europe’s evolving energy landscape. 

One of its most significant contributions is a comprehensive review of current grid codes, identifying critical gaps and proposing updates that reflect the needs of today’s – and tomorrow’s – electricity systems.

Grid codes: Fit for purpose?

The existing network code on high voltage direct current connections, adopted in 2016, was developed at a time when HVDC systems were largely point-to-point and operated in isolation. Today, HVDC is being used to connect offshore wind farms, link national grids and form complex multi-terminal networks. 

Despite this evolution, the code remains focused on AC-connected HVDC systems, leaving DC-to-DC connections, offshore AC hubs and emerging technologies like grid forming converters largely unaddressed.

HVDC-WISE has conducted a detailed analysis of EU legislation, national grid codes and technical standards across several countries, including Denmark, Norway, Germany and Great Britain. The findings reveal a number of critical gaps. For instance, there are no defined power quality standards for DC networks, no requirements for energisation and synchronisation in multi-terminal systems and limited guidance on how to manage offshore consumers such as hydrogen electrolysis platforms or electrified oil and gas installations.

These gaps will need to be addressed as Europe moves toward more integrated offshore grids and multi-terminal HVDC systems that span multiple jurisdictions and involve multiple TSOs.

Coordination among TSOs is another area where the current regulatory framework falls short. In systems where multiple TSOs share responsibility for different parts of a DC grid, the absence of harmonised requirements can lead to inefficiencies, delays and even risks to system stability. 

HVDC-WISE emphasises the need for clearer roles and responsibilities, especially in multi-vendor, multi-owner environments.

Institutional influence and national variations

Beyond technical gaps, the project explores the role of key EU institutions in shaping HVDC operations. Entities such as ENTSO-E, the regional coordination centres (RCCs) and nominated electricity market operators (NEMOs) influence everything from capacity allocation and outage planning to system restoration and market integration. 

Their involvement underscores the need for regulatory frameworks that are not only technically sound but also institutionally aligned.

ENTSO-E, for example, coordinates TSO activities and develops methodologies for system operation and restoration. It also leads working groups on multi-vendor HVDC systems and grid forming capabilities. 

RCCs manage tasks like coordinated security analysis, capacity calculation and outage planning, all of which impact HVDC operations. Meanwhile, NEMOs and the joint allocation office (JAO) influence HVDC flows through market mechanisms and capacity auctions.

These institutions shape how HVDC systems are integrated into both technical operations and market frameworks, highlighting the need for aligned regulatory approaches.

National implementation of HVDC-related codes also varies significantly. Denmark aligns closely with EU codes and supplements them with annexes on voltage quality and simulation models. Norway uses national guidelines that reflect EU standards but are not formally transposed. Germany applies VDE standards and FNN notes to formalise HVDC requirements, including detailed technical connection rules. Great Britain relies on the grid code and the security and quality of supply standard (SQSS), which include deterministic and probabilistic elements. 

These national variations highlight the importance of harmonisation, especially as HVDC systems increasingly span multiple jurisdictions.

Technical gaps and future work

The HVDC-WISE team has grouped the technical articles of the network code on HVDC connections into five categories – active power control and frequency support, reactive power control and voltage support, resilience and recovery, robustness and control, and compliance testing and simulation – and analysed each for gaps. 

For example, the code lacks clear definitions of synthetic inertia and does not adequately address coordination across multiple TSOs in multi-terminal systems. Requirements for reactive power capability and control modes need harmonisation with other codes like the requirements for generators (RfG). Fault ride-through, black start and post-fault recovery requirements need updates to reflect HVDC systems’ role in system restoration. 

Topics like energisation, power oscillation damping and subsynchronous torsional interaction require clearer boundaries of responsibility and coordination across TSOs.

Finally, compliance testing procedures for multi-terminal, multi-vendor HVDC systems are complex and undefined, necessitating standardised approaches.

Looking ahead, HVDC-WISE proposes several areas for future work. These include defining compliance testing procedures for multi-terminal DC grids, developing harmonised standards for offshore and onshore systems, clarifying roles and responsibilities in multi-vendor environments and updating definitions and performance expectations for emerging technologies.

Additionally, all the aforementioned codes assume underlying assumptions of system reliability to standard commonplace power systems contingencies, such as line losses and generator outages. The increasing impact of extreme events such  as weather events or cyber attacks highlights the need to develop power systems that are resilient to such large shocks. 

Recent regulations, such as the FERC 1920 order in the United States, recognise the need to explicitly consider such large high impact low probably events in power systems. HVDC-WISE will propose recommendations on incorporating resilience into system codes, based on the studies conducted during the project.

Building a resilient future

Ultimately, HVDC-WISE is helping Europe move beyond traditional grid planning. It is creating a roadmap for building energy systems that are resilient by design – systems that can withstand disruptions, recover quickly and support the transition to a low carbon future.

As the energy system becomes more dynamic and interconnected, the rules that govern it must evolve too. HVDC-WISE is making sure they do.

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