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From Point-to-Point HVDC to Converter-Dominated Networks: Why Benchmark Models Matter

10 September 2026, By Hong Rao, JWG B4/C4.105 Convenor

Introducing CIGRE Joint Working Group B4/C4.105 – Benchmark Models for Multi-Infeed HVDC Studies

 

From Point-to-Point HVDC to Converter-Dominated Networks: Why Benchmark Models Matter

Hong Rao, JWG B4/C4.105 Convenor

 

1. The Changing Landscape of HVDC Transmission

 

Few technologies have transformed modern transmission systems as profoundly as HVDC. As the global energy transition fundamentally reshapes power systems, ambitious decarbonisation targets, rapidly increasing renewable energy penetration, and the growing need for long-distance electricity transmission have accelerated the deployment of High Voltage Direct Current (HVDC) technology around the world. What was once regarded as a specialised transmission solution has now become one of the key enabling technologies supporting the development of future power systems.

Over the past several decades, HVDC applications have evolved considerably. Conventional Line-Commutated Converter (LCC)-HVDC schemes continue to provide efficient bulk power transmission over very long distances, while Voltage Source Converter (VSC)-HVDC technology has opened entirely new application areas, including offshore wind integration, asynchronous interconnections, urban power supply and flexible transmission networks. At the same time, Flexible AC Transmission Systems (FACTS) devices have become increasingly common, providing enhanced controllability and operational flexibility for interconnected AC systems.

This technological evolution is changing not only the equipment used within transmission networks, but also the way power systems are planned and operated. Instead of isolated point-to-point HVDC links, many modern transmission systems now contain several HVDC schemes operating simultaneously within the same AC network. Such configurations are commonly referred to as multi-infeed HVDC systems. These installations often combine LCC-HVDC, VSC-HVDC and FACTS technologies, creating highly interconnected converter-dominated environments in which multiple power-electronic devices continuously interact with one another.

Consequently, multi-infeed HVDC systems are no longer exceptional engineering cases. They are becoming an increasingly common characteristic of large interconnected power systems and are expected to play an even more significant role as renewable generation, offshore energy development and international interconnections continue to expand.

 

2. A New Generation of Engineering Challenges

 

The growing complexity of converter-dominated power systems has introduced challenges that extend well beyond those traditionally considered in single-HVDC studies. While each converter can generally be designed and commissioned to satisfy its own performance requirements, interactions among multiple converters connected to the same AC network may produce dynamic behaviours that are difficult to predict using conventional analytical approaches.

These interactions may influence system stability, control performance and operational security under both normal and disturbed operating conditions. Voltage stability, frequency response, electromechanical oscillations and converter control interactions are increasingly coupled, requiring engineers to consider the behaviour of the entire AC/DC system rather than individual transmission projects.

The engineering community has made significant progress in understanding these phenomena. Extensive research has been carried out by utilities, manufacturers, universities and research organisations, and valuable practical experience has been accumulated through numerous HVDC projects worldwide. Nevertheless, much of this knowledge remains project-specific. Different organisations often develop their own simulation models, assumptions and study procedures based on particular system characteristics, software platforms and engineering practices.

While such project-oriented approaches are entirely appropriate for engineering design, they inevitably make it difficult to compare technical studies across organisations. Differences in modelling philosophy, software implementation and model fidelity often lead to inconsistent analytical results. Furthermore, many detailed engineering models contain proprietary information that cannot be publicly shared, limiting opportunities for technical comparison and collaborative research.

As power systems continue to evolve, engineering practice has advanced rapidly, but common analytical references have not always kept pace. The challenge is no longer simply to analyse individual HVDC schemes, but to understand the collective behaviour of multiple converter-based technologies operating as an integrated power system. This shift highlights the growing need for internationally recognised benchmark models and harmonised study methodologies.

 

3. Why Benchmark Models Matter

 

Benchmark models have long played an important role in the development of engineering disciplines. They provide common reference systems that enable researchers and practising engineers to compare methodologies, validate new analytical techniques and reproduce technical studies under consistent assumptions. Rather than replacing detailed engineering models, benchmark models establish a common technical language through which different organisations can exchange knowledge and objectively evaluate new approaches.

Within the power engineering community, benchmark systems have supported advances in power system stability analysis, electromagnetic transient simulation, protection studies and renewable energy integration. Their value lies not in representing a specific project, but in capturing the essential characteristics of practical engineering problems while remaining sufficiently transparent for international collaboration.

Despite the rapid growth of multi-infeed HVDC applications, no internationally recognised benchmark models currently exist for analysing these increasingly complex AC/DC systems. Existing interaction assessment methods, including the widely applied Multi-Infeed Interaction Factor (MIIF) [1], have historically provided valuable guidance for conventional LCC-HVDC systems. However, modern transmission networks increasingly incorporate combinations of LCC-HVDC, VSC-HVDC and FACTS devices, introducing interaction mechanisms that extend beyond the original assumptions underlying traditional methodologies.

CIGRE has previously developed benchmark models for DC grid studies [2] and has recently examined interaction phenomena among nearby VSC-HVDC converters, FACTS devices and conventional AC equipment [3]. Building directly on this legacy, the new Joint Working Group extends the benchmark approach to multi-infeed HVDC systems.

 

4. A New International Collaboration

 

Against this background, CIGRE has established Joint Working Group B4/C4.105, Benchmark Models for Multi-Infeed HVDC Studies [4]. Bringing together the complementary expertise of Study Committees B4 (DC Systems and Power Electronics) and C4 (Power System Technical Performance), the Joint Working Group provides an international platform for addressing one of the emerging technical challenges associated with future converter-dominated power systems.

Rather than focusing on individual transmission projects, the work aims to establish representative benchmark systems that reflect typical multi-infeed HVDC applications encountered around the world. The activity will progress through four complementary stages:

 

  • International survey: The first stage of the activity will involve an international survey of representative system configurations, converter technologies and operational characteristics. This survey will provide the technical foundation for defining benchmark models with broad engineering relevance.
  • Review of modelling practices: Building on this knowledge, existing modelling practices and interaction assessment approaches will be systematically reviewed. Particular attention will be given to modelling requirements for different types of stability studies, including electromagnetic transient (EMT) and RMS simulations, together with an assessment of the applicability and limitations of existing interaction indices such as MIIF.
  • Benchmark model development: Representative benchmark models covering typical combinations of LCC-HVDC, VSC-HVDC and relevant FACTS devices will be developed. The intention is not to reproduce detailed vendor-specific engineering models, but rather to establish transparent, technology-neutral reference models that facilitate objective technical comparison while respecting the confidentiality of proprietary information.
  • Harmonised study methodologies: Study methodologies will be proposed for evaluating interaction phenomena together with voltage stability, frequency stability and power-angle stability in multi-infeed HVDC systems. Emphasis will be placed on providing practical engineering guidance, improving the consistency of technical studies and supporting reproducible analyses across different organisations.

 

The principal outcome of this international collaboration will be a CIGRE Technical Brochure documenting the benchmark models, modelling principles and recommended analytical methodologies. It is anticipated that these deliverables will provide valuable references for utilities, manufacturers, consultants, universities and research institutions involved in the planning, analysis and operation of modern AC/DC transmission systems.

 

5. Looking Beyond the Technical Brochure

 

Although the preparation of a Technical Brochure represents the formal objective of the Joint Working Group, the broader significance of this initiative extends well beyond a single publication. The establishment of internationally recognised benchmark models has the potential to strengthen technical collaboration across the global HVDC community, facilitate comparison of emerging analytical methods and provide common reference systems for future research, education and engineering applications.

Since its establishment in 2026, the Joint Working Group has already attracted experts from utilities, manufacturers, universities and research institutes representing eleven countries. The kick-off meeting is planned for the CIGRE Paris Session in August 2026, marking the beginning of what is expected to become a highly collaborative international activity. As participation continues to expand, the Working Group will provide an open platform for technical exchange between industry and academia, encouraging the sharing of experience across different regions and application environments.

Ultimately, the success of this initiative will not be measured simply by the publication of a Technical Brochure. Its lasting contribution will be the establishment of a common technical foundation for analysing increasingly complex multi-infeed HVDC systems and, more importantly, the development of a shared engineering language capable of supporting the next generation of converter-dominated power systems.

 

6. References

 

[1] CIGRE Technical Brochure 364, "Systems with multiple DC infeed", WG B4.41, 2008.

[2] CIGRE Technical Brochure 804, "DC grid benchmark models for system studies", WG B4.72, 2020.

[3] CIGRE Technical Brochure 934, "Interaction between nearby VSC-HVDC converters, FACTS devices, HV power electronic devices and conventional AC equipment", WG B4.81, 2024.

[4] Terms of Reference of JWG B4/C4.105, "Benchmark Models for Multi-Infeed HVDC Studies".