Thesis (PhD) - "AC-side HVDC interoperability"

General Context

Achieving multi-vendor multi-terminal HVDC interoperability is identified as a key target by the European Commission. The Horizon Europe InterOPERA project proposal is a unique initiative to define and validate the appropriate HVDC Interoperability frameworks, through the development of a real-time Demonstrator. It encompasses functional design and specification frameworks, control and protection subsystems integration test frameworks, cooperation frameworks, procurement frameworks. The Demonstrator development consists of the specification, engineering development and HIL (Hardware-In-the-Loop) integration test of the full control system of a multi-terminal HVDC grid with sub-systems provided by at least three HVDC manufacturers.  This is a four-year project gathering 21 partners (Transmission System Operators, Off-Shore Wind developers, HVDC converter manufacturers, Off-shore wind turbine manufacturers, …).

Within the InterOPERA project, SuperGrid Institute will lead the development of a generic functional framework, for multiterminal multivendor HVDC systems. The objective of the functional design framework is the following: A/ to define functional split and interface between the various sub-systems (some control and protection functions belong to the DC grid level and others belong to converter station level or to other components), B/ to express functional requirements and parameter ranges for each subsystem, with the aim to maximise interoperability (plug and play property) while not limiting innovation potential by subsystem providers. The interoperability subject relates to control and protection functions organization, at system level, subsystem level, component level. During the first two years of the project, SuperGrid will lead Task 2.1 – Basic functional requirements for multi-vendor HVDC Grid Systems and Subsystems. During the last two years of the project, SuperGrid will contribute to Task 2.3 – Connection network code recommendations for multi-vendor multi-terminal HVDC systems.

To support this work SuperGrid Institute plans to hire a research engineer who will carry out a PhD project related to the AC-side interoperability of multivendor multiterminal HVDC grids. The PhD project will especially address research issues that couldn’t be handled by the main operational resources of InterOPERA project Task 2.1, due to demonstrator-focused priorities, but remain important to be addressed before the conclusion of the InterOPERA project. Such research issues raised by Task2.1 will be processed through the PhD project, to contribute to Task2.3 and to project final conclusions.

Description of the thesis topic

HVDC interoperability can be classified into DC-side interoperability and AC-side interoperability. Whereas all converters belonging to a given DC grid must be interoperable on their DC-side, AC-side interoperability is not always a concern, this depends on AC-side system and configuration.

Nowadays, a HVDC converter connected to an offshore wind farm grid is controlled to form the AC wind farm grid frequency and evacuate the power generated by the farm: this control is often named Vf control. A single HVDC converter is connected to a single wind farm. Moving forward, new offshore wind will be connected through 2GW bipolar HVDC scheme, instead of 900MW monopolar HVDC scheme. It may then be beneficial for wind farm operation (availabity optimization), to interconnect through their AC-side, the positive pole converter and the negative pole converter. Both converters would then share the grid forming duty and the evacuation of the power, leading to AC-side interoperability issue (#1).

Down the road, HVDC-connected OWF will be required to provide onshore grid forming services. This requirement will lead to a new way of operating the OWF AC grid. Wind turbine converter will have to adjust their power output to the dynamic demand from the onshore side. In such scheme, the offshore HVDC converter and the Wind Turbine converters would need to cooperate, leading to AC-side interoperability issue (#2).

The PhD project may address this background context, as well as complementary scientific issues that would be raised during InterOPERA project.

Scientific work:

Work objectives and content will be defined according to Task2.1 inputs and research issues that are relevant to select for the PhD project, considering InterOPERA project aim.

Objectives / Tasks

• Bibliography and state of the art analysis

• Selection of scientific locks and research issues

• Electro-Magnetic-Transient (EMT) modelling of the HVDC system and the OWF system with its protection and controls,

• Theoretical approach of AC-side stability issues, based on simplified models,

• Formalization of AC-side control framework concepts and options

• Assessment of AC-side control framework options, also taking DC-side constraints into account

• Key findings validation, possibly on Supergrid HIL Simulation Platform 

References

[1] Düllmann P. , et Al.: European Offshore  grid : On protection system design for radial bipolar multi-terminal HVDC networks – Publication 11087 CIGRE Paris 2022

[2] Equinor : multivendor hvdc links providing O&G installations, perspectives and challenges - https://ec.europa.eu/energy/sites/ener/files/documents/10._sharifabadi_kamran_-_multivendor_hvdc_links_supplying_oil_and_gas_installations.pdf

Candidate Profile

Engineering degree (Master 2)

Background required in Electrical engineering

• Power System

• Power Electronics

• Control Engineering

Soft skills

• Sens of deduction, ability to work within a research team

• Written and oral communication in English