InterOPERA Enabling Interoperability of Multi‑Terminal Multi‑Vendor HVDC Grids

The paper presents the InterOPERA initiative and an EMT‑based study framework to enable interoperability in multi‑terminal, multi‑vendor HVDC grids, covering project scope, demonstrators, functional requirements, and the use of EMTP for interaction and grid‑design studies. The program runs from January 2023 to April 2027 under European funding and coordination by SuperGrid Institute, targeting multi‑vendor HVDC grids to support large‑scale offshore wind integration in Europe. A demonstrator combines building blocks from different vendors—three 2‑GW/525‑kV AC/DC converter stations usable onshore and offshore, four DC switching stations, four power park modules, and a DC grid controller—organized as a three‑terminal base case (with a five‑terminal extension offline) and complemented by a real‑time setup. Functional requirements are structured into sequential control, continuous control, DC grid protection, and AC/DC security and dispatch; examples include onshore DC‑voltage–power droop, DC‑voltage sensitive modes (including limited variants), power‑limiting and DC‑voltage‑limited modes, offshore constant active‑power operation, and DC‑fault ride‑through with fault‑separation zones. EMT is positioned for interaction studies (near steady‑state, energisation/de‑energisation and reconfiguration, withstand, and small‑signal stability) and for HVDC grid‑design studies following a consistent methodology (capability ranges, N‑1 criterion, scenarios and contingencies, modelling assumptions, and DC load‑flow plus dynamic simulations). Using EMTP on the three‑terminal base case, reported study sets cover DC load‑flow and contingency analyses and dynamic responses, with totals including numerous DC load‑flow scenarios (pole and bipole outages), blocking cases with AC faults on the grid side, and DC‑fault events at the DC point of connection, DC switching‑station busbars, and along DC cables. Key messages highlight open‑box models with defined exceptions via tool‑independent DLLs validated in multiple EMT tools, ongoing dry‑run tests, the central role of interface documentation, and real‑time step‑setting trade‑offs. - Carmen Cardozo (RTE, France)