Coordinated Frequency Support in Multi-Terminal HVDC Network Via Grid-Forming Converter with Dynamic Power Allocation

MT‑HVDC links connecting offshore wind farms (OWFs) and asynchronous AC systems can provide frequency support, but conventional GFL droop schemes offer limited coordination and can stress converter and DC‑voltage limits during disturbances. This paper proposes a coordinated frequency‑support framework for MT‑HVDC using GFM terminals and OWF reserves. The Multi‑terminal HVDC Frequency Support Coordination (MHFSC) strategy is decentralized and event‑triggered: each terminal detects events from local frequency deviation, exchanges only a minimal request/margin/droop dataset and evaluates feasible support considering headroom and ramp-rate. A severity‑aware allocation law blends margin‑based participation with droop‑stiffness weighting to deliver fast response while maintaining stable sharing. Allocated setpoints are injected into outer active‑power controls of GFM converters and the OWF supervisory controller without changing inner loops. EMT simulations of a three‑terminal system with two onshore grids and an OWF show improved frequency nadir with bounded DC‑voltage excursions and compliance with operating limits, demonstrating scalable coordinated support for future MT‑HVDC networks.