As power systems decarbonise, offshore wind power plants (OWPP)s have been proposed as replacements for conventional blackstart units. This work reviews state-of-the-art OWPP blackstart capabilities, focusing on HVDC-connected OWPPs, whose wind turbine generators (WTG)s—upgraded with grid-forming (GFM) controls in their voltage source converters (VSC)s—will lead the restoration operation.

Traditional restoration guidelines rely on synchronous generators, but modern standards emphasise converter-based resources for resilience. OWPPs can theoretically provide fast blackstart service, but practical realisation remains challenging. Electromagnetic Transient (EMT) simulations suggest that a few GFM WTGs can energise AC networks and HVDC links. Studies show both hard and soft energisation methods—a hard start applies full voltage in one step, whereas a soft start ramps up to limit surges. This review synthesises research breakthroughs, knowledge gaps, and standards, distilling them into five main challenges:

1. GFM/Grid-Following (GFL) WTG mix: Not all WTGs in a large OWPP will be GFM, and the minimum GFM share needed to stabilise a dead network is unclear; studies often assume 100% GFM or add a battery energy storage system (BESS), leaving mixed GFM/GFL dynamics poorly understood.
2. Energisation sequencing: The optimal sequence of a system restoration—from self-start at the WTG-level to blackstart an HVDC-connected OWPP and beyond—is not established. Few studies detail the full procedure, and uncertainties remain in controlling inrush currents and overvoltages at each stage, especially with large HVDC DC-link capacitors.
3. Control interactions: Interactions between multiple GFM VSCs and remaining GFL units—WTGs, HVDC transmission, BESS, reactive compensation, etc.—remain under investigation. Unintended coupling can occur when GFM inverters run without coordinated control. Most studies focus on a single GFM, and system-wide stability analyses are lacking.
4. WTG sub-model limitations: Many simulation studies oversimplify WTG models by neglecting detailed models of the machine-side converter (MSC) of the GFM WTGs, turbine shaft dynamics, or assuming an ideal DC-link. Such simplified modelling can misrepresent phenomena like DC-link capacitor inrush. More detailed WTG models are needed.
5. Validation, standards and protection: No full-scale OWPP has performed an autonomous blackstart. Testing and certification standards remain nascent; design verification, protection coordination (e.g. FRT/UVRT thresholds, current-limit settings, relaxed relay logic during soft-ramp), and on-site testing for OWPP-led blackstart are still insufficient.

The recent April 2025 peninsula-wide blackout in Spain—triggered by two rapid generation trips during a period of unusually high penetration of converter-based resources—has reignited debate on inertia-less systems and highlighted the urgency of developing GFM, blackstart-capable converter technology to ensure stability and restartability in renewable-dominated grids.

This literature-based analysis finds GFM-controlled OWPPs promising but underutilised for blackstart; prior studies demonstrate feasibility in simulations and small tests yet highlight unresolved stability, control coordination, and component stress issues. Key knowledge gaps include mixed GFM/GFL behaviour, HVDC energisation from wind, and need for high-fidelity WTG models. By bringing together findings from diverse sources into a single narrative, this work provides a comprehensive overview of the state-of-the-art and identifies critical research gaps. These insights set the stage for developing robust blackstart-capable OWPPs and inform stakeholders of the technical challenges that must be overcome to certify OWPPs as blackstart units.