Coordinated black start feasibility from a bipolar MTDC network integrating multiple offshore wind power plants

As thermal power plants make way for an increasing penetration of offshore wind in Great Britain (GB), transmission owners and National Grid Electricity System Operator must consider how low carbon technologies can deliver ancillary services once provided by conventional generation. With practical applications of grid-forming control emerging on converter-based resources, black start capability is a potential functional specification for future offshore wind power plants (OWPPs). Much of the literature has investigated black start feasibility of OWPPs in both AC and DC-connected point-to-point configurations. However, it is proposed that in future OWPPs in GB will share transmission assets, connecting to the onshore system through integrated offshore network topologies. In this paper, the feasibility of coordinated black start solutions based on a future offshore network scenario is studied. The work is undertaken by means of electromagnetic transient simulation in RTDS/RSCAD. A three-ended multi-terminal HVDC (MTDC) network, of bipolar configuration, is developed for the study, which incorporates two OWPPs and a co-located onshore BESS. The study sets out to investigate start-up requirements of the offshore AC island and the MTDC system. Coordinated energisation scenarios are then studied to evaluate the benefits of the network arrangement to the onshore system during restoration. Benefits include supporting the onshore system from multiple points of infeed simultaneously, power sharing, faster restoration, and reduced vulnerability to local wind variability.