The integration of inverter-based resources into modern power systems has attracted significant interest from the industry. Extensive research has been conducted to understand the performance of these resources under various network conditions, particularly in low short-circuit level or weak grid conditions. Despite this progress, system operators still face challenges in fully understanding modern grid behavior during extreme operating events. These challenges are further amplified when offshore wind farms are considered for black start restoration, as this rare operating mode involves extremely low short-circuit levels and introduces additional technical complexities.

To address these challenges, this research project investigates the use of detailed electromagnetic transient (EMT) modeling approach to study offshore wind farm black start behavior. The work is based on an EMT model of an offshore wind farm located in the northeastern United States. The wind farm is connected through an inter-array sub-transmission network to three offshore substations, each equipped with multiple step-up transformers that export power to shore via long subsea cables. The model includes aggregated Type 4 wind turbine generators, plant-level controllers, offshore and onshore transmission components, reactive compensation devices, and an MMC-based STATCOM capable of operating in grid-forming (GFM) mode. The objective is to develop and assess a modeling framework suitable for offshore wind black start and system restoration studies.

Results from detailed EMT simulations performed in PSCAD software demonstrate that the modeled offshore wind plant can exhibit stable control behavior across a range of operating conditions relevant to restoration. For restoration analysis, wind turbine groups are aggregated, with a subset configured as self-starting GFM black start units capable of islanded operation following loss of grid supply. Active power ramping and voltage setpoint tests confirm smooth power regulation and effective voltage control, while disturbance studies (including fault events, frequency deviations, and black start energization sequences) show stable system recovery, appropriate grid-forming inverter responses, and controlled soft energization of large interconnecting transformers.

Building on these results, preliminary black start engineering studies were conducted for staged energization of multiple MW-level modules to assess the minimum required GFM wind turbines needed to successfully energize offshore and onshore equipment. Detailed switching simulations identify key technical challenges, including temporary overvoltages, high inrush currents, zero-missing phenomenon, and sympathetic inrush. The model is subsequently used to evaluate potential mitigation options, such as voltage setpoint reduction prior to energization, pre-insertion resistors, virtual impedance tuning, and supplemental onshore voltage support.

Overall, the results demonstrate that offshore wind farms equipped with grid-forming capability can be represented to study black start restoration behavior under a range of operating conditions, and to identify technical challenges and evaluate potential mitigation measures. The findings are relevant to system planners and operators as inverter-based resources play an increasing role in future power system restoration and resilience strategies.