Offshore wind power plants with VSC-HVDC transmission: Grid code compliance optimization and the effect on high voltage ac transmission system

The development of large offshore wind power generation in the North Sea has been significantly accelerated in the last years. The large distance from shore in combination with the need for large transmission capacity has raised the interest for the voltage source converter high voltage direct current technology (VSC-HVDC). Transmission system operators in order to ensure high degree of the power system security of supply, impose strict grid connection requirements to offshore wind power plants and their HVDC transmission. Based on these boundary conditions, the overall research objectives that have been assessed in the context of this thesis include the following. Assessment of the state of the art coordinated fault-ride through strategies for offshore wind power plants with VSC-HVDC transmission. Analysis of unbalanced grid faults for wind power plants with VSC-HVDC transmission. Investigation of the effect of negative sequence current control for onshore and offshore AC faults. Analysis of the effect of typical grid codes on the power system voltage and rotor angle stability. The developed methodologies, models and control schemes proposed within the context of this thesis could facilitate the analysis and stable operation of transmission systems with VSC-HVDC connected offshore wind power plants.