Blackstart from HVDC‐connected offshore wind: Hard versus soft energization

Abstract

Abstract In recent years, renewable energy sources have been integrated on a large scale in power systems all around the world to address the environmental sustainability concerns. With conventional thermal generators being phased out, large offshore wind power plants present a viable alternative to provide blackstart services for power system restoration. By means of simulations, grid‐forming wind turbines are shown to successfully energize the offshore transformer and the high‐voltage direct current (HVDC) export link in a controlled manner, to ultimately supply onshore block load. Two methods for energizing the offshore network have been compared: the prevalent hard‐switching approach and the more complex soft‐start method. Additionally, control has been implemented to mitigate the significant transients in the export link associated with pre‐charging of the onshore converter. It is shown that soft‐start can provide faster energization with smaller transients compared to hard‐switching. Moreover, the sensitivity analyses performed in this study illustrate the impact of pre‐insertion resistor and voltage ramp‐up rates on transients during hard‐switching and soft‐start, respectively. The results presented also show that grid‐forming wind power plants can deal with controlled pre‐charging of the onshore converter from its DC terminals that is essential for the safe energization and operation of the export link.

Keywords

• Wind power plants
• Control of electric power systems
• Distributed power generation
• Power system management, operation and economics
• d.c. transmission