Grid code compliance of VSC-HVDC in offshore multi-terminal DC networks

This paper studies grid code compliance of offshore wind farms (OWFs) when connected to a multi-terminal dc network (MTDC) using VSC-HVDC technology. As the wind farms become decoupled from the ac grids via the dc network, the onshore VSC-HVDC terminals are responsible for complying with the grid codes. However, the onshore VSCs are an active part of the MTDC network control. Voltage-source converters can independently control active and reactive power, but only within their rated capability. If reactive power requirements are too strict, it detriments the converter active power capability, influencing the MTDC network operation. The work is divided as follows: at first, the most common grid codes requirements are introduced. Secondly, the capability chart of a VSC-HVDC terminal is analyzed. Afterwards, the operation of VSC-HVDC terminals inside MTDC networks is explained. Lastly, dynamic simulations verify whether VSC-HVDC terminals fulfill the grid codes requirements when inside MTDC networks.