The Impact of Synchronous Grid Forming on the Rating of HVDC Transmission Links

HVDC system provides dynamic power support to one AC system as this necessitates a reduction in DC voltage, hence an increase in DC current for a given active power, thereby impacting the cost of the major scheme components (valves and wound components) unless limits are applied to the SGFM operating range. The paper considers the basic requirements for DC voltage stability, and how the inclusion or omission of an on-load tap changer can impact on the design. Whilst one end of the HVDC link is providing the SGFM response the other end of the HVDC link must act to limit the DC voltage transient leading to a constraint on the SGFM capability of the controller [1]. Hence, the coordination of these two controllers is considered. The paper also provides guidance as to the assessment of the available energy within the HVDC link. Finally, the paper provides a dynamic assessment of the SGFM response of the DC link so that the scheme rating can be coordinated with the required dynamic response.