Steady-state operational range evolution from a two-terminal to a multiterminal HVDC transmission system

DC grids are anticipated to grow organically with one possible initial configuration being formed by interconnecting an additional HVDC converter into an existing shore-to-shore (StS) HVDC link. In order to ensure the performance of this MTDC system, the DC voltage at each converter terminal within the system should stay within a certain allowable range. The steady-state DC voltage operational range of this MTDC system is not only determined by the StS link, but also the DC voltage limits of the interconnected converter(s). This paper explains how the operational range of the MTDC system can vary depending on several factors, e.g. power rating and DC voltage range of the additional converter, the distance from this converter to the DC hub, and how close the DC hub is located from one of the StS link’s end. The study results provide valuable input for the StS link owner to plan or appraise the expansion of its link or to establish a requirement for the additional converter that can minimize the impact when it interconnects with an existing StS link. Furthermore, the principles given in this paper can be extended for any numbers of additional converters to be interconnected with the existing StS link.