DC voltage droop control structures and its impact on the interaction modes in interconnected AC-HVDC systems

Different dc voltage droop control structures for future multi-terminal HVDC systems have been proposed in literature. This paper contributes to the evaluation of those structures by an analysis of their impact on the coupling of the interconnected subsystems. In particular, the modes of the systems are classified in different subsets according to the participation of the various subsystems. Those subsets are then evaluated qualitatively and quantitatively indicating which impact the choice of the droop control structure has on the degree of coupling between the connected ac and dc systems respectively the different HVDC converters. The lowest damped interaction modes of the different subsets are analyzed in more detail.