Abstract
This paper presents a structured approach for analysing the effect of HVDC transmission system expansion on the small signal dynamics. The methodology decomposes the expansion of the system into a sequence of steps and aims especially at identifying the eigenvalues associated with interactions between the initial system and an added converter terminal. The procedure is illustrated with an example of expanding a point-to-point HVDC connection to a three-terminal radial configuration. The modes highlighted as responsible for the interactions between the initial system and the added third terminal are compared to the interaction modes identified by participation factor analysis. The presented results demonstrate that these two approaches present an excellent correlation and reveal complementary information.