  Modern power system is undergoing a paradigm shift from the synchronous
generators-based system to the power electronics converters-dominated system.
With the high penetration of converters, serious stability problems are
provoked, especially the wideband oscillations. Various studies have been
conducted in this respect, while most of them separate the ac-side stability
with the dc-side stability. However, for the stability analysis of the hybrid
AC/DC grid, it is necessary to consider the converter ac-side and dc-side,
simultaneously. In this paper, the stability analysis of voltage source
converters (VSCs) considering both ac and dc dynamics is carried out. At first,
the three-port AC/DC admittance model of VSCs is established, and the
corresponding measurement method from simulations is presented to validate its
accuracy. Secondly, based on such three-port model, two stability analysis
methods are presented: the one is based on the system open-loop model, where
the stability can be judged via the Generalized Nyquist Criterion (GNC); the
other one is based on the system closed-loop model, whose stability can be
predicted through the pole-zero calculation. At last, a test AC/DC system is
built in MATLAB/Simulink, by which the effectiveness of the three-port
model-based stability analysis is validated.
