  With the advancement of the idea of the HVDC grid, it becomes imperative to
study the interaction of controller and identification of modes of
oscillations. The paper presents the complete model of HVDC grid with detailed
modeling of controllers, phase lock loops (PLLs), dc grid and the ac systems.
An analytical method combining participation factors and Eigen-sensitivity is
proposed to determine the relative stability of the HVDC grid with respect to
parameter variations. The paper also proposes the identification of inter-area
and controller interaction modes on the basis of the nearest distance between
the eigenvalues using the derived sensitivity indices. The critical parameters
are varied in a mixed short circuit ratio (SCR) HVDC grid and predictions from
the analysis method are confirmed with time-domain simulation in PSCAD
simulator
