The performance of an HVDC–MMC link connected in parallel
with an ac line was evaluated in this study. A complete overview on
the abnormal interactions that can occur during small and large disturbances
was presented. A small-signal analysis model was used
to study interactions in this system. This model was verified using
nonlinear time-domain simulations in EMTP-RV and the impact of
SCR was evaluated. The analysis of eigenvalues and mode shapes
was used to assess interactions between different variables of the
system.
It was found that during small perturbations, the parallel ac
line can improve the dynamic performance of the HVDC link and
that the risk of negative interaction between both HVDC stations is
negligible.
The parametric studies conducted under EMTP-RV have con-
firmed the small-signal studies for small perturbations, but it was
found that for large disturbances, negative interactions can occur
when an ac line is in parallel with the HVDC link. Therefore, it is
important to perform parametric studies using EMT-type models
in order to cope with negative interactions.