Nyquist stability analysis of a VSC-HVDC system using a distributed parameter DC-cable model
Paper in proceedings, 2014
In this paper a two terminal VSC-HVDC system embedded in a strong grid ACenvironment
is considered, emphasizing modeling, controllers design and small-signal stability
analysis. Traditionally, DC cables are most often modeled by Π-sections, and when using them
for higher frequencies or in case of transmission over long distances, approximation accuracy
aspects must be considered. Here, a distributed parameter cable model, based on the damped
wave equation, is used to overcome this limitation. It is shown that the VSC-HVDC system can
be described by a forward transfer function cascaded with a feedback loop. The first transfer
function will be different, due to which input and output variables that are considered but is in
all realistic cases stable. The feedback loop, where the forward path is a rational function and
the return path is a dissipative infinite dimensional system, remains the same in all cases. The
stability is then analyzed, using the Nyquist criterion, in a straight forward manner. Numerical
examples are given by MATLAB.
VSC-HVDC system
Distributed parameter cable model
Nyquist stability criterion