In this manuscript, a novel Δ-circuit approach is
proposed, which enables the fast calculation of fault currents in
large islanded AC microgrids (MGs), supplied by inverter-based
distributed generators (IBDGs) with virtual impedance current
limiters (VICLs). The concept of virtual impedance for limiting
the fault current of IBDGs has gained the interest of research
community in the recent years, due to the strong advantages it
offers. Moreover, Δ-circuit is an efficient approach, which has
been widely applied in the past, for the calculation of short?circuit currents of transmission and distribution networks.
However, the traditional Δ-circuit, in its current form, is not
applicable in islanded MGs, due to the particular characteristics
of such networks, e.g., the absence of a slack bus. To overcome
this issue, a novel Δ-circuit approach is proposed in this paper,
with the following distinct features: a) precise simulation of
islanded MGs, b) fast computational performance, c) generic
applicability in all types of faults e.g., single-line, 2-line or 3-line
faults, d) simple extension to other DG current limiting modes,
e.g., latched limit strategy etc. The proposed approach is
validated through the time-domain software of Matlab Simulink,
in a 9-bus and 13-bus islanded MG. The computational
performance of the proposed fault analysis method is further
tested in a modified islanded version of the IEEE 8500-node
network.
Short-Circuit Calculation in Distribution Networks with Distributed Induction Generators
