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An Efficient Δ-Circuit approach for Online Short-Circuit Calculation in Large Islanded AC Microgrids

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.