  This paper presents a two-layer, four-level distributed control method for
networked microgrid (NMG) systems, taking into account the proprietary nature
of microgrid (MG) owners. The proposed control architecture consists of a
MG-control layer and a NMG-control layer. In the MG layer, the primary and
distrib-uted secondary control realize accurate power sharing among distributed
generators (DGs) and the frequency/voltage reference following within each MG.
In the NMG layer, the tertiary control enables regulation of the power flowing
through the point of common coupling (PCC) of each MG in a decentralized
manner. Furthermore, the distributed quaternary control restores system
frequency and critical bus voltage to their nominal values and ensures accurate
power sharing among MGs. A small-signal dynamic model is developed to evaluate
dynamic performance of NMG systems with the proposed control method.
Time-domain simulations as well as experiments on NMG test systems are
performed to validate the effectiveness of the proposed method.
