On the modelling of DC microgrids for steady-state power flow studies

Abstract

This paper introduces a comprehensive modelling framework for power flow studies of DC microgrids (MG). Suitable AC/DC and DC/DC converter models based on voltage source converters and dual-active bridges are firstly derived. In turn, these are seamlessly combined with battery energy storage systems (BESS) and distributed generators (DG) such as cogeneration, wind generators and photovoltaic systems to give rise to a complete MG representation. The hallmark of this formulation is that all MG component models are derived following basic principles of operation in steady-state in such a way that their internal variables are calculated during the iterative process. The method features a unified formulation through the widely-used power injection concept. For validity purposes, a 13-node MG comprising three DG, two DC/DC converters and one BESS is studied considering both grid-connected and island operation modes. The same MG model was implemented in Matlab/Simscape Electrical using detailed models. Both solutions are shown to agree well with each other since errors inferior to 1% and 2% were obtained for nodal voltages and power flows, respectively. A 118-bus MG including 15 DG units, 5 DC/DC converters and 4 BESS was additionally studied to confirm the practicality of the new approach in larger MG facilities.