Unbalanced Model and Power-Flow Analysis of Microgrids and Active Distribution Systems

This paper presents a three-phase power-flow algorithm, in the sequence-component frame, for the microgrid (μgrid) and active distribution system (ADS) applications. The developed algorithm accommodates single-phase laterals, unbalanced loads and lines, and three/four-wire distribution lines. This paper also presents steady-state sequence-component frame models of distributed energy resource (DER) units for the developed power-flow approach under balanced/unbalanced conditions. The DER models represent the synchronous-generator based and the electronically-coupled DER units. Both constant power (PQ) and regulated-voltage (PV) modes of operation of DER units are considered. The application of the developed power-flow method for two study systems is presented. The study results are validated based on comparison with the detailed solution of the system differential equations in time domain, using the PSCAD/EMTDC software tool.