Distributed AC power flow method for AC and AC-DC hybrid autonomous microgrids with droop control

Abstract

Power flow methods are one of the powerful tools used in the analysis of stable and reliable operation of the electric power systems. Conventional power flow methods make use of slack bus, PV and PQ bus, low R/X ratio in the formulation of the power flow. These assumptions while considering autonomous microgrids (MGs), with small sources and low voltage connection lines, are not suitable. Present MGs incorporate AC and DC sources and loads along with storage and power electronic conversion devices. In light of these facts, a distributed power flow method (DPFM) for autonomous microgrids is presented here that solves the power flow problem node-wise, minimizing losses and does not consider slack, PV or PQ buses. In order to have proper control over the load sharing among the sources, a modified droop control is used. The proposed DPFM can be used for AC low voltage (LV) autonomous microgrid systems with added advantages of remedying the dependency on voltage level and R/X ratio in the formulation itself. DPFM is applied on a 10 bus, low voltage, microgrid system giving a better voltage profile..

Keywords: Microgrid (MG), Distributed Energy Resources (DER), Particle Swarm Optimization (OPF), Time varying inertia weight (TVIW), Distributed power flow method (DPFM)