Comparative Study of Droop Control Methods for AC Islanded Microgrids

This paper presents a comparative study of two Droop-Based Control (DBC) schemes that have a hierarchical structure to manage power sharing among distributed generations (DGs) in AC islanded microgrids (MGs). DBC schemes are designed based on assumptions regarding feeder lines impedances that limit the design utility. In this comparative study, a control scheme is designed based on a purely inductive feeder lines assumption. The first control scheme consists of three combined controls: (1) a conventional (P/f and Q/V) Droop control, (2) a negative phase sequence virtual impedance control, and (3) an unbalanced power and small signal frequency droop control. A second control scheme is also designed based on a purely resistive feeder line assumption. This control consists of (1) a P/V and Q/$\delta$ droop control, also known as Inverse Angle Droop control, and (2) a virtual resistive output impedance control. This research examines the impact of both the feeder line model and the effects of unbalanced loads on power sharing in the islanded MGs.