Tan-Sun Transformation based Virtual Inductance Control Loop for Unbalanced Power Sharing of Islanded AC Microgrids

Abstract

In this paper, a hierarchical control scheme, including a Tan-Sun coordinate system primary control structure, for islanded AC Microgrids with unbalanced conditions is presented. The proposed control strategy involves the application of the Closed-loop Initial Phase Detection Adaptive (CIPDA) system based on the Tan-Sun coordinate system in each distributed generation (DG) unit. Furthermore, an adjustable Notch Filter (ANF) with Microgrid frequency is employed for the unbalanced currents detection unit. The traditional droop control method is presented through using Proportional-Integral controller (PI) for the regulation of voltage and current in each unit as well as the determination virtual inductance (DVI) for the opposite droop relation between the unbalanced power, negative-sequence virtual inductance, and transient coupling unit to determine the opposite droop reference. The negative-sequence virtual impedance unit generates a negative-sequence voltage reference using the Tan-Sun inverse matrix for the switching units by receiving the valid inductance from the DVI unit. The results obtained from simulation in the environment of MATLAB/Simulink software confirm the correct operation of the proposed control structure under unbalanced conditions.