Hierarchical Control of Paralleled Voltage Source Inverters in Islanded Single Phase Microgrids

Abstract

Voltage source inverters (VSIs) are key elements of microgrids (MGs), their control presents an important challenge in order to ensure the system stability. In this paper, a modeling and hierarchical control of single-phase paralleled VSIs forming a MG is presented. The diagram of the hierarchical control consists of inner, primary, and secondary control levels. The inner control commonly referred as zero level is used to regulate the VSI output voltage. The primary control is based on the droop control method and the virtual impedance loop with the objective of sharing the power accurately regardless of the line impedance of the inverters. Secondary control is used to regulate the voltage and frequency to their rated values and eliminating the deviation caused by the primary control as well as synchronizes the MG voltage with the main grid for a smooth transition. The simulation was conducted to show the feasibility of the control system. The results demonstrate the disturbance rejection performance and the stable operation of the studied MG with the proposed control scheme.