A brief review on the application of the virtual impedance method in islanded alternating current microgrids to control reactive power sharing

Abstract

To preserve power quality in islanded alternating current (AC) microgrids (MGs), precise line voltage regulation is crucial, especially in the presence of non-linear and unbalanced loads. Effective coordination among multiple distributed generation units is essential to meet the load requirements and maintain system stability. Disparities in line impedance often lead to unequal power distribution among distributed generation units in microgrids. This paper provides an overview of virtual impedance (VI) techniques and droop control. Typically, these techniques are combined to achieve equitable power distribution among dispersed generation units in microgrids with lines of varying impedances. In a stable state, the frequency of the distributed generation units within the microgrid remains uniform, facilitating accurate active power sharing. However, the voltage measurements from distributed generation units are often non-uniform, making reactive power sharing challenging in the microgrid. To address this issue, virtual impedance (VI) can be introduced by placing an additional impedance virtually between the inverter and the load in the physical circuit. This adjustment allows for modification of the inverter's control strategy. By integrating VI with droop control, the impedance observed at the converter's output is adjusted to counteract the coupling effects between active and reactive power, thus improving reactive power sharing and overall system performance in the microgrid.