Accurate Reactive Power-Sharing Using Modified Droop Method Based on Virtual Impedance Control in the Islanded Microgrids

In the islanded microgrids, distributed energy sources are responsible for power-sharing, and accurate power-sharing is essential among these microgrids. Due to the mismatch of the physical impedance of power lines, poor reactive power-sharing is observed. Therefore, in this paper, the use of virtual impedance in the form of two methods of virtual positive impedance and virtual negative impedance is proposed to improve the accuracy of reactive power-sharing in a conventional droop controlled islanded microgrid. In this paper, in addition to presenting a controller to properly adjust the virtual impedance, the concept of virtual negative impedance is used to correct the effective impedance of the power supply line and improve the common bus voltage, and increase the output power of energy sources. To evaluate the proposed control methods, a test islanded microgrid is simulated in PSCAD/EMTDC software. The results show that both proposed methods have a good effect on the proper reactive power-sharing in the microgrid. In addition, the results show that the virtual negative impedance method can improve the common bus voltage and increase the output power of the source by reducing the effective line impedance.