Effective Active and Reactive Power Sharing Among Multiple DG Units Using Coordinated Virtual Impedance

Microgrids (MGs) with special infaces on renewable energy sources (RESs) have the potential to solve several problems in electric power grid. However, MGs encounter a major problem in case of mismatched feeders connecting the RESs to the loads via point of common coupling (PCC). This situation results in inaccurate reactive power sharing between RESs due to the different voltage drop on the feeders. Droop control along with virtual impedance (VI) approaches were combined in the literature to solve this problem. In addition, different VI evaluating techniques were merged to accurately specify the value of the inserted component. These techniques have good results. However, they compensated the system impedance to different points and the evaluation of these points was fully unaddressed in the literature. So, this work proposes evaluating these different compensation points and conducting a comparison in terms of controller overshoot, settling time, error percentage, circulating current reduction, and their effect on the PCC voltage with achieving accurate active and reactive power sharing between RESs.

I. Introduction

Microgrids (MGs), as single controllable entities with interconnected distributed generators (DGs) and loads, could be operated in grid connected mode or islanded mode. MGs have the advantages of reducing the power losses in the electric system with near zero carbon emissions. In islanded mode, these entities suffer from inaccurate reactive power sharing [1]–[3].