Synchronization Stability of Interconnected Microgrids with Fully Inverter-based Distributed Energy Resources

In this paper, the synchronization stability challenges of same-rated frequency interconnected microgrids (IMGs) with fully inverter-based generation units are studied. In this type of weak power grid with low X/R ratios and low line impedances, no strong source with a high-inertia rating exists with which other generation units can be synchronized. Two IMGs controlled using a pinning consensus-based control architecture are considered. The inrush power flow at the beginning of the interconnection process is modeled and analyzed. This power flow is affected by the voltage/phase/frequency difference of the IMG points of common coupling. A small-signal model of the IMGs is obtained that includes a synchronization control unit, and small-signal stability is analyzed based on sensitivity analysis of the most important control and operational parameters. In addition, the transient stability of a nonlinear model of the IMGs under study as implemented in SimPowerSystems/MATLAB is investigated. Stable synchronization is more challenging than the synchronization of multi-area strong power grids and grid-connected MGs. However, synchronization can still be performed by selecting more limited ranges for the control gains and threshold values of the synchronization algorithm. Nevertheless, different disturbances such as high load conditions can cause synchronization instability.