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. Never-theless, different disturbances such as high load conditions can cause synchronization instability.