Model Reduction for Inverter-Dominated Networked Microgrids with Grid-Forming Inverters

The increasing penetration of grid-forming inverters has significantly complicated the operating characteristics of modern power grids, which calls for reduced-order models that preserves the system's main responses for large-scale analysis. This paper presents a model reduction approach to study the dynamic responses of inverter-dominated networked microgrids (MGs) under disturbance. Coherency-based aggregation technique is used to identify the study area and external area. The study area is modeled in detail while the external area is successively simplified. Specifically, the reduced-order model of the external area is first simplified by developing reduced-order models of inverter and network; it is then further simplified using linear truncation. To replicate the interactions between the two areas, the external area is aggregated into a controllable voltage source whose operating states are collaboratively determined by the states from both areas. The developed reduced-order model represents a closed-loop simulation that combines both linear model reduction for reduced system dimensions and detailed nonlinear model for better accuracy. At last, the performance of the developed model reduction approach is validated using time-domain simulation.