Modeling and Stability Analysis for Inverter-based Stand-alone Grids: Examining Grid-forming Methods and the Interactions

As emerging technologies for power grids dominated by renewable energy, grid-forming (GFM) inverters, as well as the motor-generator pair (MGP), were proposed to enhance the inertia, damping, and system strength. Although some researches have been conducted on the transient stability of GFM inverters and MGPs, the dynamics of grid-connected generators can be dictated by the bulk power system. As a result, the stability of a stand-alone grid with mixed GFM generators should be thoroughly investigated. To fulfill this gap, first, this paper adopts a component connection method (CCM) for modeling a standalone grid integrated with multiple generators; second, the models of synchronous generators (SGs), grid-following (GFL) inverters, GFM inverters, and MGPs are studied in detail; then, the full-order state-space models of four systems with interconnected generators are built in this paper, and the simulation models are established to verify the effectiveness of the parameters; finally, the small-signal dynamics of different grids and interactions between GFM and traditional generators are fully examined.