Lyapunov-based Large-signal Stability Analysis of Inverter-based Microgrids

Inverter-based microgrids are vulnerable to instabilities due to the low inertia of installed inverter-based resources (IBRs). Both large-signal and small-signal stability analyses have been used to assess the response of microgrids to various changes and disturbances. Although small-signal stability models and analysis methods for microgrids have been well developed, these models and methods do not capture system dynamics to large disturbances and faults. On the other hand, developing accurate and well-established large-signal models for microgrids is a complicated and time-consuming task. Most of existing large-signal stability studies for microgrids consider an IBR connected to an infinite bus, which does not model the interactions between interconnected IBRs. In this paper, a nonlinear model for large-signal stability analysis is developed for a large-scale inverter-based microgrid under different events, including load reconfiguration, line outages, and distributed generation (DG) disconnection. A state-space model for inverter-based microgrids is developed with a Synchronous Reference Frame Phase-Locked Loop (SRF-PLL)-based droop controller for stability sensitivity analysis. The Lyapunov function is used as a criterion for the stability analysis. The proposed model and approach are tested on a microgrid under different disturbances.