Small-Signal Modeling and Stability Analysis of a Droop-Controlled Grid-Forming Inverter

Grid-forming inverters present a promising control philosophy for inverter-dominated power grids. However, further research is required to better understand the modeling and control of such devices, yielding design and performance improve-ments alike. This paper systematically develops a small-signal model predicated upon a state-space framework, accurately capturing dynamics associated with the current and voltage regulators, droop controller, modulation scheme, LCL filter, and grid connection. Participation factor analysis compares and contrasts the modal characteristics of grid-forming and grid-feeding inverter topologies, with the main differences observed in the states contributing to the fastest modes (eigenvalues). Moreover, small-signal analysis of the current and voltage regulators' proportional gains demonstrates the latter's significance concerning the grid-forming inverter's stability. Time-domain simulations validate the small-signal model's predictions.