Low-Frequency Passivity-Based Analysis and Damping of Power-Synchronization Controlled Grid-Forming Inverter

This article presents a passivity-based analysis and damping method for the low-frequency dynamics of grid-forming (GFM) control. A closed-form analytical solution to the positive realness of control input admittance is developed, which reveals the inherent nonpassive property of GFM control. This feature gives rise to the risk of instability, especially in connection with a nearby nonpassive GFM inverter, which may induce undesired control interactions. It is further revealed that the passivity index is determined by a low-frequency resonance around 10 Hz in the dq -frame, and this resonance can be better dampened, therefore, with enhanced passivity index, by using a virtual reactance (VRA) than using a virtual resistance (VRS). Finally, the theoretical findings are verified by the experimental results.