Grid-synchronization modeling and its stability analysis for multi-paralleled three-phase inverter systems

Synchronization instability issue and the corresponding low-frequency power oscillation phenomenon between synchronous generators were already found in electric power systems and addressed by various solutions. However, the grid-synchronization behaviors and the potential instabilities between multi-paralleled power electronic inverters have not been well-understood due to the different synchronization mechanisms. This paper presents a set of small-signal modeling methodologies to predict the low-frequency behaviors of the grid-synchronization loops in multi-paralleled inverter systems. The proposed model can predict the low-frequency unstable oscillation in large-penetrated renewable-energy systems as well as assess the effectiveness of frequency-based islanding-detection under multi-paralleled inverter conditions.