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Grid-Synchronization Modeling and Its Stability Analysis for Multi-Paralleled Three-Phase Inverter Systems

Fig. 1. Multi-paralleled power electronic converter system.
The issue of synchronization instability and the corresponding low-frequency power oscillation phenomenon between synchronous generators is 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 is not well-understood due to the different synchronization mechanisms.

CPES researchers present 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.

Fig. 2. Experimental test result showing the unstable PLL output: vga [100 V/DIV], iC1a [10 A/DIV], ωC1, ωC2 [0.05 Hz/DIV].