Small-Signal Modeling and Stability Analysis of Paralleled Grid-Feeding Voltage Source Inverters

Paralleled grid-feeding inverters are now ubiquitous as interfaces between renewable energy and power grids. However, interactions between inverters can lead to system instability. Thus, there is a pressing need for suitable models to study such systems' stability and behavior. This paper focuses on the small-signal modeling and stability of paralleled grid-feeding inverters. First, we present a small-signal model for a single grid-feeding inverter incorporating modulation transport delays and inverter-side current control. We subsequently extend the model to a generalized multi-inverter system. A case study comprising three paralleled inverters then examines small-signal stability. Participation factor analysis shows that the modulation transport delays and inverter-side current participate heavily in the fastest system modes. Moreover, eigenvalue analysis identifies the system's stability limit range given increases in the grid inductance, verified with time-domain simulations.