Modeling and Resonance Analysis of Parallel Grid-Connected Inverters with LCL Filters

This paper investigates the complex resonances issue encountered in parallel grid-connected inverters. In this context, the presence of connecting LCL filters give advantages in cost and dynamic compared to L filters. Nevertheless, each LCL filter induces its specific resonance in the system, which results in complex resonance characteristics, especially in case of different LCL filter parameters. These resonances can lead to the whole micro-grid instability. To understand the resonance origins, this paper presents a comprehensive modeling method to illustrate the complex resonance phenomena. These phenomena are highlighted for the case of two parallel inverters with similar and different LCL filters.