Research on the Parallel Circulating Current Resonance of LCL-type Grid-connected Inverters

When LCL-type grid-connected inverters operate in parallel, they generate circulating current paths that can cause resonance, jeopardizing the safe and stable operation of the grid-connected system.This paper establishes the equivalent circuit for circulating currents in the parallel grid-connected model of LCL-type inverters and provides a theoretical derivation. By analyzing the harmonic content of each current, this study investigates the distribution of resonant components in the system and the causes of circulating current resonance. To suppress the parallel circulating current resonance, capacitive current feedback is introduced into one of the parallel modules. Simulation and experimental results show that the circulating current resonance from parallel LCL-type grid-connected inverters exists only in the system's circulating current path and does not flow into the grid. Introducing capacitive current feedback control into one of the parallel modules effectively suppresses circulating current resonance.