Damping for Multi-Paralleled Grid Tied Inverters with LCL Filters

This paper addresses the resonance issue in a multi-paralleled LCL-based grid-tied inverter system. Compared to the single grid-tied inverter where the resonance is fixed by the inverter output LCL filter and grid impedance (if considered), the multi-paralleled grid-tied inverters present more challenging resonances which are varied due to the coupled grid impedance and the number of paralleled inverters. In order to suppress resonances, system damping has to be implemented. An active damping technique based on a high-pass filter (HPF) applied to feedback current controlled is employed so as to improve the conversion efficiency with no extra measurements required. A novel design method based on the D-decomposition tool is proposed for readily determining the stability region in parameter space. Phase and gain margins are considered leading to an optimum system control condition. Both simulation and experiment are carried out to demonstrate the validity and effectiveness of the method.