LCL Filter Design and Damping Analysis for Grid-Connected Inverters in Modern Uncertain Grid Impedance Conditions

This work proposes a LCL-filter design method and its current control to grid-connected inverters. It is well known that the LCL filter may excite instabilities due to its resonance characteristics. For instance, in modern grids, the impedance is uncertain and the LCL resonant frequency might be driven towards the control system bandwidth, what might excite instabilities or oscillations. The design methodology proposed in this work ensures that the LCL resonant frequency is within a desired frequency region even under severe grid impedances variations. Along with, the control system is also designed regarding such extreme scenarios. A comparison between active and passive damping techniques is done and a dq reference frame current control is used for evaluation. For experimental purposes, an equivalent single-phase prototype is used for validation of the proposed methodology.