Analysis and Design of Grid-Tied Inverter With LCL Filter

The LCL filter represents the state-of-the-art passive interface type for grid tied power converters as a cost and space reducing alternative to single coil solutions for switching harmonic attenuation. However, a simple PI controller can cause instabilities when applied to control the current of this filter. Thus a general analytically closed approach is presented to determine the safe operating areas for both grid current control mode (GCM) and inverter current control mode (ICM), both with and without additional active damping feedback of the capacitor current. The proposed approach consequently applies the Nyquist criterion in the continuous frequency domain, facilitating the determination of very simple expressions of parameter stability limits. These design guidelines, which partially also confirm previous findings, are for the first time summarized all together as the results of proposed approach to aid corresponding controller design.