LCL Filter Design for Single-Phase Grid-Connected PV Inverters with Double-frequency Unipolar PWM Switching

The current injected by PV inverters to the grid must contain low harmonic content within the standard limitations. However, the output voltage of inverters consists of large harmonic components at switching frequencies due to the PWM switching. Thus, an LCL filter is normally installed at the inverter output to efficiently reduce the current harmonics. Among different PWM switching schemes, double-frequency unipolar PWM has drawn little attention due to the issue of common-mode leakage current in transformerless inverters. However, this switching method offers advantages such as a lower harmonic content and higher efficiency. This paper paves the way for the implementation of double-frequency PWM switching scheme in transformerless single-phase grid-connected PV inverters by introducing a detailed description on LCL filter design. Theoretical and simulation studies on a complete PV converter are conducted in MATLAB/SIMULINK to prepare a straightforward LCL filter design procedure.