LCL-filter design for grid-connected inverter to suppress grid-induced low-order current harmonics

For grid-connected inverter, an LCL-type filter is widely used to suppress switching harmonics, and the capacitor current feedback is used to suppress the LCL resonance. In the published literatures, the relation among LCL parameters, capacitor current feedback and resonance damping was discussed; however, their relation with the low-order current distortion was not seriously considered. Considering that the main objective of using the LCL-type filter is to fulfill the current quality standard, the optimized design of LCL-type filter for low-order current harmonic suppression is deeply discussed in this paper. It is demonstrated that the suppression of grid-induced low-order current harmonics is closely related to the LCL parameters. On the basis of selecting the inverter-side inductance according to the switching ripple requirement of inverter-side current, the rest two parameters including the capacitance and the grid-side inductance are designed to enhance the low-order current harmonic suppression. Finally, two sets of LCL parameters are tested in this study, one of which is obtained by the proposed design procedure. Experimental results have demonstrated a good grid current quality under a distorted grid.