Individual Channel Design-Based Precise Analysis and Design for Three-Phase Grid-Tied Inverter With LCL-Filter Under Unbalanced Grid Impedance

Three-phase grid-tied inverter with LCL filter is usually designed to operate under symmetric grid impedance. However, in actual operations, the equivalent three-phase grid impedance tends to be unbalanced, which turns the three-phase grid-tied inverter with LCL filter into a highly coupled multiple-input-multiple-out system. Traditionally, the impact of the cross-coupling on the stability is directly overlooked, which may lead to imprecise stability analysis. To overcome this issue, this article proposes an analysis and design method for three-phase grid-tied inverter with LCL filter under the unbalanced grid impedance based on the individual channel analysis and design. First, the effect of unbalanced grid impedance on the structural robustness is comprehensively evaluated. Then, the control system is simplified with no loss of structural information. Thus, the stability can be precisely analyzed and, simultaneously, the controller parameters can be easily tuned by applying Bode/Nyquist plots. Simulation and experimental results are provided to demonstrate the validity and effectiveness of the proposed method.