A Step-by-Step Design Procedure of a Robust Control Design for Grid-Connected Inverter by LCL Filter in a Weak and Harmonically Distorted Grid

摘要

The current-controlled grid-connected inverter with LCL filter is widely utilized in the distributed power generation systems at remote places with weak grids. Oscillations in weak grids have raised the stability issue in grid-tied inverter systems, and the quality of the injected power into the grid is highly affected by the variations of grid-side inductance. In this study, a multi-loop control has been applied in the LCL-type grid-connected inverter based on capacitor current feedback control method. Computational delays in the control unit can remarkably influence the damping capability of this method. The accuracy of the modeling has been increased by considering the computational delays of the capacitor current active damping inner loop as well as the grid current outer loop. The impact of the computational delay is eliminated by the proposed approach, and the performance of the control system has been remarkably enhanced. The harmonic attenuation of the grid voltage has been improved by utilizing virtual series and parallel impedances, which leads to strong stability-robustness and high harmonic-rejection-ability even in severe variations of the grid-side inductance. Simulation results verify the credibility of the proposed approach, and the quality of the injected power is proved to be improved in a weak and harmonically distorted grid.