Robust Control of Grid-connected Inverters Based on PLL Bandwidth Decoupling in Weak Grids

Under weak grid conditions, the increase in PLL bandwidth easily leads to the decrease in the stability margin of the grid-connected system. For this reason, we propose a new control structure based on phase-locked loop (PLL) bandwidth decoupling, which can improve the system adaptability in weak grids. Firstly, the output admittance model of the three-phase grid-connected inverter is constructed, and the bandwidth decoupling control loop is optimized. This approach can effectively eliminate the influence of the PLL bandwidth on the stability of the grid-connected system. Secondly, the output admittance model of the inverter system is reshaped through the incorporation of a band-pass filter. This measure contributes to further improving the stability of the grid-connected inverter in weak grid. Finally, the effectiveness of the proposed method is verified through the RT-LAB hardware-in-the-loop experimental platform. The results show that the proposed control structure not only effectively eliminates the impact of PLL bandwidth on system stability, but also significantly enhances the robustness and dynamic performance of the system under weak and even extremely weak grid conditions.