Impedance Reshaping and Robustness Enhancement of Grid-Following Inverters Considering Phase-Locked Loop Frequency Coupling Effects

This paper proposes a phase-compensated enhanced second-order generalized integrator phase-locked loop (ESOGI-PLL) to suppress the frequency coupling effect (FCE) and its associated power quality degradation in grid-following inverters (GFLIs). An output impedance model incorporating FCE dynamics is formulated via signal perturbation analysis to quantify grid-current harmonic amplification and weak-grid instability boundaries. To suppress the FCE, the proposed ESOGI-PLL structurally embeds a phase-lead compensator, directly neutralizing the inherent phase lag of conventional filters. Simulation results demonstrate that the proposed ESOGI-PLL effectively mitigates PLL-induced frequency coupling, thereby improving the output-current quality and stability of GFLIs under weak-grid conditions. Compared with the synchronous reference frame phase-locked loop (SRF-PLL), the total harmonic distortion (THD) of the grid-current decreases from 24.33% to 2.47% under harmonic disturbances, while the transient settling time is significantly reduced, confirming the effectiveness of the proposed approach in enhancing both dynamic performance and output-current quality.