Analysis and Suppression of Medium-High Frequency Oscillations in Grid-Connected Inverters

Focusing on the 125Hz medium-high frequency oscillation issues observed in renewable energy power stations, this study investigates the influence of phase-locked loop (PLL) coefficients on oscillation frequency and stability, combined with a typical second-order system model and impedance analysis method. By establishing an impedance model of grid-connected inverters, it reveals that the capacitive phase-frequency characteristics within the 50-150Hz frequency band interact with grid impedance, leading to underdamped oscillations. MATLAB/Simulink simulations further validate the impact of short-circuit ratio (SCR) related variables on oscillations. Results demonstrate that increasing the PLL proportional coefficient significantly broadens bandwidth and elevates oscillation frequency, while reducing the integral coefficient suppresses the capacitive region magnitude and enhances system phase margin. A parameter design method based on PLL bandwidth adjustment is proposed, providing theoretical foundations and practical guidance for suppressing medium-high frequency oscillations in renewable energy power stations.