Interaction Stability Analysis and Oscillation Suppression Method of Hybrid Grid-Forming and Grid-Following Inverters System With Varying Power Levels

Grid-forming inverters (GFMIs) are increasingly being integrated into grid-connected systems dominated by grid-following inverters (GFLIs) to enhance the stability of weak grids. However, the capability of traditional grid-forming control to enhance system stability remains limited. Specifically, when the output power of GFLI increases, the hybrid system consisting of GFMI and GFLI remains susceptible to oscillations and potential instability. To address these limitations, the interaction stability of the hybrid system is comprehensive analyzed and a passivity-enhanced oscillation suppression method is proposed. First, a decomposition impedance model is established to analyze the interaction mechanisms between GFLI and GFMI, as well as the impact of varying power levels. The analysis reveals that increasing the output power of GFMI does not inherently improve its ability to suppress system oscillations. Subsequently, a coupling term responsible for oscillations in the hybrid system is identified and a novel power-adaptive active damping is introduced into the GFMI control to enhance system passivity. In this case, the oscillation of hybrid system can be effectively suppressed under varying power levels and grid impedances. Finally, the experimental results verify the effectiveness of the proposed method.