With the accelerated introduction of renewable energy into the grid, the problem of power oscillations has emerged among inverter-based resources (IBRs). In conventional eigenvalue analysis, systems with constant grid frequency are assumed, and line dynamics are often omitted to avoid higher-order systems. In this study, however, a microgrid (MG) consisting of grid-forming (GFM) and grid-following (GFL) inverters is assumed. A comprehensive mathematical model, including transmission lines and inverter controls, is constructed, where the frequency of the MG varies from the nominal value due to the frequency droop characteristic of the GFM. Sensitivity analyses were conducted to identify parameters with high sensitivities to eigenvalues and to determine control parameters contributing to power oscillations. Additionally, the mechanisms by which these parameters are mutually interfered with were investigated. The effect of suppressing power fluctuations by preferentially adjusting these parameters was confirmed through both numerical analysis and experiments. These results are based on the assumption that the system consists of typical GFM and GFL. In other words, the preferential adjustment method of the identified parameters can be applied to general IBRs even if their controls are confidential, leading to improved grid stability.
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