A Critical Assessment of Oscillatory Modes in Multi-Microgrids Comprising of Synchronous and Inverter-Based Distributed Generation

This paper provides a critical assessment of oscillatory modes for a droop-controlled multi-microgrid (MMG) consisting of inverter-based and synchronous-based distributed generation (DG). Local and inter-microgrid oscillatory modes similar to conventional interconnected power systems are observed. However, an additional new and more “dominant” oscillatory mode caused by interactions between close-by coherent synchronous-based and inverter-based DGs in the MMG is identified. Sensitivity analysis is employed to assess the impact of various MMG configurations and parameters such as: interconnecting line length, droop gain, exciter gain, and governor gain on MMG oscillatory modes. Parametric studies are conducted to highlight the impact of oscillatory modes on MMG transient and dynamic performances. Consequently, power system stabilizers (PSSs) are developed for both inverter-based and synchronous-based DGs to improve the transient and dynamic performances of the MMG. Residues are calculated and therefore utilized to determine the effect of PSS placement on the MMG oscillatory modes. Finally, small-signal stability analysis results and the performances of the PSSs are validated through time domain simulations on MATLAB/Simulink.