State-Space Modeling and Small-Signal Stability Analysis of an Independent Microgrid with Multiple Distributed Generation Resources

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The integration of distributed generation (DG) resources, energy storage systems (ESS), and local electric loads within a specific region has given rise to the concept of microgrid as a significant aspect of smart grids. This research addresses the small signal stability analysis of a an independent microgrid with multiple DG resources while considering the modeling of each DG resource through eigenvalue analysis and frequency response analysis. The microgrid comprises a squirrel cage induction generator-wind turbine (SCIG-WT) as DG1, a diesel synchronous generator (DSG) set equipped with governor and excitation controllers as DG2, an inverter-based battery energy storage system (BESS), and a set of lines and loads. At first, each resource is individually modeled in its respective local state-space reference frame. These individual models are then combined in a global reference frame. The microgrid’s global model is linearized around a specific operating point, resulting in the derivation of the system state matrix, from which the eigenvalues of the microgrid are obtained. The impact of varying system parameters and different operational conditions on the stability margin and microgrid dynamics is assessed by examining changes in eigenvalue locations and conducting sensitivity analysis. Finally, transfer functions of energy storage controllers are determined, allowing for a frequency response analysis concerning the controller coefficients.