Hybrid DC Micro-grid Modeling and Dynamic Stability Analysis

DC micro-grids (DC-MGs) have attracted significant attention as a promising solution for integrating distributed renewable sources to main utility. Compared to AC systems, DC-MGs offer higher efficiency; however, their varied structures and control strategies introduce considerable dynamic complexity. This paper investigates the dynamic stability of an islanded DC-MG comprising a photovoltaic (PV) unit, battery unit, and the supercapacitor (SC) unit connected to the main bus through DC-DC power converters. The system is modeled using state-space averaging method, and the linearized equations are analyzed using system eigenvalue analysis method to examine the system stability. The impact of various parameters including capacitor size, inductor values, line resistances, and constant power loads (CPLs) on the system's dynamic behavior is verified systematically. Results indicate that larger capacitors and inductors shift eigenvalues further into the left half-plane, improving damping and stability, whereas resistances and CPLs have a destabilizing effect. All simulations and verifications are conducted in MATLAB/Simulink to ensure analytical accuracy. The presented framework offers valuable insights for designing reliable DC-MGs with hybrid energy storage systems for future modern power grids.