Stability Enhancement with VSG Integration on Microgrid Systems: A Numerical Trajectory-Based Approach for Transient Analysis

Stability enhancement in microgrid systems poses significant challenges, especially with high penetration of inverter-based resources. This paper proposes the integration of Virtual Synchronous Generators (VSGs) into microgrids to provide additional virtual inertia, thereby improving system stability during disturbances. A quantitative transient stability assessment based on Critical Clearing Time (CCT) is introduced to comprehensively evaluate system dynamics with VSG integration. CCT serves as a practical metric for determining the maximum allowable fault-clearing time to maintain stability, with the CCT value derived through fault trajectory analysis using the fourth-order Runge-Kutta numerical method. Resulting trajectories are classified as Stable Trajectory (ST) or Unstable Trajectory (UT) based on post-fault system response. The study is conducted on a modified IEEE 9-bus microgrid system comprising three diesel generators, with VSG integration modeled under two penetration scenarios: 11% and 29%. Simulation results show that VSG integration significantly enhances transient stability margins. However, system response is highly sensitive to fault location and duration, underscoring the need for careful system planning.