Grid-forming inverters as synchronous machine replacements: stability analysis and overcurrent protection strategies

The increasing integration of renewable energy sources into power systems is driving the progressive replacement of traditional synchronous generators with power electronic converters. While essential for decarbonization, this shift leads to a significant reduction in system inertia, thereby compromising frequency sta- bility and dynamic performance. Grid-forming inverters (GFMs) have emerged as a promising solution to these challenges, as they autonomously regulate voltage and frequency, effectively emulating the behavior of conventional syn- chronous machines. This thesis presents a comprehensive study of three major grid-forming control strategies: droop control, Virtual Synchronous Machine (VSM), and dis- patchable Virtual Oscillator Control (dVOC). Each approach is evaluated based on its dynamic response and stability characteristics. Time-domain simulations are carried out in MATLAB/Simulink on a modified IEEE 9-bus test system. Scenarios include systems dominated by synchronous machines, mixed- generation configurations, and grids with 100% inverter-based renewable sources. The results highlight the critical role of GFMs in enhancing frequency stability and grid resilience. In addition, the thesis includes detailed modeling of the inverters DC-side power supply, consisting of a photovoltaic plant coupled with a Hybrid Energy Storage System (HESS) based on batteries and supercapaci- tors. This configuration reflects realistic operating conditions and ensures stable power injection into the AC grid. Finally, the thesis explores protection mech- anisms to mitigate overcurrent conditions during disturbances. These control strategies are vital to ensure the secure operation of GFMs under fault scenarios and to support the long-term reliability of renewable-based power systems.