Calculation Method and Characteristic Analysis of Short-Circuit Current for Grid-Forming VSGs Under Symmetrical Faults

With the increasing penetration of renewable energy, grid-forming inverters that provide voltage and frequency support are receiving significant attention. However, due to the voltage source characteristics of grid-forming Virtual Synchronous Generators (VSGs), they are prone to excessive short-circuit currents during three-phase grid faults. Moreover, conventional short-circuit current analysis methods developed for grid-following inverters cannot be directly applied to VSG-based systems. Consequently, research on fault current calculation for grid-forming VSGs has become critically important. To address this issue, this paper employs mathematical analysis to derive a short-circuit current calculation method for VSG grid-connected systems under three-phase fault conditions. Based on the derived analytical expressions, the short-circuit current characteristics of the VSG system are systematically analyzed. The correctness of the proposed analytical expressions is validated through simulations conducted on the MATLAB/Simulink(R2024b) platform. Simulation results show that the error between the analytical and simulated values remains within 8%, and decreases to below 3% after 2–3 cycles, indicating that the proposed analytical model can effectively capture the dynamic behavior of the fault current.