On the Fault-Ride-Through Dynamics of Grid-Forming Converters - A Multi-dimensional Adaptive Inertia Approach

Grid-forming (GFM) converters are gaining momentum as one of the keys to enabling large-scale integration of distributed energy resources (DER) with the grid. Among the desired functionalities, GFM converters must demonstrate a stable fault-ride-through (FRT) behavior, i.e., during and after a fault is cleared in the system. As GFMs exhibit voltage source behavior, current needs to be limited under fault conditions. In addition, the GFM control should ensure that the load angle does not go into an unstable region. Also, once the fault is cleared, the converter should return to the nominal operating point swiftly. Analysis of GFM during and after faults reveals a dichotomy in the inertia required for a smooth and stable FRT. Consequently, this paper proposes a multi-dimensional adaptive inertia function for GFM converters to increase the critical clearing time while reducing the post-fault recovery/resynchronization time. The efficacy of the proposed method is analyzed in MATLAB/Simulink EMT simulations using a virtual synchronous machine GFM controller as the benchmark control scheme and comparing it with a fully adaptive inertia/damping GFM controller.