Power angle based fault recovery analysis for grid-connected GFM inverters with current limiting

To meet both the requirements of current limiting and ancillary services during fault ride-through (FRT) of the GFM inverters, various current limiting strategies are developed. Recently, their post-fault behaviors and the switching characteristics have been found to have a significant impact on fault recovery capability. However, the correspondence between the switching conditions and the fault recovery capability has not been fully revealed. The commonalities and uniqueness of various current limiting strategies during fault recovery have not been thoroughly investigated and summarized. To fill these gaps, this paper first graphically illustrates the switching conditions of three typical current limiting strategies. Then, on the basis of the graphical illustration, the initial current-based conditions are converted to be based on the power angle with a fixed range. In addition, the fault recovery capability of three current limiting strategies is investigated and summarized based on the proposed power angle-based switching model. The correspondence between the fault recovery capability and switching conditions is revealed. Consequently, sufficient conditions are obtained for a successful fault recovery. The correctness of the theoretical analyses is verified and validated by numerical simulations and experimental tests.