Dynamic Modeling of Asymmetrical-Faulted Grid by Decomposing Coupled Sequences via Complex Vector

To study the electromagnetic dynamics of grid-connected voltage source converter (VSC)-based devices during asymmetrical grid fault ride-through, this article presents a generic dynamic modeling method for asymmetrical-faulted power grids. In the generic case, the asymmetrical impedances and the grounding inside a faulted grid introduce complicated couplings among the harmonic-contained sequence components. By employing complex vectors, the dynamics of each sequence, especially that of zero sequence, can be depicted clearly and the complicated couplings can be decomposed. With dynamic composite sequence networks figured out, the characteristics of asymmetrical-faulted grids can be studied further. The presented modeling approach is validated by simulation, and its effectiveness is demonstrated by a case study of small-signal stability analysis for an exemplified grid-connected VSC injecting positive and negative sequence reactive currents to the faulted grid.