  Grid-synchronization stability (GSS) is an emerging stability issue of
grid-tied voltage source converters (VSCs), which can be provoked by severe
grid voltage sags. Although a qualitative understanding of the mechanism behind
the loss of synchronization has been acquired in recent studies, an analytical
method for quantitative assessment of GSS of grid-tied VSCs is still missing.
To bridge this gap, a dedicated Lyapunov function is analytically proposed, and
its corresponding stability criterion for GSS analysis of grid-tied VSCs is
rigorously constructed. Both theoretical analysis and simulation result
demonstrate that the proposed method can provide a credible GSS evaluation
compared to the previous EAC/EF-based method. Therefore, it can be applied for
fast GSS evaluation of the grid-tied VSCs as is exemplified in this paper, as
well as an analytical tool for some GSS-related issues, e.g., GSS-oriented
parameter design and stabilization control.
