Settling Angle-Based Stability Criterion for Power-Electronics-Dominated Power Systems

Impedance-based analysis methods are widely applied to the small-signal stability analysis of grid-connected converters. As the initial step to carry out the impedance-based stability analysis, it is critical to select whether to represent the converter as a Norton or Thevenin equivalent circuit. However, there is lack of definition on the representation of converters, and inappropriately selected impedance model choice leads to improper stability analysis. Moreover, existing impedance-based stability analysis methods, e.g., return-ratio matrix (RRM)-based method, only apply to minimum phase systems where the RRM does not contain right-half-plane poles. In complex and power-electronics-dominated power systems, interactions between multiple converters lead to nonminimum phase power systems, where current methods can no longer be directly applied. To address these problems, a stability criterion is proposed by introducing the concept of settling angle. As the main contribution of this article, the settling angle of total admittance is proven as the intrinsic hallmark of power systems and directly reflects the system stability. The proposed settling-angle-based stability criterion is validated by control hardware-in-the-loop experimental results for a three-terminal system that integrates grid-forming and grid-following converters through a common bus.