Impedance-based power system stability analysis based on a power quality assessment toolbox - advantages and challenges

Due to their fast control, inverter-based resources (IBR) can interact with the network impedance, other converters or rotating machines over a wider frequency range than synchronous generators. This increases the risk of resonances at sub- and super-synchronous frequencies. Impedance-based stability analysis is a suitable method for investigating the small-signal stability in the frequency domain. IBR dominated power systems require network analysis software tools for a system wide analysis. The paper focuses on the approach of using the frequency sweep function of a power system analysis software’s power quality assessment toolbox in the frequency domain. Provided that suitable frequency-dependent impedance characteristics of IBRs and rotating generators are given (or can be derived), the frequency sweep function is capable of determining resonance frequencies and predicting whether a resonance is stable or unstable. The pros and cons of this approach and possible limitations are discussed. For a complete stability analysis, the frequency sweep function needs to be extended in order to determine stability margins by analysing the Nyquist curve and criterion for IBRs. Examples are given for the analysis of single IBR connections and multiple IBR connections to power systems. The advantages and challenges for practical application are discussed.