Impedance-Based Stability Analysis of Power System Wideband Oscillations: A Bridge between s Domain and Frequency Domain

Existing impedance-based stability analysis in frequency domain has limitations in identifying potential oscillation modes and providing the interpretability of frequency responses to deal with emerging wideband oscillations. In this paper, a bridge between s domain and frequency domain is established to essentially explain why existing impedance-based stability criteria fail to identify oscillations in some cases, and then a frequency response gradient-enabled impedance-based stability criterion (FRGISC) is proposed to tackle the limitations of existing criteria. Firstly, different zero-pole distributions and their corresponding frequency responses are analyzed. Then, novel concepts named zero-zero interference, pole-pole interference, and zero-pole interference are proposed to explain the frequency responses that would make oscillation analysis infeasible in frequency domain. On this basis, the FRGISC is proposed to determine the frequencies, stability, and margins of potential wideband oscillations. A modified IEEE-68 bus power system with converter-interfaced generation is employed to verify the validity of the given explanations and the effectiveness of the proposed criterion in s, frequency, and time domains, respectively.