“…Thevenin's theorem was utilised to deal with multi‐machine system. In [18], Soliman suggested an interval arithmetic approach for computing the admissible set of robust proportional–derivative‐based PSS using interval Routh–Hurwitz arrays. The authors of [19] applied a generalised Kharitonov's theorem to PSS parameter perturbations in the state‐space model of the power system where the region of stability was computed using the edge theorem and the segment lemma, for an arbitrary operating point subject to uncertainties in controller parameters only.…”