The closest unstable equilibrium point method for power system dynamic security assessment

The closest unstable equilibrium point (u.e.p.) method is an important tool for problems associated with power system dynamic security assessment. A study is made of the closest u.e.p. method from both theoretical and computational points of view. Issues regarding the existence and uniqueness of the closest u.e.p. are investigated. A dynamical characterization of the closest u.e.p. is derived, and the problem of its robustness with respect to changes in different parameters of a power system is studied. This robustness property highlights the practical applicability of the closest u.e.p. method to power system dynamic security assessment. An improved closest u.e.p. method is then proposed on the basis of theoretical results which uses a reduced model approach and is shown to be optimal, in the sense that the estimated stability region characterized by the corresponding energy function is the largest one within the entire stability region. Examples are given to illustrate the robustness of the closest u.e.p. and improved closest u.e.p. methods