Saddle-node index as bounding value for Hopf bifurcations detection - Souza, Antonio Carlos Zambroni de; Lopes, B. I. Lima; Guedes, Renato Braga de Lima; Bretas, Newton Geraldo; Martins, André Christovão Pio; Mello, L. F. (IEE Proceedings - Generation, Transmission and Distribution, 2005)