Directional Derivative-Based Transient Stability-Constrained Optimal Power Flow Pizano-Martinez, Alejandro ; Fuerte-Esquivel, Claudio R. ; Zamora-Cardenas, Enrique Arnoldo ; Lozano-Garcia, Jose Merced Abstract Publication: IEEE Transactions on Power Systems Pub Date: September 2017 DOI: 10.1109/TPWRS.2016.2633979 Bibcode: 2017ITPSy..32.3415P