An optimal power flow (OPF) problem formulates constraints and operation of an electric power system. A method and system is provided for generating a secure OPF solution that solves the OPF problem. A list of contingencies is created from system data. An OPF solution is computed for the electric power system to optimize an objective function value under the constraints of the electric power system. Voltage stability analysis is performed on the electric power system that operates in states represented by the OPF solution. Then the contingencies are ranked according to load margins of the electric power system. If there is at least an insecure contingency with a non-positive load margin in the list of contingencies, a set of preventive controls are computed and applied to control components in the electric power system. The method is performed iteratively to obtain the secure OPF solution.