Security constrained Optimal Power Flow for mixed AC and multi-terminal HVDC grids

In this paper an algorithm is developed for solving the Optimal Power Flow (OPF) and Security Constrained OPF (SCOPF) problem in mixed AC/DC grids. Non-linear models are used for power lines and AC/DC and DC/DC converters. The converter models include terminal losses and power rating constraints. The formulation of the SCOPF problem is such that it works for preventive OPF where no corrective actions are allowed after the contingency, as well as for corrective OPF with adjustable control actions limits. A case study has been performed on a customized version of the IEEE 14-bus system that includes a Multi-Terminal HVDC grid. The corrective SCOPF was found to produce a cheaper initial economic dispatch than the preventive one, depending on the selection of the range of corrective actions on each generator and converter. A method for speeding-up the convergence time of the algorithm is also presented and tested in another case study.