Voltage security cost assessment of integrated AC-DC systems using semidefinite programming

In this paper, a convex optimal power flow (OPF) and a voltage stability constrained OPF (VSC-OPF) formulation for integrated AC-DC transmission systems are developed using semi-definite programming (SDP). These methods calculate the optimum operating points for AC and DC system together. The main advantages of the proposed methods are: a) it finds the optimal schedule when compared to other non-convex methods or separate scheduling of AC-DC systems b) it calculates the cost of increasing voltage stability margin through comparison of operating cost from AC-DC OPF (minimizing operating cost) and VSC-OPF (maximizing stability margin). The effectiveness of proposed methods are evaluated using IEEE 14-bus and 57-bus incorporating HVDC transmission system. The results show the capability of convex formulations to find the optimal operating schedule and critical loading point.