A method for quickly bounding the optimal objective value of an OPF problem using a semidefinite relaxation and a local solution

•A method to speed-up the process of bounding the objective values of OPF is proposed.•A candidate local solution information and convex relaxation are used for this aim.•Unlike other works, the local solution and convex relaxation are not fully separated.•The results show that the method is faster but weaker than SDP relaxation.•The results show that the method is slower than the SOCP and QC relaxations. Optimal power flow (OPF) is an important problem in the operation of electric power systems. Due to the OPF problem's non-convexity, there may exist multiple local optima. Certifiably obtaining the global optimum is important for certain applications of OPF problems. Many global optimization techniques compute an optimality gap that compares the achievable objective value corresponding to the feasible point from a local solution algorithm with the objective value bound from a convex relaxation technique. Rather than the traditional practice of completely separating the local solution and convex relaxation computations, this paper proposes a method that exploits information from a local solution to speed the computation of an objective value bound using a semidefinite programming (SDP) relaxation. The improvement in computational tractability comes with the trade-off of reduced tightness for the resulting objective value bound. Numerical experiments illustrate this trade-off, with the proposed method being faster but weaker than the SDP relaxation and slower but tighter than second-order cone programming (SOCP) and quadratic convex (QC) relaxations for many large test cases.