A Review of The Convexification Methods for AC Optimal Power Flow

This paper reviews existing convexification methods for AC optimal power flow (OPF), which is normally nonlinear, nonconvex, and very hard to solve. Different types of convexification methods are reviewed, from conventional methods like DC OPF, to relaxation methods, like convex relaxation (semidefinite program - SDP, second order cone program - SOCP, quadratic convex - QC), strengthened convex relaxation, and convex hull, and finally convex restriction methods. The focus is given to relaxation methods due to the great attention in recent research. The exactness of the relaxation methods and the sufficient conditions that guarantee the exactness are reviewed as well. This gives an insight into these relaxation methods and helps to select suitable and efficient relaxation method for different applications.