Strengthened SDP Relaxation for an Extended Trust Region Subproblem with an Application to Optimal Power Flow

Abstract: We study an extended trust region subproblem minimizing a nonconvex function over the hollow ball $r \le |x| \le R$ intersected with a full-dimensional second order cone (SOC) constraint of the form $|x - c| \le b^T x - a$. In particular, we present a class of valid cuts that improve existing semidefinite programming (SDP) relaxations and are separable in polynomial time. We connect our cuts to the literature on the optimal power flow (OPF) problem by demonstrating that previously derived cuts capturing a convex hull important for OPF are actually just special cases of our cuts. In addition, we apply our methodology to derive a new class of closed-form, locally valid, SOC cuts for nonconvex quadratic programs over the mixed polyhedral-conic set ${x \ge 0 : | x | \le 1 }$. Finally, we show computationally on randomly generated instances that our cuts are effective in further closing the gap of the strongest SDP relaxations in the literature, especially in low dimensions.