Toward Distributed OPF Using ALADIN

This paper discusses the application of the recently proposed augmented Lagrangian alternating direction inexact Newton (aladin) method to non-convex ac optimal power flow problems (ac-opf) in a distributed fashion. In contrast to the often used alternating direction of multipliers method (admm), aladin guarantees locally quadratic convergence for ac-opf. Numerical results for 5-300 bus test cases indicate that aladin is able to outperform the admm and to reduce the number of iterations by about one order of magnitude. We compare aladin to numerical results for the admm documented in the literature. The improved convergence speed comes at the cost of increasing the communication effort per iteration. Therefore, we propose a variant of aladin that uses inexact Hessians to reduce communication. Additionally, we provide a detailed comparison of these aladin variants to the admm from an algorithmic and communication perspective. Moreover, we prove that aladin converges locally at a quadratic rate even for the relevant case of suboptimally solved local nonlinear programs.