Fast Mixed-Integer AC Optimal Power Flow Based on the Outer Approximation Method

  • Lee, Sungwoo ;
  • Kim, Hyoungtae ;
  • Kim, Wook
  • Received : 2017.05.01
  • Accepted : 2017.08.16
  • Published : 2017.11.01


In order to solve the AC optimal power flow (OPF) problem considering the generators' on/off status, it is necessary to model the problem as mixed-integer nonlinear programming (MINLP). Because the computation time to find the optimal solution to the mixed-integer AC OPF problem increases significantly as the system becomes larger, most of the existing solutions simplify the problem either by deciding the on/off status of generators using a separate unit commitment algorithm or by ignoring the minimum output of the generators. Even though this kind of simplification may make the overall computation time tractable, the results can be significantly erroneous. This paper proposes a novel algorithm for the mixed-integer AC OPF problem, which can provide a near-optimal solution quickly and efficiently. The proposed method is based on a combination of the outer approximation method and the relaxed AC OPF theory. The method is applied to a real-scale power system that has 457 generators and 2132 buses, and the result is compared to the branch-and-bound (B&B) method and the genetic algorithm. The results of the proposed method are almost identical to those of the compared methods, but computation time is significantly shorter.


Optimal power flow;MINLP;Unit commitment;Relaxed AC OPF;Outer approximation;Branch-and-bound


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Supported by : National Research Foundation of Korea(NRF), Korea Institute of Energy Technology Evaluation and Planning(KETEP)