A new decomposition method for optimal operation of transmission/generation and subtransmission/distribution systems

The level of automation in electric power systems and, particularly, in subtransmission/distribution (SD) systems is becoming higher and higher. The continuous surprising increase of the number of control actions should be properly taken into account in optimal power flow (OPF) programs. This is important, in order to avoid deficiencies and inaccuracies which can degrade the usefulness of the OPF application. In the first part of the paper a generalized formulation of the OPF problem is provided which takes into account the entire set of controls and involves specific goals for the SD systems. This leads to the definition of a non-linear multiobjective optimization problem which can be solved off-line only with a very heavy computational burden. To overcome this difficulty, the second part of the paper deals with the development of an optimization procedure which exploits the naturally decomposable structure of the power system model. Namely, on the basis of a Decomposition-Coordination technique, the proposed method turns the global optimization problem to the solution of several decoupled subproblems. The validity of the suggested procedure and the accuracy of the results are illustrated by a numerical example.