New bus classification and unbalanced power flow of large-scale networks with electronically interfaced energy resources

The nature of transmission and distribution networks has drastically changed over the last several decades, due to a high penetration of electronically interfaced energy resources (EIERs). Consequently, the complexity of the operation and the management of these networks have considerably increased. This strongly affected the energy management systems and distribution management systems, especially the power flow calculation as their basic power application. Electronically interfaced energy resources can employ a wide range of control strategies that cannot be represented with traditional single-phase bus types used for traditional alternating current machines in a symmetrical operation. Power flow is the main subject of this paper, and the main objectives are as follows: (i) to prove that the traditional bus classificationV (slack bus), PQ, and PVis not sufficient for an unbalanced power flow formulation and the calculation of emerging large-scale unbalanced electric networks containing traditional alternating current machines and particularly EIERs; (ii) to introduce a new bus classification suitable for the power flow modeling and calculation of these networks; and (iii) to present a robust and accurate unbalanced power flow method based on the new bus classification and a bus type inspection principle. Numerical tests show that the developed power flow method can be successfully applied in the on-line calculation mode of both energy management system and distribution management system dealing with large-scale networks.