Summary
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 classification—θV (slack bus), PQ, and PV—is 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.
We aim to systematically review challenges imposed by emerging distributed energy resources (DERs) to model in two basic distribution management system (DMS) online applications-power flow and short-circuit analysis, as well as to offer a systematic review of potential solutions. In the last decade, electronically coupled DERs became increasingly popular. DERs can employ a wide range of control strategies for power, current, or voltage control, in both normal and faulted conditions. Therefore, DERs cannot be modeled with the traditional PQ (load or generator bus), and PV (generator bus) bus types used for modeling synchronous and induction machines in online power flow calculations. Moreover, because fault currents of DERs are limited to predefined maximal values, electronically coupled DERs cannot be represented with traditional voltage source behind impedance models for online short-circuit calculation (SCC). However, most of the DMS software packages still use the traditional models to represent all DER types, including those that are electronically coupled. This paper shows that there will be high calculation errors in such practice, which makes the system model be an inadequate representation of the system. And this will lead to serious errors in managing, control, and operation of distribution systems. Nonetheless, potential solutions to the challenges are systematically reviewed. Finally, calculation results on a distribution test system with all DER types are used to prove the claim.
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