Modeling and Analysis of Open-Delta Step Voltage Regulators for Unbalanced Distribution Network With Photovoltaic Power Generation

Open-delta connected step voltage regulators (SVRs) have been widely installed into distribution networks, and their characteristic model (auto-transformer model) has been established over the years for power system analysis. However, these models are not fully developed to a complete bus admittance matrix form, which can be readily used for unbalanced load flow programs. Further, the debate on the neutral shift after implementation of open-delta SVRs has added difficulties on the modeling. There have been confusions on what is the neutral shift for a three-wire network without neutral and where the neutral is shifted to. Recently, accurate modeling of such a network component has become exceptionally important especially with the rapid proliferation of photovoltaic (PV), and there is a strong requirement of evaluating PV integration impacts on distribution systems. Propelled by all these necessity of modeling, this paper develops a new mathematical model of the open-delta SVR in a bus admittance matrix form which can be easily incorporated into suitable unbalanced load flow programs. Further, the neutral shift issue is also clarified during the model development, and in addition a method for tap position estimation is derived. All the established models are validated by field measurement.