Abstract
The emergence of distributed energy resources can lead to congestion in distribution grids. DC distribution grids are becoming more relevant as more sources and loads connected to the low voltage grid use dc. Bipolar dc distribution grids with asymmetric loading can experience partial congestion resulting in a nodal price difference between the two polarities if a respective market model is applied. In order to take into account this price difference, this paper presents an optimal power flow (OPF) model formulated in terms of voltage and current. In the case of bipolar dc distribution grids, the single line approximation is no longer valid because current can flow in the neutral conductors as well. Moreover, loads and sources can be connected between any two nodes in the network. The proposed exact OPF formulation includes bilinear equations. The locational marginal prices (LMP) are derived by linearizing the problem at the optimal solution. Example cases show the various phenomena that can appear under asymmetric loading, such as pole-to-pole connections combined with pole-to-neutral connections, parallel sources, meshed grids, and their effect on the LMP.
Highlights
D ISTRIBUTION GRIDS are expected to experience more congestion problems due to the emergence of electrical vehicles, renewable energy sources, and other distributed energy resources
In order to take into account this price difference, this paper presents an optimal power flow (OPF) model formulated in terms of voltage and current
This paper proposes a method to model the OPF problem for unbalanced bipolar dc grids
Summary
D ISTRIBUTION GRIDS are expected to experience more congestion problems due to the emergence of electrical vehicles, renewable energy sources, and other distributed energy resources. In bipolar dc distribution grids [1] the lines can be loaded asymmetrically (unbalanced), i.e., devices connected between pole and neutral, to allow smaller devices to connect to lower voltage. Due to this likely asymmetric loading of both polarities in distribution grids, partial line congestion can appear. Congestion of distribution grids occur when power flows are subject to physical or operational limitations These are likely to occur in distribution networks in the future due to the increase of installed power capacity (e.g. electric vehicles and photovoltaics). This paper proposes a method to model the OPF problem for unbalanced bipolar dc grids.
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