Abstract
A key issue in Low Voltage(LV) distribution systems is to identify strategies for the optimal management and control in the presence of Distributed Energy Resources (DERs). To reduce the number of variables to be monitored and controlled, virtual levels of aggregation, called Virtual Microgrids (VMs), are introduced and identified by using new models of the distribution system. To this aim, this paper, revisiting and improving the approach outlined in a conference paper, presents a sensitivity-based model of an LV distribution system, supplied by a Medium/Low Voltage (MV/LV) substation and composed by several feeders, which is suitable for the optimal management and control of the grid and for VM definition. The main features of the proposed method are: it evaluates the sensitivity coefficients in a closed form; it provides an overview of the sensitivity of the network to the variations of each DER connected to the grid; and it presents a limited computational burden. A comparison of the proposed method with both the exact load flow solutions and a perturb-and-observe method is discussed in a case study. Finally, the method is used to evaluate the impact of the DERs on the nodal voltages of the network.
Highlights
Existing distribution networks present an inflexible structure which makes them inadequate to allow a large spread of Distributed Energy Resources (DERs), such as distributed generators from renewable energy sources, cogeneration facilities, energy storage systems, and controllable loads [1,2,3]
Let us consider the Low Voltage (LV) distribution system reported in Figure 1: an Medium/Low Voltage (MV/LV) substation supplies m feeders; the h-th feeder is composed of nh branches and nh + 1 nodes; along the feeders, uncontrolled loads and/or DERs can be connected
The model is based on a linearized formulation of the branch flow equations and of the MV/LV supplying system
Summary
Existing distribution networks present an inflexible structure which makes them inadequate to allow a large spread of Distributed Energy Resources (DERs), such as distributed generators from renewable energy sources, cogeneration facilities, energy storage systems (including electric vehicles), and controllable loads (i.e., adopting active demand) [1,2,3]. To identify VMs, new models of the distribution system are required These models must be able to overcome the classical formulation adopted at the transmission level (based on non-linear equations written for each node of the grid) so as to facilitate the aggregation of portions of network on the basis of the impact of DERs on specific control actions (i.e., voltage regulation [9,10] and current flow limitation [11]). This paper, adopting the approach outlined in [16], proposes a sensitivity-based model of an LV distribution system supplied by an MV/LV substation and composed by several feeders, which is suitable for the optimal management and control of the grid and, for VM definition Such a model provides, in a closed form, the variations of the electrical variables characterizing each node of a feeder (e.g., out-flowing active and reactive powers, nodal voltage) as linear functions of the powers injected/absorbed by each DER connected to the LV network.
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