A key issue in Low Voltage (LV) distribution systems is to identify strategies for the optimal\nmanagement and control in the presence of Distributed Energy Resources (DERs). To reduce the\nnumber of variables to be monitored and controlled, virtual levels of aggregation, called Virtual\nMicrogrids (VMs), are introduced and identified by using new models of the distribution system.\nTo this aim, this paper, revisiting and improving the approach outlined in a conference paper,\npresents a sensitivity-based model of an LV distribution system, supplied by an Medium/Low\nVoltage (MV/LV) substation and composed by several feeders, which is suitable for the optimal\nmanagement and control of the grid and for VM definition. The main features of the proposed\nmethod are: it evaluates the sensitivity coefficients in a closed form; it provides an overview of the\nsensitivity of the network to the variations of each DER connected to the grid; and it presents a\nlimited computational burden. A comparison of the proposed method with both the exact load flow\nsolutions and a perturb-and-observe method is discussed in a case study. Finally, the method is used\nto evaluate the impact of the DERs on the nodal voltages of the network.
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