Contents I. Introduction
In recent years, electricity grids have experienced huge modifications, due to the high increase of non-programmable renewable sources distributed generation and the liberalization of the electricity market [1] –[4]. These changes have led to the evolution of the network concept itself, no longer seen as a passive network, with few centralized generation systems and unidirectional power flows (bulk model), but as an active intelligent network, a smart grid, characterized by the presence of distributed energy resources (DER) also in medium voltage and low voltage MV/LV grid (distributed model). On the other hand, the variability of distributed energy production, due to the aleatory nature of the renewable energy sources, can cause instability and malfunctioning of the network, such as voltage and frequency variation, unwanted islanding operation and even blackout of the whole network. Moreover, the phenomenon of power flow inversion is particularly critical for the safe operation of the network. As previously mentioned, in fact, the network has been originally designed to have unidirectional power flows and this could cause problems for the correct operation, coordination of protections and power quality [5] –[9]. Different papers can be found in literature, which analyse the new challenges caused by distributed generations increase, both from the technical and the economical point of views [8] [11]. This paper starts from the already known challenges of distributed generation DG and analyse them into a real scenario, which is especially sensible to distributed generation increase, i.e. the case study of the small island Ustica.
