Voltage regulation issues for smart grid

In the past, distribution networks were designed to be operated as a passive system, i.e. without Dispersed Generation (DG) connected. Nowadays, the large amount of energy produced by small renewable plants makes the system more difficult to manage. Therefore, new solutions towards an improved manage operation have to be implemented in order to ensure a good level of quality of supply to the customers. For the effective employment of renewable sources it is necessary to upgrade the way in which distribution networks operate, moving from a passive to an active management. In this paper, some tools and control strategies to deliver a high quality of service (with particular reference to voltage quality) are discussed in detail. Firstly an effective local voltage control, that exploits DG units as control resources, is introduced in order to improve voltage quality. Then interface protections behavior, and the relevant impact of rapid voltage changes are analyzed. Finally Low Voltage Fault Ride Through (LVFRT) characteristic, that allows DG to sustain the grid in critical conditions, is presented.