Control Issues in MV Distribution Systems with Large-scale Integration of Distributed Generation

In this work an overview of the problems and challenges posed on the distribution networks by this new scenario is given together with a description of the possible provisions and control strategies which may be adopted in the medium and long term in order to achieve the necessary levels for a safe, economical and sustainable network operation. Becoming the distribution system an “Active Network”, it requires several control actions whose necessity and complexity depend on the degree of DG penetration and on the adopted grid structure (i.e.: radial, doubly fed ridge-lines, meshed, microgrids, etc.). In order to identify such “Control Actions”, defining them as those actions aimed at mitigating the internal and external disturbances that could modify the desired set point of the generators, it is necessary to foresee provisions on both frequency (i.e.: smoothing of electromechanical transients) and voltage (i.e.: volt-VAr regulation at each network bus). In fact, the existing distribution systems and components may pose a severe limitation to the diffusion of distributed generation. First of all the protection systems must be suitably adapted or re-designed in order to face with the variations of short circuit currents and different intervention requirements.