The voltage control on MV distribution networks with aggregated DG units (VPP)

In this paper a procedure that allows Distributed Generation plants (DGs) to be operated as a Virtual Power Plant (VPP), maintaining meanwhile the voltage profiles on Medium Voltage (MV) feeders within the permissible interval, is presented. To this aim a co-ordinated controller is proposed. It acts both on the On Line Tap Changer (OLTC) and on the reactive power production of specific plants so that voltage regulation is performed whatever the working condition (generation units disconnected or partially loaded or working at maximum power). In particular this controller can influence a VPP economic criteria dispatch by bounding, for example, the maximum active power generated by each unit in order to obtain the DG reactive generations required by the management of the distribution system. Thus, as a consequence some lower variable cost productions might have to limit their active outputs which represent a possible cost increase in VPP management. These automatic limitations, imposed by the controller, allow the Distribution System Operator (DSO) to control voltage on the whole distribution system and the DG plants to guarantee their connection to the network. Simulations on a realistic network case study are carried out to compare the VPP management impact on voltage profiles with a traditional voltage regulation (only OLTC action) and with a coordinated control system. Results demonstrate that the proposed procedure is able to preserve distribution network from dangerous under and over voltages with limited interferences with the VPP optimisation algorithm.