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Management of Low Voltage Grids with High Penetration of Distributed Generation: concepts, implementations and experiments A.BERTANI*, A.BORGHETTI+, C.BOSSI§, L.DE BIASE°, O.LAMQUET*, S.MASSUCCO^, A.MORINI^, C.A.NUCCI+, M.PAOLONE+, E.QUAIA°, F.SILVESTRO^ *CESI, +University of Bologna, §CESI Ricerca, °University of Milan, ^University of Genoa Italy SUMMARY The interconnection of distributed generators in low voltage (LV) networks, together with storage systems, could cause a substantial change in grid operational practice: currently a rising idea proposes to treat generators, storage systems and even loads as distributed energy resources (DER), able to supply services to the grid and accept on-line requests. To emphasise the advantages of Distributed Generation (DG) it is necessary to face the problem with a system approach. In this work both type of services, namely those provided by each generator and those deriving from the co-ordination of different resources, have been investigated. The option represented by a complex master-slave configuration has been discarded in order to avoid its fast communication and control requirements. Instead a prototype based on a centralised resource management solution and a somewhat plug-and-play functionality for each generator has been developed. For this purpose, different control systems have been implemented in order to act during fast transient dynamics due to random load or configuration changes, or to manage the slow modifications of the system conditions due to daily, weekly and seasonal load variations. The regulators of every distributed resource are requested to give response to fast and unpredictable transient dynamics, i.e. to participate to voltage and frequency regulations, harmonic compensations and phase balancing, while a central dispatcher has been conceived as to periodically update the regulators set-points in order to exploit the capabilities of each distributed resource either for present and foreseen grid operating conditions. For voltage and frequency regulations, a specific droop control algorithm has been designed so to be implemented on board of generators connected to the LV grid by an inverter device. In the conceived scenario, each machine, working in parallel with the others, takes on part of the regulation according to its capabilities. For the optimal update of the distributed resources’ operating conditions, the developed central dispatcher incorporates the following main functions: short-term forecast of the power produced by renewable energy sources (RES), short-term load forecast and day-ahead load profile prediction, distribution system state estimation, day-ahead economic dispatching and on-line scheduling of the optimal distributed resources’ operating conditions. The developed regulators and central dispatcher prototypes have been installed in a test facility set up at Cesi, where several distributed generators of different technologies, storage devices and loads have been interconnected with secondary LV network that can be arranged in different configurations. 21, rue d’Artois, F-75008 PARIS C6-304 CIGRE 2006 http : //www.cigre.org PUBBLICATO A6000736 (PAD – 750694)
2 Some preliminary experiments have been carried out in order to assess the system performances. In particular, according to the view that the high penetration of DG could become an opportunity rather than a problem, as it is frequently considered, the results of this experimental activity show that distributed resources could be suitably used in order to control grid voltage profiles, power flows, and to handling intentional and unintentional islanding condition after separation of the LV grid from the MV distribution grid. The research activity described in this paper was supported in the framework of a National Research Project named GENDIS 21 – Distributed Generation for the Improvement of Power Quality and Environment. KEYWORDS Distributed Generation – Renewable Energy Sources – Low Voltage Distribution Systems – Load Forecast – Renewable Energy Forecast – State Estimation – Test Facility – Dispatcher
31 Dicembre 2005
La generazione distribuita per il miglioramento della qualità del servizio elettrico e dell’ambiente (GENDIS 21)