1,721,027 research outputs found
L'architettura dei giorni di festa
No full textLa mongolfiera luminosa sulla sommità, in omaggio alla lampadina a incandescenza, e la forma ispirata alle settecentesche architetture visionarie di Ledoux e Boullée sono i capisaldi del progetto di un nuovo, contemporaneo tipo di cassa armonic
Valutazione comparativa delle tecniche di immunodiffusione su agar e counter-elettroforesi nella ricerca dell'antigene Australia.
No full textPower quality disturbances due to interaction between AC and DC traction systems
No full textThe growing complexity of the AC and DC traction systems in terms of both new technologies and automation requires a careful control of the power quality disturbances they cause. In some cases-as in Italy-both traction systems operate in the same transmission network area, so that the power quality problems have become much more complex because of the interactions between the two systems. In this paper the problem of a careful evaluation of these interactions is analyzed. The study is performed with reference to a mixed (2×25 kV-50 Hz) and 3 kV DC traction system, similar to the one adopted for the Italian railways, and by using computer simulations developed by means of Matlab power system blockset. Waveform distortions and voltage unbalances are assessed and suggestions are given to solve the interaction problems. (6 pages
Exponential weighted method and a compromise programming method for multi-objective operation of plug-in vehicle aggregators in microgrids
No full textAn Optimal Control of Distributed Energy Resources to Improve the Power Quality and to Reduce Energy Costs of a Hybrid AC-DC Microgrid
No full textIn this paper an optimal strategy is proposed for the real time control of a hybrid microgrid (μG). Hybrid μGs are characterized by the presence of two sections operating in alternating current (AC μG) and in direct current (DC μG), respectively. They include dispatchable and non-dispatchable renewable generation units, battery energy storage systems and controllable loads. These different resources are connected to the AC or DC μGs through static converters that are optimally controlled for the simultaneous improvement of waveform distortions and minimization of the energy costs. In order to show the effectiveness and feasibility of the proposed approach, the control strategy was applied to a hybrid μG derived from the distribution system of an actual industrial facility
Site and System Indices for Power Quality Characterization of Distribution Networks with Distributed Generation
No full textThe problem of developing a definition that adequately assesses power-quality (PQ) levels in the presence of distributed generation (DG) is addressed by using proper probabilistic indices for distribution networks. In the planning of new DG installations, these indices take the variation of PQ level into account and use weighting functions properly. They are useful in quantifying the impact of the installation of DG units because they can consider several PQ disturbances simultaneously. Also, they indicate how each PQ disturbance may affect the decision concerning the installation of DG units. Several tests on real distribution networks were performed and discussed in order to show the usefulness of these indices in evidencing the impact of DG on PQ levels. The analysis of the electrical distribution systems on the basis of the considered indices is valuable also to help decide the best allocation and size of distributed generators
On the comparison between ensemble Kalman filter and Kalman filter for the dynamic harmonic state estimation in a hybrid microgrid
No full textThe management of micro grids requires the dynamic harmonic state estimation of the system in order to perform control strategies that optimize waveform distortions. In industrial context, AC and DC devices and sources coexist and, therefore, micro grids can be a hybrid combination of AC and DC power sections. Also for such hybrid AC/DC micro grids optimal control strategies that optimize waveform distortions are mandatory. In this paper, the comparison of two different methods for the dynamic harmonic state estimation of hybrid AC/DC micro grids is performed analyzing both theoretical and numerical aspects. In particular, the Kalman Filter- and Ensemble Kalman Filter-based dynamic harmonic state estimations are compared in terms of accuracy and computational efforts. The numerical applications were performed on a hybrid AC/DC μG proposed for an actual industrial facility in southern Italy
Day-ahead probabilistic wind power forecasting based on ranking and combining NWPs
No full textDispatching energy in transmission and distribution networks and bidding on electricity markets require probabilistic wind power forecasts available several hours before the actual occurrence. The volatility of the wind over large time horizons complicates the generation of skilled, reliable wind power forecasts. Exploiting numeric weather predictions (NWPs) is generally considered mandatory to increase the skill of probabilistic predictions, and forecasts may further be enhanced by adding several spatially distributed predictions. However, feature selection becomes a more complicated and time consuming as the number of NWPs increases. In this paper, we predict the power generated by a wind farm developing a new technique on the basis of ranking and combining spatially distributed NWPs, easing the feature selection and reducing the computational efforts, as well as maintaining high the skill of probabilistic forecasts. Several spatially distributed NWPs, provided for the area surrounding the wind farm, are ranked for each individual generator, and the ranked NWPs are combined to form an ensemble set of predictors for the probabilistic forecasting model. This ensemble is obtained using three different weighted combination approaches. Gradient boosting regression tree models and quantile regression neural networks generate probabilistic wind power forecasts. The proposed methodology is applied for day-ahead wind power forecasting of individual generators and of the entire wind farm. Numerical experiments carried out on an actual wind farm in southern Italy suggest that ranking NWPs may keep the skill of forecasts at high levels even under a simplified, less computationally intensive procedure. The performance is also enhanced up to 1.8% with respect to standard techniques
Probabilistic Management of Power Delivery Based on Dynamic Transformer Rating
No full textThe smart grid paradigm pushes for intelligent operation of the transformers that are already installed in the networks, to cope with peak load and/or to enable more intense exploitation of renewables. However, transformer loading is affected by several factors that should be considered, among which the thermal stress is recognized as the most influencing one. In this context, the dynamic thermal rating concept is of great interest and it allows fixing the maximum allowable current in different operating conditions, still maintaining acceptable risk levels based on the consequences of loading the transformers beyond the nameplate ratings. A probabilistic procedure for managing the delivery of power to load by the dynamic transformer rating is presented in this paper. The procedure is based on the risk analysis related to the thermal stress introduced by the transformer (over)load, which determines loss of life and potential dielectric failure. Numerical experiments based on actual data are performed for several scenarios, and several cases are presented to support the procedure for the intelligent exploitation of the potentialities of transformers
- …
