1,721,125 research outputs found
Analysis of failure rates of AC and DC micro-grids
No full textNowadays dc distribution is gaining importance, as an increasing amount of loads is natively biased in dc. In addition, dc micro-grids are usually characterized by high efficiency and simple design. Moreover, they can better accommodate renewable generation and storage systems. These are the main benefits attributed to dc distribution grids. Reliability aspects, usually, are not sufficiently taken into account. This paper describes an initial methodological approach to compare (in both analytic and numerical way) ac and dc micro-grids. In particular, the analysis has been focused on the effects on loads of main supply interruptions. The performed analysis showed that dc micro-grids have a higher immunity to these events than that displayed by ac micro-grids. On the other hand, the front-end converter (FEC) interfacing ac main supply and dc micro-grid is a single point failure for the whole system. The paper describes (and analyses) some technical solutions to reduce the effect of FEC failure on loads. Moreover, the signals and alarms that should be used in order to maximize the obtained quality-of-service levels are reported, along with some diagnostic considerations
A Methodology for Sizing Energy Storage Systems for Grid-Supporting Services
No full textFollowing the rise in demand for clean energy production in order to reduce CO 2 emissions, power systems are facing challenges caused by the growing use of non-programmable renewable energy sources (RESs). In this regard, storage systems can play a role of primary importance since they are supposed to provide ancillary services. These are necessary for supporting RESs and thus keeping the grid stable. The present paper illustrates a methodology to guide a potential investor with the choice of a battery energy storage system (BESS) for the provision of grid-supporting services, considering both grid necessities and profitability. In particular, the methodology proposes a model that simulates the battery behaviour and the provision of the services including also an economic analysis to evaluate the profitability of the investment
An Optimization Problem for Day-Ahead Planning of Electrical Energy Aggregators
Full text linkThe widespread diffusion of distributed energy resources, especially those based on renewable energy, and energy storage devices has deeply modified power systems. As a consequence, demand response, the ability of customers to respond to regulating signals, has moved from large high-voltage and medium-voltage end-users to small, low-voltage, customers. In order to be effective, the participation to demand response of such small players must be gathered by aggregators. The role and the business models of these new entities have been studied in literature from a variety of viewpoints. Demand response can be clearly applied by sending a dedicated price signal to customers, but this methodology cannot obtain a diverse, punctual, predictable, and reliable response. These characteristics can be achieved by directly controlling the loads units. This approach involves communication problems and technological readiness. This paper proposes a fully decentralized mixed integer linear programming approach for demand response. In this framework, each load unit performs an optimization, subject to technical and user-based constraints, and gives to the aggregator a desired profile along with a reserve, which is guaranteed to comply with the constraints. In this way, the aggregator can trade the reserve coming from several load units, being the only interface to the market. Upon request, then, the aggregator communicates to the load units the modifications to their desired profiles without either knowing or caring how this modification would be accomplished. The effectiveness is simulated on 200 realistic load units
Analysis of the sensitivity of extended Kalman filter-based inertia estimation method to the assumed time of disturbance†
Full text linkThe frequency behavior of an electric power system right after a power imbalance is determined by its inertia constant. The current shift in generation mix towards renewable energy sources is leading to a smaller and more variable inertia, thereby compromising the frequency stability of modern grids. Therefore, real-time inertia estimation methods would be beneficial for grid operators, as their situational awareness would be enhanced. This paper focuses on an inertia estimation method specifically tailored for synchronous generators, based on the extended Kalman filter (EKF). Such a method should be started at the time of disturbance, which must be estimated accurately, otherwise additional errors could be introduced in the inertia estimation process. In this paper, the sensitivity of the EKF-based inertia estimation method to the assumed time of disturbance is analyzed. It is shown that such sensitivity is influenced by the initially assumed inertia constant, the use time of the filter and by the time required for primary frequency regulation to be activated
Management strategy for unbalanced LV distribution network with electric vehicles, heat pumps and domestic photovoltaic penetration2014 IEEE PES General Meeting | Conference & Exposition
No full textA Formal Approach to the Verification of Protection Systems in Low-Voltage Distribution Grids
No full textApplicazione della metodologia della continuazione numerica per la determinazione di biforcazioni locali e caos nei sistemi elettrici per l’energia
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Indices for fast contingency ranking in large electric power systems
No full textThe liberalization of the electricity market induces a large variety of scenarios that may lead power systems close to their operation limits. This supports the need for on–line dynamic security assessment (DSA) of the grids, in order to provide operators with a clear insight of the current network state. The on–line application of DSA to a realistic network needs adequate methods to screen the large amount of contingencies to be examined by DSA tools. This paper proposes some practical heuristic indices for Transient Stability contingency pre–filtering and ranking in an on–line DSA session
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