D. Proto

Optimal Integration of Distributed Energy Storage Devices in Smart Grids

Energy storage is traditionally well established in the form of large scale pumped-hydro systems, but nowadays is finding increased attraction in medium and smaller scale systems. Such expansion is entirely complementary to the forecasted wider integration of intermittent renewable resources in future electrical distribution systems (Smart Grids). This paper is intended to offer a useful tool for analyzing potential advantages of distributed energy storages in Smart Grids with reference to both different possible conceivable regulatory schemes and services to be provided. The Smart Grid Operator is assumed to have the ownership and operation of the energy storage systems, and a new cost-based optimization strategy for their optimal placement, sizing and control is proposed. The need to quantify benefits of both the Smart Grid where the energy storage devices are included and the external interconnected grid is explored. Numerical applications to a Medium Voltage test Smart Grid show the advantages of using storage systems related to different options in terms of incentives and services to be provided.

Optimal design of DC electrified railway stationary storage system

The improvement of the energy efficiency is a key issue for electrified railway systems in order to reach an increased competitiveness compared to other transportation technologies in terms of both costs and environmental pollution. An important step towards this direction has been made with the increasing development of storage technologies. The installation of stationary or on-board storage technologies, as well known, allows the recovery of the braking energy of the rolling stocks for increasing the energy efficiency of the whole system as well as improving the voltage profile. In the paper an optimization procedure is proposed for choosing in the planning stage the fundamental characteristics of a stationary storage device. The optimal parameters of the storage system can be determined by taking contemporaneously into account the energy saving aspects, substation current minimization and reduction of voltage drops along the feeder. The considered storage system is based upon a bidirectional dc-dc converter with ultracapacitors. A sliding mode control is implemented for tracking the optimal trajectory determined by the previously mentioned optimal technique. Numerical applications put in evidence the effectiveness of the proposed procedure.

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A 2×25-kV 50 Hz traction power system was analyzed and modeled in the time domain in order to simulate short-circuit conditions and to attain a practical method to identify the short circuit behavior of the traction system. In particular, due to the difficulty in assessing the track-line parameters which mainly depend on changing environmental conditions, the possibility of neglecting the capacitive parameters was analyzed. A complete model of the 2×25-kV 50 Hz traction power system was developed and validated through comparison with the results of referenced models and experimental tests performed on real systems. Simulations, addressed to reduce the short-circuit modeling complexity, demonstrate that neglecting the capacitive effects between conductors and to ground does not affect the calculation accuracy for standard analyses. The obtained results show that the proposed model can be remarkably useful for the traction system design as well as for investigating the effects of short-circuit conditions on other circuits, such as telecom circuits, power-supply equipment, and signaling track circuits.

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Plug-in Electric Vehicles (PEVs) could become remarkable resources for improving quality and reliability of future grids, if adequate control of their onboard storage systems is provided. Hence, the problem of PEVs optimal control strategies is a crucial topic of research in modern power system operation. This is particularly true in the Smart Grid (SG) context, where the presence of bi-directional communications among distributed energy resources and customers makes it possible to obtain an optimized operation of the grid. In this paper a critical overview of some of the most significant single-objective optimization methodologies proposed for the optimal operation of PEVs in electrical distribution networks is presented in order to verify their feasibility in the context of SGs. These methodologies allow the performance of several services, which aim to meet both needs internal to the SG (for example, the losses minimization or the minimization of average voltage deviations) and external to it (for example, ancillary services to the electrical system to whom the SG is interconnected). This paper reports the theoretical aspects of the optimization models, whereas the companion paper “Part II: numerical applications to vehicle fleets” proposes the results of the analysed models.

25-kV 50 Hz High-Speed Traction Power System: Short-Circuit Modeling

This is the companion paper to “Part I: theoretical aspects”. Part I reviews and critically analyses some of the most significant single-objective optimization methodologies proposed for the optimal operation of plug-in electric vehicles (PEVs) operating in Smart Grids. This Part II applies the models presented in Part I to a low voltage test Smart Grid. Analysis of the results highlights the behavior of the considered control strategies in terms of their compliance with both the objective functions and constraints. In the final part of this paper the results are summarized and compared in order to give an useful tool for understanding the more appropriate objectives and constraints to be taken into account for an optimal control of the Smart Grids.

A review of single-objective optimization models for plug-in vehicles operation in smart grids part I: Theoretical aspects

This paper investigates the problem of contemporaneously choosing optimal locations and sizes for both shunt capacitors and series voltage regulators in three-phase unbalanced distribution systems. The sizing and placement procedure not only minimizes the power losses along distribution feeders but also makes sure that both capacitors and series regulators will have the minimum possible impact on the harmonic distortion of bus voltages in the system. The fact that distribution systems can operate under unbalanced loading conditions means that the optimization will have to account for any unbalances in the system. A genetic algorithm, which successfully solves the above-described problem, is developed and tested. This paper presents the results of simulations for a 34-bus IEEE distribution test system.

A review of single-objective optimization models for plug-in vehicles operation in Smart Grids Part II: Numerical applications to vehicles fleets

This paper presents initial results of a three-year research project entitled ATLANTIDE, which is aimed at developing a comprehensive digital archive of reference models of Italian distribution networks, including forecasted load and generation development evolving towards future smart grid scenarios. Such reference network models and evolutionary scenarios should provide a useful benchmark for testing and comparing different control methodologies, distribution schemes and operation strategies for dealing with the new challenges caused by the envisaged widespread diffusion and integration of distributed generation, renewable generation and distribution storage devices. The paper focuses on the criteria adopted for defining a set of evolutionary scenarios for the reference networks, accounting for current drives and future trends, valuable to a wide range of the stakeholders of the distribution business.

Voltage Regulators and Capacitor Placement in Three-phase Distribution Systems with Non-linear and Unbalanced Loads

Electrical energy storage systems can provide several benefits along the entire value chain of the electrical system. In this paper attention is paid to the end user point of view, with particular reference to industrial customers. An optimal operating strategy is proposed for energy storage systems with the aim of reducing the electricity bill costs sustained by an industrial customer and contemporaneously satisfying technical constraints for the maximization of the storage system efficiency and life cycle. The proposal, which is developed in this paper by means of computer simulations, will be realized in an industrial facility located in the South of Italy in the frame of the GREAT project, a research plan aimed at developing advanced methods and tools for micro-grid applications.

Analysis of the Italian distribution system evolution through reference networks

This paper details an approach for the optimal scheduling of microgrids, including different distributed resources such as datacenters, electric vehicles, and distributed generation units. Management of both loads and generation systems is considered to be a strategic approach to optimally operate the grid. At this purpose, a multi-objective strategy was formulated, including several objectives that are considered essential for the efficient grid operation. Numerical simulations were performed to test the effectiveness of the proposed approach and the results were compared with those obtained through uncontrolled scenarios.

Optimal operation of electrical energy storage systems for industrial applications

Distributed generation units in microgrids are typically inadequate to meet the total loads demand during the peak hours, whereas a surplus of energy can be available during the hours of the day characterized by low demand. On the other hand, the foreseeable large use of plug-in electric vehicles storage systems could enable to modify the microgrid daily load demand; plug-in electric vehicles batteries, in fact, can have the multiple role of loads and energy sources. On the basis of the above considerations, this paper focuses on the economical scheduling of electric vehicles powers by proposing a single-objective optimization model that minimizes the total amount of daily cost suffered for the energy imported from the upstream network. The model includes also a constraint on the active power at the interconnection bus of the microgrid, thus enabling the peak shaving service. The effectiveness of the single-objective strategy is demonstrated with numerical applications to a low voltage test microgrid.