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This paper deals with the use of distributed energy storage systems in microgrids, and proposes a planning method which accounts for the uncertainties of load and distributed generation. Objectives of the planning method are the reduction of the energy costs, while providing the supply of ancillary services as a technical support to the network. The energy costs are evaluated considering a hourly varying pricing scheme and optimizing the storage systems charging/discharging stages. The technical support is devoted to the restraint of bus voltage amplitudes, and of network components' currents/powers within admissible ranges. The input data uncertainties are managed through three decision theory criteria (i.e., the minimization of expected costs; an approach based on the weighted regret felt by the design engineer; and a stability area criterion), which allow considering the multiple design alternatives and futures (i.e., possible values of uncertain input data) in an accurate and feasible way. The design alternatives refer to the size and location of the distributed storage systems, while each future is associated with a different level of load demand and power production of distributed generation over the whole planning period. The results of numerical applications are reported and discussed with reference to a Cigré test network.

The paper proposes a tool for the optimal sizing of an end user's battery energy storage system. The sizing is performed considering demand response applications with real time energy prices. The procedure, which takes into account also the battery degradation due to some stress factors, is performed based on uncertainties of generation, load, weather conditions, discount rate and energy price. Particularly, the sizing of the storage device is aimed at maximizing the economic benefit of the end user.

Scheduling the distributed energy resources in day-ahead scenarios requires the use of accurate forecasts of loads, generation, and energy prices. Forecasting errors may significantly influence the quality of the scheduling, resulting in overestimations or underestimations of the power required from the grid by a price-responsive customer. In this paper we provide an insight on the assessment of the impact of forecasting errors in a case study regarding an industrial customer who disposes of a photovoltaic system and of an electrical energy storage system. The day-ahead scheduling procedure, developed in previous works, is applied using forecasts obtained through random forests and through a benchmark model; the obtained results are compared with the ideal scenario, using the actual realizations of the unknown variables, in order to assess the responsiveness of the scheduling procedure to forecasting errors.

Distributed generation (DG) produces many benefits for the distribution systems that are operated as active systems, even if they have been traditionally designed as passive networks. Then, new technical issues must be addressed, involving both normal and abnormal operating conditions such as short circuits. Photovoltaic systems (PVSs) are among the most diffuse DG and their contributions to the short-circuit operating conditions depend on several factors, such as environmental conditions, PVS inverter control characteristics, self-protection systems, and fault location and type. An analytical model that aims at quickly and accurately analyzing the three-phase short-circuit operating conditions in a distribution system in presence of PVSs is presented in this paper. The model is applied to a typical North American MV network characterized by large penetration of PVSs, investigating the influence of the aforementioned factors.

In the context of modern distribution systems, power quality is recognized as a crucial concern that requires advanced technical solutions in order to guarantee the correct operation of such complex systems. Among the power-quality disturbances, waveform distortions are one of the most important due to their impact on the equipment, and active filters are considered a useful technical solution to this disturbance even more significantly if they are optimally integrated into the grid. This paper addresses the problem of optimal siting and sizing of active filters in a multiconverter distribution systems by adopting a multiobjective approach. The proposed original formulation includes the control strategies of the active compensators among the decision variables and takes into account the various sources of uncertainties which characterize modern distribution systems. A heuristic simplified approach based on a trade-off/risk analysis is proposed to solve the multiobjective optimization problem under uncertainty with the aim of minimizing several conflicting objectives while meeting proper constraints.

Voltage stability has become a fundamental issue in the new, liberalized markets due to the fact that the new power systems are approaching more and more the stability limits. Then, several approaches were proposed in the relevant literature to find the critical conditions and the problem was faced also with reference to unbalanced three phase power systems. The unbalances, in fact, can be responsible of more critical stability conditions than in balanced power systems. Continuation power flow and optimal power flows were applied to analyze such conditions. In this paper a new three-phase optimal power flow is proposed that makes use of complementarity constraints to take into account the effect of reactive generation limits on voltage stability in unbalanced power systems. An application is presented on a test system highlighting the feasibility and the goodness of the proposed technique. Both load and line unbalances are taken into account to capture the dependence of voltage stability on the level of unbalances.

Electrical storage systems are a potential solution for some challenges that will face future Smart Grids due to the large number and variety of services they can perform. These services can be further enlarged if an optimal operation of the storage systems is guaranteed. This paper deals with the energy management of battery storage systems in the frame of real time pricing. An optimal control strategy is proposed in order to minimize the electricity bill costs of an industrial facility. Firstly, the optimization model is formulated considering a multi-battery system. Then, two algorithms are applied to solve the problem: the linear programming and the dynamic programming. Numerical applications to an actual industrial facility demonstrate the effectiveness of the proposed procedure and the differences obtained applying linear and dynamic programming algorithms.

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.

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.

In this paper, the problem of the use of dispersed generation (DG) for providing ancillary services in electrical distribution systems is addressed. Fuel cell-based, photovoltaic cell-based, and wind generation systems are connected to the distribution network through power electronic interfaces, each with a proper storage system for the optimal grid operation. Thanks also to the storage system, the DG units are able to provide ancillary services such as load following, back-up, peak shaving, reactive power support and power quality disturbance compensation. A centralized control system coordinates the DG units. Time domain simulations on an actual distribution system are reported and discussed.

The paper deals with the reactive power control in a MV distribution system in presence of Dispersed Generation (DG). The control variables are the reactive powers of DG units and capacitors, and the tap position of the on-load tap changer of the HV/MV transformer. Single-objective and multi-objective optimization problems are formulated and solved in order to achieve the optimal control, even containing the impact of the waveform distortions. Numerical applications performed on a 109-bus test distribution system give evidence of the effectiveness of the proposed procedure.

The presence of the new liberalized markets has increased interest in power quality disturbances due to their economic value. Customers have more choices; then disturbances are becoming bigger issues and suppliers and customers should regulate them in the frame of power quality contracts. A single global power quality index can be very useful for characterizing the overall level of the voltage waveform quality; in particular, this index can provide global indications regarding different aspects of voltage quality and allows a strong reduction of the measurement data needed to cover all power quality disturbances, in this paper, a global power quality index (GPQI) for discrete disturbances is proposed, based on the discrete severity indicators (DSI). We present the results of a GPQI evaluation of an Italian distribution system on voltage dips, whose measured data are available on the website of the project QuEEN led by CESI Ricerca.

Dispersed Generation (DG) is often connected to the network with power-electronic interfaces for a proper coupling with the distribution networks (e.g. photovoltaic panels, fuel cells, microturbines, wind turbines, etc.). Such power electronics can perforin functions other than the supply of real power thus representing an opportunity to increase the value of DG as provider of new additional services. In particular, the innovation and the improvements in electronic devices allow using DG for the provision of ancillary services (voltage control, power quality disturbance compensation, and so on), representing, in this way, an interesting chance to improve the quality of the service. For these reasons, specific planning tools for the optimal siting and sizing of DG should be adopted to take into consideration the multiple and contrasting goals that the Distribution System Operators (DSO) strive to achieve. In the paper the optimal siting and sizing of DG connected through electronic interfaces is performed by means of multiobjective programming and an -constrained technique is used for the solution of the problem. Particular attention is paid to the modelling of electronic interfaces in order to obtain the required ancillary service provision. Simulation results on a test system demonstrate the usefulness of the proposed methodology as well as the advantages obtained by the use of electronic interfaces in comparison to solutions employing electric generators directly coupled to the distribution network.

The paper deals with the problem of assessing the impact on the service Power Quality (PQ) of new installations of embedded generation. To face with this problem, two types of indices are proposed: variation and benefit index. Their definition is irrespective to the specific disturbance to be considered so that it is possible to indicate them as generalised indices to properly and quickly quantity the influence of different EG solutions on the PQ disturbance levels. Numerical applications on an actual distribution system give evidence of the useful indications that can be derived.

One of the main problems for waveform distortion assessment that is to reduce the effects of the spectral leakage due to fundamental and harmonics on interharmonic components. In the framework of DFT approaches, line frequency synchronization techniques or algorithms to compensate desynchronization are necessary; alternative approaches as those based on the Prony methods are not sensitive at all to desynchronization but can require not negligible computation burden. In the paper, different proposals by the same authors regarding both DFT based and Prony based advanced methods are recalled and compared to each other. The results of several numerical experiments are reported and analyzed; some of them are in accordance with IEC guidelines and some others are related to more open scenarios.

Probabilistic and time-frequency aspects of time varying waveforms in power systems are considered with reference to DC arc furnaces and adjustable speed drives using line commutated inverters. These loads are characterized by waveform whose spectral components are time-varying in amplitude and frequency. The problems of understanding and assessing their waveform distortion is taken into account. Some considerations on the most adequate techniques for the spectral component representation and calculation are effected

The widespread use of advanced technologies and automation in AC and DC railway systems requires an accurate investigation of the Power Quality disturbances they suffer. In some cases, both railway systems operate in the same transmission network area, so that voltage unbalances and waveform distortions can be complicated by the interactions between the two systems. In this paper, a robust electronic compensation device is proposed in order to solve the interaction problems; the solution is based upon a two-phase inverter with a non-linear and variable structure control system. Several numerical applications give evidence of its rejection action against disturbances and power parameters variations.

DC arc furnaces are more and more applied in large industrial power systems. They represent a source of perturbations for the feeding system, in dependence on the available short-circuit power at the point of common coupling and on the arc furnace rating. This paper deals with the problem of the compensation of perturbations due to DC arc furnaces behavior; in particular, the application of a new device, the decoupled compensator, is investigated. The study is performed with reference to a typical DC arc furnace and by using computer simulations developed by means of power system blockset, that is a tool of Matlab. Waveform distortions and voltage fluctuations indices are assessed in presence and in absence of the compensation device.