• Energy Research

In the 2000s, the liberalization of the rail markets for freight and passenger travel opened up the competition. Nowadays, local, regional, and long-distance passenger rail are gradually following suit. As a consequence of the paradigm of realizing smart and sustainable cities, the operators of local railway infrastructures (i.e., metro, light railway, and commuter) are studying strategies to improve the energy efficiency of the overall system. The operators are thus involved in renewing technological infrastructures and examining new operation models for coordinating the motion of the trains fleet. With this regard, the present work proposes a timetable adjustment approach to reduce energy consumption in metro rail transit systems. In addition, a centralized control strategy to manage the output voltage of Traction Power Substations (TPSs), train regenerative power, and charge/discharge power profiles of off-board Energy Storage Systems (ESSs) is proposed. The approach is based on a two-step procedure aimed at optimally allocating the layover time among the train stops. This approach is formulated as an optimization problem, which consider the adopted control strategy, because of the correlation between control actions and timetable. Numerical examples have been carried out based on the real data from metro line 1 of Naples, (Italy). The results highlight the capability of the strategy to achieve relevant results in terms of energy saving. In addition, the advantages introduced by the proposed centralized control strategy are emphasized through a comparison with the conventional local control strategy.

This paper deals with the optimal planning of the electrical energy storage systems in the microgrids aimed at cost minimization. The optimization accounts for the compensation of the voltage dips performed by the energy storage systems. A multi-step procedure, at the first step, identifies a set of candidate buses where the installation of a storage device produces the maximum benefit in terms of dip compensation; then, the life cycle costs in correspondence of different alternatives in terms of size and location of the storage systems are evaluated by considering an optimized use of the energy storage systems. The simulations on a medium voltage microgrid allowed validating the effectiveness of the proposed procedure.

The loadability characteristics of overhead transmission lines (OHLs) is certainly not a new topic. However, driven by sustainability issues, the increasing need to exploit existing electrical infrastructures as much as possible, has given OHL loadability a renowned central role and, recently, new investigations on this subject have been carried out. OHL loadability is generally investigated by means of numerical methods. Even though this approach allows deducing useful information in both planning and operation stage, it does not permit to capture all the insights obtainable by an analytical approach. The goal of this paper is to tailor a general analytical formulation for the loadability of OHLs. The first part of the paper is devoted to the base-case of uncompensated OHLs. Later, aiming to demonstrate the inherent feasibility and flexibility of the novel approach proposed, the less frequent case of shunt compensated radial OHLs is investigated as well. The analytical formulation is combined with the use of circular diagrams. Such diagrams allow a geometrical interpretation of the analytical relationships and are very useful to catch the physical insights of the problem. Finally, in order to show the applicability of the new analytical approach, a practical example is provided. The example concerns calculation of the loadability characteristics of typical 400 kV single-circuit OHLs.

Protection against lightning-induced voltages is a particularly critical issue, especially for smart grids, due to the presence of electronic-based equipment, as well as control and monitoring devices. Analysis of the severity of the induced voltages is then imperative; on the other hand, the random nature of the lightning phenomenon cannot be disregarded. In this paper, the severity of lightning-induced voltage is analyzed by means of a probabilistic approach which, starting from closed-form solutions, uses a Monte Carlo procedure. Parametric distributions that best fit the distributions of the induced voltages are investigated as well. The results show that the lognormal and the generalized extreme value distributions are the best candidates.

The paper deals with energy storage systems applications in Smart Grids. Several services can be performed thanks to the energy storage systems use, with objectives aimed at meeting needs internal or external to the Smart Grid. Optimal nonlinear constrained problems can be formulated and properly solved in order to perform the services in the best economical and technical way. In this paper, optimal control strategies are proposed in order to allow the Smart Grid to minimize internal losses and to sell energy and ancillary services during high power prices periods. The procedure involves the formulation of optimal power flow problems; proper objective functions and constraints are imposed to satisfying the services that have to be carried out. A numerical application on a 30-bus low voltage Smart Grid shows the effectiveness of the proposed procedure.

Worldwide expectancy of larger fleets of PEVs requires an increasing number of available fast and ultra-fast charging stations. In order to reduce the impact on the distribution grid of the power demand of large fleets of PEVs, the coordination of charging in stations equipped with multiple charging slots is mandatory. The paper suggests a smart charging profile of electrical vehicles based on an optimization problem in order to minimize the charging time. Constraints in term of limits on the power supplied by DSO, the available state of charge (SOC) of the BESS and the energy requested by the PEVs are taken into account. Some simulations are presented to validate the suggested charging strategy.

In this paper, the voltage regulation in power systems is addressed from the perspective of the modern paradigm of control logic supported by phasor measurement units. The information available from measurements is used to better adapt the regulation actions to the actual operation point of the system. The use of the online measurement data allows for identifying the sensitivity matrix and for improving the regulation performances with respect to the fast load variations that increasingly affect modern power systems. With the aim of estimating the sensitivity matrices, a preliminary action is necessary to reconstruct the phases of the network voltages, which are assumed not to be provided by the phasor measurement units. This allows for obtaining a model-free adaptive control method. It is then shown how the regulation problem can be formulated in terms of a linear quadratic Gaussian problem, properly considering the load modeling in terms of the stochastic Ornstein–Uhlenbeck process. This control strategy has the advantage of avoiding dangerous oscillations of power flows, as demonstrated through the results of some simulations on a classical test network. Particularly, the advantage of the proposed approach is shown in the presence of different levels of load disturbances.