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Despite low energy and fuel consumption levels in the rail sector, further improvements are being pursued by manufacturers and operators. Their primary efforts aim to reduce traction energy demand, replace diesel, and limit the impact of electrified overhead infrastructures. From a system‐level perspective, the integration of alternative energy sources on board rail vehicles has become a popular solution among rolling stock manufacturers. Surveys are made of many recent realizations of multimodal rail vehicles with onboard electrochemical batteries, supercapacitors, and hydrogen fuel cell systems. The ratings, technical features, and operating data of onboard sources are gathered for each application, and a comparison among different technologies is presented. Traction system architectures and energy‐control strategies of actual multimodal units are explored and compared with literature research. Moreover, the maturity and potential of recent technologies and alternative topologies of power converters for multimodal traction systems are discussed. Ultimately, onboard storage systems are compared with other solutions for energy‐saving and catenary‐free operation, with particular focus on their current techno‐economic attractiveness as an alternative to diesel propulsion.

As a consequence of the growing demand for mobility and the requirements for reduced environmental pollution, railway traction systems are receiving increasing interest. Researches are analyzing new technologies and managing solutions to increase energy efficiency in the railway infrastructures. Many studies proposed the oppor-tunity to introduce the technology of energy storage systems (e.g., Wayside Energy Storage Systems - WESS) in traction infrastructures. WESS can be able to: i) reduce voltage drops; ii) save braking energy; iii) support Traction Power Substations in supplying traction power peaks. A relevant topic in using WESSs in railway infrastructure is to verify their impact in case of faults. Studies on short circuit analyses are required to verify the correct rating of the protection devices and the opportunity to use new protection devices and mode of operating, when the new technology is integrated. In this paper, the typical Italian DC railway power system is investigated. Specifically, the contribution of WESS to the short circuit currents is assessed by examining transient and steady-state conditions.

The scientific literature is paying particular attention to Ultra-Fast Charging Stations (UFCSs) that can make charging times of Electric Vehicles (EVs) comparable with the refuelling time of internal combustion engine vehicles. In this context, scheduling charging algorithms to manage the available resources deserve significant attention. This paper proposes an online scheduling algorithm for UFCSs equipped with Battery Energy Storage Systems. The charging profile is obtained by considering the power and energetic constraints related to both infrastructure and EVs. The constraints are assessed according to the efficiency of the infrastructure, for which a power losses estimation approach was proposed and then detailed for the UFCS realized at our department. Even, the dependence of the maximum EV charging rate on the State of Charge (SoC) is considered. These aspects are usually neglected. Thus, starting from the measurements of the maximum charging rate for two commercial EVs, numerical simulations were performed using the proposed algorithm according to two different scheduling policies, i.e., the not-preemptive ‘First Come Best Served’ and the preemptive ‘Round Robin SoC’. The numerical results highlight the difference between the two policies regarding the allocation of resources among vehicles and how the SoC of the BESS affects the overall charging profiles.

The number of Plug-in Electric Vehicles (PEVs) available on the car market is continuously growing. The electrification of the mobility is definitely related to the diffusion of the charging infrastructures widely distributed on the territory. Indeed, PEV owners request for charging stations able to offer features adequate to the expectations. They are expected to be able to recharge vehicle's on-board battery in a ten of minutes. In this paper, Ultra Fast Charging Stations (UFCSs) are investigated. The stations are discussed in terms of electric schemes and modalities of control. There is a focus on components, systems, state variable and security level. Moreover, the UFCS realized at the University of Naples Federico II is highlighted. The lab prototype is discussed in terms of configuration and rated values. The results of some numerical tests are carried out. They point out both the main features of the charging slots and the requirements of load emulators for UFCS.

The paper deals with the power control of a delta connected Cascaded H-Bridge (CHB) converter equipped with photovoltaic (PV) modules. A hierarchical architecture of energy management is proposed: A 'Module level' controller performs a Maximum Power Point Tracking (MPPT) algorithm to achieve the optimal utilization of each PV module; a 'Leg level' controller manages the power flow control within the modules of a single CHB phase leg, and a 'System' level controller manages the active power flow between the three CHB phases and the reactive power generation towards the grid. The active power control is aimed at the compensation of the mismatches between the different PV-powered modules, which may come from partial shadowing phenomena. A power unbalance compensation between cascaded modules is implemented through the Pulse Width Modulation (PWM) algorithm, while the unbalance compensation between the phases is implemented through the phase currents control. To compensate the active power unbalance due to PV module mismatches, the obtained effect is equivalent to the injection of a zero sequence current. A reactive power control has been implemented to perform a power factor (PF) correction, too. A set of numerical simulations validate the effectiveness of the algorithm, which can simultaneously achieve the desired active power generation from all the PV panels and the desired PF control towards the grid.

Storage technologies devices are very interesting solutions for improving energy saving and guaranteeing contemporaneously to enhance the electrical characteristics of Light Rail Transit (LRT) systems. Onboard Energy Storage System based on Lithium Ion Capacitor (LiC) devices represent a viable engineering solution for energy saving optimization. The authors suggest a multi-objective design optimization procedure based on catenary and storage power losses minimization. A test characterization of ESS has been presented in order to use the better appropriate modeling of LiC for the examined case study. The numerical simulation allows to confirm the feasibility of the proposed design procedure.

As one of the solution for energy saving in DC-electrified railway system, wayside energy storage systems (WESSs) are recently studied. In the previous study, current based control, which regulates current of ESSs, and voltage based control, which regulates the filter capacitor (FC) voltage, have been proposed as a power control method for WESSs. However, the difference between these two power control methods has not discussed before. In this paper, a theoretical comparison between voltage based power control method and current based power control method is carried out focusing on each static characteristic. Furthermore, an influence of distance between a WESS and a rail vehicle on characteristics of each control is also considered. Though the study in this paper, theoretical comparison between both control methods is carried out. Results of this paper contribute to establish a method to design WESSs which realize maximum energy saving effect with minimum energy capacity of energy storage devices.

This paper is aimed to present an experimental criterion that allows researchers and designers to evaluate the performance of DC micro-grids dedicated to charging operations of full EV. The laboratory methodology is explained through tests on a demonstrator of power architecture, specifically designed as simplified case study of a DC charging station for fully-electrified low-power two-wheeler, such as: electric scooters and bikes. This experimental prototype is composed by a 20 kW AC/DC bidirectional grid-tied converter, which realizes the DC conversion stage, and two DC/DC power converters, interconnected with the micro-grid through a DC bus. The power architecture provides on one hand the charging operations of electric two-wheeler battery packs and on the other hand the integration of the micro-grid with an ES buffer, which has the main function of supporting the main grid while an electric vehicle is on charge. The performance of the considered architecture is characterized and analyzed in different operative conditions, through a specific management of the energy fluxes. The laboratory tests evaluate efficiency, charging times and impact on the main grid, with specific reference to the DC charging operations of electric scooters. The obtained experimental results show the advantages of adopting the DC buffer architecture, compared with an AC commercial battery charger, considered as reference in this work. Finally, the numerical data of this paper, related to the single power components and to the experimental results evaluated for the whole demonstrator, effectively support the lack of knowledge in the literature about charging stations for EVs. In fact, these pieces of information, based on experimental tests, are expected to support the building of simulation models and the identification of the best energy management and control strategies to be adopted in a smart-grid scenario, characterized by distributed generation systems including renewable energy sources.

In this paper, an advanced control strategy for grid­tied photovoltaic (PV) cascaded H­bridge (CHB) inverter is proposed. The circuit topology consists of a proper number of power cells (H­bridge configuration) connected in series and supplied by individual PV modules. The adopted control method is a mixed staircase­PWM technique performed by means of a sorting algorithm to determine cells' switching state. The cells' state is related to the need of charging or discharging a particular cell much more than the others by calculating the voltage error at each dc­link (e.g., by considering the difference between the maximum power point tracking (MPPT) reference and the measured quantity). A dedicated PO thus, increasing the power extraction even in mismatched conditions. In order to prove the effectiveness and feasibility of the proposed approach, a set of experiments are performed on a laboratory prototype of a single­phase five­level PV CHB. The control section is implemented on FPGA by using a dSPACE real­time hardware platform; thus, obtaining fully dedicated digital circuits. Experimental results show good performance in terms of MPPT efficiency, total harmonic distortion, and power factor in both normal operation and mismatch conditions.

This paper presents a control strategy for the power flow management of a wayside energy storage system based on a supercapacitor technology installed in a tramway network. The control is based on the management in real time of voltage levels at catenary point connections in order to optimize the energy flow among the running tramcars and substations with the goals of improving the energy saving and reducing the voltage drops in the supply network. The suggested control algorithm was experimentally validated using a laboratory-scale model to verify the effectiveness of the strategy. A lithium-ion capacitor module with 72 series-connected laminated cells of the JSR Micro ULTIMO type was used. Thus, an emulation of a real tramway network in the city of Naples (ANM) was implemented to evaluate the potential impact in terms of costs/benefits of the next installation on the ANM network.

Purpose – The purpose of this paper is to propose a new converter topology for integrating PV plants constituted by many panels into the grid. The converter is capable of implementing MPPT algorithms on different subset of modules and can balance the different energy supplied by panels differently irradiated. The output voltage presents a very low ripple also if small filters are used for grid connection. Design/methodology/approach – In the paper, at first the converter configuration is presented. Then a control strategy for obtaining, at the same time the distributed MPPT and the power balancing on the three phases is proposed. Finally, by means of numerical simulations, the good performances of the proposed converter are shown. Findings – The proposed converter, lent from MMC configurations, is deeply studied and a suitable control strategy is well analyzed in the paper. Analytical model for voltage and current balancing are given. Research limitations/implications – The analysis presented in the paper complete some studies started in the last years and partially presented in previous scientific papers. It reaches a final point and gives all the specific for the realization of the converter and of its control. Practical implications – The paper gives all the instrument to design and realize a PV power plant integrated into building façade. Originality/value – The converter and the control for voltage and current balancing presented in this paper represent a significant original contribution of this work.

In this paper, a photovoltaic (PV) module-level Cascaded H­Bridge (CHB) inverter with an integrated Battery Energy Storage System (BESS) is proposed. The advantages and drawbacks of the CHB circuit architecture in distributed PV generation systems are highlighted. The main benefits are related to the higher granularity of the PV power control, which mitigates mismatch effects, thus increasing the power harvesting. Nevertheless, heavy unbalanced configurations due to the intermittent nature of PV sources need to be properly addressed. In order to smooth the PV fluctuations, a Battery Energy Storage System is used to provide both an energy buffer and coordination of power supply and demand to obtain a flat profile of the output power. In particular, by exploiting the inherent modularity of the conversion circuit, a distributed storage system is also implemented by splitting the battery into smaller units each of which represents the backup module of a single power cell of the PV CHB. The proposed design and control strategy allows overcoming the operating limits of PV CHB inverter. Simulation results, carried out on a single­phase nineteen­level PV CHB inverter, evidence the effectiveness of the proposed design and control approach to minimize the adverse impact of deep mismatch conditions, thus enabling continuous power output by compensating PV power fluctuations.

This paper is focused on the evaluation of theoretical and experimental aspects related to the different operation modes of a laboratory power architecture, which realizes a micro grid for the charging of road electric and plug-in hybrid vehicles. The analyzed power configuration is based on a {DC} bus architecture, which presents the main advantage of an easy integration of renewable energy sources and buffered storage systems. A first phase of simulations is aimed to evaluate the main energy fluxes within the studied architecture and to identify the energy management strategies, which optimize simultaneously the power requirements from the main grid and charging times of different electric vehicles. A second phase is based on the experimental characterization of the analyzed power architecture, implementing the control strategies evaluated in the simulation environment, through a laboratory acquisition and control system. Then the experimental results coming from the laboratory prototype are compared with the simulation results, in order to achieve a better parameter setting of the simulation model for the analyzed structure. This preliminary analysis makes possible other simulations to be carried out on more complex architecture of micro-grids, taking into account the integration of renewable energy sources and high power buffer storage systems. Particular attention is also given to the analysis of ultra-fast charging operations and the related performance in terms of total efficiency, charging times, total power factor and power requirements from the main grid. This study represents a further step toward the new concept of smart grid scenario for electric vehicles.

The paper suggests an energy management control strategy of wayside Li-ion capacitor (LiC) based energy storage for light railway vehicles (LRV). The installation of wayside supercapacitor (SC) storage devices, as widely recognized, allows the recovery of the braking energy for increasing the system efficiency as well as a better pantograph voltage profile. A new type of SC, LiC, interfaced with dc-interleaved converter has been presented. This technology has an energy density comparable to batteries and power density much higher than the batteries. The authors propose a control strategy based on the maximum kinetic energy recovery throughout braking operations of the running vehicles. The stored energy comes back to the vehicles during the accelerations. The strategy stays on the knowledge of the state of charge of LiC device and the actual vehicle speeds. In particular, the control algorithm evaluates, in real time, the actual value of LiC voltage and current references on the basis of the vehicles inertial forces and acceleration estimations, taking into account the power losses of the system. Experimental tests made on electromechanical simulator, equipped with a 136-V, 30.5-F LiC module, fully confirm the validity of the suggested control. Finally, experimental characterization of LiC module has been achieved.

Storage systems are recognized as a viable mean for improving the performances of electrified transportation systems. The recent literature highlighted some significant solutions to design problems thanks to procedures-based upon optimization theory. More specifically, an analytical solution can be deduced based on the formulation of an isoperimetric problem. This formulation exhibits the intrinsic ability to determine the optimal storage size, once the train power absorption has been fixed. Unfortunately, the analytical expression is not very advantageous to the control because it includes terms that require both real-time traction load estimation and its prediction over the whole traction cycle. The originality of this paper lies in the suitable simplification of the control structure, avoiding both traction load estimation and the heavy computations linked to predictive analysis. The storage device control law is reduced to an appropriate constant voltage over the whole traction cycle. The traction load prediction is performed offline, and the robustness of the consequent control law is tested against random variations in significant traction parameters. Some comparisons are made using other control strategies proposed in the technical literature. Finally, numerical and experimental results confirm the validity of the affected assumptions.

The installation of stationary ultracapacitor storage devices, as widely recognized, allows the recovery of the braking energy for increasing the energy efficiency as well as a better pantograph voltage profile. In the paper a new methodological mean is proposed for determining the fundamental characteristics of this kind of storage device, characterized by high power density, interfaced with the railroad by a bidirectional dc–dc converter. More specifically, the parameters of the storage system can be determined by employing an optimization technique which in a quite general way is able to take contemporaneously into account several aspects in an integrated manner. Some considerations are performed for properly taking into account the stochastic aspects of the design procedure. Numerical simulations with respect to a case study are presented, pointing out the potentiality of the tailored technique. Experimental results are also reported, with reference to an electromechanical simulator, in order to put in evidence the effectiveness and the actual implementation of the proposed optimization technique.

In this work a new control strategy for grid-tied photovoltaic cascaded H-bridge multilevel inverters is presented. The topology analyzed in the paper is made by series connected power cells, each supplied by an individual PV source, thus providing a distributed conversion scheme. The algorithm ensures stable operation even in power unbalance condition among cells thanks to a sorting algorithm which properly selects the switching state of each H-bridge. The control is implemented on FPGA in order to obtain dedicated digital circuits in parallel operation, which is mandatory when the cells' number increases. The effectiveness of the proposed approach is evidenced by means of experimental tests performed on a single phase 7-level laboratory prototype of H-bridge inverter. The results show good performances in terms of maximum power point tracking efficiency, power factor, and total harmonic distortion.

This work deals with an optimal control strategy for a three-phase grid-tied photovoltaic (PV) cascade H-bridge inverter. The main challenge for the control of this system topology derives from the inherent power imbalance among the phases as well as from the different power levels of the H-bridge cells in each phase leg. The power imbalance among the phases is compensated by the injection of a proper zero-sequence voltage. The power distribution among the cells of each phase could be affected by uneven irradiance and temperature conditions of PVGs (PV Generators). This latter issue is addressed by means of an adaptive modulation method especially suited to manage unequal dc sources, while assuring stable circuit operation and maximizing the power extraction through a dedicated MPPT (Maximum Power Point Tracking) algorithm. The digital controller is developed and tested in Matlab/Simulink environment integrated with XSG (Xilinx System Generator), thus allowing an easy transfer on FPGA embedded in dSPACE real-time platform. Simulations and experimental results prove the validity of the proposed design and control approach.

The paper proposes a new design method of a distributed controller of an articulated or not transport system, composed of n units, each one driven by an asynchronous motor powered by an inverter. The proposed methodology allows to design a controller that ensures distances between the various units having generic temporal behaviors with bounded derivative and, at the same time, any speed of the head unit with bounded acceleration, despite the action of any disturbances with bounded derivative and the presence of bounded parametric uncertainties. The validity of the method is illustrated with application to an articulated transport system composed of three units.

The paper analyses generator operations of asynchronous machines when they are connected to a passive electrical network either directly or by an intermediate static power converter. The analysis is performed by taking into account the saturation phenomena of the main magnetic circuits of the machine. Mathematical models of both physical configurations are given and their non-linearities are evidenced. The paper investigates the existence of periodical solutions related to stable operations of the systems. Numerical and experimental results support the theoretical analysis.

The paper presents a project, I-ECO, Inductive Charging Station for Ebike Clever Mobility. It consists of the development of integrated high-tech components for the design and implementation of eco-friendly cycle-stations making use of inductive charging systems or so-called 'wireless', with integrated photovoltaic generation systems, for the' power assisted bicycles. In particular, the project aims to design, implementation and testing of field of a system of bike-sharing power at the service of intermodal mobility aimed at staff and students of the University of Naples.

This paper presents a control technique for smoothing voltage oscillations in the sub-modules of Modular Multilevel Converter during start-up operations of high-power medium-voltage induction motor drive. At steady-state, the power fluctuations in each sub-module at fundamental and 2 nd harmonic frequencies generate capacitor voltage oscillations which are much higher as the current frequency decreases and tend to infinite at zero frequency. This is a problem in variable speed drives, where very low frequency values are needed during start-up. The control injects a homopolar component of the converter output voltage and an alternative high frequency circulating current, whose magnitude is much higher than the induction motor one during start-up operations. A space vector modulation technique is used in the control implementation. A numerical investigation is carried out with reference to some relevant cases-study in order to show the validity of the proposed control which allows an effective reduction of voltage oscillations on the dc-link capacitors of the different converter sub-modules.

The paper studies a three-phase PV power system connected to the LV power grid. The power system consists of a PV source, and a DC boost converter. The DC link is connected to the grid via a new cascade H-bridge converter, typical for modular multilevel converter application. A control approach is formulated. The control strategy aims at delivering to the grid the maximum power available from the PV sources with unity power factor. The control is formulated in case of inhomogeneous irradiation and the line current symmetry is assumed as system requirement. Aiming at verify the feasibility of the proposed approach, a numerical simulator for a 12 kW PV power plant is realized in ®Matlab. The results of the numerical simulations are used to give evidence to the approach in case of building facade application.

Lithium-ion capacitors (LiCs) are novel storage devices with a high power density and high energy density compared to conventional supercapacitors (SCs). This paper proposes a method to validate the previously developed characterization and modeling methods, which are the same as those used for a conventional SC with double-layer-activated carbon technology. This paper presents two relevant contributions. First, a full frequency range model and the experimental parameter identification of two kinds of LiC cells are presented. In order to extend the LiC cell parameter identification to a module composed of several series-connected cells, an aggregate model of the LiC module was investigated and validated. The results of experiments and numerical simulations demonstrate the value and effectiveness of the proposed model when the cells operate at room temperature.

The paper focuses on an innovative energy management control strategy of a wayside supercapacitor (SC) applied in DC electrified light transit networks. In order to achieve minimum energy demand from the electric feeding substations, the target of the control is the optimal tracking of the storage device voltage subject to the minimization of the mean square of the supply currents and, consequently, the reduction of power losses along the line. Hence, optimization theory has been used for the analytical determination and implementation of real time control strategy. Therefore the proposed strategy has been verified and validated via numerical simulations with reference to realistic LRV operation and different headway among the operating vehicles. A comparison with a classical energy storage system (ESS) state of charge control has been also carried out, as well as the energy saving improvement has been highlighted and the energy storage system integration and challenges are addressed. The results validate the theoretical approach and prove that the suggested control strategy is quite effective, putting in evidence its potentiality and the possibility of an actual implementation.

In this paper a power converter based on a modular multilevel topology is discussed. The Modular Multilevel Converter (MMC) is one of the emerging technology for high- or medium-voltage transformerless power conversion. The paper presents a space vector modulation technique developed for a MMC with arbitrary number of voltage levels; the presented technique integrates the modulation of the homopolar component of the converter output voltage. A numerical investigation is carried out with reference to some relevant cases-study in order to show the validity of the proposed modulation technique which allows an effective control of the converter recirculating currents.

In this paper an analysis of a power converter based on a modular multilevel topology is discussed. A mathematical model of the MMC is developed in order to evaluate its dynamic behavior and to better understand the incidence of the circulating current phenomenon which could compromise converter performance in variable speed drive applications. In fact, if such problem is not properly addressed reliability problems arise.

The paper presents power converter architectures for ultra-fast charging of road electric vehicles with the integration of distributed energy storage systems, which work as energy buffer between the grid and the electric vehicle in recharge. The study is introduced by an overview of the main issues related to the charging infrastructures in terms of electric vehicles charging times and their impact on the main grid. The paper continues with an analysis of ultra-fast charging infrastructures with particular focus on applications based on three-phase low voltage AC grid. Then, the proper design of modular multilevel converter architectures is presented taking into account its integration with energy storage modules of different technology, in order to reduce power requirements from the grid during the ultra-fast recharging phase. Different control strategies was proposed and simulated in terms of power flux control, during the charging and the discharging phase of the energy buffers, and voltage balancing among the different energy storage modules on the grid side.

This work deals with the design of a three-phase grid-tied photovoltaic (PV) cascade H-bridge inverter for distributed power conversion. The power balancing among the phases must be properly addressed. In fact, an intra-phase power imbalance—arising from uneven irradiance and temperature conditions—generates a per-phase power imbalance. This latter can be compensated by the injection of a proper zero-sequence voltage, while the intra-phase balance is ensured by means of a hybrid modulation method which is able to guarantee the handling of unequal DC (Direct Current) sources, stable circuit operation, and maximization of PV power production. The digital controller is developed and tested in Matlab/Simulink environment integrated with XSG (Xilinx System Generator), thus allowing an easy transfer on a field-programmable gate array (FPGA) platform and accurately describing the behavior of a real hardware implementation. Thus, numerical results have been considered to prove the effectiveness of the proposed approach.

This paper presents an overview of issues and technologies related to the proper design of charging infrastructures for road electric vehicles. The analysis is carried out taking into account that the recharging stations of electric vehicles might be integrated in smart grids, which interconnect the main grid with distributed power plants, different kinds of renewable energy sources, stationary electrical storage systems and electric loads. The study is introduced by an analysis of the main characteristics concerning different kinds of storage systems to be used for stationary and on-board applications. Then, different charging devices, modes and architectures are presented and described showing their characteristics and potentialities. DC and AC configurations of charging stations are compared in terms of the issues related to their impact on the main grid and the design of their main components. Specific attention was devoted also to the ultra-fast DC architecture, which appears a possible solution to positively affect a wide spread of plug-in hybrid and full electric road vehicles.

In this paper a power converter based on a modular multilevel topology integrated with energy storage devices for directly supplying of traction motors is discussed. The Modular Multilevel Converter (MMC) is one of the emerging technology for high- or medium- voltage transformerless power conversion. The possibility to directly control the traction motors by means of a dc/ac MMC topology, using also integrated energy storage systems (ESS) for recovering the kinetic energy, is exploited. Furthermore, a simplified mathematical model of the MMC with integrated ESS has been developed in order to evaluate the behavior of the traction unit during a typical load-cycle. The control law of the traction motor, integrated with energy storage flow management, has been introduced. The numerical results reported in the paper permit to confirm the feasibility of the proposed design and control strategy for light travel vehicle.

The present paper deals with the energy management of stationary Li-Ion Capacitor energy storage (LC-ESS) applied in DC electrified mass transit systems. These transportation systems can benefit substantially from wayside energy storage devices for the recuperation of the kinetic energy during brakings and the limitation of supply currents during motoring. The proposed control evaluates analytically the LC-ESS reference current on the basis of the actual vehicles kinetic energies, taking properly into account the several efficiencies of the energy conversion chain. Some numerical simulations with respect to a case study and to realistic railway vehicles operations are presented, pointing out the potentiality of the tailored control technique. The results obtained show that the control is very effective and that the final choice of the storage size is a trade-off between energy saving and equipment cost.

In the paper a methodology for optimal controlling storage devices at the aim of improving the performances of an electrified mass transit system is proposed. A rational procedure is arranged for counteracting the unavoidable stochastic variables involved in the description of the characteristics of this complex system. The core of the control procedure is based upon an optimization technique which should result particularly effective where plant parameters exhibit random behavior. The potentiality of the procedure is shown with reference to the reduction of the network power fluctuations. In this case the control law can be expressed in an analytical way in terms of power mean value over the interest time cycle. Kalman filter is employed to dynamically estimate the mean value of the total required power. A numerical application is reported so to demonstrate the feasibility and the goodness of the proposed control strategy.

Recently a great interest has been paid in the relevant literature to the use of energy storage systems for the performance improvement of electrified light transit systems. In this context, the main targets are the increase of the energetic efficiency and the reduction of pantograph voltage drops. Therefore, it can be very interesting the determination of the optimal characteristics of a storage device for satisfying these objectives, both in stationary and onboard case. In this paper, this problem is approached for a sample case study, by showing that the optimal design of a stationary storage device can be regarded as a classical isoperimetric problem, whose solution is very attractive in order to determine also the optimal allocation of the storage device. For more complex configurations of the transit system, the methodology presented can be extended by solving a constrained optimization problem, which in a quite general manner is capable of matching all the assigned technical requirements. The reported simulations confirm the validity of the proposed design approach.

Light transportation systems are not new proposals since their utilization started at dawn of electric energy spreading at industrial level. The light transportation systems class includes tramways, urban and subway metro-systems as well as trolley buses. These systems are intrinsically characterized by low investment costs and high quality service in terms of environmental impact and energy efficiency. The vehicle technology, which is continuously improving, allows lighter and economical solutions. These attractive characteristics has generated a renewed interest of the researchers and transportation companies in trying to obtain better performances of these systems, being foreseeable their remarkable spreading in the next future. However, even though the perspectives appear to be particularly bright, the increase of the electrical power demand associated to the higher number of vehicles circulating at the same time, require to investigate new solutions for optimizing the whole transportation system performance and particularly the energy consumption, also by exploiting the possibility tendered by the advent of technology innovation. The improvement of the energy efficiency is a crucial issue, both in planning stage and during operating conditions, which cannot be deferred. It has to be highlighted that also for already existing light transportation systems, the energy saving can be pursued by integrating new technological components or apparatuses as energy storage systems (Chymera et al,2006), which allow contemporaneously to obtain high energy saving and to reduce the of load peaks requested to the supply system. More specifically, the storage devices employment, which may be on board (Steiner et al,2007), or located at both the substations or along the track (Barrero et al,2008), are attractive means for obtaining contemporaneously energy saving, energy efficiency, pantograph voltage stabilization and peak regularization (Hase et al,2003). Storage devices may play also a fundamental role in enhancing the dynamic response of the overall light transit system, if they are used in combination with properly controlled power converters. All these previously mentioned benefits surely are convincing arguments for persuading to upgrade the existing light transportation systems, all the more that capital costs exhibit very reduced payback periods. The high energy densities make the supercapacitors attractive means for real time energy optimization, voltage regulation and high reduction of peak powers requested to feeding substations during the acceleration and braking phases. Many solutions have been suggested in the relevant literature, both oriented to the employment of distributed

The paper deals with the control of onboard storage devices with supercapacitors for urban railway trains. The practical utilization of supercapacitors requires suitable power converters for the regulation of power flows between the catenary and the electrical drives of the power-train. These converters operate in DC current and have to be bi-directional in order to allow the charge and discharge of supercapacitors. The mathematical model of the whole electrical drive has been developed and the main features of the control strategy have been presented. The control is capable of limiting the peak currents of the contact line and recovering partially the kinetic energy of the train during the braking periods. Simulations prove that the suggested control strategy is very effective for both purposes. Experimental tests made on a scaled prototype, representing the translating masses of a train, fully confirm the results of the simulations.

In the paper a new design methodology of storage devices for improving the performances of light transportation systems is proposed. A critical analysis is performed with respect to the stochastic variables involved in the description of the behavior of this complex system. Some considerations are performed in order to properly take into account various uncertainties at the aim of optimizing the size of storage devices and satisfying all the technical constraints. The core of the design procedure is a multivariable constrained optimization technique stochastically applied. In the numerical application, for sake of clarity, only the time displacement between two trains is considered as a stochastic variable described as a lognormal distribution function. The probabilistic properties of the output variables of the optimization procedure are then investigated.

Electrical storage devices can be very useful in electrified mass transit and in particular in trolleybus lines and tramways. In fact, storage devices are capable of supporting the line voltages of old lines, avoiding the opening of minimum voltage protective relays, especially when the new generation vehicles of greater power circulate. Among electrical storage devices, supercapacitors seem to be the most suitable for the application in traction systems, due to their high power densities and short charge/discharge times. The paper shows that the boosting of the line voltage can be more easily performed when supercapacitors are placed wayside. Their correct sizing requires the definition of suitable criteria, which take into account the topology of the line, the type of electrical supply and the movement of the vehicles. For this reason, the sizing criterion suggested in the paper refers to the optimization theory. The design procedure is capable of individuating the minimum set of the supercapacitors that guarantee at the same time the substation currents minimization and the line voltage stabilization. The sizing procedure has been applied to the sample case of a branch of the tramway in the city of Naples. Numerical results show the capabilities of the methodology in the selection of both the location and the capacitance of supercapacitors and that the set designed in this way is well tailored for the requirements of the line.

The paper deals with isotropic PM-brushless drives in configuration “single-inverter, dual-motor” operating with unbalanced load-torques. After a short review of some control techniques based on the classical control methodologies of single-motor PM drives, an innovative control algorithm is presented. It is suitable to minimize the resultant armature current needed to obtain an assigned resultant motor torque, whatever is the load unbalance. Simplified analytical expressions are given in order to quickly evaluate optimized reference currents with good approximation. From these reference values, a predictive feeding algorithm evaluates the reference voltage space-vector for the inverter supplying the two motors in parallel. Current and torque oscillation, torque/current ratio, dynamic response and stability are the mainly observed quantities. Effectiveness of proposed control technique is highlighted.

The paper deals with the use of onboard supercapacitors for metro trains. The practical utilization of supercapacitors requires suitable power converters for the regulation of power flows between the catenary and the electrical drives of the power-train. These converters operate in dc current and have to be bi-directional in order to allow the charge and discharge of supercapacitors. The mathematical model of the whole electrical drive has been developed and the main features of the control strategy have been presented. The control is capable of limiting the peak currents of the contact line and recovering partially the kinetic energy of the train during the braking periods. Simulations prove that the suggested control strategy is very effective for both purposes. Experimental tests made on a scaled prototype, representing the translating masses of a train, fully confirm the results of the simulations.

In this paper a control strategy for an induction generator based stand-alone power system is examined. The tested system consists of a prime motor, an induction generator, a Voltage Source Inverter STATCOM and a variable load. The paper focus on dynamics performance and stability margin of the system under alternative control strategies. The regulation strategy is based on the control of dc and ac voltage profiles in order to contain the ac voltage droop on load. The control acts on prime mover torque and delay angle between inverter and induction generator voltages. The results of numerical simulation evidence the feasibility of control strategy.

The paper deals with the analysis of an active power filter with two legs for three-phase systems. Although the converter topology is not symmetric, a suitable control of the power switches allows the achievement of balanced currents. The control technique for the compensation of the harmonics and reactive power of the load is derived directly from the mathematical model of the converter. The reference signals of the currents are used for the space vector modulation (SVM) both for balanced and unbalanced voltages of the dc-link capacitors. Numerical simulations validate the proposed control showing the capabilities of the active filter in reducing the total harmonic distortion and reactive powers in supplying of the source currents.