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The reduction of climate-changing emissions is vital, particularly in urban areas. To achieve this goal, the decarbonization of the transport sector is decisive. Trolleybus systems represent a solution towards sustainability as long as the integration of the electrical infrastructure with renewable sources as well as the introduction of full-electric fleets are actualized. To ensure a smart electrical transition the circuit modelling phase is crucial and must enable the most accurate simulations possible. The modularity of the catenary model and a versatile graphical user interface, which allows extensive topological change flexibility, distinguish the novel trolleybus network simulator presented in this study. The model completes the gaps left by earlier block-based simulation tools with its high precision and low processing effort. The suggested model’s enhancement in precision is evidenced by a graphical study of the voltage distribution examined in a section of Bologna’s trolleybus grid. Finally, albeit non-iterative and thus computationally even cheaper, the proposed model is applicable for the simulation of more complex realistic scenarios involving the non-linearity of the equivalent power grid. The article will show satisfactory results on the convergence of the simulator.

This manuscript proposes a novel approach for determining phase and neutral-current-ripple RMS in grid-connected four-leg inverters with the neutral inductor. The harmonic pollution is determined for any arbitrary pulse width modulation (PWM) technique and a generic value of the neutral inductor. Thanks to the proposed approach, it is possible to describe the neutral inductor in a parametric way with respect to phase inductors and obtain a wide range of results, ranging from a direct neutral connection (no neutral inductor) to a conventional three-phase inverter (no fourth wire) for any value of modulation index and common mode injection. The results permit one to compare different design choices in multiple scenarios effectively. The findings were validated by numerical simulations and experimental tests employing the most popular PWM techniques, such as space vector PWM (SVPWM) and discontinuous PWM (DPWM).

SMES technology based on MgB2 superconductor and cryogenic-free cooling can offer a viable solution to power-intensive storage in the short term. One of the main obstacles to the development of dry-cooled SMES systems is the heat load removal due to the AC loss of the superconductor during fast charging and discharging cycles at high power. Accurate knowledge of the amount and distribution of AC loss in the coil is of paramount importance for the sizing and the design of the cooling system and for assessing the possible operational limits of the technology. In this manuscript, the AC loss of a 500 kJ/200 kW multifilamentary MgB2 SMES during charge–discharge cycling at full power is numerically investigated. The methodology and assumptions of the calculation are briefly resumed, and numerical results are reported and discussed in detail. In particular, the time profile and the distribution of the dissipated power all over the coil are reported. An average dissipation of 85.5 mW/m is found all over the coil during one charge–discharge cycle at full power, with a peak of 150.1 mW/m in the turns lying at the ends of the coil.

This brief proposes a new Multiple Input Multiple Output (MIMO) control for off-board Electric Vehicle (EV) DC fast chargers. The proposed feedback matrix design avoids multiple tuning of controllers in multiple and interconnected loops while improving the performance of interleaved DC buck converters over classical PI/PID controls. The innovative features of the presented strategy are the reference current monotonic tracking from any initial state of charge with an arbitrarily fast settling time and the fast compensation of both load variations and imbalances among the legs. Numerical results validate the performance improvements of the proposed discrete-time MIMO algorithm for interleaved buck converters over classical PI/PID controls. Full-scale hardware-in-the-loop and scaled-down prototype experimental results prove the feasibility and effectiveness of the proposal. 

A new state observer-based current balancing method for Modular Multilevel Converters with Interleaved half-bridge Sub-Modules (ISM-MMC) is presented in this paper. The developed observer allows estimating currents through interleaved half-bridge legs in each submodule of ISM-MMC basing only on arm current and submodules capacitor voltage measurements. Then, the interleaved current balancing control uses the estimated currents to reduce the interleaved currents imbalance caused by upstream control actions. This technique minimizes the number of required current sensors in ISM-MMC, thereby reducing the converter's cost, weight, and volume. Capabilities of the proposed sensorless interleaved currents balancing control has been tested against standard parameter tolerances of the composing passive elements. In addition to that, a novel capacitor voltage balancing strategy for MMCs is developed. The new algorithm contains main advantages of the classical sorting-based capacitor voltage balancing methods while provides an opportunity to decouple two balancing tasks of ISM-MMC, namely capacitor voltage and interleaved legs current balancing. The feasibility of the proposed methods is verified by extensive simulation and experimental tests on a laboratory prototype by the corresponding system response under the output characteristics variation and interleaved current control perturbation.

A new Modular Multilevel Converter with Interleaved half-bridge Sub-Modules (ISM-MMC) is proposed in this paper. The ISM-MMC exhibits a higher modularity and scalability in terms of current ratings with respect to a conventional MMC, while preserves the typical voltage level adaptiveness. The ISM-MMC brings the known advantages of classical MMC to low-voltage, high-current applications making it a novel candidate for the sector of ultra-fast chargers for all types of electrical vehicles (EV). This advanced topology makes it possible to easily reach charging power of the EV charging system up to 4.5 MW and beyond with low-voltage supply. To operate the new converter, a hybrid modulation scheme that helps to exploit advantages of the interleaving scheme, is implemented, and explained in this paper. It has been verified that the typical MMC control methods are still applicable for ISM-MMC. A comparative study between classical MMC and ISM-MMC configurations in terms of output characteristics and efficiency is also given. Furthermore, it has been demonstrated that the number of ac voltage levels is synthetically multiplied by the number of interleaved half-bridge legs in submodules. Simulations, Hardware-in-the-Loop and Experimental tests are carried out to demonstrate the feasibility of the proposed topology and implemented modulation scheme.

This paper describes the preliminary analysis, design and implementation phases of a DC/DC boost converter dedicated to the Futura catamaran propulsion chain developed by the UniBoAT team at the University of Bologna. The main goal of the project was the reduction of the converter’s weight by eliminating the use of heat sinks and by reducing the component size, especially inductors and capacitors. The obtained converter is directly integrated into the structure containing the fuel-cell stack. The realized converter was based on an interleaved architecture with six phases controlled through the average current mode control. The design was validated through simulations carried out using the LT-Spice software, whereas experimental validations were performed by means of both bench tests and on-field tests. Detailed thermal and efficiency analyses were provided with the bench tests under the two synchronous and non-synchronous operating modes and with the adoption of the phase-shedding technique. Prototype implementation and performance in real operating conditions are discussed in relation to on-field tests. The designed converter can be used in other applications requiring a voltage-controlled boost converter. 

In the context of smart cities, direct current overhead contact lines, usually adopted to power urban transportation systems such as trolleybuses, tramways, metros, and railways, can serve as a backbone to connect different modern emerging technologies. Among these, in-motion charging (IMC) trolleybuses with on-board batteries are expected to be very impactful on the DC network’s power flow and may require specific voltage and current control. These factors motivate the development of a simulation tool able to emulate these devices’ absorption and their effect on the supply infrastructure. The main innovative value of the work is to improve a simulation model of a trolleybus grid through a data-driven approach by using measurements of voltage and current output from a traction substation. The measurements are essential for understanding the behavior of vehicle weight variation throughout the day. Thanks to this information, a characterization of the current draw by conventional trolleybuses and IMC trolleybuses is then provided for each trolleybus route in a specific power section of the Bologna trolleybus system. By integrating the variation in vehicle weight within the model, a simulation of a possible daily operation of a trolleybus feeding section has been performed, obtaining a 7% error between the daily energy calculated from the simulation and that obtained through measurements. This analysis demonstrates the feasibility of the adopted simulation tool, which can also be used to evaluate additional hypothetical trolleybus operation scenarios. One of these possible scenarios considers IMC vehicles, and it is also evaluated in this paper. 

This article proposes a dual-active-bridge control to support the fast synthetic inertial action in DC microgrids. First of all, the selection of the isolated DC/DC converter to link an energy storage system with the DC bus in a microgrid is analyzed and the advantages of the dual-active-bridge converter controlled by a single-phase shift modulation justify its selection. An active front-end can be then adapted to connect the DC bus with an AC grid. Secondly, this paper presents the design of a discrete PI controller for supporting fast synthetic inertial action. In particular, a discrete dual-active-bridge model based on the transferred power between both converter bridges, which overcomes the approximations of the output current linearization model, is proposed. Moreover, the article introduces a novel equation set to directly and dynamically tune discrete PI parameters to fulfill the design frequency specifications based on the inversion formulae method. In this way, during the voltage/power transients on the DC bus, the controller actively responds and recovers those transients within a grid fundamental cycle. Since the developed set of control equations is very simple, it can be easily implemented by a discrete control algorithm, avoiding the use of offline trial and error procedures which may lead to system instability under large load variations. Finally, the proposed control system is evaluated and validated in PLECS simulations and hardware-in-the-loop tests.

Trolleybus systems are resurfacing as a steppingstone to carbon-neutral urban transport. With an eye on smart city evolution, the study and simulation of a proper monitoring system for trolleybus infrastructures will be essential. This paper merges the authors’ engineering knowledge and sources available in the literature on designing and modeling catenary-based electric traction networks and performs a critical review of them to lay the foundations for proposing possible optimal alternatives. A novel multi-vehicle motion-based model of the DC catenary system is then devised and simulated in Matlab-Simulink, which could prove useful in predicting possible technical obstacles arising from the next-future introduction of smart electric traction grids, inevitably featuring greater morphological intricacy. The modularity property characterizing the created model allows an accurate, detailed, and flexible simulation of sophisticated catenary systems. By means of graphical and numerical results illustrating the behavior of the main electrical line parameters, the presented approach demonstrates today’s obsolescence of conventional design methods used so far. The trolleybus network of the city of Bologna was chosen as a case study.

Inverter’s performance and operating mode may be negatively affected by inverter input (dc-link) current and voltage ripple. It is a common experience that even theoretically balanced loads with perfectly balanced supply voltages, such as multiphase ac motors supplied by PWM inverters, in practice show a certain degree of current unbalance, in the range of a few percent, which introduces a low-frequency instantaneous power oscillation. This reflects in current and voltage low-frequency ripple on the dc-link inverter side (i.e., at the double-fundamental frequency). A possible method to analyze this matter is through the symmetric sequence components. In particular, based on the first negative current sequence component and by considering the equivalent dc-link impedance calculated at the dominant double-fundamental frequency, the amplitude of the corresponding dc-link voltage ripple component is calculated in this paper for a general multiphase load. Finally, the design of the dc-link capacitor in multiphase inverters is proposed considering requirements referred to the double-fundamental dc voltage ripple. The feasibility of proposed developments has been verified for three-, five- and seven-phase inverters by both numerical simulations and comprehensive experimental tests, always showing a good matching.

Three-phase, four-wire, split-capacitor inverters, thanks to their capability to deal with unbalanced systems, are currently employed in photovoltaic installations, electric vehicles battery chargers, active power filters, and many other grid-tied applications. The minimization of ac output current ripple and switching losses positively impacts the inverter's efficiency, volume, weight, and cost optimization. For this reason, a novel variable switching frequency driving strategy independently tunable on each phase is proposed in this paper. Taking advantage of phase current ripple prediction, a proper variable switching frequency strategy is applied for obtaining a flat current ripple profile. Having tuned the driving strategy parameters, it is possible to optimize and compare individual metrics such as the maximum peak-to-peak value of the current ripple, current ripple rms, average switching frequency, and switching losses. By applying the proposed modulation method, a significant inverter performance enhancement has been obtained. Converter efficiency is improved without introducing detrimental effects on the current harmonic quality. Analytical derivations are expressed as a modulating index function and the power factor for balanced and unbalanced systems. All the theoretical developments are verified throughout numerical simulations and experimental tests.

The growing penetration of distributed renewable energy sources (RES) together with the increasing number of new electric vehicle (EV) model registrations are playing a significant role in zero-carbon energy communities' development. However, the ever-larger share of intermittent renewable power plants, combined with the high and non-modulable aggregate-EV charging demand requires an evolution towards new planning and management paradigms of energy districts. Thus, in this context, this paper proposes novel smart charging (SC) techniques that aim to integrate as much as possible RES generation and EV charging demand at the local level, synergically acting on power flows and avoiding detrimental effects on the electrical power system. To make this possible, a centralized charging management system (CMS) capable of individually modulating each charging power of plugged EVs is presented in this paper. The CMS aims to maximize the charging self-consumption from local RES, flattening the peak power required to the external grid. Moreover, the CMS guarantees an overall good state of charge (SOC) at departure time for all the vehicles without requiring additional energy from the grid even under low RES power availability conditions. Two methods that differ as a function of the EV power flow direction are proposed. The first SC only involves unidirectional power flow, while the second one also considers bi-directional power flow among vehicles, operating in vehicle-to-vehicle (V2V) mode. Finally, simulations are presented considering an actual case study validate the SC effects on a reference scenario consisting of an industrial area having a PV plant, non-modulable electrical loads, and EV charging stations. Results are collected and performance improvements by operating the different SC methods are compared and described in detail in this paper.

Electrical power grids are rapidly evolving into smart grids, with smart homes also making an important contribution to this. In fact, the well-known and emerging technologies of renewables, energy storage systems and electric mobility are each time more distributed throughout the power grid and included in smart homes. In such circumstances, since these technologies are natively operating in DC, it is predictable a revolution in the electrical grid craving a convergence to DC grids. Nevertheless, traditional loads natively operating in AC will continue to be used, highlighting the importance of hybrid AC/DC grids. Considering this new paradigm, this paper has as main innovation points the proposed control algorithms regarding the role of front-end AC DC converters in hybrid AC/DC smart homes, demonstrating their importance for providing unipolar or bipolar DC grids for interfacing native DC technologies, such as renewables and electric mobility, including concerns regarding the power quality from the smart grid point of view. Furthermore, the paper presents a clear description of the proposed control algorithms, aligned with distinct possibilities of complementary operation of front-end AC DC converters in the perspective of smart homes framed within smart grids, e.g., enabling to control smart homes in a coordinated way. The analysis and experimental results confirmed the suitability of the proposed innovative operation modes for hybrid AC/DC smart homes, based on two different AC DC converters in the experimental validation. 

The paper proposes a full hybrid driveline based on an electric Continuously Variable Trans-mission (e-CVT), inspired by the car industry’s most successful solution. The paper describes the operating principle, the system architecture and the control scheme of the proposed driveline. The analysis of four possible operating modes shows that the e-CVT driveline leads to performance similar to that of conventional tractors, as well as unusual features such as power boost, full-electric mode, optimized auxiliary drive and electric power delivery capability. The compact layout proposed for the e-CVT also makes it possible to simplify the overall layout of the tractor, in particular on the installation of both the thermal engine and the cooling system.

The verification of the limits of the population’s exposure to the magnetic field generated by double-circuit power lines from field measurements carried out on site is not trivial. It requires knowledge of the power line current instant values during the measurement period, the determination of the relationship between current and field at the measurement points (made more complex by the double-circuit overhead line configuration) and the use of that relationship to extrapolate the field values. Nevertheless, the verification of exposure limits for double-circuit power lines from on-site measurements is often conducted with rough, or not particularly stringent, procedures. A practical and straightforward procedure of general validity for non-optimized double-circuit lines is proposed here. No specific measurement position or conductors disposition knowledge is required as well as no complex three-dimensional finite element method code is necessary. The procedure, potentially also applicable to high- and extra-high-voltage lines, is validated on a medium-voltage (15 kV) double-circuit overhead power line study case. Exposure limits assessment suggests that if the line is operated at its rated capacity (230/285 A), the 3 μT quality target is missed. Results are provided with a 95% confidence interval ranging from ±100 nT to ±140 nT in all the cases.

The current switching ripple in a three-phase four-wire split-capacitor converter is analyzed in this paper for all the four ac output wires in relation to both balanced and unbalanced working conditions. Specifically, analytical formulations of the peak-to-peak and root mean square (RMS) current ripples are originally evaluated as a function of the modulation index, separately for the three phases and the neutral wire. Initially, the single-carrier sinusoidal pulse width modulation (PWM) technique is outlined, as it generally concerns a straightforward and effective modulation. With the aim of mitigating the current ripple in the neutral wire, the interleaved multiple-carrier PWM strategy is adopted, also avoiding any repercussion on the phase one. Numerical simulations and experimental tests were carried out to verify all the analytical developments.

This paper presents a thorough prediction of DC-link voltage switching ripples in the three-phase four-leg inverters operating in balanced and unbalanced working conditions. The unbalanced modes examined here employ the highest degree of AC current imbalance while still preserving three-phase operation. This behavior can be found in many grid-connected or standalone grid-forming three-phase converters that supply “heavy” single-phase loads, comprising a recent trend in smart-grid, smart electric vehicle (EV)-charging applications. In this sense, for instance, the smart EV chargers might be employed in conditions when different power is drawn/injected from/to the grid, providing power conditioning services to the latter. The analysis of three-phase four-leg inverters is then extended to single-phase operations typical of home-charging or vehicle-to-home (V2H) applications. Their performances in terms of DC-link voltage switching ripple are demonstrated. Two of the most common carrier-based PWM modulation techniques are employed to drive the three-phase inverter—namely, sinusoidal PWM and centered PWM (carrier-based analogy of the space vector modulation). The derived mathematical expressions of peak-to-peak and RMS values of DC-link voltage switching ripple for balanced and unbalanced conditions are handy for designing the associated DC-link capacitor and estimating the overall efficiency of the converter. Extensive numerical simulations and experimental tests have been performed to validate the presented analytical developments.

This paper presents a comprehensive study of peak-to-peak and root-mean-square (RMS) values of AC current ripples with balanced and unbalanced fundamental currents in a generic case of three-phase four-leg converters with uncoupled AC interface inductors present in all three phases and in neutral. The AC current ripple characteristics were determined for both phase and neutral currents, considering the sinusoidal pulse-width modulation (SPWM) method. The derived expressions are simple, effective, and ready for accurate AC current ripple calculations in three- or four-leg converters. This is particularly handy in the converter design process, since there is no need for heavy numerical simulations to determine an optimal set of design parameters, such as switching frequency and line inductances, based on the grid code or load restrictions in terms of AC current ripple. Particular attention has been paid to the performance comparison between the conventional three-phase three-leg converter and its four-leg counterpart, with distinct line inductance values in the neutral wire. In addition to that, a design example was performed to demonstrate the power of the derived equations. Numerical simulations and extensive experimental tests were thoroughly verified the analytical developments.

Three-phase four-leg voltage-source converters have been considered for some recent projects in smart grids and in the automotive industry, projects such as on-board electric vehicles (EVs) chargers, thanks to their built-in ability to handle unbalanced AC currents through the 4th wire (neutral). Although conventional carrier-based modulations (CBMs) and space vector modulations (SVMs) have been commonly applied and extensively studied for three-phase four-leg voltage-source converters, very little has been reported concerning their pollution impact on AC grid in terms of switching ripple currents. This paper introduces a thorough analytical derivation of peak-to-peak and RMS values of the AC current ripple under balanced and unbalanced working conditions, in the case of three-phase four-leg converters with uncoupled AC-link inductors. The proposed mathematical approach covers both phase and neutral currents. All analytical findings have been applied to two industry recognized CBM methods, namely sinusoidal pulse-width modulation (PWM) and centered PWM (equivalent to SVM). The derived equations are effective, simple, and ready-to-use for accurate AC current ripple calculations. At the same time, the proposed equations and diagrams can be successfully adopted to design the conversion system basing on the grid codes in terms of current ripple (or total harmonic distortion (THD)/total demand distortion (TDD)) restrictions, enabling the sizing of AC-link inductors and the determination of the proper switching frequency for the given operating conditions. The analytical developments have been thoroughly verified by numerical simulations in MATLAB/Simulink and by extensive experimental tests.

Three-phase, four-wire split capacitor inverters are currently employed in many applications, such as photovoltaic systems, battery chargers for electric vehicles, active power filters, and, in general, in all grid-tied applications that deal with possible grid voltage and/or current unbalances. This paper provides a comprehensive evaluation of the capacitor-switching voltage ripple and dc-link switching voltage ripple for the three-phase, four-wire, split capacitor inverters. Specifically, analytical formulations of the peak-to-peak and rms values of the voltage ripples are originally pointed out in this paper and determined in the case of balanced three-phase and unbalanced (two-phase and single-phase) output (ac) currents. The obtained results can help in designing the considered inverter and sizing of the dc-link capacitors. Reference is made to the sinusoidal PWM modulation and sinusoidal three-phase output currents with an almost unity power factor, representing a grid-connected application. Extensive numerical simulations have been carried out to thoroughly verify all the analytical developments presented in this paper. Furthermore, some experimental tests, having balanced output currents on the ac side, have been accomplished, validating numerical simulations and analytical developments.

In the context of electric vehicle (EV) development and positive energy districts with the growing penetration of non-programmable sources, this paper provides a method to predict and manage the aggregate power flows of charging stations to optimize the self-consumption and load profiles. The prediction method analyzes each charging event belonging to the EV population, and it considers the main factors that influence a charging process, namely the EV’s characteristics, charging ratings, and driver behavior. EV’s characteristics and charging ratings are obtained from the EV model’s and charging stations’ specifications, respectively. The statistical analysis of driver behavior is performed to calculate the daily consumptions and the charging energy request. Then, a model to estimate the parking time of each vehicle is extrapolated from the real collected data of the arrival and departure times in parking lots. A case study was carried out to evaluate the proposed method. This consisted of an industrial area with renewable sources and electrical loads. The obtained results show how EV charging can negatively impact system power flows, causing load peaks and high energy demand. Therefore, a charging management system (CMS) able to operate in the smart charging mode was introduced. Finally, it was demonstrated that the proposed method provides better EV integration and improved performance.

A complete analysis of the ac output current ripple in four-leg voltage source inverters considering multiple modulation schemes is provided. In detail, current ripple envelopes and peak-to-peak profiles have been determined in the whole fundamental period and a comprehensive method providing the current ripple rms has been achieved, all of them as a function of the modulation index. These characteristics have been determined for both phase and neutral currents, considering the most popular common-mode injection schemes. Particular attention has been paid to the performance of discontinuous pulse width modulation (DPWM) methods, including DPWMMAX and DPWMMIN, and their four most popular combinations DPWM0, DPWM1, DPWM2, and DPWM3. Furthermore, a comparison with a few continuous techniques (sinusoidal, centered pulse width modulations, and third harmonic injection) has been provided as well. Moreover, the average switching frequency and switching losses are analyzed, determining which PWM technique ensures minimum output current ripple within the linear modulation range at different assumptions. Numerical simulations and laboratory tests have been conducted to extensively verify all the analytical claims for all the considered PWM injections. 

Selected as the cover article for MDPI Energies Issue 17, Volume 13, 2020 - link 

This paper presents the modeling and the implementation of the digital control of a multileg interleaved DC-DC buck converter for electrical vehicle (EV) charging. Firstly, we derive a discrete averaged model of an n-leg interleaved buck converter (IBC). Secondly, we present a direct tuning procedure for one primary discrete PIDF (PID + filter) and multiple secondary PI controller. The objective of the control system is to regulate the current flow in each leg of the converter. This task is accomplished by introducing a novel control paradigm that simultaneously addresses two aims: on the one hand, the control scheme must guarantee an acceptable level of robustness under load variations; while on the other, an even distribution of power on each leg must be ensured at any operational condition. The proposed strategy hinges on a technique that combines simplicity and precision in the fulfillment of design frequency specifications. We use simulations and a digital signal processor (DSP) based experimental implementation of the design technique to validate the proposed methodology.

An off-board dc fast battery charger for electric vehicles (EVs) with an original control strategy aimed to provide ripple-free output current in the typical EV batteries voltage range is presented in this article. The proposed configuration is based on modular three-phase interleaved converters and supplied by the low-voltage ac grid. The ac/dc interleaved three-phase active rectifier is composed of three standard two-level three-phase converter modules with a possibility to slightly adjust the dc-link voltage level in order to null the output current ripple. A modular interleaved dc/dc converter, formed by the same three-phase converter modules connected in parallel, is used as an interface between the dc link and the battery. The use of low-cost, standard and industry-recognized three-phase power modules for high-power fast EV charging stations enables the reduction of capital and maintenance costs of the charging facilities. The effect of coupling on the individual input/output inductors and total input/output current ripples has been investigated as well, considering both possible coupling implementations, i.e., inverse and direct coupling. Numerical simulations are reported to confirm the feasibility and the effectiveness of the whole EV fast charging configuration, including the proposed control strategy aimed to null the ripple of the output current. Experimental results are provided by a reduced scale prototype of the output stage to verify the ripple-free output current operation capability. 

This paper provides a comprehensive analysis of the capacitors voltage switching ripple for three-phase three-level neutral point clamped (NPC) inverter topologies. The voltage ripple amplitudes of the two dc-link capacitors are theoretically estimated as a function of both amplitude and phase angle of output current and the inverter modulation index. In particular, peak-to-peak distribution and maximum amplitudes of the capacitor voltage switching ripple over the fundamental period are obtained. A comparison is made considering different carrier-based pulse-width modulations in the case of almost all sinusoidal load currents, representing either grid connection or passive load with a negligible current ripple. Based on the voltage switching ripple requirements of capacitors, a simple and effective original equation for a preliminary sizing of the capacitors has been proposed. Numerical simulations and experimental tests have been carried out in order to verify the analytical developments. 

Dual-active-bridge (DAB) converters have gained popularity primarily owing to their appealing features for electric vehicle (EV) charging and smart-grid applications. One among them is soft-switching commutation that comes inherently with the device control techniques. However, DAB converters lose the zero-voltage-switching (ZVS) commutation on either bridge for large output voltage variation, especially under light-load conditions. In this context, this paper provides insights into the behavior of the auxiliary inductor-based DAB converter in terms of ZVS operations. The integration of auxiliary inductors makes it paramount to study the RMS currents through the power switches to gain awareness about the effects on the converter performance. A graphical analysis proved useful in this direction. Finally, simulations are carried out over various operating conditions to validate the analytical developments.

This paper provides design considerations for a wireless power transfer (WPT) charging system for drones in civil applications employing a modular paradigm referred to the Qi Specifications. Three different designs are developed and compared, under different possible mounting positions. The designs are analyzed by means of electromagnetic and circuit simulations to evaluate the main characteristics in terms of losses, weight, and other specific performance indicators discussed in the text. Particular attention is devoted to the evaluation of the possible interaction with the drone frame materials.

The integration of renewable sources to catenary-powered electric traction systems is a paramount step to satisfy sustainability and smart city objectives, albeit necessitating accurate simulations of the infrastructure. This paper presents an innovative trolleybus network simulator, characterised by the modularity of the catenary model and built on an intuitive graphical user interface that offers significant topological change flexibility. The model is distinguished by high precision and moderate processing effort, bridging the gaps of existing block-based simulation tools. A graphical analysis of the voltage distribution evaluated in a section of Bologna's trolleybus network shows the advances in precision of the proposed model.

This paper presents a novel approach based on random variable algebra to study the neutral current ripple in three-phase four-wire split-capacitor inverters. The proposed method provides a more intuitive way of understanding and quantifying current ripple cancellations occurring on the neutral wire. Furthermore, thanks to its more straightforward approach, the extension over the whole modulation index range of neutral current ripple RMS in the case of interleaved PWM is presented. Finally, a comprehensive analysis of the neutral current ripple RMS in the case of unevenly displaced PWM carriers is also discussed. All the developments are validated by employing numerical results tested over various operating conditions.

Three-phase four-wire DC/AC converters are crucial for applications like electric vehicle (EV) chargers and solid-state transformers (SST). For ensuring galvanic isolation, dual-active-bridge (DAB) converters are often selected to be associated with the front-end AC/DC stage. In this context, this paper explores the possibility of delivering and driving the additional neutral wire directly from the DAB converter without introducing any additional and dedicated fourth-leg, as well as an independent-controlled neutral module. Further, a modified single phase-shift strategy capable of providing common-mode injection is presented and discussed under different operating conditions and modulation schemes. Finally, numerical results are presented to validate the correctness of all developments.

The reduction of climate-changing emissions is vital, especially in urban areas. To reach this goal, the decarbonization of the public transport sector is crucial. Dynamic conductive power transfer through catenary systems is potentially a carbon-neutral solution. This paper focuses on trolleybus grids, already established in several metropolises, which are re-emerging as a smart city-oriented electrified transport system. A better integration of trolleybus grids with renewable sources, energy storage, and the existing electric network of the urban area is necessary to increase the efficiency of the system and optimize energy flows, favouring the transition towards smarter and greener cities. Moreover, trolleybus systems may act as a DC backbone for charging stations powering private electric vehicles, thus contributing to a closer interconnection between public and private mobility. A modular model of the electric traction grid in Matlab-Simulink is explored to simulate the actual complexity of novel trolleybus network topologies. By means of graphical and numerical results illustrating the behaviour of the main electrical line parameters, the model flexibility towards the inclusion of smart city-oriented technologies, such as stationary battery energy storage systems and electric vehicle chargers, is verified in this work. The trolleybus electrical infrastructure of the city of Bologna was chosen as a case study.

The trolleybus system is already part of the urban environment of several metropolitan cities. In view of the emergence of smart cities, it appears reasonable to look at how the trolleybus grid can become a more active part of the urban’s electricity network. However, the infrastructure design approaches adopted so far make the current trolleybus networks overdesigned to handle the improbable worst-traffic case scenarios. Consequently, the trolleybus electrical supply system is both underutilized and oversized. Through modeling, simulations, and a cluster of measured trolleybus and corresponding network data, various new functionalities may be explored, among which electric vehicle chargers and energization of auxiliary equipment, towards a more sustainable and smart trolleybus grid. This paper merges the authors’ engineering knowledge and sources available in the literature on designing and modelling trolleybus networks and performs a critical review of them to lay the foundations for proposing possible optimal alternatives. Being the city of Bologna organized with multiple electrically powered zones with either basic or complex topologies, the respective trolleybus system has been chosen as a case study.

This paper presents an energy management strategy for a battery-based stationary energy storage system (BESS) capable of supporting the operation of trolleybus power networks while adhering to the DC network's current and voltage requirements, as well as considering the limitation of the C-Rate, to avoid stress on the battery itself. This work also proposes the dimensioning of this BESS and the comparison of different battery capacities based on a Matlab/Simulink-based model able to simulate a one-day operation of the transit trolleybuses. This manuscript illustrates the effect of the proposed management and the chosen battery through comparisons of the voltage and current profiles along the line. The simulation results show an increase in the voltage level and a decrease in the line current along the catenary with the use of the BESS, indicating that the battery can be a solution to improve the operation of trolleybus systems, even though it is not usually used for this type of network.

In the context of urban transportation electrification, trolleybus systems can be modernized by using vehicles based on the so-called In-Motion-Charging (IMC) technology. The current required by IMC vehicles is higher than traditional trolleybuses because, in addition to traction, they must also absorb the current needed to recharge the batteries on board. With the aim of reducing voltage drops in trolleybus networks even in case of high-power demands, the impacts of the inclusion of a mid-line stationary energy storage system to maintain a high voltage level and to reduce the network energy losses are analyzed in this paper. This work consists of the development of Monte Carlo-based simulations to treat as random variables the initial positions of the trolleybuses in the DC catenary system and their respective current draws. A current absorption profile of the IMC trolleybus has been used in conjunction with a model able to simulate the movement of multiple vehicles in a DC network section. According to the achieved results, it is possible to observe an improvement in the network voltage profile and an indication of energy savings.

In the context of electric vehicles integration in energy districts with the growing penetration of renewable energy sources (RES), this paper provides a method to manage the aggregate charging power flows optimizing self-consumption for flattening the load curve, and optimally exploit the intermittent RES. Under low internal RES availability, the proposed smart charging algorithm aims to guarantee an overall good state of charge of vehicles at the departure instant. This is achieved through a charging management system that differently allocates the power among the electric vehicles based on their battery charging level without involving absorption from the external grid. A reference scenario based on a real case study is performed to evaluate the proposal. This consists of an industrial area with photovoltaic plants and electrical loads. Finally, improvement in smart charging performance, especially under medium-low irradiance availability, is shown.

This paper reports a novel modular multilevel converter with interleaved sub-modules (ISM-MMC). The ISMMMC exhibit a higher scalability in current rating then conventional MMC structures with parallel devices. It can employ low-cost, low-current power switches rather than their bulky and expensive counterparts normally designed in classical MMCs. Another remarkable feature is that the number of the output voltage levels is synthetically multiplied by the number of interleaved SMs. The ISM-MMC is capable of bringing the known advantages of MMC to low voltage – high power applications making it a good candidate for the sector of ultrafast chargers for electrical vehicles where typical power rating in excess of 1 MW is required for the low voltage supply. A proper modulation scheme is implemented and explained in this paper. A comparison with a classical MMC topology is also provided in terms of number of voltage levels, output voltage harmonic content, and number of components by fixing the number of SMs. Simulation results are given to demonstrate the feasibility of the proposed topology and the implemented modulation scheme. Despite this paper is dealing with a singlephase configuration, the extension to a three-phase scheme can be obtained in a straightforward manner.

In this paper, a ripple-free output current interleaved DC/DC converter has been analyzed for Electric vehicle charging stations. Firstly, a ripple-free control strategy able to ensure a theoretically flat output current profile and input voltage ripple minimization at any working conditions is discussed. This strategy drives the active front-end to regulate the DC-link voltage and, at the same time, the interleaved back-end converter to operate in zero ripple working points. Secondarily, a generalized designing algorithm able to consider constraints like AC grid voltage and battery voltage is proposed. Finally, simulations support ripple mitigation capabilities in steady-state and transient conditions for a 12-leg scheme.

This chapter introduces a ripple correlation control (RCC) algorithm for tracking the maximum power point (MPP) for a flying capacitor three-level three-phase photovoltaic (PV) system. Although RCC maximum power point tracking (MPPT) method has been widely used on single-phase plants, a three-phase implementation based on sinusoidal carrier PWM has not been presented yet. The inherent oscillations of the PV current and voltage are employed as a perturbation for the RCC MPPT system. The proposed algorithm adopts the PV current and voltage 3rd harmonic component for estimating the power (or current) derivative, dPpv/dVpv (or dIpv/dVpv). Firstly, referring to the carrier-based sinusoidal pulse width modulation (SPWM), the flying capacitor inverter modulation scheme is presented. Secondly, the proposed RCC MPPT method is introduced. Finally, multiple MATLAB-/Simulink-based simulations of the RCC MPPT algorithm acting on a grid-connected PV system are provided. Both steady-state and dynamic (irradiance increase and decrease) conditions present good performances.

This paper deals with a split capacitor three phase four-wire inverter, able to deal with unbalanced ac currents and/or voltages. The considered topology can be used in many applications such as photovoltaic systems, chargers for electrical vehicles, active filters, and in general all the grid-connected applications. One parameter that must be considered in the converter design is the ac (output) current ripple, which should be determined and minimized in order to improve the system efficiency. In this paper, the evaluation of the ac current ripple for the three-phase split-capacitor inverter is developed with reference to both balanced and unbalanced output conditions. In particular, the peak-to-peak and the rms current ripple are analytically determined as a function of the modulation index, for each phase. Initially, reference is made to single carrier sinusoidal PWM, being, in general, a simple and effective solution. The interleaved multiple-carrier PWM strategy is then considered in order to mitigate the current ripple in the neutral wire, while not affecting its phase counterpart. Numerical simulations have been carried out in order to verify the analytical developments.

Awarded as the Best Paper in the 6th edition of IEEE ENERGYCON - link

Lithium-Ion batteries are playing an essential role in electric vehicles and renewable sources development. In order to reduce the charging time, high power chargers are necessary. However, lithium-ion chemistry limits the maximum current and charging speed. The diffusion rate of lithium ions into the electrodes determines the rate of charging. The slow lithium diffusion, especially experienced after high current rates, inevitably results in concentration polarization. The increase of the concentration polarization, in addition to the growth of the charging time, may lead to a faster battery deterioration. To deal with this obstacle, the Pulse Charging (PC) protocol has been proposed. There is no common opinion about the benefits given by the PC to the battery charging process in comparison with the conventional constant-current, constant-voltage (CCCV) protocol. Nevertheless, the purpose of this work is to provide an overview of possible methods that can be used to generate current pulses, without focusing on its advantages. Different techniques with the corresponding control algorithms have been implemented and analyzed through simulations in MATLAB/Simulink environment.

Three-phase four-leg voltage-source inverters (VSIs) are currently considered for several renewable-energy and automotive applications, due to their inherent ability to deal with unbalanced ac currents through the 4th wire (neutral). Although conventional carrier-based and space vector modulations have been commonly applied and extensively studied for various power electronic configurations, very little has been reported concerning the impact of these modulation strategies on ac current switching ripple for three-phase four-leg VSIs. This paper presents a comprehensive analytical derivation of peak-to-peak profile and rms value of the ac current ripple for this converter topology in case of sinusoidal pulse-width modulation, also including the neutral wire. The analytical developments for all examined subcases have been verified by numerical simulations, carried out in the MATLAB/Simulink environment. 10.1109/ISIE45063.2020.9152511

This paper provides an extensive theoretical analysis of the capacitors voltage ripple for three-phase three-level neutral point clamped inverter topologies. The capacitor voltage ripple amplitudes are theoretically estimated as a function of both amplitude and phase angle of output current, and the modulation index. Each capacitor voltage basically consists of switching frequency and the third harmonic components, thereby both components are considered in the analysis. In particular, peak-to-peak distribution and maximum amplitudes of the capacitor voltage switching ripple over the fundamental period are obtained. As a first simplified approach, reference is made to sinusoidal carrier-based PWM with sinusoidal load currents, representing either grid connection or passive load with a negligible current ripple. Based on the ripple requirements of capacitors voltage, a simple and effective original equation for designing capacitors has been proposed. Numerical simulations have been carried out by Mat-lab/Simulink in order to verify the analytical developments. 

This paper presents an off-board DC fast battery charger for electric vehicles (EVs) based on modular three-phase interleaved converters supplied by the low-voltage AC grid. The charger rectifies the grid voltage to a common DC-bus voltage having a slightly adjustable level by means of AC/DC interleaved three-phase active rectifier, composed of three standard commercial two-level three-phase converter modules. Three identical three-phase modules connected in parallel form a modular interleaved DC/DC converter to supply the battery. This structure offers a use of low-cost, unified and industry-recognized three-phase power modules for high- power fast EV charging stations that will reduce capital and maintenance costs of the charging facilities, enhancing further expansion of the eco-friendly transport. An original control strategy has been proposed to provide ripple-free output current in the typical EV batteries voltage range. The effect of coupling on the individual input/output inductors and total input/output current ripples has been investigated, considering both possible coupling implementations, i.e. inverse and direct coupling. Simulation results, carried out in MATLAB/Simulink environment, are reported in to confirm the feasibility and the effectiveness of the proposed EV fast charging configuration. 

A new state observer-based current balancing method for Modular Multilevel Converters with Interleaved half-bridge Sub-Modules (ISM-MMC) is presented in this paper. The developed observer allows estimating currents through interleaved half-bridge legs in each submodule of ISM-MMC basing only on arm current and submodule’s capacitor voltage measurements. Then, the interleaved current balancing control uses the estimated currents to reduce the interleaved currents imbalance caused by upstream control actions. This technique minimizes the number of required current sensors in ISM-MMC, thereby reducing the converter's cost, weight, and volume. Capabilities of the proposed interleaved currents sensorless balancing control has been tested against standard parameter tolerances of the composing passive elements. The feasibility of the proposed method is verified by extensive simulation and experimental tests.

This paper presents a closed-loop current balancing control for Modular Multilevel Converters with Interleaved half-bridge Sub-Modules (ISM-MMC). The new control loop solves the well-known problem of proper current balancing among interleaved half-bridge legs in each ISM-MMC submodule while preserving a simple and reliable structure. In addition to that, a novel capacitor voltage balancing strategy for MMCs is developed. The new algorithm contains main advantages of the classical capacitor voltage balancing methods while provides an opportunity to decouple two balancing tasks of ISM-MMC, namely capacitor voltage and interleaved legs current balancing. The proposed control methods feature good dynamic performance and are compliant with a digital processor's operational constraints. The effectiveness of the new balancing methods was verified during extensive numerical simulations and experimental tests on a laboratory prototype by the corresponding system response under the input/output characteristics variation and interleaved current control perturbation.

A new Modular Multilevel Converter with Interleaved half-bridge Sub-Modules (ISM-MMC) is proposed in this paper. The ISM-MMC exhibits a higher modularity and scalability in terms of current ratings with respect to a conventional MMC, while preserves the typical voltage level adaptiveness. The ISM-MMC brings the known advantages of classical MMC to low-voltage, high-current applications making it a novel candidate for the sector of ultra-fast chargers for all types of electrical vehicles (EV). This advanced topology makes it possible to easily reach charging power of the EV charging system up to 4.5 MW and beyond with low-voltage supply. To operate the new converter, a hybrid modulation scheme that helps to exploit advantages of the interleaving scheme, is implemented, and explained in this paper. It has been verified that the typical MMC control methods are still applicable for ISM-MMC. A comparative study between classical MMC and ISM-MMC configurations in terms of output characteristics and efficiency is also given. Furthermore, it has been demonstrated that the number of ac voltage levels is synthetically multiplied by the number of interleaved half-bridge legs in submodules. Numerical simulations and Hardware-in-the-Loop tests are carried out to demonstrate the feasibility of the proposed topology and implemented modulation scheme.