Search

Vehicle electrification and digitalization are even more and more increasingly pushed by several aims, such as the improvement in sustainability, wellness, safety, and reliability. The need for onboard power electronics is a common factor for the different types of electric vehicles. Similarly, the increasing presence of onboard Internet of Things items as well as systems implementing artificial intelligence asks for additional power electronics that ensure supplying them according to their rating plate. Additionally, power converters have to perform this task also for traditional loads (infotainment; climate control, and so on) and new ones (USB and wireless chargers; Light detection and ranging, LiDAR applications, and so on). The transaction towards full electrification and digitalization requires highly efficient and compact power electronics converters. In this perspective, the Gallium nitride (GaN) high-electron-mobility transistors (HEMTs) are the best enabler device technology. This paper analyses the current and prospective improvement in sustainability and cost achievable with GaN in the automotive sector. Then, the advantages of the system in package GaN devices in power converter supporting this transaction, such as 48 V–12 V converters, onboard charges, and cell phone wireless chargers are experimentally investigated. The results have highlighted that, already in 2023, the use of Si devices in these applications does not enable further a lower overall converter cost with respect to GaN-based solutions. The reduction of passive costs enabled by using higher frequency thanks to the GaN features compensates for its higher cost. On the other hand, GaN HEMT enables high efficiency in all the aforesaid automotive applications as also experimentally proved in this paper, making it the best solution in terms of sustainability.

The growing use of electric vehicles is requiring the implementation of power electronics applications with ever faster devices, such as silicon carbide (SiC) MOSFET, to reduce switching power losses and reach higher power density, with the final objective of improving performance and lowering the system cost. A side effect of such faster switching devices is the generation of high-frequency harmonics with significant energy, so their impact must be evaluated in terms of conducted and radiated electromagnetic interference (EMI). The optimal design of PCBs and filters for facing electromagnetic compatibility issues requires properly estimating the EMI level of different design solutions. Analysis of the current state of the art reveals that previous approaches can not effectively support a design focusing on a reduction in radiated EMI. To surpass these limits, the paper defines an electromagnetic simulation flow aimed at evaluating the radiative fields in the case of an integrated power electronics module operating in automotive applications and featuring fast SiC power devices. Then, the proposed simulation was applied to an LLC resonant converter featuring an STMicroelectronics SiC-based ACEPACK module. The work also highlights that future research efforts must concentrate on finding the best compromise between computational effort and estimation accuracy.

Power electronics is becoming pervasive in electricity-based applications, making power device reliability an increasingly important topic. Maintenance operations are necessary to ensure the functioning of power electronic apparatuses [1]. Guessing the time for maintenance operations is challenging due to the related tradeoff between maintenance costs and reliability improvements. Lifetime prediction techniques and condition monitoring methods (CMMs) are useful tools for determining the actual need [2].

This article—framed as a methodological contribution and at the intersection between the critical urban, urban political ecology and world-ecology disciplines—builds on Corboz’s metaphor of ‘territory as a palimpsest’ to explore the representation of the socio-economic and ecological processes underpinning uneven development under extractive capitalist urbanization. While the palimpsest approach has typically been used to map transformations of more traditional urban morphologies, this work focuses instead on remote extraction territories appropriated by the global economy and integral to planetary urbanization. The article suggests the central notion of ‘palimpsests of appropriation’ as a lens to map the extraction processes. It does so in its multi-scalar and temporal dimensions and on the basis of the three intertwined frames—i.e., the productive, distribution and mediation palimpsest—shortly exemplifying its use on the ground for the iron ore extraction territory in the Swedish-Norwegian Arctic. With this, the article contributes to the development of an expanded representational methodology and conception of territories of extraction—where social and natural production are brought together—illustrating how appropriation has been (re)shaping each of the frames throughout historical thresholds, but also how socio-natures are being (re)made in its image. Validerad;2020;Nivå 2;2020-07-01 (johcin)

This paper accurately estimates the dependency of the efficiency of multi-output Flyback converters from different designing parameters. This task has been accomplished by proposing a dedicated simulation circuitry that accurately models the MOSFET and the passive components. Through a dedicated parametric script, an automatic set of simulations has been performed aiming at providing a powerful tool to identify the optimum value of each designing parameter to maximize efficiency. A prototype of a double-output Flyback converter has been used to prove the effectiveness of the proposed model by comparing the bench measurements with the simulation results.

This paper describes a particular use of the hybrid FEM-DBCI, for the computation of low-frequency electromagnetic fields in open-boundary domains. Once the unbounded free space enclosing the system has been truncated, the FEM is applied to the bounded domain thus obtained, assuming an unknown Dirichlet condition on the truncation boundary. An integral equation is used to express this boundary condition in which the integration surface is selected in the middle of the most external layer of finite elements, very close to the truncation boundary, so that the integral equation becomes quasi-singular. The method is described for the computation of electrostatic fields in 3D and of eddy currents in 2D, but it is also applicable to the solution of other kinds of electromagnetic problems. Comparisons are made with other methods, concluding that FEM-DBCI is competitive with the well-known FEM-BEM and coordinate transformations for what concerns accuracy and computing time.

A technique to improve the performance of grid-connected induction motors by exploiting an auxiliary winding set is proposed in this paper. This auxiliary winding features the same distribution of the main winding, although with a reduced number of turns and it is fed by an inverter a fraction of the power in comparison with the rated size of the induction motor. As shown in the paper, through the auxiliary winding, it is possible to set the machine power factor, increasing the efficiency of the power conversion system and mitigating speed oscillations due to torque disturbances. A mitigation of the grid current peaks due to motor start-up is obtainable. First, the proposed technique is theoretically introduced, then a feasibility assessment is accomplished by simulations.

Condition monitoring (CM) of power semiconductor devices enhances converter reliability and customer service. Many studies have investigated the semiconductor devices failure modes, the sensor technologies, and the signal processing techniques to optimize the CM. Furthermore, the improvement of power devices’ CM thanks to the use of the Internet of Things and artificial intelligence technologies is rising in smart grids, transportation electrification, and so on. These technologies will be widespread in the future, where more and more smart techniques and smart sensors will enable a better estimation of the state of the health (SOH) of the devices. Considering the increasing use of power converters, CM is essential as the analysis of the data obtained from multiple sensors enables the prediction of the SOH, which, in turn, enables to properly schedule the maintenance, i.e., accounting for the trade-off between the maintenance cost and the cost and issues due to the device failure. From this perspective, this review paper summarizes past developments and recent advances of the various methods with the aim of describing the current state-of-the-art in CM research.

This work presents a step-by-step procedure to estimate the lifetime of discrete SiC power MOSFETs equipping three-phase inverters of electric drives. The stress of each power device when it is subjected to thermal jumps from a few degrees up to about 80 &deg, C was analyzed, starting from the computation of the average power losses and the commitment of the electric drive. A customizable mission profile was considered where, by accounting the working conditions of the drive, the corresponding average power losses and junction temperatures of the SiC MOSFETs composing the inverter can be computed. The tool exploits the Coffin&ndash, Manson theory, rainflow counting, and Miner&rsquo, s rule for the lifetime estimation of the semiconductor power devices. Different operating scenarios were investigated, underlying their impact on the lifetime of SiC MOSFETs devices. The lifetime estimation procedure was realized with the main goal of keeping limited computational efforts, while providing an effective evaluation of the thermal effects. The method enables us to set up any generic mission profile from the electric drive model. This gives us the possibility to compare several operating scenario of the drive and predict the worse operating conditions for power devices. Finally, although the lifetime estimation tool was applied to SiC power MOSFET devices for a general-purpose application, it can be extended to any type of power switch technology.

In a high-power factor quasi-resonant Flyback, an ideal zero current detection (ZCD) circuit and control circuitry enable the power switch turn-on in the exact instant a zero ringing current is reached after demagnetization. A nonzero current at the turn-on instant affects the input current shape and; consequently, affects its Total Harmonic Distortion (THD). This paper firstly deeply analyzes the effect on the distortion due to a nonideal ZCD circuit. After, some typical implementations of the ZCD circuit and their effect on the THD are analyzed, identifying their pros and cons. Finally, some experimental results are obtained to validate the analytical investigation.

The linear pattern of production-consumption-disposal of cities around the world will continue to increase the emission of pollutants and stocks of waste, as well as to impact on the irreversible deterioration of non-renewable stocks of raw materials. A transition towards a circular pattern proposed by the concept of ‘Circular Cities’ is gaining momentum. As part of this urban transition, the emergent use of Nature-based Solutions (NBS) intends to shift public opinion and utilize technology to mitigate the urban environmental impact. In this paper, an analysis of the current research and practical investments for implementing NBS under the umbrella of Circular Cities is conducted. A combined appraisal of the latest literature and a survey of ongoing and completed National-European research and development projects provides an overview of the current enabling tools, methodologies, and initiatives for public engagement. It also identifies and describes the links between facilitators and barriers with respect to existing policies and regulations, public awareness and engagement, and scientific and technological instruments. The paper concludes introducing the most promising methods, physical and digital technologies that may lead the way to Sustainable Circular Cities. The results of this research provide useful insight for citizens, scientists, practitioners, investors, policy makers, and strategists to channel efforts on switching from a linear to a circular thinking for the future of cities.

A distribution system upgrade moving towards Smart Grid implementation is necessary to face the proliferation of distributed generators and electric vehicles, in order to satisfy the increasing demand for high quality, efficient, secure, reliable energy supply. This perspective requires taking into account system vulnerability to cyber attacks. An effective attack could destroy stored information about network structure, historical data and so on. Countermeasures and network applications could be made impracticable since most of them are based on the knowledge of network topology. Usually, the location of each link between nodes in a network is known. Therefore, the methods used for topology identification determine if a link is open or closed. When no information on the location of the network links is available, these methods become totally unfeasible. This paper presents a method to identify the network topology using only nodal measures obtained by means of phasor measurement units.

This study explores connectivity for soft mobility in the winter season. Working with residents from the sub-arctic city of Lule&aring, Sweden, the research examines how the interaction between the built environment and winter season affects people&rsquo, s use of the outdoor environment. The research questions for this study are (1) How do residents perceive the effects of winter on an areas spatial structure and pattern of streets and pathways? and (2) What enablers and barriers impact resident soft mobility choices and use of the public realm in winter? Methods used were mental mapping and photo elicitation exercises. These were used to gain a better understanding of people&rsquo, s perception of soft mobility in winter. The results were analysed to identify how soft mobility is influenced by the winter season. The discussion highlights that at the neighbourhood scale, residents perceive that the winter alters an areas spatial structure and pattern of streets and pathways. It was also seen to reduce ease of understanding of the public realm and townscape. In conclusion, it is argued that new and re-tooled town planning strategies, such as extending blue/ green infrastructure planning to include white space could help better enable all year outdoor activity in winter cities.

Grounding systems are essential parts of substations and power generation stations. The evaluation of transferred potentials from an active grounding system to other passive ones or to any near conductors is an important aspect to be considered, because transferred potentials may cause serious and fatal events. Moreover, it is an intrinsic issue of the Smart Grid where the ground systems of the power and ICT systems could be close to each other. Therefore, the estimation of the transferred potential is necessary at grounding system design stage for people safety and electric components safeguard. Numerical methods are the best choice to perform a truthful estimation, especially when large and complex grounding systems have to be designed. However, this task is complicated by the &ldquo, unbounded&rdquo, nature of the electromagnetic field and by the presence of components of extremely different size in the analysis domain. In this paper, an efficient hybrid finite element method is applied for the accurate and fast computation of transferred earth potentials from grounding systems. Moreover, the small dimensions of the components in the analysis domain are taken into account by the use of one-dimensional finite elements inserted in the tetrahedral mesh. It is worth mentioning the additional advantage of obtaining the electric potential on the earth surface without any post-processing operation.

Future smart electrical distribution systems could adopt switch remote control and advanced automation systems to operate in autonomous mode (islanding) some portions of the network in order to improve system reliability. In this perspective, a free code able to assess distribution reliability by using analytical or Monte Carlo simulation methods accounting for intentional islanding operation is presented. An effective network representation and data structure, which have led up to the implementation of two automatic and general procedures, are proposed. The procedures share common underlying information in order to speed up calculation. A further merit of the tool is that it enables the user to quickly and simply create the input files. The reliability indices of three distribution networks have been computed by means of the developed software for different scenarios, that is when island mode of operation is not permitted by regulation, and when island mode is permitted (intentional islanding) with the local load either partially or totally supplied by renewable distributed generators. The free code, the input files and the results related to the considered networks are available online at: http://www.dieei.unict.it/users/sconti/psrs.htm.

Global maximum power point tracking (GMPPT) in case of rapidly variable irregular shading conditions is a complex task, which is exacerbated in case of inexpensive solutions where sensors for acquiring environmental conditions are excluded, that is there is not any information about irradiance and temperature distribution along the photovoltaic system. In such a context, the paper deals with the feasibility study and implementation of a novel easy and cost-effective hybrid two-stages GMPPT algorithm. The first stage synergically combines two different methods to predict the optimal operating condition: an artificial neural network based algorithm and a segmentation-based approach. A traditional hill-climbing method is used in the second stage to finely track the maximum power point. The theoretical aspects of the proposed solution are firstly described, then a wide simulative and experimental tests campaign have been executed to validate the effectiveness of the GMPPT method, confirming that a very simple artificial neural network structure combined with a standard segmentation based method leads to excellent performance for applications where the environmental conditions vary very frequently.

This paper extends the hybrid finite-element method–Dirichlet boundary condition iteration method for the solution of open-boundary electrostatic problems to the case, in which some floating potential conductors are present in the system. The iterative solution scheme of the basic method is modified in order to deal with the unknown values of the potential of these conductors.

The progressive reduction of global oil reserves and the issues related to the emission of air pollutions have spotlighted the urgent need for the production of vehicles enabling the reduction of both the fuel consumption and pollution. Nowadays, the hybrid electric vehicles are a viable option to guarantee reduction of both oil consumption and emissions. In the last decade, it is also appearing the diffusion of vehicles having photovoltaic (PV) panels: the hybrid solar vehicle (HSV). This survey deepens and reviews the actual state-of-the-art of the HSV, the improvements and the issues related to them, the latest development in the related technologies and the future trend. Finally, the outlook of the main themes of research, useful for a wider diffusion of HSV, are highlighted. From the review, it come to light a lack of a depth studies of HSVs considering the interaction and impact on the grid and the need for high efficiency PV panels.

In the design of a grounding system, technical and normative constraints have to be met. Therefore, it is necessary to use a tool that is able to accurately estimate the values of the significant parameters of the grounding system, such as earth resistance and touch-and-step voltages. The computation of such quantities calls for the solution of a 3-D open-boundary static electromagnetic field problem, which should take into account the nonhomogeneous structure of soil. The hybrid finite-element method–Dirichlet boundary condition iteration method is applied to the solutions of such problems. A great advantage of this method is that it directly provides the electric potential distribution on the earth surface as part of the solution. Some grounding systems are analyzed, and the comparisons of the results with those obtained by other methods are made.

In this paper, we optimize the size and position of silver hemispherical nanoparticles arranged in a regular array embedded in a thin-film heterojunction solar cell. The metallic nanoparticles are added in order to improve solar cell efficiency by exploiting the phenomenon of plasmon resonance. A finite-element code has been employed to compute the light scattered from the device and the optimization was performed at first by means of a genetic algorithm and then by means of the parallel self-adaptive low–high evaluation evolutionary algorithm.

Urban form can moderate the effects of weather on human movement. As such, the interrelationship between built environment, weather and human movement is a critical component of urban design. This paper explores the impacts of weather on non-motorised human movement (soft-mobility). Throughout we look at soft-mobility from the citizen’s perspective and highlight the barriers to soft-mobility in winter. The aim of this study was to test the traditional pallet of winter city urban design considerations. Those of solar-access, wind and snow management and explore other weather and terrain conditions that act as barriers to soft-mobility in winter. This study is based on survey responses from 344 citizens in the sub-arctic area of Sweden. Outcomes from the research highlight that rain, icy surfaces and darkness are today’s most significant barriers to soft-mobility in winter. Results from this study link changing barriers to soft-mobility in winter with climate change. The paper concludes that future urban design and planning for winter cities needs to consider a wider pallet of weather conditions, especially rain. Validerad;2017;Nivå 2;2017-09-14 (andbra)

In the last years, Internet is evolving towards the cloud-computing paradigm complemented by fog-computing in order to distribute computing, storage, control, networking resources, and services close to end-user devices as much as possible, while sending heavy jobs to the remote cloud. When fog-computing nodes cannot be powered by the main electric grid, some environmental-friendly solutions, such as the use of solar- or wind-based generators could be adopted. Their relatively unpredictable power output makes it necessary to include an energy storage system in order to provide power, when a peak of work occurs during periods of low-power generation. An optimized management of such an energy storage system in a green fog-computing node is necessary in order to improve the system performance, allowing the system to cope with high job arrival peaks even during low-power generation periods. In this perspective, this paper adopts reinforcement learning to choose a server activation policy that ensures the minimum job loss probability. A case study is presented to show how the proposed system works, and an extensive performance analysis of a fog-computing node highlights the importance of optimizing battery management according to the size of the Renewable-Energy Generator system and the number of available servers.

Telecontrol of distribution switching devices is recognized as a major means for reducing interruption duration after a fault occurrence in modern distribution systems, since it allows one to isolate the faulted sections and to restore the healthy ones as quickly as possible. In order to reduce interruption frequency as well, it is necessary to increase the number of series automatic circuit breakers. Further benefits in terms of service continuity improvement can be obtained by allowing islanded operation of relatively small portions of distribution network (microgrids) in the presence of distributed energy resources in order to supply the local load autonomously during upstream faults. This paper aims to describe an innovative systematic method and its related analytical formulation to evaluate distribution system reliability indices accounting for advanced operation practices such as those based on telecontrol and islanding.

The self-adaptive low-high evaluation evolutionary-algorithm (SALHE-EA) is used to solve multimodal optimization problems. SALHE-EA is able to find the multiple optima of a single objective function (OF) and to give an idea of the fitness landscape in the neighborhood of these optima. This aspect is of crucial importance when the single OF is obtained using the weighted sum of the OFs, each related to a different goal of the optimization problem. This paper presents an improved version of SALHE-EA. This new version has several new features and, mainly, the suitability for parallelization.

In multi-objective optimization problems, the optimization target is to obtain a set of non-dominated solutions. Comparing solution sets is crucial in evaluating the performances of different optimization algorithms. The use of performance indicators is common in comparing those sets and, subsequently, optimization algorithms. A good solution set must be close to the Pareto-optimal front, well-distributed, maximally extended and fully filled. Therefore, an effective performance indicator must encompass these features as a whole and must be Pareto dominance compliant. Unfortunately, some of the known indicators often fail to properly reflect the quality of a solution set or cost a lot to compute. This paper demonstrates that the Degree of Approximation (DOA) quality indicator, is a weakly Pareto compliant unary indicator that gives a good estimation of the match between the approximated front and the Pareto-optimal front. Moreover, DOA computation is easy and fast.