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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.

In this paper, a behavioral static model of GaN HEMT is proposed. Different mathematical formulas have been tested to find the best for emulating the static behaviour of a 650V GaN HEMT prototype manufactured by STMicroelectronics. In literature, almost all the proposed formulas did not satisfy the target characteristics. The study of the new mathematical formulas, proposed in this paper, starts from the analysis of the models present in the literature that are rewritten and adapted for this model. Furthermore, these new equations are temperature dependent. The simulated curves of the static characteristics have been compared with those extracted by means of laboratory measurements. The model has been developed exploiting some features of STMicroelectronics models of SiC power MOSFETs.

A full optimization procedure that combines the parallel self-adaptive low-high evaluation-evolutionary algorithm with the finite element method-robin boundary condition iteration numerical method is proposed for the design of electromagnetic mantle cloaks enclosing arbitrary objects. The procedure is efficiently applied to optimize an ultrathin, conformal frequency selective surface (FSS), placed around an inhomogeneous dielectric cylinder to be made invisible. Two very different optimal solutions have been found, and this can be a great advantage for the designer using the proposed optimization strategy.

The use of proper models of the power devices is important when the design of the power conversions systems is performed. The optimal design requires high accuracy of the power device behaviour and low computational effort, especially fast simulation. Obtain quickly the power device model endowed with the previous two features is an important additional target of manufactures. Finally, they also want provide a tool which has to be effortlessly handled by the users. In this context, the behavioural model is useful since it includes a set of equations that emulates the device behaviour at its terminals and it is easy to implement in simulation tools (e.g. SPICE). Thus tree targets are reached: best compromise between accuracy and simulation burden, friendly-user. The major issue is to choose quickly the model parameters. In this work, this issue is taken on by means of a multi-objective genetic algorithm. A double test has been used to compare the measured and simulated waveforms. Such a comparison in an inverter module has highlighted the accurateness of the proposed solution.

In this paper, on-state dynamic drain source resistance (R DS(ON) ) phenomenon in GaN based power switches is analyzed. Dynamic R DS(ON) may increase the power losses in converters, thus reducing the benefits of using GaN power devices in this field. The operating parameters having an impact on dynamic R DS(ON) are investigated by analyzing the research works available so far from industry and academia. The objective of this work is to highlight the key operating parameters that influence this phenomenon, in order to give useful information to designers. Another objective is the identification of the lack of information on the topic, thus suggesting the analysis useful for an all-embracing understanding of the influence on dynamic R DS(ON) due to the different operating conditions. To these aims, the collected data are harmonized since the variety of test conditions, the different methods adopted to report the results and to obtain them. The comparison has highlighted that the working frequency is the main factor influencing the dynamic R DS(ON) . Moreover, the analysis has drawn attention to the necessity to make extensive experimental analyses on various technologies types and mission profiles. Finally, the main research topic to be properly investigated concerns the deep analysis of the correlations among the parameters which affect the dynamic R DS(ON) .

The main aim of this work is to provide a straightforward tool to modelize the thermal behavior of power module packages. The proposed circuit-based modeling approach takes into consideration the mutual thermal interaction among the dies, which plays a key role in the estimation of their working temperature. Furthermore, this modeling method features a compact and modular structure that can be easily tailored for different package configurations, maintaining limited complexity and computational burden. Last but not least, this thermal model includes both heating and cooling effects, thus allowing to evaluate thermal stresses even under pulse width modulated power devices. The thermal model is obtained starting from the temperature profiles carried out through a finite element analysis (FEA), by applying a power loss step to each single die. Starting from these profiles, a fitting curve algorithm is used to identify the elements of the RC networks used to represent the auto and mutual thermal impedances. The thermal model is thus an algebraic linear system including the RC networks parameters, and it can be exploited to identify the thermal status of each die of the power module even operating at different load conditions. The method has been applied in a SiC 3 phase inverter power module in which the high side and low side switches are formed with four parallel connected 1200V 350A SiC MOSFET dies. The results outgoing from the proposed model are confirmed by that carried out from FEA.

Power device modeling plays an important role at the design stage of power conversions systems, especially in the automotive and aircraft sectors. In this context, it is important to obtain in short time an accurate model that account for the mutual interaction of thermal and electrical quantities. The behavioral model is the best approach because it consists of a set of equations that emulates the device behavior at terminals level and can be easily implemented in a SPICE simulation tool, largely adopted both in industrial and academic contexts. The major issue of the behavioral model is to choose the equations parameters such that the simulations results fit the measurement data. In this paper, this problem is tackled by means of a particle swarm optimization algorithm. It is applied to automatically find the optimal parameters for an accurate behavioral model of an automotive grade SiC MOSFET that properly fits the datasheet curves. The comparison between the waveforms obtained by experimental tests and the SPICE simulations in a double test has confirmed the accuracy of the model.

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.

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.

There is an increasing interest in developing unmanned aerial vehicles (UAVs) for small size objects delivering. The efficiency and cost of the on board power converters are important aspects for their rapid spreading. Moreover, lifetime, safety, and reliability of the converter in the powertrain are crucial. In this perspective, voltage overshoots and oscillations due to the parasitic phenomena are important stresses to be cared. In this work, their effects in a half bridge converter have been analyzed since it can represent a leg of a three phase inverter feeding a motor of the UAV. Automotive grade super junction (SJ) MOSFET has been considered because it presents high reliability level with increased lifetime expectancy and it is less subjected to overshoot and oscillation issues. Moreover, SJ MOSFET is a mature technology with better cost. In this paper, an extensive parametric analysis has been carried out by performing several LTspice simulations to highlight the effects of the parasitic phenomena on both the drain source-voltage and efficiency. The results have been firstly validated, then useful design constraints have been identified.

Purpose The optimization of the cross section of an axisymmetric induction heating device is performed by means of genetic algorithms (GAs). Design/methodology/approach The hybrid finite element method–Dirichlet boundary condition iteration method is used to deal with the unbounded nature of the field. The formulation of the electromagnetic problems takes into account skin and proximity effects in the source currents. Findings The convergence of GAs towards the optimum is very fast, since less than a thousand analyses have been necessary. Originality/value A special derivation of the finite element global system is presented which allows us to save computing time.

In this paper, a stop-band filter realized by a high impedance surface for reducing electromagnetic interference from printed circuit boards is studied. Starting from an existing high impedance surface, Design of Experiments techniques and numerical simulations were employed to analyze the effect of its geometrical parameters on the desired forbidden band-gap of the filter. Finally, an improved high impedance surface is proposed.

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.

Super junction (SJ) MOSFET is a well-established device in high-density and high frequency power conversion. Soft-switching techniques are usually adopted at high frequency to reduce the power losses into the power devices. However, new challenging issues appear always when the paradigm changes. In fact, unexpected heating and efficiency reduction due to $\boldsymbol{C}_{\mathbf{oss}}$ related phenomena are key issues to be faced when SJ MOSFETs are adopted in high-frequency soft-switching applications. The phenomenon appears when large voltage transients are applied to the drain-source terminals as in the case of soft-switching applications. This paper provides analysis of the electrical hysteresis, and proposes an equivalent circuit that may model such a behavior in case of SJ MOSFETs. The loss model of $\boldsymbol{C}_{\mathbf{oss}}$ has been validated by comparing the measurements with the simulation runs performed by means of the Simulink package.

The hybrid FEM-BEM and FEM-DBCI numerical methods are proposed for the computation of transferred earth potentials from grounding grids. The method foresees the decomposition of the analysis domain in detached subdomains to be analyzed by means of FEM and linked together by means of integral equations, which involves the Green's function of the stratified soil. A great advantage of these methods is that the numerical solution directly gives the electric potential on the earth surface.

High switching frequencies in power converters allow to use small-size passive components that, in turn, means high-density (kW/kg) power conversion. The use of silicon MOSFETs manufactured with super junction technology is an additional feature towards the achievement of very high-density converters. The concurrent factors of increased switching frequency and power density may lead to thermal issues to be faced. Aiming to reduce the overall power losses, soft switching techniques are adopted to reduce dramatically the switching power losses, thus increasing the efficiency. The application of super junction (SJ) MOSFETs in soft-switching based conversion schemes has revealed unexpected power losses due to the dielectric hysteresis phenomenon into the parasitic output capacitance Coss of the MOSFET. In this respect, the experimental evidence has proved that there is a very large performance difference among the devices available into the market. This paper studies the Coss power losses that have been experimentally measured, modeled and simulated by a PSpice package. The proposed model is a nonlinear resistor whose average value is equal to the equivalent series resistance calculated from the experimental hysteresis loop (Q- V characteristic) and the related power losses at a given switching frequency.

Today the technologies regarding the solid-state devices are in huge development. Well-established Silicon power devices in the field of the power conversion belong to several families having a large range of rated value of currents and voltages. The new entries are innovative devices exploiting the good properties of wide band gap materials, like the Silicon Carbide and the Gallium Arsenide. Industrial and academic research interests focus on the development of well-established and new devices, looking to obtain good performances and enhanced energy savings. This paper explores and discusses the application of the power devices in aviation, highlighting the crucial aspects and the challenges to deal with for a full implementation of the more electric aircraft paradigm.

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.

In this paper, the optimization of the shielding of an axisymmetric levitation melting system is performed by means of the Particle Swarm Optimization algorithm. A non-standard Hybrid FEM-BEM is used to deal with the unbounded nature of the electromagnetic field problem and to reduce the computing effort required for optimization. The shape of the shield is derived by using Bezier curves. Moreover, for each analyzed configuration, the equilibrium position of the workpiece to be melted is determined by means of a Newton-Raphson algorithm.

In this paper, the hybrid finite-element method-Galerkin Dirichlet boundary condition iteration method is described for the finite-element solution of a variety of low-frequency electromagnetic field problems in open boundary domains. The method assumes a Dirichlet boundary condition on the truncation boundary and its imposition is made by means of a Galerkin integral equation over another surface strictly enclosed by the truncation boundary.

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.

In this paper, the hybrid finite-element method (FEM) singular Dirichlet boundary condition iteration method, already developed for 2-D skin-effect problems, is extended to the 3-D solution of time-harmonic eddy current problems. The method is similar to the well-known FEM-boundary-element method (BEM), but it assumes a Dirichlet boundary condition on the truncation boundary instead of a Neumann one. Shorter solving times are obtained with respect to FEM-BEM.

In this paper the FEM-RBCI method is successfully applied to the analysis of the scattering of time-harmonic electromagnetic waves at optical frequencies from metallic nanoparticles. Plasmons are taken into account by modelling the nanoparticles by means of appropriate complex permittivities. The method is valid whatever the shape of the nanoparticles. Numerical examples are provided to validate the method.

In this paper an improved placement of the integration surface for the integral equation in the hybrid finite element method-Dirichlet boundary condition iteration (FEM-DBCI) method is achieved by selecting it as lying in the middle of the tetrahedral or hexahedral finite elements. A better accuracy is obtained with respect to the case in which the integration surface lies along the element faces. Some numerical examples are provided.

PurposeThis paper aims to discuss various numerical implementations of the integral equation in the hybrid finite element method‐Dirichlet boundary condition iteration (FEM‐DBCI) method for the numerical solution of unbounded static and quasi‐static electromagnetic field problems.Design/methodology/approachThree numerical implementations are described and compared from the point of view of accuracy and complexity, by means of two examples regarding simple electrostatic problems.FindingsThe implementation by means of a pair of integration surfaces made of element sides leads to accuracy levels which are much better than that of a single surface (made of element sides) and only a little worse than that of a single surface connecting point in the middle of finite element sides.Practical implicationsThe former implementations, however, are simpler since they are practically the same as that of a standard boundary element method integral equation.Originality/valueThe paper constitutes a useful guide to the implementation of the FEM‐DBCI method.

In this paper, the authors propose a modified version of the hybrid finite element method-Robin boundary condition iteration (FEM-RBCI) method to solve scalar scattering problems, such as 2-D electromagnetic and 3-D acoustic ones. In the modified method, called FEM-singular RBCI, the integration surface coincides with the truncation one, so that the integral equation becomes singular.

In multi‐ and many‐objective optimization problems, the optimization target is to obtain a set of non‐dominated solutions close to the Pareto‐optimal front, well‐distributed, maximally extended and fully filled. Comparing solution sets is crucial in evaluating the performance of different optimization algorithms. The use of performance indicators is common in comparing those sets and, subsequently, optimization algorithms. Therefore, an effective performance indicator must encompass these features as a whole and, above all, it 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.

Purpose – The purpose of this paper is to present a modified version of the hybrid Finite Element Method-Dirichlet Boundary Condition Iteration method for the solution of open-boundary skin effect problems. Design/methodology/approach – The modification consists of overlapping the truncation and the integration boundaries of the standard method, so that the integral equation becomes singular as in the well-known Finite Element Method-Boundary Element Method (FEM-BEM) method. The new method is called FEM-SDBCI. Assuming an unknown Dirichlet condition on the truncation boundary, the global algebraic system is constituted by the sparse FEM equations and by the dense integral equations, in which singularities arise. Analytical formulas are provided to compute these singular integrals. The global system is solved by means of a Generalized Minimal Residual iterative procedure. Findings – The proposed method leads to slightly less accurate numerical results than FEM-BEM, but the latter requires much more computing time. Practical implications – Then FEM-SDBCI appears more appropriate than FEM-BEM for applications which require a shorter computing time, for example in the stochastic optimization of electromagnetic devices. Originality/value – Note that FEM-SDBCI assumes a Dirichlet condition on the truncation boundary, whereas FEM-BEM assumes a Neumann one.

FEM/DBCI (Dirichlet Boundary Condition Iteration) is a hybrid method which has been successfully applied to the finite element solution of static and quasistatic unbounded field problems. It is based on the iterative improvement of a Dirichlet condition on a fictitious boundary enclosing all the conductors, making use of the free-space Green's function. In this paper it is shown that for two-dimensional skin effect problems a more robust solving strategy can be pursued by means of GMRES, obtaining a reduction in both CPU and storage requirements.

Genetic algorithms (GAs) are widely used in the optimization of electromagnetic devices. However, if finite element analyses are needed for the evaluation of the objective function, GAs require a long computation time. They also need a difficult tuning session before starting optimization, to select the best configuration of the parameters that control the algorithm. This paper proposes a universal choice of the GA parameters in order to spare the designer the tuning session and to reduce the computing time for the whole procedure.