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Due to their superior material properties, wide bandgap (WBG) semiconductors enable the application of power electronics at higher temperature operation, higher frequencies, and higher efficiencies compared to silicon (Si). However, the commonly-used aluminum wire bonding as topside interconnection technology prevents WBG semiconductors from reaching their full potential, due to inherent parasitic inductances, large size, heat dissipation, and reliability issues of wire bonding technology. Therefore, this article presents a comprehensive review of topside interconnection technologies of WBG semiconductor power devices and modules. First, the challenges and driving factors for the interconnection of WBG semiconductor dies are discussed. Second, for each widely commercially used WBG semiconductor, i.e., silicon carbide and gallium nitride, technical details and innovative features of state-of-the-art interconnection techniques in packages are reviewed. Then, the majority of existing topside interconnection materials for WBG semiconductors are categorized and compared, followed by a discussion of their advantages, challenges, and failure modes. Based on this elaborate discussion, potential future directions of the interconnection technology development are given. It is concluded that the superior performance of WBG semiconductors can be obtained by combining novel materials with innovative designs for the topside interconnections. [ABSTRACT FROM AUTHOR]

Diesel generators in small electricity grids are mostly not used in a very efficient way. The reason for this is twofold. First of all, the efficiency of a diesel generator is dependent on the ratio determined by the average power divided by the peak power of the generator. The smaller this ratio is, the lower the efficiency. Furthermore, some loads can regenerate energy. In small grids, this energy is mostly not needed elsewhere and should be dissipated. A solution solving both problems previously mentioned is using an energy storage device in the system. This storage can be used for peak shaving and storing regenerated energy. This paper focuses on a generator-set with energy storage. Six different power management strategies are discussed. Calculation of the costs shows that adding an energy storage device lowers the cost for all methods. Verification with simulation and experiments has been carried out. Index Terms--Costs, diesel-driven generators, energy conservation, energy storage, lithium-ion battery, power electronics, supercapacitor.

In this paper, the possibility of reaching high power densities in multikilowatt dc-dc converters with galvanic isolation is demonstrated and the main design issues are discussed. The issues related to converter topology, transformer design, and thermal management are addressed, and new conceptual solutions are proposed. Implementing zero-voltage-switching quasi-zero-current-switching topology, optimized transformer design with leakage layer, and thermal management based on conduction enhanced by heat pipes at critical places resulted in very high power density and efficiency. The power density reached by the converter prototype is 11.13 kW/L with water cooling and 6.6 kW/L with air cooling. In the same time, the measured efficiency exceeded 97% in a broad load range. The new design concepts are demonstrated on a 50-kW converter prototype that was successfully tested at full-load conditions. Index Terms--DC-DC converter, galvanic isolation, high-frequency transformer, high power density, thermal management.

In this paper, a very high power density dc/dc converter module for automotive applications is investigated. The 14-V/42-V converter is specified to operate at a power level of 2.1 kW with a water cooled heat sink at 85[degrees]C. The design and implementation of very high density passive components are discussed. Using the results of the passive component design, a prototype converter is built, achieving a final power density of 170 W/[in.sup.3]. The thermal performance of the passive components and the converter module under different electrical and thermal excitations is investigated and recorded. Results are presented over the full excitation range. Index Terms--Converter module, thermal performance.

Passive components, and inductors, in particular, contribute greatly to the overall volume of power electronic converters. These components are normally packaged individually with little concern for the overall system. For high-density switching power supplies it is imperative to minimize the volume to as great an extent as possible which implies that the passive component volume usage needs to be improved. This can be accomplished by applying suitable packaging and cooling techniques to these components. In this paper, two inductor structures finding application in a 2.1-kW synchronous automotive converter are described. The air-gap placement, losses, cooling methods, and thermal profiles are analyzed and verified experimentally with an inductor designed for operation at 85[degrees]C ambient. Index Terms--Direct heat removal, high power density, high temperature, indirect heat removal, packaging, passive component.

This paper covers the experimental investigation and theoretical calculation of losses in a planar inductor under load. Finite-element software is used to perform the loss calculations. Thermally controlled experiments are performed for a range of frequencies to validate the corresponding finite-element method loss calculations. The thermal dependence of the loss mechanisms is also considered. Index Terms--Finite-element method (FEM) calculations, loss analysis, loss measurement, planar inductor, thermal measurement.

The layout of a capacitor bank with clamping diodes is investigated based on an experimental 5.5-kJ energy storage unit for pulsed power applications. While the current sharing between parallel-connected capacitors is good, it is not the case with parallel-connected clamping diodes. Despite a very-low-inductance busbar and attention to symmetrical layout, unequal current sharing results. Good agreement was obtained between measured waveforms and a detailed simulation model. The simulation model indicated that the unequal current sharing is due to small differences between the coupling factors of the parasitic busbar inductances near the capacitors at the ends and at the middle of the bank. It is concluded that the best solution is to place the parallel diodes as close as possible to each other at a position where best averaged coupling is achieved with the individual capacitors of the bank. Index Terms--Current sharing, high-frequency busbar, pulsed power, resonant forced commutation.

The low-pass filter (LPF) is a fundamental component of many power electronic systems, for example, the output filters of dc-to-dc converters. The volume of the two components that constitute the LPF contribute a majority of the final system's volume, thus affecting the overall power density of the system. To be able to reach the high power densities that are required nowadays, the packaging of these components needs to be addressed. A new packaging approach is considered where the main criteria is to increase the packaging density of the LPF. The filter is considered volumetrically, and the minimum possible volume is derived. The construction and losses of such a filter are also discussed. Index Terms--Energy density, high-density packaging, loss distribution, low-pass filter, shield, volumetric optimization.

Design and optimization of high-frequency magnetic components usually involve a number of tradeoffs between performance functions. This paper investigates the relationships between some of these factors by direct implementation of the thermal reference model previously presented by the authors. This unique thermal model provided the foundation for a more flexible approach to design and optimization, forcing uninterrupted coherence between electromagnetic behavior and predefined thermal conditions. Generic scaling of transformer parameters is performed herein, under simultaneous control of the temperature rise. Relationships for performance functions, such as maximum power rating, power density, total losses, efficiency, and leakage impedance are determined, tabulated, and plotted as functions of several different scaling conditions. Index Terms - Design, high-frequency power transformers, magnetic components, optimization, scaling, thermal models.

A new thermal model is introduced which is based on unique references, specifically suited to design and optimization of high-frequency high-power magnetic components. This thermal reference model is independent of shape, size, and orientation, so that a general set of data may be used to optimize transformer structure. The model, its limitations, and applications are described in detail. Unique measurement techniques are used for experimental verification and empirical sets of practical reference data, which are also provided. Index Terms - Design, high-frequency power transformers, magnetic components, optimization, thermal models.

In this paper, a coupled-inductor-based LCC resonant converter with the primary-parallel–secondary-series (PPSS) configuration is proposed to achieve output-voltage sharing ability for HV generator applications. The PPSS configuration of the LCC resonant converter with the voltage multipliers is introduced to achieve high output-voltage and increase the output-power level. However, the variations of the magnetizing inductance, leakage inductance, and winding capacitance of the HV transformer and voltage multiplier impact on the output-voltage sharing performance. Subsequently, the resonant inductors in the primary side of the conventional LCC resonant converters with the PPSS configuration are coupled to achieve the output-voltage sharing without any additional circuits and control efforts. Furthermore, an analytical equivalent circuit model considering the magnetizing inductor of the HV transformer is derived to analyze the output-voltage sharing ability. Moreover, the design method for the coupled inductors considering the output-voltage sharing performance affected by the leakage inductance of the coupled inductors is presented. Finally, the output-voltage sharing performance of the proposed coupled-inductor-based LCC resonant converter with the PPSS configuration is validated by the experimental results of a 50-V input, 5-kV output 100-W prototype. The prototype experimental results show that the unbalance voltage degree decreases from 67.7% to 8.5% with the utilization of the coupled inductor. [ABSTRACT FROM AUTHOR]

This paper investigates the diode reverse recovery process and reduction of a half-wave (HW) series Cockcroft–Walton (CW) voltage multiplier based on the steady-state analysis for high-frequency high-voltage (HV) generator applications. The diode reverse recovery process for a multistage voltage multiplier is analyzed after the introduction of steady-state operation. The diode reverse recovery problem is the bottleneck to further increase the circuit operation switching frequency for achieving high power density and short HV pulse rise and decay times. The diode reverse recovery problem is mainly caused by the diodes in the first-stage voltage multiplier. It is suggested that the most effective and economic way to alleviate the diode reverse recovery problem is by employing diodes without reverse recovery such as silicon carbide Schottky diodes in the first stage only. The silicon carbide Schottky diode without reverse recovery needs to be used only in the first stage of the voltage multiplier to effectively mitigate the reverse recovery problems at high frequency. The 300 kHz switching frequency three-stage voltage multiplier circuit hardware prototype experimental results finally validate the analysis. A technology demonstrator of a 300 kHz 8 kW 160 kV HV generator based on the proposed hybrid silicon carbide and silicon diode solution for the HW series CW voltage multiplier is provided finally. [ABSTRACT FROM AUTHOR]

Integrated inductor--capacitor-transformer L-C-T technology has been the subject of research over the last few years. Research into producing optimum design equations has been conducted. To determine some of the physical and technological limitations of the integrated L-C-T technology, a 1-kW 1-MHz resonant dc-dc converter was designed and built. The design was limited only by in-house material, construction, and technological restrictions. Through this process, it is hoped that some of the current technological limitations can be quantified. The design and construction process is given, while some of the limits of this technology are derived from experimental results. Index Terms--Hybrid converters, integrated capacitance-inductance, passive integration, resonant converters.

Capacitors are utilized in a variety of different ways in power electronic circuits. Typical applications are in snubber, clamping, and resonant circuits. For design purposes, it is necessary to make an accurate measurement of the actual behavior of the capacitance that is added to the circuit under conditions related to those prevailing in a converter. For this purpose, a number of different measurement systems or techniques can be utilized. Four of these measurement systems are compared. These are small-signal variable-frequency measurement, large-signal quasi-dc measurement, in--situ high-voltage measurement, and small-signal with large dc bias voltage measurement. Each of these measurement techniques returns characteristic values based on its particular model of the test capacitor. These tests are done on both ceramic and nonceramic capacitors at room temperature. The results are discussed. Index Terms--Capacitor measurement, dielectric measurement, in--situ measurement, large-signal measurement.

In this paper, a unified equivalent circuit model which can simplify the design and analysis of a family of high-voltage (HV) generation architectures based on the series–parallel (LCC) resonant converter is proposed. First, four HV generation architectures are reviewed in terms of the modularization level of HV transformers and rectifiers. Next, the steady-state, unified equivalent resistor and capacitor (RC) model that can be easily embedded into the resonant tank to replace the complex HV transformers and rectifiers is derived. The generic model can be applied to the HV generators with different architectures, different voltage multiplier topologies, stage, and polarities number. Further analysis of the power factor of the resonant tank, the voltage gain of HV generators, and electrical stresses of power components is achieved with the derived equivalent circuit model. The analysis reveals the inherent circuit properties among HV generators with different configurations. Subsequently, a comprehensive design methodology considering the power factor, conduction angle, and quality factor is presented, which leads to low electrical stresses on the components and high efficiency. Furthermore, the parameter selection constraint based on the power factor, conduction angle, and quality factor is derived, which can ensure the effective design outputs. Finally, the proposed unified equivalent model and comprehensive design methodology are validated by the experimental results of a 250 V input, 20 kV output 500 W HV generator hardware prototype with distributed transformers and voltage multipliers. [ABSTRACT FROM AUTHOR]

This paper deals with a generic methodology to evaluate the magnetic parameters of contactless power transfer systems. Neumann's integral has been used to create a matrix method that can model the magnetics of single coils (circle, square, rectangle). The principle of superposition has been utilized to extend the theory to multi-coil geometries, such as double circular, double rectangle and double rectangle quadrature. Numerical and experimental validation has been performed to validate the analytical models developed. A rigorous application of the analysis has been carried out to study misalignment and hence the efficacy of various geometries to misalignment tolerance. The comparison of single-coil and multi-coil inductive power transfer systems (MCIPT) considering coupling variation with misalignment, power transferred and maximum efficiency is carried out. [ABSTRACT FROM AUTHOR]

Brushless doubly‐fed induction machines (DFIMs) have great potential as variable‐speed generators in wind turbines. Undesired space‐harmonics exist because the special rotor needs to couple to two stator windings with different pole‐pair numbers and different frequencies. These undesired space‐harmonics could lead to noise, vibrations and low power quality. Applying skewed slots can overcome the above drawbacks. Previously, a two‐dimensional (2D) multi‐slice finite element (FE) method was applied to study the effects of skew which was time consuming. In the stage of initial design, it is not efficient to use such a model to predict how much the average torque and the torque ripple would be reduced by skewing slots. This study makes use of normal 2D FE results and applies skew factors in post‐processing to investigate the influence of rotor skew. It also proves that to apply skew factors appropriately, not only the space‐harmonic order needs to be considered, but also the time‐harmonic order. The proposed method can give an approximate prediction of skew effects with limited computing time. The results also indicate that skewing the rotor slot over one stator slot pitch could be a good choice to minimise the torque ripple in a brushless DFIM with a nested‐loop rotor. [ABSTRACT FROM AUTHOR]

The air-gap magnetic fields of brushless doubly fed induction machines (DFIMs) are complicated because of the cross-coupling between two stator fields via a special nested-loop rotor. Compared with classical analytical models, transient finite-element (FE) modeling is easier to evaluate the machine performance taking saturation into account. However, it is not efficient to evaluate lots of candidates in a large design space using transient FE models considering the time cost. In the transient simulation, the induced rotor currents are calculated by solving several time differential equations using the backward differentiation formula. This paper presents a computationally efficient FE analysis for brushless DFIMs. The induced rotor currents can be calculated using a single magnetostatic FE simulation. The average torque, losses, and efficiency can also be predicted using one magnetostatic solution. One candidate design can be evaluated within 1 or 2 min on a personal workstation. The efficient analysis is validated by the transient FE results. The presented model is applied to the optimization of a prototype. The influence of two construction variables, namely, pole-pair combinations and the number of loops per nest, is studied. One pole-pair combination is selected for manufacturing a prototype. [ABSTRACT FROM AUTHOR]

This paper analyzes short circuits in high-speed permanent-magnet (PM) machines. Analytical models are used to estimate the consequences of single-strand, parallel-strand, and phase-to-phase turn-to-turn short circuits, as well as open-circuit faults. The parameters for the analytical models are obtained from 3-D finite-element simulations and consider the actual position of each strand inside the slot. It is shown that parallel-strand short circuits are less severe than single-strand short circuits, both before and after fault mitigation actions. The potential for large fault current densities in high-speed PM machines is also demonstrated, with measured rms current densities up to 450 \A/mm^2 . A simple fault detector based on the synchronous detection of the machine and inverter neutral voltage difference is proposed, which is suitable for hardware implementation and can function as an independent observer of a drive system. The dependence of the detectability on the short circuit location and the effects of natural imbalances on the detector output are investigated. Experiments are performed to demonstrate the concept, showing that faults of at least 0.4% can be detected. [ABSTRACT FROM PUBLISHER]

The authors' previous paper presents the complete model of parasitic capacitances in a high-voltage (HV) multiplier in the HV generator in a medical X-ray machine. The equivalent parasitic capacitance of the multiplier Cem based on the model is exhibited to interpret the role of the parasitic capacitances in circuit operation of the generator. Without derivation of the analytical expression of Cem, its dependence on the component parameters is directly shown, which leads to guidelines for minimization of Cem. However, the complete capacitance model has a complicated structure and contains voltage-dependent capacitances and voltage sources, which gives complexity to derivation of Cem as well as difficulties to clear understanding of the voltage dependence of Cem. Thus, this paper presents the detailed derivation and analytical expression of Cem. Exactly speaking, the key part of Cem, namely, the total chain capacitance CDcht that determines the voltage dependence of Cem, is conducted. A simple way is presented for the derivation of CDcht. The derivation enables a clear understanding of the voltage dependence of CDcht. Moreover, a design procedure for minimization of Cem is created, accompanied by a case study. It gives designers step-by-step rules to make an optimal HV multiplier with a minimum Cem. [ABSTRACT FROM AUTHOR]

This paper compares the conducted electromagnetic interference (EMI) in Si insulated gate bipolar transistor (IGBT) and silicon carbide (SiC) junction field-effect transistor (JFET) based motor drives. Two inverters, with the SiC and Si transistors, respectively, are built using the same circuit layout and investigated accordingly. Their conducted EMI levels are compared under the conditions of without filter and with traditional common mode (CM) filters. Reasons of the exhibited different noise emissions are analyzed. To verify the discussions, two inverters are tested in the CM. This allows for the identification and analysis of their maximized CM and differential mode (DM) wave shapes. It is shown that the excited parasitic oscillations during the switching transients are magnified more in the SiC JFET inverter, which is the main cause of the noise difference. Lastly, improved filtering solutions are proposed, which effectively suppressed the increased high-frequency noise due to the faster SiC switching speed. [ABSTRACT FROM AUTHOR]

This paper systematically investigates the conducted electromagnetic interference (EMI) using separated heat sinks for a silicon carbide (SiC) JFET inverter for motor drives. The inverter circuit layout is implemented with discrete SiC JFETs attached on top of the heat sink, which creates extensive capacitive couplings and moreover increases parasitic oscillations. To minimize the influence, the solution of using separated heat sinks is proposed. For better common mode performance, the high-side heat sink is grounded to avoid fast dv/dts that occur between the drain of the lower switch and the low-side heat sink. For better differential mode performance, the RC snubber circuit and ferrite beads are used to damp parasitic oscillations. Two 2.2 kW inverter prototypes, with six discrete SiC JFETs on one common heat sink and separated heat sinks, respectively, are built using the same circuit layout. Their EMI spectra are compared under unfiltered and filtered conditions. The experiments show that the separate heat sinks inverter system exhibits significantly reduced EMI. Last, three improved solutions are proposed, which effectively suppresses the emitted EMI to the target level. [ABSTRACT FROM PUBLISHER]

This paper presents the suppression of conducted common-mode (CM) electromagnetic interference (EMI) in an inverter for motor drive with discrete silicon carbide (SiC) JFETs attached on top of the insulated metal substrate (IMS). The EMC performance of the IMS inverter is compared with that of a heat sink inverter in a similar circuit layout. Both are under the same influence of parasitic capacitive couplings between the SiC JFET drains and the substrate base plate. It is found that although the application of conventional CM filters effectively suppresses the emitted noise in the low-frequency (LF) range, the influence of this capacitive coupling results in slight or no improvement in the middle-frequency (MF) and high-frequency (HF) ranges. To deal with this problem, a system CM equivalent circuit model with extracted parasitic parameters is proposed. The model is able to evaluate the filter insertion losses over a broad conducted EMI frequency band, which is essential to achieve an optimized filter design balanced between performance and cost. The presented experimental and calculated results form the step-by-step guideline that effectively suppresses the generated EMI to comply with the standard prescribed by IEC61800-3 C2: Qp. [ABSTRACT FROM PUBLISHER]

The use of slotted stator permanent-magnet machines with concentrated windings is increasing in industry. In this paper, the effect of the slot opening on flux linkage, internal voltage, mean torque, rotor eddy current loss, and stator iron losses is evaluated. This gives new insight into the influence of slotting on the performance of machines with a small slot opening. In addition, the slot opening can be chosen to maximize the internal voltage and the mean torque while minimizing the total iron loss. The limitations of the traditional analytical design model with small slot openings for permanent magnet machines are reported. Carter factor expressions found in literature are evaluated by comparing them with finite-element computations. The finite-element computations in turn are validated using measurements on two machines with semi-open slots and one machine with fully open slots. The measured and simulated values for amplitude and waveform of the flux linkage and internal voltages are in good agreement. [ABSTRACT FROM AUTHOR]

The objective of this paper is to compare the energy yield and generated electricity cost of several commercially available small wind turbines under low wind speed condition. Many small wind turbines were not able to generate the amount of electricity promised by the manufacturers. The predicted annual energy yield simulated using manufacturers' power curve were sometimes higher than actual measured values by up to a factor of two. Furthermore, above a rotor size of 3 m, large diameter turbines performed better, having both low generated electricity cost ( ? /kWh) and high annual energy yield per swept area (kWh/m^2). [ABSTRACT FROM PUBLISHER]

An automotive electric-power-steering synchronous machine driven from a multifunctional converter has the advantage of increased system voltage. The integration of the boost converter in the inverter and the electrical machine leads to new requirements for the machine design due to dc currents and increased high-frequency ripple currents in the motor windings. In this paper, the ripple currents of a synchronous machine with a multifunctional converter are investigated. Three winding arrangements are analyzed and compared to reduce the ripple currents together with interleaved pulsewidth modulation. This paper contains finite-element simulations of the zero-sequence flux and analyses of the ripple currents with and without low-frequency ac modulation and, hence, when operated at high and low rotational speed. The magnitude of the ripple current depends on the zero-sequence inductance. By rearranging the coils in the stator slots, the zero-sequence inductance is significantly increased. Experimental results are correlating well with theoretical predictions and demonstrate that the phase and star-point ripple currents are almost halved. [ABSTRACT FROM AUTHOR]

This paper investigates the switching behavior of normally OFF silicon carbide (SiC) JFETs in an inverter for a motor drive. The parasitic ringing caused by different parasitic effects is analyzed. Two different methods, the use of an RC snubber and the use of suppression ferrite component, are investigated for dampening the parasitic oscillations. It is found that applying a ferrite bead not only dampens the parasitic oscillations, but also results in significantly lower switching losses. Furthermore, it is shown that the capacitive coupling between SiC devices in the bridge leg and heat sinks significantly deteriorates the JFETs' switching performance. The effect of two substrates, an insulated metal substrate and a printed circuit board, on the capacitive coupling is investigated. A method in which the use of two separate heat spreaders minimizes the capacitive coupling, thus, exploiting the full potential of fast SiC JFETs is proposed. [ABSTRACT FROM AUTHOR]

This paper looks into a new concept for reducing the structural weight of large direct-drive generators used in wind turbines. The concept uses magnetic bearings to position the rotor of the generator. The use of magnetic bearings allows structural flexibility in the generator. The weight of the rotor using the new concept is compared to the weight of a rotor designed with conventional methods. For a 5-MW generator, the result is that the structural weight of the rotor reduces by 45%. [ABSTRACT FROM AUTHOR]

Permanent-magnet (PM) machines are considered the most suitable machine type for very high speed applications. Still, due to the growing demand for the ever higher rotational speeds, PM machines are approaching their limits. The focus of this paper is the different factors that lie behind the inherent speed limitations of PM machines. The limits - thermal, elastic, and rotordynamical - are defined, classified, and correlated to basic machine parameters. [ABSTRACT FROM AUTHOR]

Deals with a study which developed an enhanced version of a method to minimize the amount of permanent-magnet (PM) material required to create a certain flux linkage in the stator winding of a PM machine. Determination of PM volume; Shaping in single-sided surface-mounted machines; Discussion; Conclusion.

Presents a study that described the design of an innovative integrated planar passive module for use in a power electronic converter. Comparison of the experimental values with the design; Use of magnetic material; Conductors in the L-C-T structure.