Dielectric elastomer transducers (DETs) are commonly modeled by lumped-element models (LEMs), however such models do not capture the cutoff behavior that manifests at relatively low frequencies due to the high resistivity of the stretchable electrodes. Moreover, the contribution of the electrodes into the lumped series resistance is not accurately known. The aim of this work is to define the accuracy and frequency limits of the LEM and to derive the exact values of its lumped components. This is achieved by developing a detailed three-dimensional distributed-element model (DEM) of the transducer structure. Based thereon, analytical expressions are developed for the LEM components and limits are explored. Through numerical evaluation of the DEM it is found that only two-third of the single-polarity electrode resistance contributes to the lumped series resistance, which is three times lower than predicted by existing models. Comparison between the LEM and DEM further shows that the LEM is adequate for frequencies significantly below the cutoff frequency. Thereafter, capacitance and resistance fall off as a result of signal propagation limitations. This has been experimentally verified. The developed DEM and established validity range of the simple LEM allows for more accurate sensors and better optimized transducers designs, with up to three times less electrode material.

The snubber circuit is a cost-effective solution to reduce the severe turn-off overvoltage and oscillation caused by the fast switching characteristics of SiC MOSFET. However, the turn-on switching losses will significantly increase as the snubber decouples the power loop parasitic inductance during the switching process. In this article, the effect of the power loop parasitic inductance on the switch performance of SiC MOSFETs and the quasi-zero voltage switching (QZVS) turn-on condition are studied. On this basis, an SiC MOSFET overvoltage and oscillation suppression circuit (OVSC) with not only the switching losses optimization feature but also the clamping energy feedback characteristic is proposed. The overvoltage and oscillation can be effectively suppressed by clamping capacitors, and those capacitors do not participate in the switching process until the overvoltage occurs, which is of benefit to the switching losses reduction compared with the other normal snubber circuits. Besides, the turn-off overvoltage and oscillation energy stored in the clamping capacitors can be feedback to dc and load side through a passive branch composed of an energy feedback inductor and a diode. The experimental studies and comprehensive comparison studies are carried out to verify the validity of the proposed OVSC. The experimental results show that OVSC has excellent overvoltage and oscillation suppression performance and can significantly reduce the switching losses.

SiC devices are promising for outperforming Si counterparts in high-frequency applications due to its superior material properties. Conventional wirebonded packaging scheme has been one of the most preferred package structures for power modules. However, the technique limits the performance of a SiC power module due to parasitic inductance and heat dissipation issues that are inherent with aluminum wires. In this article, low parasitic inductance and high-efficient cooling interconnection techniques for Si power modules, which are the foundation of packaging methods of SiC ones, are reviewed first. Then, attempts on developing packaging techniques for SiC power modules are thoroughly overviewed. Finally, scientific challenges in the packaging of SiC power module are summarized.

In this article, a novel fan-out panel-level printed circuit board (PCB)-embedded package for phase-leg silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (MOSFET) power module is presented. Electro-thermo-mechanical co-design was conducted, and the maximum package parasitic inductance was found to be about 1.24 nH at 100 kHz. Compared with wire-bonded packages, the parasitic inductances of the PCB-embedded package decreased at least by 87.6%. Compared with blind via structure, the thermal resistance of the proposed blind block structure reduced at most by about 26%, and the stress of the SiC MOSFETs decreased by about 45.2%. Then, a novel PCB-embedded packaging process was developed, and three key packaging processes were analyzed. Furthermore, effect of PCB-embedded package on static characterization of SiC MOSFET was analyzed, and it was found that: 1) Output current of PCB-embedded package was decreased under a certain gate-source voltage compared to SiC die; 2) Miller capacitance of SiC MOSFET was increased thanks to parasitic capacitance induced by package; and 3) compared with SiC die, nonflat miller plateau of the PCB-embedded package extends, and as drain-source voltage increases, the nonflat miller plateau extends. Lastly, switching characteristics of the PCB-embedded package and TO-247 package were compared. The results show that the PCB-embedded package has smaller parasitic inductances.

A novel modular high frequency high voltage (HV) generator with silicon carbide (SiC) power semiconductor devices is proposed in this paper to achieve high efficiency, sharp HV pulse and compact size. The modular architecture is introduced for high frequency operation firstly. The switching characteristics and detailed design consideration on the gate driver circuit are given. Finally, the 8kW output-power, 110kV output-voltage HV generator prototype with 300 kHz500 kHz switching frequency is built to validate the design. Compared with existing design, 2 times high power density, around 10% higher efficiency and 4 times faster HV pulse can be achieved from the proposed modular SiC HV generators.

This paper investigates a modular high frequency high voltage (HV) power supply architecture with planar transformer to achieve compact size and high efficiency. The insulation stress and voltage distribution different architectures with planar transformer are analyzed in firstly. An optimized modular high frequency HV generator architecture with planar transformer is proposed with even voltage distribution, low high frequency AC stress, easy insulation design and good thermal performance. The HV insulation and electric design of the HV planar transformer are provided. A prototype with 300kHz 4kW 140kVDC HV power supply with modular HV generation architecture and planar transformer is built to validate the concept finally.

This paper presents a multilevel, cascaded converter topology that allows for integrations of combined photovoltaic and battery storage units. The modular features of the system enable the series connection of PV panels that, in turn, have a parallel connection to a specified voltage level. These voltage levels stem from a series string of power electronic submodules. Likewise, low voltage energy storage units are interfaced to the upper arm of the system via identical converter modules and provide various directions of dc and ac active power flow, depending on the mode of operation. By implementing additional, nestled current loops, guided by passive filters, the system controls the power flow between the photo-voltaic string, batteries and the low voltage dc terminal. The enhanced level of power flow allows the converter to achieve both a controlled energy exchange as well as various auxiliary services in the DC system. This paper demonstrates three distinct types of power flow that are achievable with by combining the multilevel topology along with multifrequency operations. Simulation results from a representative system model are utilised to demonstrate the three possible modes of operation.

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.

In this paper, a novel fan-out panel-level printed circuit board (PCB) embedded package technology for silicon carbide (SiC) MOSFET power module is presented to address parasitic inductances, heat dissipation, and reliability issues that are inherent with aluminum wires used in conventional packaging scheme. To withstand high temperature beyond 175 °C and high voltage over 1.2 kV and improve thermomechanical reliability of the fan-out panel-level PCB embedded SiC power module, bismaleimide-triazine (BT) laminate and prepreg with high-temperature stability, high dielectric strength, coefficient of thermal expansion (CTE) matching with SiC, and high T-g are selected as PCB embedded package materials. Then, high-temperature stabilities, dielectric breakdown strength, and thermomechanical performances of the embedded materials are characterized. The experimental results show that the PCB embedded materials can withstand high temperature beyond 200 °C and a high voltage above 1.2 kV. T-g is as high as over 260 °C, and CTE is matching with SiC. Besides, in order to provide one guideline for the high-temperature and high-pressure laminating process during the PCB embedded SiC MOSFETs packaging, cure kinetics of BT prepreg are analyzed. The results show that 1-h curing time at 280 °C curing temperature and 2-h curing time at 210 °C curing temperature can ensure the full cure of the BT prepreg.

The transition from the conventional electrical power distribution system to ones that incorporate more stochastic electrical sources is resulting in a need for more robust and dynamic forms of power delivery. One solution to the various issues of power balancing and control is the utilization of additional frequencies within the distribution network. By having a greater variety of operational frequencies, the resulting decoupled power flow enables the system to have a higher degree of flexibility and functionality. This paper presents a controller for load-interfacing power electronic converters that operate within a system consisting of several ac frequencies as well as a superposed dc offset. The power exchange capabilities of this multifrequency converter, such as the decoupled power transfer between different operating frequencies are analyzed and demonstrated. Likewise, the underlying control structure is easily modifiable for a wide range of frequency combinations. The resulting increased level of active and reactive power control can then be utilized by the distribution network to ensure a more enhanced and stable transition to an electrically diverse and smarter microgrid. Simulation results for several different operating points are presented.

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.

This paper presents a medium frequency transformer with high insulation level design which is used for the DAB DC-DC converter. The transformer size is largely reduced when operating at medium frequency compared with conventional power frequency transformer which provides the possibility for higher power density. However, there is a trade-off between the high power density and thermal performance. First of all, the exposed cooling surface is reduced accordingly. And the dissipated heat is proportional to the exposed cooling surface directly. Secondly with higher frequencies, effects such as skin and proximity and hysteresis losses are significantly increased compared to transformer operation at 50/60 Hz. Besides the design process should consider high isolation requirement. And this again defects the transformer thermal performance and this is because firstly insulation material adds extra losses to the system, secondly the construction of the insulation will block some cooling surfaces and thirdly those insulation materials normally have relatively low thermal conductivity. As a consequence, the thermal design should be carefully considered and evaluated. To solve this problem, only the high voltage side winding is impregnated in epoxy resin which reduces the insulation material. The stacked transformer cores are gapped from each other which have helped the transformer heat dissipation. Such that, a design with low thermal resistance and high power density is achieved. FEM models are developed to analyze the transformer electric and thermal performances. Finally prototypes are built and tested to verify our design concept.

Medium voltage dc microgrids seeks to compete with conventional ac systems by providing various benefits regarding electrical power availability and efficiency. One method of achieving this goal is to provide a more effective and reliable interface to renewable energy sources and es pecially electrical storage devices. This paper presents a multilevel, cascaded converter topology that allows for the integration of various low voltage power sources and storage units into a single string of series connected half-bridge submodules. The resulting topology allows the system to function as medium-voltage dc voltage source. By implementing an additional, nestled current loop, guided by passive tuned filters, the converter controls the power flow between the submodules and the system, thus achieving power balance in all operating modes. This paper presents the underlying converter control principle for configurations containing electrical battery interfacing devices. Simulation and experimental results from a scaled prototype demonstrate the converters capabilities for a wide range of output power delivery.

In this work, an experimental study on the aluminum plate fin evaporator based on a compact two-phase cooling system for high heat flux electronic packages is presented. Single-chip and multi-chip wire-bonded thermal test vehicles (TTVs) were fabricated and assembled in the PCB grooves designed to emulate high heat flux sources. The issue of heat dissipation was addressed by applying the evaporator to the TTVs, respectively, to evaluate their thermal characteristics. It is found that, the evaporator system could dissipate over 380 W/cm² for the TTV1 while maintaining its temperature at about 90 °C. As the effective heat source area and thermal design power (TDP) increased, the maximum heat flux that the system could dissipate decreased given the same chip temperature rise. Furthermore, the addition of a second evaporator and heat source following the main evaporator, increased the dissipation of the system. As a result, an increase of 48 W/cm² in heat removal capacity was observed in our test system. Finally, the effect of the differential pressure between the condenser and the evaporator was investigated. The increase in the differential pressure could improve the heat dissipation capacity of the two-phase cooling system. The temperature of the TTV2 dropped by 19 °C when the differential pressure increased by 2.7 bar. It can be concluded that the compact two-phase cooling system is a promising solution for removing heat from high heat flux electric packages.

Vehicle ergonomics is one of the most important objectives for automotive applications. Reducing the size and weight is a prime concern for mobility. A novel unified converter with battery integration is proposed as an alternative to the existing power train configuration for hybrid electric vehicles. The power train has three phase PWM rectifier at the output of the alternator with battery connected to the neutral of the induction generator stator. With the proposed topology, vehicle size and weight can be reduced considerably. The topology is analysed for its control and performance specifications. Simulation studies are carried out in MATLAB/SIMULINK and results are presented.

Multiple pickup operation is a common scenario for IPT applications. In this scenario, constant current output is often required at the transmitter to avoid a complicated control method at the pickups. The LCL-T topology has been widely used to produce a constant output current for variable loads. This paper will present the analysis, simulation and test of a LCL-T resonant converter. The work here considers the load as a variable impedance comprising both a variable resistance and a variable inductance. The trade-off of LCL-T topology is discussed in the frequency domain to solve the off-resonant problem in a large load range. A 100W LCL-T resonant inverter operating at 50kHz is developed and the experimental results verify that the proposed method can reduce the reactive power required at partial load and ensure constant current output and ZVS in the whole load range.

The power electronic converter, especially the power semiconductor, is a major contributor to the failure rates of the wind turbine drivetrain. As the temperature is a major driving factor behind the failure mechanisms of these power semiconductors the choice of topology and switching strategy can have a significant effect on the reliability of the converter. This paper presents a detailed comparison of several three level converter topologies and switching strategies on the basis of loss distribution, thermal, and lifetime performance. This investigation is done through simulations on a 10MW direct drive permanent magnet drivetrain. The study shows that over-rating in the form of using overrated topologies, or the use of overrated components can result in large gains in lifetime expectancy and quantifies these gains. It concludes that the improvements offered by overrated topologies and overrated components are comparable and that use of the overrated topologies do not offer a significant advantage over the use of topologies with overrated components.

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.

Modularity is promising from a view to increasing turbine availability through fault tolerant operation as well as reduced downtimes, especially for offshore wind turbines. This paper focuses on a quantitative analysis of large scale (or extreme) modularity in power electronic converters of wind turbine generator systems. It uses mathematical models to investigate the effect of the choice of module number on the availability of a converter. It further analyses the availability in conditions where increased levels of modularity lead to a reduction of failure rates in the system. The paper extends this analysis by quantifying the benefits for a 10MW case study turbine. Finally, it concludes that extreme modularity holds merit only when it is accompanied by a reduction in failure rates.