High Power Applications Research Articles

Digital Close-Loop Active Gate Driver for Static and Dynamic Current Sharing of Paralleled SiC MOSFETs

SiC power devices have been extensively for the high-power density application scenarios. To increase the current rating, SiC devices are usually connected in parallel. However, the mismatching current brought by unbalanced electrical parameters can increase the current stress of a device and pose reliability concern of the converter system. Aiming at addressing the current imbalance for paralleled SiC devices, this paper reports the application of an improved active gate driver (AGD) on the paralleled SiC MOSFETs to address the current imbalance problems. The three-level driver voltage can minimize the overshoot voltage and current. The adjustable turn-on voltage and gate signal delay time can realize the current sharing of both static and dynamic process. Current sensors and a digital controller are utilized for close-loop control. The functionality of the proposed AGD is validated in continuous operating experiment.

Reduction of off-state drain current in AlN/[formula omitted] HEMT by trap state engineering

In this work, we report various strategies to reduce the off-state drain leakage current (IOFF) in AlN/β−Ga2O3 high electron mobility transistor (HEMT) by 2D device simulation. We have investigated the effect of access region, channel doping concentration, barrier layer thickness, and trap state engineering on IOFF. The formation of a parallel channel deep into the substrate has been found to be responsible for large IOFF. All other strategies except trap state engineering have an incremental effect on IOFF. However, the device’s IOFF was reduced by around 12 orders of magnitude by trap-state engineering. Simultaneously, the on-state performance was unaffected, resulting in an elevated ION/IOFF current ratio of (1013). A steep subthreshold slope of 0.267 (V/dec) was also obtained. Further, we have investigated the impact of both donor- and acceptor-type traps on subthreshold characteristics. These promising results highlight the potential of AlN/β−Ga2O3 HEMT as a switch and for future high-power nanoelectronics applications.

Enhancing the piezoelectric properties and thermal stability of PMN-PMS-PSZT high-power piezoelectric ceramics through defect engineering

The development of high-power piezoelectric ceramics with superior piezoelectric properties and broad temperature usage ranges is vital for the thriving progress of electromechanical applications. However, achieving high piezoelectricity, high mechanical quality factor, and temperature stability often presents a trade-off. In this study, we present an advanced ceramic material with excellent high-power piezoelectric properties and superior temperature stability. The piezoelectric coefficient d33 reaches 348 pC N−1, the electromechanical coupling factor kp is 54%, the mechanical quality factor Qm is 1501, the dielectric loss tanδ is 0.35%, and the d33 variation is less than 10% within 25–210 °C in 0.05Pb(Mg1/3Nb2/3)O3-0.05Pb(Mn1/3Sb2/3)O3-0.9Pb0.95Sr0.05(Zr0.48Ti0.52)O3 ceramic. The excellent piezoelectricity is attributed to the enhancement of intrinsic ionic displacement and reversible domains wall motion because of symmetry-conforming short-range distribution of oxygen vacancy, while the high Qm is a result of increased domain size and oxygen vacancy. The outstanding temperature stability is related to the stable non-180°domains structure due to the oxygen vacancy pinning effect. These properties hold great potential for advanced applications, particularly for piezoelectric high-power applications requiring constant d33 over a broad temperature range.

Three-Level DC-DC Boost Converter for Wind Energy Conversion

In recent years, advancements in power converter technology for wind energy conversion systems have aimed to enhance power output, increase reliability, and improve overall efficiency. However, achieving a fixed and high-power DC output remains a challenge. This study explores three modes of operation for a DC-DC boost converter to enhance fixed DC output, essential for various applications like battery charging and electronics. The research categorizes DC system topologies based on factors such as setup complexity, cost-effectiveness, and performance metrics. It proposes a DC/DC conversion approach that offers cost-effectiveness and efficiency, aiming to set a new standard in topology for future converters. The study addresses key challenges in the efficiency of the step-up process of DC/DC converters, focusing on parameter design, operational principles, and control strategies. Simulation results confirm the effectiveness of the suggested approach, emphasizing its future potential for non-isolated high step-up DC/DC converters. Reduced device voltage stress and increased efficiency represent the two advantages of the suggested three-level DC-DC boost converter, which combines a standard boost converter with a switched capacitor function to supply three capacitors in series. Simulation results demonstrate the converter’s effectiveness in a wind energy conversion system, showcasing its potential for high-power applications.

Novel Series-Parallel Phase-Shifted Full-Bridge Converters with Auxiliary LC Networks to Achieve Wide Lagging-Leg ZVS Range

Under light load conditions, the phase-shifted full-bridge (PSFB) converter often has difficulty in realizing the zero-voltage switching (ZVS) of the lagging-leg by relying on the energy of its resonant inductor; however, for the series-parallel PSFB converter applied in high-power applications, the lagging-leg still has the problem of difficult realization of ZVS. Based on this, the paper analyzes the reasons why the series-parallel PSFB converter has difficulty in achieving ZVS for the lagging-leg under light and heavy loads. Under interleaved control, the ZVS of the lagging-leg over the full load range is realized by adding an auxiliary LC branch at the midpoint of the lagging-leg of both submodules. Based on the double-bridge input-parallel-output-series (IPOS) PSFB converter, analyzing the working principle of the circuit after adding the auxiliary LC branch and extending it to the series-parallel PSFB converter. The design requirements of the LC auxiliary branch of the dual-bridge series-parallel PSFB converter are given and the effects of the LC auxiliary branch on the module operating state and device stress are analyzed. On this basis, an extension is carried out to give the working principle and design method of the auxiliary LC branch of the N-bridge series-parallel PSFB converter. Finally, a 100 kW Matlab/Simulink simulation model verifies the superior performance of the proposed LC auxiliary branch to realize the lagging-leg ZVS of the series-parallel PSFB converter under light and heavy loads and achieves a 1.09% peak efficiency improvement at rated load.

A Comparative Study of 9-Level Inverter and 15-Level Multi Inverter for a Grid Connected System

Abstract: Recently, the emergence of single phase multilevel inverter has been increased due to its advantages over traditional one. Multilevel Inverters [MLI] are the ones which can give out a stepwise output waveform with the use of power electronic switches, power diodes and some DC voltage source which might be a series/parallel connected PV cells, a renewable source or a battery. Multilevel inverters not only produce low harmonic distortion but also decrease the dv/dt stresses on the equipment Multilevel inverters is a good option as the output voltage of a Multilevel inverter is a stepped waveform which approaches a sinusoid providing lesser harmonic distortion. As the number of levels are increased the harmonic distortion reduces but at the same time the number of switching devices and the DC voltage sources required increases, thus increasing the complexity of the system design and control. Multilevel inverter proposed in this paper uses only 7 switches to provide 9 levels and 15 levels of output voltage. A symmetrical Cascaded H bridge Multi level inverter (SCHBMLI) and Asymmetrical Cascaded H bridge Multilevel Inverter (ASCHBMLI) using PD-PWM technique have been analysed in this paper for grid connection. The Asymmetric Cascade H Bridge [ASCHMLI] implemented in real time system using PIC16F877A microcontroller with RL load. This type of proposed system is used for high power applications in photovoltaic and it’s reduce overall cost as well as size of the system.

Dual-modified LiNi0.8Co0.1Mn0.1O2 cathode materials with lithium conducting hybrid oligomer and single-walled carbon nanotube for improving electrochemical performance and thermal stability of lithium-ion batteries: A novel approach for high-power and high-safety applications

In this study, we investigated the synergetic effect of a novel lithium-ion conducting hybrid oligomer [N, N′-bismaleimide-4, 4′-diphenylmethane (BMI), lithiated trithiocyanuric acid (Li-TCA) and Jeffamine®-M1000 (JA®); Li-BTJ] coating layer on a nickel-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode material wrapped with highly electron-conductive single-walled carbon nanotubes (SWCNTs) to enhance electrochemical performance and thermal stability for high-power and high-safety lithium-ion batteries (LIBs). Morphological analyses using scanning electron microscopy/energy dispersive spectroscopy and transmission electron microscopy showed that the NCM811 active material surface was uniformly coated with a hybrid oligomer to form NCM811@Li-BTJ, which was subsequently wrapped with SWCNTs (NCM@Li-BTJ/SWCNT composite cathode). CR2032 coin-type cells with optimized NCM811@1 wt% Li-BTJ/0.2 wt% SWCNT composite electrodes delivered a significantly enhanced capacity retention (CR) of 90.1 % relative to that of bare NCM811 electrodes (CR: 82.1 %) at 1C for 200 cycles from 2.8 to 4.3 V (vs. Li/Li+). Electrochemical impedance spectroscopy and cyclic voltammetry revealed that this superior cycling performance resulted from a lower charge transfer resistance (Rct: 96.2 vs. 324.3 Ω) and a lower polarization voltage (∆V: 0.243 vs. 0.411 V vs. Li/Li+). The in-situ micro-calorimetric results presented the total heat generation (Qt) values of the coin cells with the delithiated NCM811@Li-BTJ and NCM@Li-BTJ/SWCNT electrodes at 5C and 35 °C were substantially lower by ~9.3 % and ~ 14.6 %, respectively, compared to the bare NCM811 counterpart, indicating that the surface modifications on the NCM811 active materials could prevent the LIBs' thermal instability. Furthermore, X-ray photoelectron spectroscopy studies revealed that the Li-BTJ hybrid oligomer coating layer effectively suppressed the formation of residual Li side products such as Li2CO3 evidently on the surface of the NCM811 active material particles, thereby inhibiting undesirable side reactions. Post-mortem analyses of the dual-modified NCM811 electrode after cycling revealed that the microstructure and particle morphology of the NCM composite cathode material were extensively maintained through the synergistic effects of the Li-BTJ ion-conductive and SWCNTs electron-conductive agents.

A Low-Reflection Tuning Strategy for Three-Stub Waveguides

In high-power microwave applications, the reflection of energy can be effectively reduced by adjusting the three-stub waveguide. However, most of the existing tuning algorithms do not make an arrangement for the adjustment sequence of stubs, and accurately calculating the depth of the stubs requires a great deal of time via electromagnetic (EM) simulations, which may cause large reflection in the matching process. To solve these problems, we first propose an improved calculation method that can accurately calculate the input impedance of a three-stub waveguide. Then, an impedance matching algorithm is designed based on the equivalent circuit model that can quickly and accurately calculate the optimal depth of the stubs. Finally, we present a low-reflection tuning strategy to suppress the large reflection during the adjustment of the stub process. An experimental system is built to verify the calculation method and the tuning strategy. The results show that the strategy can avoid large reflection in the case of load mutation and can maintain low reflection when the load changes continuously. The algorithm meets the needs of the industry and can be used for automatic and real-time adjustment of three-stub waveguides of different specifications.

Physician's autonomy in the face of AI support: walking the ethical tightrope.

The introduction of AI support tools raises questions about the normative orientation of medical practice and the need to rethink its basic concepts. One of these concepts that is central to the discussion is the physician’s autonomy and its appropriateness in the face of high-powered AI applications. In this essay, a differentiation of the physician’s autonomy is made on the basis of a conceptual analysis. It is argued that the physician’s decision-making autonomy is a purposeful autonomy. The physician’s decision-making autonomy is fundamentally anchored in the medical ethos for the purpose to promote the patient’s health and well-being and to prevent him or her from harm. It follows from this purposefulness that the physician’s autonomy is not to be protected for its own sake, but only insofar as it serves this end better than alternative means. We argue that today, given existing limitations of AI support tools, physicians still need physician’s decision-making autonomy. For the possibility of physicians to exercise decision-making autonomy in the face of AI support, we elaborate three conditions: (1) sufficient information about AI support and its statements, (2) sufficient competencies to integrate AI statements into clinical decision-making, and (3) a context of voluntariness that allows, in justified cases, deviations from AI support. If the physician should fulfill his or her moral obligation to promote the health and well-being of the patient, then the use of AI should be designed in such a way that it promotes or at least maintains the physician’s decision-making autonomy.

Computational study and ion diffusion analyses of native defects and indium alloying in β-Ga2O3 structures

Wide band gap semiconductors like gallium oxide are promising materials for high-power optoelectronic device applications. We show here a combined density functional theory and molecular dynamics study of diffusion pathways for different defects in β-Ga2O3. Molecular dynamics simulations result in a smaller equilibrium volume compared to density functional theory, but the overall lattice remains relatively unchanged even with the inclusion of defects, outside of the local distortions that occur to accommodate the presence of a defect. Slight thermal expansion occurs with elevated temperature and a combination of electron localization function and Bader charge analysis reveals that the oxygen interstitial is the most mobile defect as temperature is increased. However, interstitial cations may diffuse at elevated temperature due to a relatively small amount of charge transfer between the defect and lattice. The mobile oxygen defects are shown to increase the mobility of oxygen ions from the lattice, which can be beneficial for electrochemical applications when controlled through annealing processes.

Effect of Anisotropy of Reduced Graphene Oxide on Thermal and Electrical Properties in Silicon Carbide Matrix Composites.

Reduced graphene oxide, due to its structure, exhibits anisotropic properties, which are particularly evident in electrical and thermal conductivity. This study focuses on examining the influence of reduced graphene oxide in silicon carbide on these properties in directions perpendicular and parallel to the direction of the aligned rGO flakes in produced composites. Reduced graphene oxide is characterized by very high in-plane thermal and electrical conductivity. It was observed that the addition of rGO increases thermal conductivity from 64 W/mK (reference sample) up to 98 W/mK for a SiC-3 wt.% rGO composite in the direction parallel to the rGO flakes. In the perpendicular direction, the values were slightly lower, reaching up to 84 W/mK. The difference observed in electrical conductivity values is more significant and is 1-2 orders of magnitude higher for the flakes' alignment direction. The measured electrical conductivity increased from 1.2710-8 S/m for the reference SiC sinter up to 1.55 × 10-5 S/m and 1.2410-4 S/m for the composites with 3 wt.% rGO for the perpendicular and parallel directions, respectively. This represents an enhancement of four orders of magnitude, with a clearly visible influence of the anisotropy of the rGO. The composite's enhanced electrical and thermal conductivity make it particularly attractive for electronic devices and high-power applications.

A Novel Supercapacitor Model Parameters Identification Method Using Metaheuristic Gradient-Based Optimization Algorithms

This paper addresses the critical role of supercapacitors as energy storage systems with a specific focus on their modeling and identification. The lack of a standardized and efficient method for identifying supercapacitor parameters has a definite effect on widespread adoption of supercapacitors, especially in high-power density applications like electric vehicle regenerative braking. The study focuses on parameterizing the Zubieta model for supercapacitors, which involves identifying seven parameters using a hybrid metaheuristic gradient-based optimization (MGBO) approach. The effectiveness of the MGBO method is compared to the existing particle swarm optimization (PSO) and to the following algorithms proposed and developed in this work: ‘modified MGBO’ (M-MGBO) and two PSO variations—one combining PSO and M-MGBO and the other incorporating a local escaping operator (LCEO) with PSO. Metaheuristic- and gradient-based algorithms are both affected by problems associated with locally optimal results and with issues related to enforcing constraints/boundaries on solution values. This work develops the above-mentioned innovations to the MGBO and PSO algorithms for addressing such issues. Rigorous experimentation considering various types of input excitation provides results indicating that hybrid PSO-MGBO and PSO-LCEO outperform traditional PSO, showing improvements of 51% and 94%, respectively, while remaining comparable to M-MGBO. These hybrid approaches effectively estimate Zubieta model parameters. The findings highlight the potential of hybrid optimization strategies in enhancing precision and effectiveness in supercapacitor model parameterization.

Relative contribution of contact force to lesion depth using high-power short-duration radiofrequency applications

Relative contribution of contact force to lesion depth using high-power short-duration radiofrequency applications

Design and Optimisation of a 5 MW Permanent Magnet Vernier Motor for Podded Ship Propulsion

The evolution of electric propulsion systems in the maritime sector has been influenced significantly by technological advancements in power electronics and machine design. Traditionally, these systems have employed surface-mounted permanent magnet synchronous motors (PMSMs) in podded configurations. However, the advent of permanent magnet Vernier motors (PMVMs), which leverage magnetic gearing effects, presents a novel approach with promising potential. This study conducts a comparative analysis between PMVMs and conventional PMSMs at a power level of 5 MW for podded ship propulsion, with a particular focus on the impact of gear ratios (Gr). An objective function was developed that integrates motor dimension constraints and the power factor (PF), a critical yet frequently neglected parameter in existing research. The findings indicate that PMVMs with lower Gr have lower mass and cost compared to those with higher Gr and traditional PMSMs, at a PF level of 0.7, which is high for Vernier machines. Moreover, PMVMs with lower Gr achieve efficiencies exceeding 99%, outperforming both their higher Gr counterparts and conventional PMSMs. The superior performance of PMVMs is attributed to lower current density and reduced copper loss, which contribute to their enhanced thermal performance. These details are elaborated on further in the paper. Consequently, these findings suggest that PMVMs with lower Gr are particularly well suited for high-power maritime propulsion applications, offering advantages in terms of compactness, efficiency (EF), cost-effectiveness, and thermal performance.

Tin dioxide coated rice husk silica as lead-acid battery positive additive for enhancing the performance under power-intensive applications

Lead-acid batteries rapidly response to instantaneous high-current, rendering them particularly effective for high-power applications, including power traction batteries, starter batteries, and start-stop systems. However, issues arise during intense working rate (6–10C), causing significant polarization that leads to severe oxygen evolution side reactions and softening and shedding of positive active material (PAM), limiting the battery's cycle life. This study introduces a tin dioxide (SnO2) coated rice husk silica (RH-SiO2) composite as an positive additive in lead-acid batteries. The composite (SnO2/RH-SiO2) has a hierarchical pore structure from RH-SiO2, provides a robust conductive framework. The lattice structure of the SnO2 is similar to that of PbO2, while induces the formation of a PbSnO3 intermediate phase during formation process. SnO2/RH-SiO2 can also accelerates lead dioxide deposition and improves the interphase conversion efficiency, while significantly enhances the transformation of α- and β-PbO2, leading to a 20.7% increase in discharge specific capacity. Compared to a standard battery, up to 3.7 times longer at 100% deep discharge cycle life and 4.7 times longer in start-stop-mode testing. In our finding the SnO2/RH-SiO2 composite serves as a highly effective additive for augmenting the performance and longevity of lead-acid batteries in high-power applications, presenting a significant advancement in battery technology.

Revolutionizing Fe doped back barrier AlGaN/GaN HEMTs: Unveiling the remarkable 1700V breakdown voltage milestone

This research investigates the enhanced device breakdown capabilities of silicon-based AlGaN/GaN High Electron Mobility Transistors (HEMT). By incorporating various back barrier materials, a significant improvement in peak electric field and breakdown voltage is observed. Specifically, the integration of iron (Fe) doping into the Gallium Nitride (GaN) back barrier layer, combined with different back barrier materials such as Aluminum Gallium Nitride (AlGaN) and Indium Gallium Nitride (InGaN), results in an impressive increase of up to 1700 V. This improvement is attributed to the reduction of peak electric field at the gate edge. The optimized layer configurations significantly contribute to the overall performance of silicon substrate GaN HEMT devices, making them promising candidates for high-voltage applications in electric vehicles and high-power applications.

Growth optimization, optical, and dielectric properties of heteroepitaxially grown ultrawide-bandgap ZnGa2O4 (111) thin film

Ultrawide bandgap ZnGa2O4 (ZGO) thin films were grown on sapphire (0001) substrates at various growth temperatures with a perspective to investigate the electrical and optical characteristics required for high-power electronic applications. Due to the variation in the vapor pressure of Zn and Ga, severe loss of Zn was observed during pulsed laser deposition, which was solved by using a zinc-rich Zn0.98Ga0.02O target. A pure phase single-crystalline ZGO thin film was obtained at a deposition temperature of 750 °C and an oxygen pressure of 1 × 10−2 Torr. The out-of-plane epitaxial relationship between the sapphire and ZGO thin film was obtained from φ-scan. The x-ray rocking curve of the ZGO thin film grown at 750 °C exhibits a full width at half maximum of ∼0.098°, which indicates a good crystalline phase and quality of the thin film. Core-level x-ray photoelectron spectroscopy of ZGO grown at 750 °C indicated that Zn and Ga were in the 2+ and 3+ oxidation states, respectively, and the atomic ratio of Zn/Ga was estimated to be ∼0.48 from the fitted values of Zn-2p3/2 and Ga-2p3/2. The high-resolution transmission electron microscopy images revealed a sharp interface with the thickness of the ZGO film of ∼265 nm, and the signature of minor secondary phases was observed. The bandgap of the ZGO film at different growth temperatures was calculated from the ultraviolet-diffuse reflectance spectroscopy spectra, and its value was obtained to be ∼5.08 eV for the 750 °C grown sample. The refractive index (n) and the extinction coefficient (k) were determined to be ∼1.94 and 0.023 from the ellipsometric data, respectively, and the real dielectric function (ɛr) was estimated to be ∼6.8 at energy 5 eV. The ultrawide bandgap and dielectric function of ZGO recommend its possible potential applications in deep-ultraviolet optoelectronic devices and high-power electronics.

Nanoscale structural heterogeneity enhanced temperature-stable energy storage in Bi0.5Na0.5TiO3-based relaxor ceramics via domain and defect dipoles engineering

Ceramic-based dielectric capacitors are showing great potential in advanced high-power applications. However, simultaneous achievement of high energy density (Wrec) and temperature stability is still a main bottleneck. Herein, an extraordinary nanoscale structural heterogeneity is developed to promote temperature-stable energy storage in Er/Mn co-doped Bi0.5Na0.5TiO3 based ceramics via domain and defect dipoles engineering. The composition-driven domain reconstruction by Er/Mn co-doping can induce internal random fields with rapid response to the electric field, and thus enhance ΔP and η. Meanwhile, the donor-accpetor Er/Mn doping could manipulate defect dipoles coupling to resist the applied field evolution to elevate BDS and η. Besides, the improved relaxor feature and core-shell structure give rise to the enhanced temperature stability. Ceramics with 2 mol % Er2O3 demonstrate high Wrec ∼2.79 J/cm3, large efficiency ∼89.4% and outstanding dielectric stability within 70–500 °C. The proposed nanostructural heterogeneity was verified as a promising pathway to manufact temperature-stable energy storage ceramics.

A current sharing snubber of parallel IGBTs based on duality principle

Parallel connection of multiple insulated gate bipolar transistors (IGBTs) is an important approach to improve the current level of equipment in applications of power electronics. The key to ensure the safe and stable operation of parallel IGBTs is to realize current sharing for them. A novel current sharing snubber of parallel IGBTs is proposed for high-power applications, which is derived from a voltage sharing snubber of series IGBTs by duality principle. It not only effectively suppresses the overcurrent and static and dynamic current imbalance, but also possesses advantages of simple structure and easy implementation. The operating principle and deficiencies of the proposed snubber are first analyzed, and then the improved topology is presented. In order to apply the snubber to multiple IGBTs, various topologies and their derivation processes are given. The improvements are carried out and suitable structures are determined by analysis and comparison. In addition, the effectiveness and feasibility of the proposed snubber are verified by experiments. Finally, the proposed snubber is compared with other current sharing methods.

Photoluminescence properties of double perovskite Ca2LuTaO6:Bi3+/Sm3+ white light emitting phosphors

The high-temperature solid state reaction approach was used to successfully synthesize novel tunable-color emitting Ca2LuTaO6 phosphors with double perovskite structure that were un-doped, single-doped, and co-doped with Bi3+/Sm3+ ions. The crystal structure, microstructure, steady-state photoluminescence, time-resolved luminescence measurements, and thermal quenching features of the material were studied. The density functional theory method was used to compute the band gap of the Ca2LuTaO6, and Ca2LuTaO6: Bi3+, Sm3+ phosphors. The blue emission at 407 nm (with 313 nm excitation) is due to the host's luminescence, while the cyan emission at 480 nm (under 365 nm excitation) is related to the distinctive 3Pn − 1S0 transitions (n = 0, 1, 2) of Bi3+. Similarly, efficient red emission is observed in the case of Sm3+ single-doped Ca2LuTaO6 phosphors. In addition, the Ca2LuTaO6: 0.04Bi3+, 0.05 S m3+ phosphors exhibit energy transfer phenomena and have excellent thermal stability, the fluorescence intensity at 150 °C maintains 73% of that at 25 °C and has a small chromaticity shift. The intense blue emission at 407 nm was effectively converted to cyan, red, and white light through doping with Bi3+ and Sm3+, and the resulting energy transfer. The results obtained confirm that Ca2LuTaO6: Bi3+, Sm3+ phosphors as a single matrix have great potential for high-power WLED applications.