High Power Applications Research Articles

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.

Achieving ultrahigh hole mobility in hydrogen-terminated diamond via boron nitride modifications

Wide-bandgap semiconductors with high carrier mobility are in great demand for high-power radio-frequency applications. In the past decades, extensive efforts have been devoted to investigating the carrier transport properties of hydrogen-terminated diamond (H-diamond), however, achieving its high hole mobility remains a challenge, thereby limiting the development of diamond electronic devices. Herein, we propose a novel strategy to increase the hole mobility of H-diamond by boron nitride (BN) clusters modifications. Amorphous BN clusters were deposited on high-quality H-diamond surfaces using magnetron sputtering. The modified H-diamond exhibits an ultrahigh hole mobility of 1100 cm2 V−1 s−1, over 10-fold higher than that of H-diamond prior to BN modification. Moreover, the BN-modified H-diamond also exhibits outstanding high-temperature tolerance and excellent thermal stability benefitting from the passivation effect of BN. At 380 K, it still maintains a hole mobility of 385 cm2 V−1 s−1. Even after annealing at 350 K for over 8 h, there are no noticeable variations in its carrier transport properties. The hole mobility enhancing mechanism and the factors influencing carrier transport properties of the BN-modified H-diamond are discussed using first principles calculations analysis. The developed BN-modified H-diamond opens up new possibilities for diamond-based radio-frequency electronic devices operating in challenging temperature environments.

Heterogeneous integration of thick GaN and polycrystalline diamond at room temperature through dynamic plasma polishing and surface-activated bonding

Direct heterogeneous integration of GaN on diamond enhances device performance and reliability for high-power applications, while the implementation on thick GaN films and polycrystalline diamond (p-diamond) substrates remains challenging. In this study, the direct bonding between thick GaN films (∼370 μm) and p-diamond substrates was achieved. A dynamic plasma polishing (DPP) technique was adopted on the diamond to flatten surficial spikes from maximum 15 nm to 1.2 nm, obtaining a smooth surface with 0.29 nm Ra, achieving a robust GaN/diamond bonding with high bonding rate of ∼92% at room temperature combining the surface-activated bonding (SAB) method. The chemical status, thermal stress, and interfacial microstructures of GaN/diamond heterostructures were analyzed, revealing a residual stress of ∼200 MPa at the GaN/diamond interface, and the asymmetric increase of interfacial stress at rising temperature demonstrates the effectiveness of amorphous interlayer to release the stress.

Efficient broad-band NIR-II emitting phosphor Mg4Ta2O9: Ni2+ with satisfactory thermal stability of luminescence

The applications of near-infrared (NIR) spectroscopy in the fields of medicine and food safety require efficient and compact NIR light sources, for example, NIR phosphor converted light-emitting diodes (pc-LEDs). In recent years, Ni2+ has become one of the main activators for its broadband NIR-II (1000–1700 nm) emission under ultraviolet or visible light excitation. However, two important effects (Concentration quenching which decreases the emission intensity and temperature quenching which decreases the adaptability of phosphor in high-power applications) seriously hinder the development of Ni2+ doped NIR-II emitting phosphors. It is an urgent and important task to restrain both concentration and thermal quenching of the Ni2+ luminescence to develop an efficient NIR-II emitting phosphor. Here, novel NIR-II emitting Mg4Ta2O9: Ni2+ phosphors with perovskite-like structure were synthesized and investigated. In Mg4Ta2O9, the quenching concentration of Ni2+ is as high as 0.045. This is a relatively high value for Ni2+ activated NIR-II emitting phosphors. Mg4Ta2O9: 0.045Ni2+ presents broadband emission (1100–1700 nm, the full width at half maximum (FWHM) = 218 nm) with internal and external quantum efficiency of 64.2% (IQE) and 7.2% (EQE), respectively. The phosphor exhibits excellent luminous thermal stability (at 423 K, it keeps 84.85% of initial intensity at room temperature). High structure stiffness of Mg4Ta2O9 is responsible for the high quenching concentration and desirable luminous thermal stability. This work developed an efficient NIR-II emitting phosphor which exhibits desirable thermal stability of luminescence. Theoretically, this work points out a direction for future development of efficient NIR-II emitting phosphors, selecting an inorganic compound with high structural rigidity as the host for Ni2+ doping.

An Overview of BMS Technologies in Electric Vehicles

Batteries are used extensively in high-power applications, including hybrid and electric vehicles (EVs), where the proper battery management system (BMS) is essential to the batteries' dependable and safe performance. The purpose of this study is to provide a quick overview of several important BMS technologies, such as battery charging, state estimation, and battery modelling. The most common battery types utilized in EVs are first examined, and then important BMS technologies are introduced. The most crucial step in determining the energetic range of an EV is the valuation of the electrical properties of batteries. It’s vital to apprehend the variability of battery performance characteristics in order to understand battery behavior in several environments. Finally, the performance characteristics of EV charging and batteries are analyzed to raise the demand for electric vehicles globally.

Unlocking superior safety, rate capability, and low-temperature performances in LiFePO4 power batteries

The safety concerns associated with lithium-ion batteries (LIBs) have sparked renewed interest in lithium iron phosphate (LiFePO4) batteries. It is noteworthy that commercially used ester-based electrolytes, although widely adopted, are flammable and fail to fully exploit the high safety potential of LiFePO4. Additionally, the slow Li+ ion diffusion and low electronic conductivity of LiFePO4 batteries limit their utility in high-power applications. Despite the crucial role played by liquid electrolytes in LIBs, achieving simultaneous improvements in safety, rate capability, and low-temperature performance remains a formidable challenge. In this study, we addressed these challenges by innovatively applying a single solvent ethyl vinyl sulfone (EVS) electrolyte to graphite/LiFePO4 batteries. While renowned for its broad electrochemical window, low freezing point and superior safety performance, the EVS electrolyte exhibited compatibility issues with the graphite anode. To overcome this hurdle effectively, we utilized vinylene carbonate as an additive with lower reductive reactivity than EVS to modify the interphase formed by EVS successfully. Simultaneously, the EVS-based electrolyte was found to create a sulfone-rich interphase on the LiFePO4 cathode surface, significantly enhancing Li+ ion diffusion both across the interphase and within the material. These modifications culminated in a conspicuous improvement in the performance of graphite/LiFePO4 batteries. Our study illuminates the potential of EVS-based electrolytes in boosting the rate capability, low-temperature performance, and safety of LiFePO4 power lithium-ion batteries. It yields valuable insights for the design of safer, high-output, and durable LiFePO4 power batteries, marking an important stride in battery technology research.

Design and characterization of cell topology effect on SiC VDMOSFETs for high power and frequency applications

In this paper, we present a comprehensive investigation of the impact of cell topology and pitch reduction on the DC and AC characteristics of 1200V-rated 4H-SiC planar VDMOSFETs. We have designed and fabricated four different cell topologies, namely linear, square, hexagonal, and staggered cell, in order to characterize their performance. Among the various cell types, the hexagonal cell exhibits the most favorable specific on-state resistance (Ron,sp) value. However, it is worth noting that the breakdown values of both the hexagonal and staggered square cells fall significantly below the simulated values. This is attributed to the interaction between the irregular cell boundaries and the edge cell termination region. Furthermore, we observed that the linear cell has the highest gate resistance compared to the other cell types. Additionally, the linear cell also demonstrates a lower input capacitance than the other cells. This can be attributed to its longer gate trasmission line and smaller area. Lastly, we performed dynamic double pulse tests on the fabricated VDMOSFETs to compare their switching characteristics. It was concluded that linear cell VDMOS is suitable for high switching applications, while square, hexagonal and S.S cell VDMOS are better suited for lower switching applications that require a high output current.

Dual Volts-per-Hertz Control of Double-Inverter-Fed Wound Rotor Induction Machine

Double-inverter-fed wound rotor induction machine (DI-WRIM) is a two-port machine capable of maintaining rated torque even at twice the rated speed. Such machines are gaining popularity in high-speed and high-power applications for their versatility and degrees of freedom in control. The existing control methods for DI-WRIM are all based on the dynamic model of the machine and the associated controller structures are complex with multiple controllers. This article proposes a novel control scheme for DI-WRIM based on the steady-state model which requires only one controller. The proposed control scheme has the capability to operate the machine in both sub and super-synchronous modes in all the four quadrants in torque-speed plane. The simplicity of the proposed dual volts-per-hertz control method can be compared to the very popular scalar control used in cage-rotor induction machine drives. Mathematical derivation of the control law with appropriate approximations is discussed. Experimental results are presented from a 5-hp, 8-pole wound rotor induction machine drive.

Study of lithium transport in Li2O component of the solid electrolyte interphase in lithium-ion batteries

In lithium-ion batteries (LIBs), as a promising energy storage device, materials with fast lithium (Li) transport are required for high-power applications such as electric vehicles. Thus, a deeper understanding of Li transport in components of LIBs is crucial for improving their rate capability. In this study, the Li transport in lithium oxide (Li2O), as one of the key components of the solid electrolyte interphase (SEI) layer, was examined by a multiscale computational approach ranging from density functional theory (DFT) to Monte Carlo simulations. The DFT calculations were used to investigate the recombination of Frenkel pairs, their first-principles total energies, and the Li diffusion mechanisms. The effect of atomic configurations on both first-principles total energies and diffusion barrier energies was formulated by periodic and local cluster expansions. These formalisms were then incorporated into the Monte Carlo and Kinetic Monte Carlo (KMC) simulations to calculate the diffusion coefficient of Li. Our calculations revealed that the vacancy-mediated jump along the 〈100〉 direction in the antifluorite structure of Li2O possesses the lowest barrier energy compared to other diffusion mechanisms. The KMC simulations indicated that the diffusion coefficient of Li better converged with the direct experimental measurement when the recombination of Frenkel pairs was integrated into the simulations. At a temperature of 300 K, the KMC simulation yielded a Li diffusion coefficient of 3.8×10-12cm2/s in Li2O. This is only one order of magnitude larger than indirect experimental measurement, suggesting the accuracy of our formalism. Thus, our formalism for studying Li transport in Li2O will pave the path to a rational design of inorganic SEI in the future development of LIBs.