Conduction Mode Research Articles

New single-switch buck–boost converter with continuous input/output currents and a wide conversion range

The main aim of this paper is to introduce a new high step-up/down buck-boost converter with a minimum number of switches which provides the benefit of having the continuity of the input/output current. This single-switch semi-quadratic converter is suitable for high step-up applications while being able to provide step-down voltage gains. Also, by applying some minor changes to the circuit elements, another single-switch buck-boost converter is suggested which has two operative outputs with different voltage gains. One of the outputs of this topology has quadratic buck-boost converter voltage gain which is appropriate for high step-up/step-down applications. The other output could vary from input voltage to minus infinity, ideally. After studying the steady-state operation of the proposed converters in Continuous Conduction Mode (C.C.M), the simulation results are presented. In addition, a comparison among related converters proposed in the literature is made. Finally, experimental results are evaluated by implementing a laboratory prototype of the proposed converter in both step-down and step-up modes. Theoretical, simulation, and experimental results are compatible with each other.

Femtosecond trimer quench in the unconventional charge-density-wave material 1T′−TaTe2

Ultrafast optical switching of materials properties promises future technological applications, enabled by fundamental insights about microscopic couplings and nonequilibrium phenomena. Transition-metal dichalcogenides (TMDCs) combine photosensitivity with strong correlations, furthering rich phase diagrams and enhanced tunability. The compound 1T′−TaTe2 exhibits an electronically and structurally unique set of charge density waves (CDWs), featuring an unusual increase in conductivity and amplitude modes of low prominence. Compared to other charge-ordered TMDCs, only very few studies addressed the ultrafast response of this material to optical excitation. In particular, the question whether such unconventional properties translate to unusual quench dynamics remains largely unresolved. Here, we investigate the structural dynamics in 1T′−TaTe2 by means of ultrafast nanobeam electron diffraction at an unprecedented repetition rate of 2MHz. We reveal a strongly directional cooperative atomic motion during the one-dimensional quench of the low-temperature trimer lattice. These dynamics are completed within less than 500fs, substantially faster than reported previously. In striking contrast, the periodic lattice distortion of the room-temperature phase is unusually robust against high-density electronic excitation. In conjunction with the known sensitivity of 1T′−TaTe2 to chemical doping, we thus expect the material to serve as a versatile platform for tunable structural control by optical stimuli. Published by the American Physical Society 2024

Membrane Activity and Viroporin Assembly for the SARS-CoV-2 E Protein Are Regulated by Cholesterol.

The SARS-CoV-2 E protein is an enigmatic viral structural protein with reported viroporin activity associated with the acute respiratory symptoms of COVID-19, as well as the ability to deform cell membranes for viral budding. Like many viroporins, the E protein is thought to oligomerize with a well-defined stoichiometry. However, attempts to determine the structure of the protein complex have yielded inconclusive results, suggesting several possible oligomers, ranging from dimers to pentamers. Here, we combined patch-clamp, confocal fluorescence microscopy on giant unilamellar vesicles, and atomic force microscopy to show that E protein can exhibit two modes of membrane activity depending on membrane lipid composition. In the absence or the presence of a low content of cholesterol, the protein forms short-living transient pores, which are seen as semi-transmembrane defects in a membrane by atomic force microscopy. Approximately 30 mol% cholesterol is a threshold for the transition to the second mode of conductance, which could be a stable pentameric channel penetrating the entire lipid bilayer. Therefore, the E-protein has at least two different types of activity on membrane permeabilization, which are regulated by the amount of cholesterol in the membrane lipid composition and could be associated with different types of protein oligomers.

Hysteresis-Free Temperature Sensing with Printable Electronic Skins Made of Liquid Polyisoprene/CNTs.

Developing an electronic skin (e-skin) is becoming popular due to its capability to mimic human skin's ability to detect various stimuli. Mostly, such skins are tactile-based sensors. However, the exploration of nontactile-based sensing capability in the e-skin is still in a nascent stage. Herein, we report an approach toward developing electrical hysteresis- and cross-interference-free nontactile e-skin using liquid polyisoprene with an ultralow concentration of multiwalled carbon nanotubes (ϕ = 0.006 volume fraction) by leveraging the stencil printing technique. The impact of cross-linking the samples was studied. Uncross-linked samples demonstrated higher electrical conductivity than the cross-linked samples. A coarse-grained phenomenological model with molecular dynamics simulation was utilized to investigate filler network formation and percolation that dictate the conductivity of uncross-linked and cross-linked samples. Simulation studies supported the fidelity of the experimental findings. The uncross-linked e-skin demonstrated a higher temperature sensitivity (-1.103%/°C) than the cross-linked e-skin (-0.320%/°C) in the thermal conduction mode. Despite the superior sensitivity of the uncross-linked e-skin, the cross-linked systems demonstrated superior cyclic stability (35 thermal cycles), ensuring reliable sensor readings over extended usage. Judicious choice of encapsulant warranted the cross-linked e-skin sensor to nullify the impact of moisture on signal output, thereby providing cross-interference-free results. The optimized e-skin sample retained a similar thermal sensitivity even when used in the nontactile mode. From the application purview, the utility of the developed sensor was tested successfully for nontactile sensing of human body temperature. Additionally, the sensor was utilized to determine the respiratory profile by integrating the developed sensor into a wearable mask. This study advances nontactile e-skin-based sensing technology and opens new avenues for creating wearable and IoT devices for healthcare and human-machine interactions.

Efficient power factor correction in single phase AC–DC boost converter for retrofitted electric bicycle battery charging: A finite element analysis approach

This research paper describes modifying a conventional bicycle into an electric bike by retrofitting it with a single-phase boost power factor correction (PFC) rectifier for low power battery chargers. The proposed work was designed and developed in a single stage, as opposed to the traditional two-stage chargers used to charge E-bicycle, to provide the desired outcomes of enhanced efficiency, good power quality, and dependability due to the charger's lower cost. Additionally, the proposed converter uses a single switch, which reduces not necessary body diode conduction and circulating current and enhances the PFC device's thermal management. Additionally, this research makes use of the diode bridge rectifier (DBR) arrangement, which offers low current stress and is suitable for electric bicycles. The converter operates at a low cost with reduced magnetics (DCM) by operating the charger in discontinuous conduction mode at such low voltage levels. It also accomplishes intrinsic power factor at the ac mains by employing a simple control method to maintain the battery in high power density constant current (CC) and constant voltage (CV) states. A thorough state space investigation is carried out in combination with modeling and testing to ensure that the electric bicycle charger operates effectively. Consequently, low power chargers are a good fit for the proposed single stage front-end converter, and a 250 W hardware prototype is used to verify the findings.

Influence of processing parameters on the fracture behaviour of 316L SS printed by laser powder bed fusion

This study explored the relationship between process parameters and fracture behavior in 316L stainless steel printed by laser powder bed fusion. Fracture testing was conducted according to ASTM E1820 for single edge notch bending, and elastic mechanical properties were determined using ultrasonic surface wave analysis. Five test sets were considered in a vertical building configuration using five different volumetric energies belonging to conduction mode. The critical fracture toughness was calculated and discussed along with the plastic deformations at the crack tip. The study found that local plastic deformation for single edge notch bending was influenced by powder bed fusion process parameters. A correlation was observed between energy density, fracture toughness, and the dimensions of the fracture process zone. The R-curves showed different fracture behaviors depending on the energy density. The energy required to grow a crack was associated with larger plastic zones, resulting in fracture toughness values ranging from 43 (43 J mm−3) to 427 kJ/m2 (68 J mm−3). Results are discussed in terms of porosity and strain hardening capacity depending on the manufacturing conditions.

Junction-Controlled-Diode-Embedded SiC-MOSFET for Improving Third Quadrant and Turn-On Characteristics

In this paper, we propose a novel 1200V SiC MOSFET featuring the embedded junction-controlled-diode (JCD-MOSFET) and demonstrate its static and dynamic characteristics through TCAD simulations. Without sacrificing blocking and conduction performance, the adoption of JCD can effectively reduce knee voltage to 1.7V based on unipolar carrier conduction mode. Due to the reduced peak reverse recovery current and reverse recovery charge, the JCD-MOSFET achieves 30.8% lower turn-on losses than conventional MOSFET. Meanwhile, the fabrication process for the JCD-MOSFET is the same as conventional MOSFET without an extra mask. This proposed JCD-MOSFET prototype shows great potential in target applications in the near future.

Control of DC-DC boost converter in discontinuous conduction mode feeding a constant power load

This article presents a new control strategy for a DC-DC boost converter used to supply a constant power load. The designed controller allows regulates the converter output voltage to a required reference value. By designing the controller based on the reduced order averaged model of the converter and using a nonlinear control technique based on feedback linearization, a simple-to-implement and stable controller for both operating modes of the converter (continuous and discontinuous conduction modes respectively) is obtained. The designed control strategy is validated through simulation and experimental results, demonstrating good dynamic performance and stability in both conduction modes, under variations in reference values and significant load changes. In addition, a comparison of the performance and implementation costs between the control strategy proposed in this paper and two strategies proposed by other authors is included.

Crucial effects of plasma gas on the weld and microstructural characteristics of plasma arc welded aero engine Ti6Al4V alloy joints

This study explores the influence of plasma gas flow rate (PGFR) on the defects, microstructure evolution and mechanical properties during plasma arc welding of Ti6Al4V titanium alloy thin sheets using microscopic analysis, spectroscopic analysis, tensile and microhardness tests. The variation in PGFR affects the welding arc in terms of its stability, pressure and constriction which results in transformation of arc from conduction mode to keyhole mode and changes in microstructure as well. All the other welding process parameters were kept constant except for PGFR which was varied to investigate its significance. Excess weld metal was observed under the weld bead is an attribute of keyhole formation. Macrographs exhibits increments in weld geometry measurements whereas weld defects such as lack of penetration and porosity decreased with increased PGFR. The microstructural examination showed a variety of phase formations that includes majorly with acicular α and Widmanstätten α morphologies. Tensile strength and hardness at the weld region of the welded joints increases with increase in PGFR. An oxygen rich brittle subsurface layer called α-case morphology was observed at the weld region of 1 L/min joint causes significant reduction in ductility.

State Space Average Modeling, Small Signal Analysis, and Control Implementation of an Efficient Single-Switch High-Gain Multicell Boost DC-DC Converter with Low Voltage Stress

This paper presents the closed-loop control of a single-switch high-gain multicell boost DC-DC converter working in a continuous conduction mode (CCM). This converter is particularly designed for applications in photovoltaic systems. One of the main advantages of the proposed converter is that it only employs one active semiconductor switch, which decreases the converter losses and cost, increases the efficiency, and simplifies the control circuit. Moreover, the multicell nature of the proposed converter offers the possibility of obtaining the required voltage gain by selecting the number of cells. State space average (SSA) modeling and small-signal analysis are used to model the switching converter power stages of the proposed converter. The parasitic series resistances of the passive elements of the converter circuit are considered to improve the accuracy of the modeling. Small-signal analysis is used to derive the open-loop transfer functions, input-to-output and control-to-output transfer functions of the proposed converter to examine its dynamic performance. The stability of the converter is analyzed to design the parameters of the voltage controller using the proposed modeling method. The experimental prototype of the proposed single-switch two-cell boost DC-DC converter was implemented. The simulation and experimental results proved the effectiveness of the proposed boost DC-DC converter under different working conditions. It has a fast dynamic response without overshoots. A comprehensive comparison between the proposed converter and previous boost converters is provided. It guarantees a required variable and constant high voltage gain with a wider duty ratio range. It compromises between the required performance, the low number of components, low voltage stress on the components, and cost-effectiveness. The experimental efficiency of the proposed converter is about 96% at a 100 W load.

Achieving excellent strength and ductility of 24CrNiMoY alloy steel fabricated by high power selective laser melting technology

In order to increase the productivity, new generation of selective laser melting (SLM) machines are evolving towards higher power lasers. In this paper, the microstructure evolution and mechanical properties of 24CrNiMoY alloy steel fabricated by high power selective laser melting (HP-SLM) have been reported. The results show that with the optimized laser power over 400 W, the powder layer thickness can be increased to 60 μm, and the theoretical productivity reaches 7.2 mm3/s, which is more than two times of the normal SLM technology. As the laser energy density increases, the structure of melt pool changes from a thermal conduction mode to a keyhole mode, and the microstructure mainly consists of martensite, bainite and pre-eutectic ferrite, and the phase composition of the specimen is α-Fe phase and a small amount of Fe3C,with fine grain size and irregular orientation. When the laser energy density is 68 J/mm3, the microhardness of the specimen is 410HV0.2, the tensile strength reaches 1121 MPa and the percentage elongation after fracture is 11.5%, which realizes a good match between strength and ductility. The fine tempered martensite and lower bainite in the microstructure is the key to excellent strength and ductility. This research is of guiding significance and serves as a technical reference for understanding the microstructure evolution and mechanical properties of HP-SLM 24CrNiMoY alloy steel.

Circuit topology aware GNN-based multi-variable model for DC-DC converters dynamics prediction in CCM and DCM

A regression model based on graph neural network, tailored for electric circuit dynamics prediction is introduced, providing converter performance predictions on converter circuit level and internal parameter variations. Regardless of the number of components or connections present in a converter circuit, the proposed model can be readily scaled to incorporate different converter circuit topologies. Moreover, the model can be used to analyse converter circuits with any number of circuit components and any control parameters variation. To enable the use of machine learning methods and applications, all physical and switching circuit properties such as converter circuits operating in continuous conduction mode or discontinuous conduction mode are accurately mapped to graph representation. Three of the most common converters (Buck, Boost, and Buck-boost) are used as example circuits applied to model and the target is to predict the gain and current ripples in inductor. The model achieves 99.51% on the R2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$R^2$$\\end{document} measure and a mean square error of 0.0263.

An improved solar step-up power converter for next-generation electric vehicle charging

This study proposes an innovative control strategy based on a quadratic equation derived from a core battery charging model. This strategy is applied to a solar step-up power converter (SSUPC), which is specifically optimized for electric vehicle charging. The model includes a 500 W SSUPC, controlled by a microprocessor, effectively converting low input voltage into high output voltage. The proposed control strategy allows the SSUPC to operate in discontinuous conduction mode, thereby achieving a higher voltage gain. In experiments with an input voltage of 20 V, the system was capable of outputting up to 480 V, while maintaining a low duty cycle of 0.3 and achieving a system conversion efficiency of 95 %. Furthermore, the SSUPC integrates a pyramid maximum power point tracking (MPPT) algorithm, initiating MPPT to capture the maximum power point when the solar output power is insufficient for electric vehicle charging, achieving an MPPT efficiency of 99 %. The developed charger is compact, boasts high power density, is cost-effective, and is well-suited for widespread application, meeting the 480 V charging requirements of electric vehicles.

Revealing the Properties of Electrically Driven Optical Antennas via Conductive Atomic Force Microscope.

Light emission from ultracompact electrically driven optical antennas (EDOAs) has garnered significant attention due to its terahertz modulation bandwidth. Typically, the EDOAs are fixed and nonadjustable once fabricated, thus hindering the attempts to investigate the influence of structural geometry on light emission properties. Here, we propose and demonstrate that the EDOAs can be constructed by carefully manipulating the gold-coated tips of atomic force microscopy operated in conductive mode into contact with the optical antennas covered by insulating film, where the position of the tunnel junction on the antenna surface can be controlled with high accuracy and flexibility. Taking gold nanorod antennas covered by HfO2 film as an example, we found that the highest light generation efficiency is obtained when the tunnel junction is located at the shoulder edge of the nanorod antenna, where the bonding dipolar surface plasmon mode in the junction is spectrally and spatially coupled with the longitudinal radiation mode of the EDOAs. Besides, position variation of the tunnel junction on the nanorod surface also strongly influences the far-field radiation angular distribution and emission spectrum. Numerical simulations are in good agreement with the experimental results. Our findings offer fundamental insights into the influence of structural parameters on the light emission performance of EDOAs, thus leading to better design of EDOAs with high light generation efficiency and powerful functionality.

Microstructural evolution in laser powder bed fusion of water-atomized high-carbon low-alloy steel: Analysis of melting mode effects

Medium/High‑carbon steels are considered susceptible to cracking during rapid cooling in laser powder bed fusion (LPBF) applications. Also, water-atomized (WA) steel powders, containing oxides, have been associated with porosity defects during this process. In this study, LPBF was employed to process WA high‑carbon low-alloy steel powders under three operational regimes – conduction, transition, and keyhole modes. Analyses based on the scaling law of keyhole stability, melt pool dimensions, and x-ray computed tomography (XCT) suggested that processing under the transition mode closely resembled a stable keyhole, enabling the successfully printing of water-atomized powders to a density of 99.93 %. Subsequent heat treatment, hardness, and residual stress assessments presented a prominent structural softening and relief of compressive stress under the transition mode. This was attributed to the intense in-situ tempering and re-austenitization that occurred within each layer. Under this condition, with no post heat treatment, an ultimate tensile strength of 1250 MPa with >2.6 % elongation was achieved. Finally, the ball-on-disk test showed that wear performance of the printed steels was primarily governed by the tribo-oxides, with a limited influence from the microstructural variation.

An Improved Cascaded Boost Converter with an Ultra-High Voltage Gain Suitable for Dielectric Quality Tests

Dielectric quality tests require a high AC voltage with a frequency range of 0.0001 Hz to 1000 Hz. However, providing a high AC voltage with such a frequency variety is challenging. Providing a high DC voltage and then applying such a voltage to an inverter to adjust the frequency can be an acceptable solution for such a challenge. Notably, a high DC voltage is required for DC tests. This study proposes an improved form of the cascaded boost converter, whose merits are as follows: (i) the high voltage gain providing low duty cycles is possible; (ii) the input current is continuous, which decreases the current ripple of the input filter capacitor; (iii) the current stress of the semiconductors is less than the input current, and most of them have a large difference with it; (iv) the voltage stress of the semiconductors is less than the output voltage with a large difference; (v) only one switch with a simple drive circuit is used; (vi) the common ground of the load and input source decreases the EMI noise; (vii) besides the high voltage gain, the voltage density of the converter based on the number of inductors, capacitors, switches, diodes, and whole components is greater than that of the recently proposed converters; (viii) only two stacked connections of the proposed topology can provide a 2.6 kV voltage for a higher DC voltage test of dielectrics. The functional details of the converter are extracted in ideal and continuous conduction (CCM) modes. Moreover, the converter’s voltage gain and density are compared with the recently proposed converters to show the superiority of the proposed converter. Finally, the experimental results are presented to validate the theoretical relations in a 140 W output power.

Analyzing porous cold storage unit in presence of hybrid nano-powders considering Galerkin method

The article presents a comprehensive simulation study on cold storage porous containers, employing the Galerkin method to analyze their thermal behavior. A key focus of the investigation is the incorporation of both radiation and conduction modes within the mathematical model, acknowledging their significant roles in the freezing process. To enhance the freezing rate, hybrid nanoparticles are introduced into H2O, aiming to speed up the solidification. Notably, the study integrates adaptive grid techniques to achieve higher modeling accuracy, with verification processes confirming a high level of agreement between simulation results and experimental data. This research also underscores the potential for improved energy efficiency in cold storage systems, contributing to the sustainability of natural resources by reducing energy consumption and enhancing the overall efficiency of thermal storage systems. Through meticulous examination, the study explores the impacts of various factors on freezing, including the fraction of hybrid nano-powders (ϕ), porosity (γ), and the radiation factor (Rd). Remarkably, the introduction of porous media causes to a substantial increment in the freezing rate, resulting in an improvement of approximately 91.19 %. Moreover, the inclusion of the radiation term in the model significantly reduces the completion time by approximately 30.85 %, underscoring the importance of considering radiation effects in such systems. Additionally, dispersing hybrid nano-powders into the water, results in a decrement in the freezing time around 7.21 %. This approach highlights the significant potential for optimizing energy use in thermal storage applications, thereby promoting the conservation and sustainable management of natural resources.

Conductive and Convective Combustion Modes of Granular Mixtures of Ti–C–NiCr

Conductive and Convective Combustion Modes of Granular Mixtures of Ti–C–NiCr

Blue Laser Conduction Spot Welding of Pure Copper Hairpins

Joining rectangular copper hairpins significantly improves the performance of hairpin motors. Copper welding poses a significant challenge due to its low laser absorptivity when using conventional infrared lasers. Although employing keyhole welding with a high-power and small-spot infrared laser can increase the absorption rate through multireflections, it introduces instabilities caused by the multi-recoil forces within the keyhole and the absorptivity differences among solid, liquid, and keyhole states of copper. The proposed solution adopts a 450 nm blue laser, which exhibits a superior laser absorptivity toward copper and facilitates stable conduction mode spot welding with an enlarged laser spot. This research achieved successful blue laser conduction spot welding of copper hairpins with a gap and, for the first time, systematically analyzed the force and instability factors of a molten pool. The results demonstrated that with a laser power of 1950 W, laser spot diameter of 0.6 mm, and defocusing amount of –3 mm, only 0.7 s of welding time was required to join copper hairpins with a 0.6 mm gap. Notably, there were no noticeable defects in weld beads during blue laser welding. Meanwhile, the study identified recoil force as a significant uncertain factor inducing defects, particularly in the keyhole mode. Compared to infrared technology, the blue laser, characterized by a higher absorption rate and a larger spot diameter, effectively reduced uncertainty through conduction welding. This research showcased the significant potential for blue lasers in manufacturing copper hairpin motors.

Machine learning based feedforward voltage control for buck converters in envelope tracking applications

Tracking the voltage envelope of 5G base station power supplies poses a significant long-term challenge. To achieve fast and accurate envelope tracking, an efficient and high-frequency power electronics circuit and an excellent voltage controller are essential. This paper presents a novel machine learning (ML) based feedforward control method for precise voltage reference tracking. The method is exemplified using a standard buck converter in both continuous conduction mode (CCM) and discontinuous conduction mode (DCM). A feedforward neural network (FNN) is trained to capture non-ideal and non-linear effects in real circuits. An automated data collection system, developed with MATLAB and Simulink, facilitates data acquisition and model training process. The trained FNN predicts the duty cycle for the buck converter to generate the targeted output voltage and output power. A simulation model is built to validate the effectiveness of the FNN controller in envelope tracking applications.