Low Duty Ratio Research Articles

Transformerless high gain boost and buck-boost DC-DC converters based on extendable switched capacitor (SC) cell for stand-alone photovoltaic system

This paper presents transformerless high gain boost and buck-boost DC-DC converters (B-BBCs) with extendable switched capacitor cells (SCs), suitable for applications operating at high voltage, above 300 V. Boosting low voltage to a high-enough level, with low duty ratio, is beyond the practical capability of the conventional boost converter. In addition, high duty ratio needed for operation of the boost converter, results in higher component stress that suppresses the overall efficiency of the converter. Therefore, by a convenient integration of SCs with conventional B-BBCs, increased voltage gain is attained with fewer losses. Such converters can be employed for Photovoltaic (PV) systems. The operational principles and modes of operation are analyzed to justify the utility of converters for stand-alone PV systems. Moreover, the proposed modular structure allows to increase SC cells in order to obtain reduced voltage stress on switching components with a higher voltage gain. Simulation and experimental results based on 100 W laboratory prototype extol the theoretical analysis.

Simulation study of the nanoparticles nucleation in a pulse-modulated capacitively coupled rf acetylene discharge

The multi-fluid plasma equations are combined with the hydrocarbon chemical kinetics to simulate the nucleation stage of the nanoparticle formation in a pulse-modulated capacitively coupled rf acetylene discharge. The simulation code is validated by comparing its results with the available experimental and simulation results, and the agreement is quite satisfactory. It is shown that, with pulsing of the rf power, periodic oscillations develop on the temporal profiles of all hydrocarbon species. The amplitude of the oscillations decreases with the increasing pulse repetition frequency and species mass. On the long time scale of several pulse periods, the average number density of neutral molecules grows linearly with time. However, due to strong wall losses, radicals are saturated after experiencing an initial linear growth. The average number density of large neutral molecules and radicals increases with the increasing pulse repetition frequency and duty ratio. Anions are strongly affected by the power modulation, and their amplitude of oscillations is much larger than that of the radicals. Cations oscillate almost simultaneously with the electrons, and as their average number density does not grow on the long time scale, they do not play a noticeable role in the nucleation process. All roots of the nanoparticle formation can be effectively suppressed when pulses of low repetition frequency and low duty ratio are applied.

An Energy Efficient Charging Technique for Switched Capacitor Voltage Converters With Low-Duty Ratio

Charging a capacitor array of a switched-capacitor (SC) dc-dc converter, supplying load circuits with a very short active period, can be pivotal to achieve high energy efficiency of its operation. This is because the capacitors may lose most of the stored energy during a long sleep period, and thus every sleep-to-active transition requires full recharging of the capacitors. In this brief, we present an energy efficient capacitor charging technique called split-capacitor charging, which charges a capacitor array in a step-wise fashion. Circuit simulations demonstrate that the proposed technique can reduce the energy wastage during sleep-to-active transition up to 66%. When tested on load circuits with a short active period, a voltage converter employing the proposed charging method shows up to 24% improvement in energy efficiency over conventional SC converters.

Single‐phase high‐voltage gain switched LC Z‐source inverters

Recently, switched-inductor Z-source inverters (SL-ZSIs) have been reported to achieve high-voltage gain and good power inversion operation at low shoot-through duty ratio D as compared to conventional ZSI. As the SL-ZSIs have high passive component count, weight, volume and losses of the system increases that lead to reduction in efficiency. To address the issues of conventional ZSI and SL-ZSIs, two single-phase switched LC (SLC)-ZSIs (Type 1 SLC-ZSI and Type 2 SLC-ZSI) are proposed in this study to achieve high-voltage gains at low values of D with lower passive component count as compared to SL-ZSIs. At low values of D , modulation index M approaches to higher values which results into improved AC output at reduced harmonic distortion. Due to low passive component count in the proposed inverters, weight, volume and losses decreases resulting into increase in efficiency. The proposed inverters can be used in various DC-AC and DC-DC power conversions in renewable energy applications due to their high-voltage gain, better immunity to EMI noise and higher reliability. The detailed steady-state analysis of the two proposed SLC-ZSIs is given in this study. Scaled down experimentation has been carried out to verify the performance of the proposed inverters.

Experimental and Theoretical Analysis of Trans-Z-Source Inverters With Leakage Inductance Effects

Transformer-based Z -source (trans- Z -source) inverters are recently proposed to extend the traditional Z -source inverter with higher buck–boost capabilities as well as reducing the passive components at the same time. A new scheme for high-boost trans- Z -source inverter is proposed in this paper. In the traditional trans- Z -source inverters for high boosting voltages, the modulation index can be high by increasing the transformer turns ratio. The proposed topology has two transformers, two capacitors, and three diodes in the Z -impedance network. With fewer active and passive components and low shoot-through duty ratio, the new topology produces an output voltage with high quality and low total harmonic distortion. The new method is compared with the previously proposed schemes in terms of voltage stresses on diodes and capacitors, efficiency, voltage gain, and switching device power factor of the diodes. The operating principles of the new scheme along with the transformer leakage inductance effects on the voltage gain have been investigated through detailed analytical and mathematical derivations. The validity and effectiveness of the new circuit have been verified by experiments and simulations.

Effects of Pulse Parameters on Weld Microstructure and Mechanical Properties of Extra Pulse Current Aided Laser Welded 2219 Aluminum Alloy Joints.

In order to expand the application range of laser welding and improve weld quality, an extra pulse current was used to aid laser-welded 2219 aluminum alloy, and the effects of pulse current parameters on the weld microstructure and mechanical properties were investigated. The effect mechanisms of the pulse current interactions with the weld pool were evaluated. The results indicated that the coarse dendritic structure in the weld zone changed to a fine equiaxed structure using an extra pulse current, and the pulse parameters, including medium peak current, relatively high pulse frequency, and low pulse duty ratio benefited to improving the weld structure. The effect mechanisms of the pulse current were mainly ascribed to the magnetic pinch effect, thermal effect, and electromigration effect caused by the pulse current. The effect of the pulse parameters on the mechanical properties of welded joints were consistent with that of the weld microstructure. The tensile strength and elongation of the optimal pulse current-aided laser-welded joint increased by 16.4% and 105%, respectively, compared with autogenous laser welding.

Enhanced-Boost Quasi-Z-Source Inverters With Two-Switched Impedance Networks

In this paper, two topologies are presented for the enhanced-boost quasi-Z-source inverters (qZSI), namely continuous input current configuration and discontinuous input current configuration of enhanced-boost qZSI with two-switched impedance networks. Similar to enhanced-boost impedance-source inverters (ZSIs), these proposed inverter topologies possess very high boost voltage inversion at low shoot-through duty ratio and high modulation index to provide an improved quality output voltage. Compared to enhanced-boost ZSIs with two-switched Z-source impedance networks, these proposed inverter topologies share common ground with source and bridge inverter, overcome the starting inrush problem, and draw continuous input current and the lower voltage across the capacitors. Moreover, the input ripple current is negligible. This paper presents the operating principles and analysis of continuous input current configuration enhanced-boost qZSI with two-switched impedance networks and compares with ZSI, switched inductor ZSI, DA/CA-qZSI, and enhanced-boost ZSIs. The theoretical analysis is done and is validated through simulation and experimental results.

Investigation of NO removal using a pulse-assisted RF discharge

In this paper, removal of nitrogen oxide (NO) is investigated in capacitive atmospheric pressure discharges driven by both radio-frequency (RF) and trapezoidal pulsed power with a one-dimensional self-consistent fluid model. The results show that the number density of NO could be reduced significantly once a short pulse of low duty ratio is additionally applied to the RF power. It is found that the process of NO removal by the pulse-modulated RF discharge could be divided into three stages: the quick reaction stage, the NO removal stage, and the sustaining stage. Furthermore, the temporal evolution of particle densities is analyzed, and the key reactions in each stage are discovered. Finally, the influence on the removal efficiency of the voltage amplitude of the pulse and the RF voltage amplitude is investigated.

Условное среднее значение очередей в системах массового обслуживания с пакетными потоками заявок

This work considers queuing systems with packet flows of demands featured for modern multiservice telecommunication networks. It presents Pollaczek-Khintchine formula generalization for systems with common type flows. We considered mean queue size dependences under low duty ratio. This work introduces a new term of conditional average value of queue, which is mean value under processor no-downtime condition, and presents algorithm for approximation of queue size dependences in queuing systems with packet flows of demands. Time delay in queues was considered. We defined duty limits, which provide desired queue size and time delays.

Enhancement of isobutane refrigerator performance by using far-infrared coating

This study evaluated the effect on refrigeration performance and feasibility of a far-infrared coating (FIRC) on the condenser of a small isobutane (R-600a) refrigerator. The evaluation was based on the no-load pull-down and 24-h on-load cycling tests. Far-infrared materials and a water-based coating material were mixed using a two-step synthesis method to obtain the FIRC material. Fourier transform infrared spectrometry established that the optimal far-infrared material was a multiwalled carbon nanotube (MWCNT). The results of the no-load pull-down test revealed that the electricity consumption, freezer temperature, and coefficient of performance (COP) of the R-600a refrigerator with MWCNT-FIRC (S2) were lower than those of the refrigerator without MWCNT-FIRC (S1) by 3.39%, 3.61%, and 2.92%, respectively. The results of the 24-h on-load cycling test showed that S2 had a lower electricity consumption, higher slope of pull-down (SPD), higher compression ratio (CR), higher COP, lower duty ratio (DR), and higher energy factor (EF), changing upon those of S1 by −7.05%, 5.66%, 3.24%, 5.92%, −5.63, and 7.89%, respectively. A MWCNT-FIRC on the condenser of an R-600a refrigerator can enhance refrigeration performance and reduce electricity consumption, resulting in energy saving and carbon reduction.

Effect of DC Pulse Patterns on Spark Plasma Sintering Process of [Fe<sub>0.8</sub>Co<sub>0.2</sub>B<sub>0.05</sub>Si<sub>0.2</sub>]<sub>96</sub>Nb<sub>4 </sub> Bulk Metallic Glass

The influence of direct current pulse on–off patterns on spark plasma sintering of [Fe0.8Co0.2B0.05Si0.2]96Nb4 on kinetics competition and coordination mechanism of the interface bonding and crystallization has been investigated systematically. No crystallization of metallic glassy matrix and good bonding state between the particles were responsible for good mechanical properties of the fabricated Fe-based bulk glassy alloy at 2:9 (on: off) pattern. The higher local micro area’s instantaneous power and larger cooling time caused by low pulse duty ratio played a vital role in consolidation of amorphous alloy powder and desired structural properties.

Effects of high-frequency and high-voltage pulsed electric field parameters on water chain formation

Separation methods utilizing high-frequency and high-voltage pulsed DC electric fields have been used extensively in the oil and petroleum industries, where the occurrence of water-in-oil dispersions is highly unwelcome because of physical constraints and the high maintenance costs required to treat these dispersions. This paper reports the results of studies of the effects of applied electric field parameters, including electric field strength, frequency, and duty ratio, on water chain formation in water-in-oil emulsions. The investigations were performed in a rectangular Perspex® cell. The results of the studies show that dipole–dipole forces dominate the process of water chain formation. At low electric field strength, frequency, or duty ratio, dipole–dipole forces are negligible; therefore, the process of water chain formation and aqueous drop coalescence are inconspicuous. However, at high electric field strength, frequency, or duty ratio, significant dipole–dipole forces give rise to water chain formation and aqueous drop coalescence. At extremely high electric field strength, frequency, or duty ratio, aqueous drops are excessively polarized and disintegrate, inhibiting the processes of water chain formation and aqueous drop coalescence. The optimum electric field parameters for separation of water-in-oil dispersions are as follows: electric field strength, 3.80 kV cm−1; frequency, 4.0 kHz; and duty ratio, 0.65.

A step‐up PWM DC–DC converter for renewable energy applications

SummaryA step‐up pulse width modulation (PWM) direct current (DC)–DC converter is presented in this paper, which has its origin in quasi Z‐source inverter. Analysis of this converter in steady state is presented, and relevant expressions are derived for the proposed converter operating in continuous conduction mode. The power loss expressions for each component of the converter are derived, and thereby, obtained expressions for overall converter efficiency are presented. Further, a dynamic model is derived to design an appropriate controller for this converter. The simulation and experimental results are presented to support the theoretical analysis. The advantages such as continuous input current, high step‐up gain at lower duty ratio, and common ground for source, load, and switch makes the converter suitable for renewable energy applications. Copyright © 2015 John Wiley & Sons, Ltd.

Isoforms Confer Characteristic Force Generation and Mechanosensation by Myosin II Filaments

Myosin II isoforms with varying mechanochemistry and filament size interact with filamentous actin (F-actin) arrays to generate contractile forces in muscle and nonmuscle cells. How myosin II force production is shaped by isoform-specific motor properties and environmental stiffness remains poorly understood. Here, we used computer simulations to analyze force production by an ensemble of myosin motors against an elastically tethered actin filament. We found that force output depends on two timescales: the duration of F-actin attachment, which varies sharply with the ensemble size, motor duty ratio, and external load; and the time to build force, which scales with the ensemble stall force, gliding speed, and environmental stiffness. Although force-dependent kinetics were not required to sense changes in stiffness, the myosin catch bond produced positive feedback between the attachment time and force to trigger switch-like transitions from transient attachments, generating small forces, to high-force-generating runs. Using parameters representative of skeletal muscle myosin, nonmuscle myosin IIB, and nonmuscle myosin IIA revealed three distinct regimes of behavior, respectively: 1) large assemblies of fast, low-duty ratio motors rapidly build stable forces over a large range of environmental stiffness; 2) ensembles of slow, high-duty ratio motors serve as high-affinity cross-links with force buildup times that exceed physiological timescales; and 3) small assemblies of low-duty ratio motors operating at intermediate speeds are poised to respond sharply to changes in mechanical context—at low force or stiffness, they serve as low-affinity cross-links, but they can transition to force production via the positive-feedback mechanism described above. Together, these results reveal how myosin isoform properties may be tuned to produce force and respond to mechanical cues in their environment.

Kinetic characterization of the sole nonmuscle myosin-2 from the model organism Drosophila melanogaster.

Nonmuscle myosin-2 is the primary enzyme complex powering contractility of the F-actin cytoskeleton in the model organism Drosophila. Despite myosin's essential function in fly development and homeostasis, its kinetic features remain elusive. The purpose of this in vitro study is a detailed steady-state and presteady-state kinetic characterization of the Drosophila nonmuscle myosin-2 motor domain. Kinetic features are a slow steady-state ATPase activity, high affinities for F-actin and ADP, and a low duty ratio. Comparative analysis of the overall enzymatic signatures across the nonmuscle myosin-2 complement from model organisms indicates that the Drosophila protein resembles nonmuscle myosin-2s from metazoa rather than protozoa, though modulatory aspects of myosin motor function are distinct. Drosophila nonmuscle myosin-2 is uniquely insensitive toward blebbistatin, a commonly used myosin-2 inhibitor. An in silico modeling approach together with kinetic studies indicate that the nonconsensus amino acid Met466 in the Drosophila nonmuscle myosin-2 active-site loop switch-2 acts as blebbistatin desensitizer. Introduction of the M466I mutation sensitized the protein for blebbistatin, resulting in a half-maximal inhibitory concentration of 36.3 ± 4.1 µM. Together, these data show that Drosophila nonmuscle myosin-2 is a bona fide molecular motor and establish an important link between switch-2 and blebbistatin sensitivity.

Recrystallization and microstructure evolution of the rolled Mg–3Al–1Zn alloy strips under electropulsing treatment

The microstructural evolution of rolled Mg–3Al–1Zn (AZ31) alloy during electropulsing treatment (EPT) was analyzed. The results indicate that EPT accelerates tremendously the recrystallization and the microstructure of the rolled Mg–3Al–1Zn alloy is refined. A fine grain microstructure with an average grain size about 2μm is obtained by the EPT with low duty ratio and high current density (LDRHCD-EPT) at low temperature below 359K for a short time of 320s. The EPT has two main effects on the samples, the Joule heat and the athermal effect. Based on the experimental data and the theory analysis, we think that the athermal effect plays a key role in the recrystallization of the deformed alloys under EPT and accelerates the nucleation rate of recrystallization during EPT. Furthermore, the subsequent growth of the recrystallization grains is more dependent on the Joule heat than the athermal effect. As a result, in order to obtain refined recrystallization grains, the athermal effect should be strengthened while the thermal effect should be weakened during EPT.

High step-up converters based on quadratic boost converter for micro-inverter

This paper proposes two DC–DC converters namely semi-tapped and fully-tapped quadratic boost converter based on the quadratic boost converter topology for high step-up applications such as micro-inverter. The proposed converters integrate the step-up capabilities of the quadratic boost converter and the tapped-inductor based converter due to which high step-up voltage gain can be achieved at lower duty ratio. Further, the proposed converters also have feature of low voltage stress on active switch. This paper presents detailed steady state analysis of proposed converters which include voltage gain and efficiency analysis with the presence of parasitic components. The theoretical analysis of proposed converters is verified by simulation and experimental results.

Magnesium Modulates Actin Binding and ADP Release in Myosin Motors

We examined the magnesium dependence of five class II myosins, including fast skeletal muscle myosin, smooth muscle myosin, β-cardiac myosin (CMIIB), Dictyostelium myosin II (DdMII), and nonmuscle myosin IIA, as well as myosin V. We found that the myosins examined are inhibited in a Mg(2+)-dependent manner (0.3-9.0 mm free Mg(2+)) in both ATPase and motility assays, under conditions in which the ionic strength was held constant. We found that the ADP release rate constant is reduced by Mg(2+) in myosin V, smooth muscle myosin, nonmuscle myosin IIA, CMIIB, and DdMII, although the ADP affinity is fairly insensitive to Mg(2+) in fast skeletal muscle myosin, CMIIB, and DdMII. Single tryptophan probes in the switch I (Trp-239) and switch II (Trp-501) region of DdMII demonstrate these conserved regions of the active site are sensitive to Mg(2+) coordination. Cardiac muscle fiber mechanic studies demonstrate cross-bridge attachment time is increased at higher Mg(2+) concentrations, demonstrating that the ADP release rate constant is slowed by Mg(2+) in the context of an activated muscle fiber. Direct measurements of phosphate release in myosin V demonstrate that Mg(2+) reduces actin affinity in the M·ADP·Pi state, although it does not change the rate of phosphate release. Therefore, the Mg(2+) inhibition of the actin-activated ATPase activity observed in class II myosins is likely the result of Mg(2+)-dependent alterations in actin binding. Overall, our results suggest that Mg(2+) reduces the ADP release rate constant and rate of attachment to actin in both high and low duty ratio myosins.

Isolated High Step-Up DC–DC Converter With Low Voltage Stress

Fuel cell stacks and photovoltaic panels generate rather low dc voltages and these voltages need to be boosted before converted to ac voltage. Therefore, high step-up ratio dc-dc converters are preferred in renewable energy systems. A new Z-source-based topology that can boost the input voltage to desired levels with low duty ratios is proposed in this paper. The topology utilizes coupled inductor. The leakage inductance energy can efficiently be discharged. Since the device stresses are low in this topology, low-voltage MOSFETs with small RDS(on) values can be selected to reduce the conduction loss. These features improve the converter efficiency. Also, the converter has a galvanic isolation between source and load. The operating principles and steady-state analysis of continuous and discontinuous conduction modes are discussed in detail. Finally, experimental results are given for a prototype converter that converts 25 V dc to 400 V dc at various power levels with over 90% efficiency to verify the effectiveness of the theoretical analysis.

Dependence of ion current on magnetic unbalancing in high power pulsed magnetron glow discharge

A high-power pulsed sputtering (HPPS) discharge is able to generate high ionization metallic plasma by applying a negative high voltage pulse-train with low duty ratio and high current capacity to a sputtering target. If HPPS discharge technique is applied to unbalanced magnetron sputtering (UBMS) system which is one of the ionized sputtering, we will get the metallic plasma ionized more. The ion current of direct-current UBMS increases with increase in magnetic un-balancing. However, high-power pulsed UBMS does not necessarily have the same characteristics as dc-UBMS. We investigated a connection between the ion current to a collector electrode and the number of peripheral magnets in the sputter target. The collector current increased with increase in the number of the magnets, but the ratio of the collector current to the target current depended more strongly on average input power than that for dc-UBMS. It was found that the current ratio indicated the maximum of 18.8% at the input power of 400 W in the hpp-UBMS with the peripheral 10-magnets.