Constant Alternating Current Research Articles

Hybrid Switching Control-Based DC to AC Inverter for Microgrid Using Renewable Energy Sources

Hybrid switching control-based direct current (DC) to alternating current (AC) inverter is a method of controlling the flow of power from DC sources such as solar panels or wind turbines to AC loads in a microgrid. In a microgrid, renewable energy sources are often used to supplement traditional sources of energy and improve overall energy efficiency. To simulate micro-grid systems, an effective three-legged IGBT inverter has been developed using Matlab R2016a/Simulink. The inverter switches are controlled by a pulse controller, which creates the switching gate pulses. This work models the output voltage and current waveforms of the three-phase 180° voltage source inverter that supplies nonlinear loads. To lower the total harmonic distortion (THD) of the current and voltage outputs of the three-phase voltage source converter (VSC), a filter circuit and a two-level pulse width modulation (PWM) generator have been presented. This pulse-width modulation generator compares the modulating signal and a high-frequency triangular carrier wave. Sinusoidal pulse width modulation (SPWM) is used for PWM control. Moreover, the hybrid switching control-based DC-to-AC inverter utilizes a combination of pulse width modulation (PWM) and hysteresis current control techniques to maintain a constant AC output voltage and frequency. PWM control is used to regulate the voltage, while hysteresis current control is used to regulate the current. Additionally, an inductor-capacitor-inductor (LCL) filter is used to improve the stability of the power converter by providing a damping effect on the system. Overall, the LCL filter is a versatile and effective tool for improving the performance of power inverters, especially in applications where high efficiency and low harmonic distortion are important. IUBAT Review—A Multidisciplinary Academic Journal, 6 (1): 25-46

Human detection thresholds of DC, AC, and hybrid electric fields: a double-blind study

BackgroundIn the course of the ongoing transition of electric energy systems, transmission corridors are often upgraded to higher voltages and other technologies leading to another quality of human exposure. The study aims to determine human detection thresholds for direct current (DC), alternating current (AC), and hybrid electric fields (various DC; constant AC).MethodsA total of 203 participants were exposed to DC, AC, and hybrid electric fields (EFs) in a highly specialized whole-body exposure laboratory using a double-blind experimental setting. Additionally, the participants were exposed to ion currents in part of the DC and hybrid sessions. To investigate environmental influences, relative humidity was changed in two subgroups during EF perception. Methods derived from the signal detection theory and the adaptive staircase procedure based on the single interval adjustment matrix were used to assess individual sensitivity and detection thresholds, respectively.ResultsThe results indicated that detection thresholds of hybrid EF were lower compared to single EF presentation of DC or AC. Ion current exposure enhanced EF perception. High relative humidity facilitated DC EF perception, whereas low relative humidity reinforced the perception of AC EFs.ConclusionsWith this systematic investigation of human perception of DC, AC, and hybrid EFs, detection thresholds were provided, which can help improve the construction processes of energy transmission systems and the prevention of unwanted sensory perception by contributing to the determination of limit values.

Cutaneous sensation of electrical stimulation waveforms

BackgroundSkin sensation is the primary factor limiting the intensity of transcranial electrical stimulation (tES). It is well established that different waveforms generate different sensations, yet transcranial stimulation has been limited to a relatively small number of prototypical waveforms. ObjectiveWe explore whether alternative stimulation waveforms could substantially reduce skin sensation and thus allow for stronger intensities in tES. MethodsWe systematically tested a range of waveforms in a series of 6 exploratory experiments stimulating human adults on the forearm and in one instance on the head. Subjects were asked to rate skin sensation level on a numerical scale from “none” to “extreme”. ResultsHigh frequency (>1 kHz) monophasic square wave stimulation was found to decrease in sensation with increasing duty cycle, baseline, and frequency, but the sensation was never lower than for constant current stimulation. For the purpose of injecting a net direct current (DC), a constant current is optimal. For stimulation with alternating current (AC), sensation decreased with increasing frequency, consistent with previous reports. Amplitude modulation did not reduce sensation below stimulation with constant AC amplitude, and biphasic square waveforms produced higher sensation levels than biphasic sinusoidal waveforms. Furthermore, for DC stimulation, sensation levels on the arm were similar to those reported on the head. ConclusionOur comparisons of various waveforms for monophasic and biphasic stimulation indicate that conventional DC and AC waveforms may provide the lowest skin sensations levels for transcutaneous electrical stimulation. These results are likely generalizable to tES applications.

Influence of Electro-Emulsification on Desulfurization of Rejected Electrolytic Manganese Metal in Electroslag Remelting Process

A transient three-dimensional comprehensive numerical model was developed to clarify the effect of electro-emulsification on sulfur mass transfer during the electroslag remelting process of rejected electrolytic manganese metal scrap. The magnetohydrodynamic thermal two-phase flow and solidification behavior were numerically clarified. The kinetics module was established to assess the sulfur mass transfer rate between molten manganese metal and molten slag. Furthermore, variations of the alternating current (AC) magnitude and direction were taken into account. A reasonable agreement between the experimental and simulated results was observed. The surface area of molten droplets was shown to enlarge and it regularly fluctuates under the Lorentz force action. At the constant frequency of 50 Hz, the desulfurization rate rises from 54.7 to 71.0 pct when the AC root mean square (RMS) value of the AC is increased from 3000 to 4000 A, while at the constant AC RMS value of 3500 A, it dropped from 63.4 to 58.5 pct with the frequency increases from 5 to 500 Hz.

Non‐Volatile Polymer Electroluminescence Programmable with Ferroelectric Field‐Induced Charge Injection Gate

Electroluminescence (EL) of organic and polymeric fluorescent materials programmable in the luminance is extremely useful as a non‐volatile EL memory with the great potential in the variety of emerging information storage applications for imaging and motion sensors. In this work, a novel non‐volatile EL memory in which arbitrarily chosen EL states are programmed and erased repetitively with long EL retention is demonstrated. The memory is based on utilizing the built‐in electric field arising from the remnant polarization of a ferroelectric polymer which in turn controls the carrier injection of an EL device. A device with vertically stacked components of a transparent bottom electrode/a ferroelectric polymer/a hole injection layer/a light emitting layer/a top electrode successfully emits light upon alternating current (AC) operation. Interestingly, the device exhibits two distinctive non‐volatile EL intensities at constant reading AC voltage, depending upon the programmed direct current (DC) voltage on the ferroelectric layer. DC programmed and AC read EL memories are also realized with different EL colors of red, green and blue. Furthermore, more than four distinguishable EL states are precisely addressed upon the programmed voltage input each of which shows excellent EL retention and multiple cycle endurance of more than 105 s and 102 cycles, respectively.

Preparation of scanning tunneling microscopy tips using pulsed alternating current etching

An electrochemical method using pulsed alternating current etching (PACE) to produce atomically sharp scanning tunneling microscopy (STM) tips is presented. An Arduino Uno microcontroller was used to control the number and duration of the alternating current (AC) pulses, allowing for ready optimization of the procedures for both Pt:Ir and W tips using a single apparatus. W tips prepared using constant and pulsed AC power were compared. Tips fashioned using PACE were sharper than those etched with continuous AC power alone. Pt:Ir tips were prepared with an initial coarse etching stage using continuous AC power followed by fine etching using PACE. The number and potential of the finishing AC pulses was varied and scanning electron microscope imaging was used to compare the results. Finally, tip quality using the optimized procedures was verified by UHV-STM imaging. With PACE, at least 70% of the W tips and 80% of the Pt:Ir tips were of sufficiently high quality to obtain atomically resolved images of HOPG or Ni(111).

AC Electrical Treeing Phenomena in an Epoxy System with Low-chlorine BDGE at Various Electric Field Frequencies

An alternating current (AC) electrical treeing phenomena in an epoxy system with low chlorine BDGE (1,4-butanediol diglycidyl ether) was studied in a needle-plate electrode arrangement. To measure the treeing propagation rate and breakdown time, a constant AC of 10 kV with three different electric field frequencies (60, 500, and 1,000 Hz) was applied to the needle-plate electrode specimen at in aninsulating oil bath. The treeing propagation rate of the DGEBA/high-chlorine BDGE system was higher than that of the DGEBA/low-chlorine BDGE system and the breakdown time of the system with high-chlorine BDGE was lower than that of the system with low-chlorine BDGE. These results implied that chlorine had a negative effect on the electrical insulation property of the epoxy system. As the electric field frequency increased, the treeing propagation rate increased and the breakdown time decreased.

Single/Double Soft-Templates Involved Synthesis of Polyaniline Blends: Interfacial Polymerization and Characterization by AC Impedance Analysis

Polyaniline (PANI) blends with single and double soft-templates (polyvinylpyrrolidone – PVP and/or sodium dodecylbenzenesulfonate – SDBS) were synthesized using interfacial polymerization. Fourier transform infrared (FTIR) spectral study confirmed blend formation. Polyaniline-polyvinylpyrrolidone (PANI-PVP) blend had submicron aggregates of 50–150 nm nanoparticles while PANI-SDBS blend had extensively agglomerated large size flakes/grains. Polyaniline-polyvinylpyrrolidone-sodium dodecylbenzenesulfonate (PANI-PVP-SDBS) blend had larger aggregates, besides significant number of smaller grains. Alternating current (AC) impedance analysis was performed to determine their electrical properties. At room temperature the AC conductivity of the blend materials was in the increasing order, PANI < PANI-PVP < PANI-SDBS < PANI-PVP-SDBS. But other parameters, like critical frequency and power law index s, exhibited a decreasing trend in the blend materials. With regard to frequency-dependence, all the materials showed constant AC conductivity at low frequencies, but at higher frequencies and at higher temperatures conductivity increased gradually. The obeyance of a universal power law and the range of s values (0.12 < s < 0.78) suggested a correlated barrier hopping (CBH) mechanism for AC conductivity of all the materials. The trends in electrical properties that were characteristic of the role of single/double soft-templates were explained in terms of improved π-electron delocalization and hopping mechanism.

Trajectory Planning of Knife Position of Slitter Robot Based on Identification of Friction and Viscous Damping, and Position Control Experiments

In this study, the trajectory planning method of the knife position of a slitter robot is proposed, and the experimental and numerical simulation results are demonstrated. The slitter robot consists of upper and lower knife driving mechanisms, and a knife driving mechanism was constructed with a worm gear, a ball screw and an alternating current (AC) motor. In the trajectory planning, first, the identification algorithm of the friction and the viscous damping is derived by using the equation of motion of the knife drive mechanism and the experimental results of the dynamic response with constant AC motor torque. Then, the trajectory planning algorithm of the knife position is presented, and a knife position control system is constructed. Furthermore, the experiments and numerical calculations have been carried out, and the usefulness of the present trajectory planning method is confirmed.

Experiments on opto-electrically generated microfluidic vortices

Strong microfluidic vortices are generated when a near-infrared (1,064 nm) laser beam is focused within a microchannel and an alternating current (AC) electric field is simultaneously applied. The electric field is generated from a parallel-plate, indium tin oxide (ITO) electrodes separated by 50 μm. We present the first μ-PIV analysis of the flow structure of such vortices. The vortices exhibit a sink-type behavior in the plane normal to the electric field and the flow speeds are characterized as a function of the electric field strength and biasing AC signal frequency. At a constant AC frequency of 100 kHz, the fluid velocity increases as the square of the electric field strength. At constant electric field strength fluid velocity does not change appreciably in the 30–50 kHz range and it decreases at larger frequencies (>1 MHz) until at approximately 5 MHz when Brownian motion dominates the movement of the 300 nm μ-PIV tracer particles. Presence of strongly focused laser beams in an interdigitated-electrode configuration can also lead to strong microfluidic vortices. When the center of the illumination is focused in the middle of an electrode strip, particles experiencing negative dielectrophoresis are carried towards the illumination and aggregate in this area.

Evaluation of constant current alternating current iontophoresis for transdermal drug delivery

Previous studies in our laboratory have demonstrated that alternating current (AC) iontophoresis can significantly decrease skin electric resistance and enhance the transport of charged permeants across skin. Flux variability of neutral permeants during AC iontophoresis was also found to be less than that of conventional direct current (DC) iontophoresis. The objectives of the present study were to evaluate flux enhancement of constant current AC transdermal iontophoresis and compare the AC flux with that of constant current DC iontophoresis. Iontophoresis studies of AC amplitude of 1, 2, and 5 mA were conducted in side-by-side diffusion cells with donor solution of 0.015, 0.15, and 1.0 M tetraethylammonium (TEA) chloride and receiver solution of phosphate buffered saline (PBS) using human epidermal membrane (HEM). Conventional constant current DC iontophoresis of 0.2 mA was also performed under similar conditions. TEA and mannitol were the model permeants. The following are the major findings in the present study. The flux of TEA increased proportionally with the AC current for all three TEA chloride concentrations and at the AC frequency used in the present study. When the permeant and its counter ion were the only ionic species in the donor chamber, the fluxes during DC iontophoresis were weakly dependent of its donor concentration. The fluxes of TEA during constant current AC iontophoresis were moderately related to the donor concentration with the highest TEA flux observed under the 1.0 M TEA chloride condition although the relationship between flux and donor concentration was not linear. A trend of decreasing electroosmotic transport with increasing donor TEA chloride concentration was observed with significant sample-to-sample variability during DC iontophoresis. Mannitol permeability was also observed to decrease with increasing TEA chloride concentration in the donor under the AC conditions, but data variability under AC was significantly smaller than that under DC. The results in the present study indicate that constant current AC iontophoresis under conditions tolerable to human (2 and 5 mA) can provide predictable fluxes that were lower than but of comparable magnitude as those of conventional constant current DC iontophoresis (0.2 mA).

Effects of electrophoresis and electroosmosis during alternating current iontophoresis across human epidermal membrane

Previous studies in our laboratory have demonstrated that skin electrical resistance can be controlled by an alternating current (AC) electric field. By maintaining constant skin resistance, AC iontophoresis has been shown to reduce the iontophoretic flux variability of neutral permeants. Recently, it was found that symmetric square‐wave AC could enhance iontophoretic transport of both neutral and ionic permeants by means of electrophoresis and/or electroosmosis in a synthetic membrane system, and a model was presented to describe the experimental results. The objective of the present study was to assess the effects of AC voltage and frequency and direct current (DC) offset on the flux of neutral and ionic model permeants with human epidermal membrane (HEM). Experiments were conducted under two different conditions: constant AC voltage iontophoresis and iontophoresis using constant HEM resistance with DC offset voltage. The following are the main findings in these experiments. In the constant AC voltage study, when the permeability data were compared at the same HEM electrical resistance, it was demonstrated that AC even at high frequency (≈1 kHz) could enhance the transport of the ionic permeant (tetraethylammonium ion) across HEM, but no enhancement was observed for the neutral permeant (arabinose). For the ionic permeant flux enhancement, the higher the applied AC voltage, the greater the flux enhancement. There was little or no AC frequency dependence of the flux enhancement in the frequency range of 50–1000 Hz. In the constant HEM resistance study of AC with DC offset, approximately linear relationships were observed between flux enhancement and the DC offset voltage for both the neutral and ionic permeants, and these results were found to be consistent with predictions of the modified Nernst‐Planck model for conventional constant voltage DC iontophoresis. When the DC offset voltage was increased, the AC component of the flux enhancement for the ionic permeant decreased, eventually appearing to contribute negligibly to the total flux enhancement at high DC offset voltages. © 2005 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:547–558, 2005

Correlation of transdermal iontophoretic phenylalanine and mannitol transport: test of the internal standard concept under DC iontophoresis and constant resistance AC iontophoresis conditions

The purpose of this study was to test the feasibility of using an internal standard approach to predict the transdermal flux of phenylalanine (Phe) across human epidermal membrane (HEM) in vitro during iontophoresis of constant direct current (DC), constant skin resistance alternating current (AC) with DC offset (AC-plus-DC), symmetric constant resistance AC (AC-only), and constant current DC with the application of a polyelectrolyte. Under the constant current DC and AC-plus-DC conditions, a linear relationship between the permeation of Phe and that of mannitol was observed with a slope close to unity. The ratios of the Phe permeability coefficients to those of mannitol during iontophoresis with different HEM samples were essentially constant with significantly smaller inter-sample and intra-sample variabilities than those of the raw Phe permeability coefficient data. This demonstrates that mannitol is a good internal standard for predicting the transdermal iontophoretic flux of Phe under these two conditions. On the other hand, the correlations of the permeability coefficients of Phe and mannitol under the AC-only iontophoresis and iontophoresis with the polyelectrolyte are poorer than those observed during DC and AC-plus-DC iontophoresis. The poor correlations are believed to be related to Phe being a zwitterion and its anionic form in HEM. Previously, iontophoretic transport of glucose has been demonstrated to be essentially the same as that of mannitol. The good correlations between Phe and mannitol transport across HEM during DC and AC-plus-DC iontophoresis in the present study therefore suggest that glucose and its extraction can be used as the internal standard for iontophoretic Phe monitoring.

In vitro and in vivo comparisons of constant resistance AC iontophoresis and DC iontophoresis

A previous in vitro constant electrical resistance alternating current (AC) iontophoresis study with human epidermal membrane (HEM) and a model neutral permeant has shown less inter- and intra-sample variability in iontophoretic transport relative to conventional constant direct current (DC) iontophoresis. The objectives of the present study were to address the following questions. (1) Can the skin electrical resistance be maintained at a constant level by AC in humans in vivo? (2) Are the in vitro data with HEM representative of those in vivo? (3) Does constant skin resistance AC iontophoresis have less inter- and intra-sample variability than conventional constant current DC iontophoresis in vivo? (4) What are the electrical and the barrier properties of skin during iontophoresis in vivo? In the present study, in vitro HEM experiments were carried out with the constant resistance AC and the conventional constant current DC methods using mannitol and glucose as the neutral model permeants. In vivo human experiments were performed using glucose as the permeant with a constant skin resistance AC only protocol and two conventional constant current DC methods (continuous constant current DC and constant current DC with its polarity alternated every 10 min with a 3:7 on:off duty cycle). Constant current DC iontophoresis was conducted with commercial constant current DC devices, and constant resistance AC iontophoresis was carried out by reducing and maintaining the skin resistance at a constant target value with AC supplied from a function generator. This study shows that (1) skin electrical resistance can be maintained at a constant level during AC iontophoresis in vivo; (2) HEM in vitro and human skin in vivo demonstrate similar electrical and barrier properties, and these properties are consistent with our previous findings; (3) there is general qualitative and semi-quantitative agreement between the HEM data in vitro and human skin data in vivo; and (4) constant skin resistance AC iontophoresis generally provides less inter- and intra-subject variability than conventional constant current DC.

Improvement on conventional constant current DC iontophoresis: a study using constant conductance AC iontophoresis

The purpose of the present study was to compare conventional constant direct current (DC) transdermal iontophoresis with a new constant conductance alternating current (AC) iontophoresis method. The new method was developed with the intent of reducing flux drift during iontophoresis and minimizing skin-to-skin variability. The constant conductance AC iontophoresis studies involved three electrical components: (1) an initial applied potential used to decrease the human epidermal membrane (HEM) electrical resistance to a target level of either 1.5 or 3.0 kΩ cm 2, (2) an applied 50 Hz square-wave AC with a variable potential adjusted to maintain the HEM conductance at the target level during the transport study, and (3) a low voltage DC offset of 0 (passive), 0.25, or 0.40 V applied simultaneously with the AC to assist permeant transport. Current densities of 0.13 and 0.26 mA/cm 2 were chosen for the conventional constant current DC iontophoresis studies. Mannitol was used as the probe permeant for all studies. The constant current DC studies showed significant increases in mannitol flux with time during a given experiment and large skin-to-skin variability. Compared to the constant current DC experiments, the mannitol flux remained more constant during the constant conductance AC iontophoresis and skin-to-skin variability was significantly reduced. On a mechanistic level, changes in the transport properties during constant current DC iontophoresis indicate changes in the membrane parameters such as porosity, effective pore size, and/or pore surface charge density during the conventional method of iontophoresis. The results from the constant conductance AC iontophoresis transport studies imply that this method effectively maintains the membrane parameters that affect transport at a constant state this providing for a relatively constant permanent flux.