Current Pulse Width Research Articles

Improve Control to Output Dynamic Response and Extend Modulation Index Range With Hybrid Selective Harmonic Current Mitigation-PWM and Phase-Shift PWM for Four-Quadrant Cascaded H-Bridge Converters

The selective harmonic current mitigation pulsewidth modulation (SHCM-PWM) technique can be used in cascaded multilevel converters to extend the harmonic reduction spectrum, reduce the coupling inductance and increase the efficiency. The offline SHCM-PWM technique has small number of switching transitions as its switching angles can only change once in a fundamental cycle and relatively long time delays because it uses FFT. As a result, its dynamic response has a lot to desire. As it will be proven in this paper, in four-quadrant power converters, to have a good transient dynamic response, both active and reactive power must be controlled at least two times in a fundamental cycle. In this paper, a hybrid modulation technique is introduced. The proposed technique uses SHCM-PWM under steady state and phase-shift PWM (PSPWM) under transient. In addition, in order to extend the modulation index range and ensure that SHCM-PWM can process four-quadrant active and reactive power, the constraints of the switching angles for the SHCM-PWM are modified. Simulations and experiments are conducted on a seven-level cascaded H-bridge converter to verify the proposed technique.

Tuning the perpendicular magnetic anisotropy, spin Hall switching current density, and domain wall velocity by submonolayer insertion in Ta/CoFeB/MgO heterostructures

By submonolayer insertion of Au, Pt, or Pd into Ta/CoFeB/MgO/Ta heterostructures, we tune the perpendicular magnetic anisotropy and the coercive field of the ferromagnetic layer. We demonstrate that this has a major influence on the spin Hall switching current density and its dependence on the external magnetic field. Despite a rather small effective spin Hall angle of θSH≈−0.07, we obtain switching current densities as low as 2×1010 A/m2 with a 2 Å Au interlayer. We find that the Dzyaloshinskii-Moriya interaction parameter D is reduced with Au or Pd interlayers, and the perpendicular anisotropy field is reduced by an order of magnitude with the Pd interlayer. The dependence of the switching current density on the current pulse width is quantitatively explained with a domain wall nucleation and propagation model. Interface engineering is thus found to be a suitable route to tailor the current-induced magnetization switching properties of magnetic heterostructures.

Modified Synchronous Reference Frame Based Shunt Active Power Filter with Fuzzy Logic Control Pulse Width Modulation Inverter

Harmonic distortion in power networks has greatly reduced power quality and this affects system stability. In order to mitigate this power quality issue, the shunt active power filter (SAPF) has been widely applied and it is proven to be the best solution to current harmonics. This paper evaluates the performance of the modified synchronous reference frame extraction (MSRF) algorithm with fuzzy logic controller (FLC) based current control pulse width modulation (PWM) inverter of three-phase three-wire SAPF to mitigate current harmonics. The proposed FLC is designed with a reduced amount of membership functions (MFs) and rules, and thus significantly reduces the computational time and memory size. Modeling and simulations of SAPF are carried out using MATLAB/Simulink R2012a with the power system toolbox under steady-state condition, and this is followed with hardware implementation using a TMS320F28335 digital signal processor (DSP), Specrum Digital Inc., Stafford, TX, USA. The results obtained demonstrate a good and satisfactory response to mitigate the harmonics in the system. The total harmonic distortion (THD) for the system has been reduced from 25.60% to 0.92% and 1.41% in the simulation study with and without FLC, respectively. Similarly for the experimental study, the SAPF can compensate for the three-phase load current by reducing THD to 5.07% and 7.4% with and without FLC, respectively.

Current mode pulse width modulation/pulse position modulation based on phase lock loop

Abstract In this paper, the fully integrated CMOS current mode PLL with current input injects at the place of input or output of the loop filter without summing amplifier circuit. It functions as PPM and PWM circuit is present. In addition, its frequency response is an analysis which electronic tuning BPF and LPF are obtained. The proposed circuit has been designed with 0.18 μm CMOS technology. The simulation results of this circuit can be operated at 2.5 V supply voltage, at center frequency 100 MHz. The linear range of input current can be adjusted from 43 μA to 109 μA, and the corresponding duty cycle of pulse width output is from 93% to 16% and the normalized pulse position is from 0.93 to 0.16. The power dissipation of this circuit is 4.68 mW with the total chip area is 28 μm × 60 μm.

Design and operation of a multifunction photovoltaic power system with shunt active filtering using a single-stage three-phase multilevel inverter

In this paper, the control of a multifunction grid-connected photovoltaic (PV) system with a three-phase three-level (3L) neutral point clamped (NPC) inverter is proposed, which can perform shunt active filtering. Normally, the shunt active filtering is achieved by detecting the harmonic and reactive currents of the nonlinear load and then injecting the compensating current into the grid. Therefore, the proposed system can inject PV power to a grid with power factor correction and current harmonic filtering features simultaneously. In addition, a single-stage compact and efficient transformerless power conversion topology is used in this paper for the grid-connected solar PV system with maximum power point tracking capability. In order to control the multilevel inverter-based combined system, a synchronous reference frame control technique and hysteresis current control pulse width modulation method have been applied. The system configuration and control strategy are verified and validated by simulations based on MATLAB/Simulink and implemented in real-time using the dSPACE DS1103 controller board. The simulation with experimental results indicates that the injected currents are sinusoidal and current total harmonic distortion is about 3.9%, lower than the IEEE 519 harmonic limit.

Parametric characterization of neural activity in the locus coeruleus in response to vagus nerve stimulation

Vagus nerve stimulation (VNS) has emerged as a therapy to treat a wide range of neurological disorders, including epilepsy, depression, stroke, and tinnitus. Activation of neurons in the locus coeruleus (LC) is believed to mediate many of the effects of VNS in the central nervous system. Despite the importance of the LC, there is a dearth of direct evidence characterizing neural activity in response to VNS. A detailed understanding of the brain activity evoked by VNS across a range of stimulation parameters may guide selection of stimulation regimens for therapeutic use. In this study, we recorded neural activity in the LC and the mesencephalic trigeminal nucleus (Me5) in response to VNS over a broad range of current amplitudes, pulse frequencies, train durations, inter-train intervals, and pulse widths. Brief 0.5s trains of VNS drive rapid, phasic firing of LC neurons at 0.1mA. Higher current intensities and longer pulse widths drive greater increases in LC firing rate. Varying the pulse frequency substantially affects the timing, but not the total amount, of phasic LC activity. VNS drives pulse-locked neural activity in the Me5 at current levels above 1.2mA. These results provide insight into VNS-evoked phasic neural activity in multiple neural structures and may be useful in guiding the selection of VNS parameters to enhance clinical efficacy.

Plasma jet seven-array discharge at atmospheric helium gas

A low temperature plasma jet array device using seven single electrodes surrounded with insulated organic glass is designed to study the discharge properties of atmospheric plasma jet. The ambient gas is atmospheric Helium gas, whose flow rate is controlled from 0 L/min to 10 L/min. This discharge device is driven by a sub-microsecond repetitive high voltage pulsed power with the pulse width about 230 ns, the rising edge about 120 ns. Using a repetitive frequency rate about 500 Hz, the high speed photographs are taken and the current pulse width is about 110 ns. The average jet length was measured under the conditions of changing gas flow rate and pulse voltage amplitudes in the experiment, in order to acquire the interactions of every plasma jet discharge. It is found that the average plasma jet length increases with the increasing voltage amplitude when the voltage amplitude is less than 20 kV and that it increases slowly when the voltage amplitude is higher, up to 35 kV. It is also found that the average jet length reaches the maximum when the gas flowrate is at a regular value, that is, the average length decreases if the gas flowrate is over or under the regular range. Besides, it is also discovered that the central electrode discharge is affected extremely by the gas flowrate. The central jet length is almost invisible when the gas flowrate is very high or very low, while the central jet with a weak discharge is longer than the surrounding jets when the gas flow rate is 1 L/min. The main reasons are that the air blocks the jet developing and the central electrode jet channel is impeded by the surrounding jets. It is easier for the surrounding electrode to develop jets.

Stimulus characteristics in electroconvulsive therapy. A pragmatic review.

The process of normalization electroconvulsive therapy (ECT) requires, among other actions, disseminating the latest information on this technique. One of the most complex aspects is the electrical stimulus, whose knowledge should be spread and put into practice. In this paper we review the available information about frequency and number of ECT sessions, and efficacy of each electrode placement. We also present two approaches to determine the ECT charge: stimulus titration versus age-based method; and the limitations of the summary metrics of charge, being necessary to expand our knowledge of the parameters that configure the stimulus: duration, current amplitude frequency and pulse width.

Xenon Z-Pinch Discharge Plasma EUV Source Driven by Ultrashort Current Pulse

The extreme ultraviolet (EUV) spectrum has significant interest both for basic science and for industrial applications, especially lithography-related studies. Discharge-produced plasma (DPP) EUV source efficiently generates EUV radiation. Current pulse parameter is the most important and sensitive factor in DPP EUV source, which is determined by the discharge loop inductance. This paper reports on shortening the current pulsewidth by reducing discharge loop inductance on a xenon gas Z-pinch DPP EUV source. The inherent inductance of the discharge loop was reduced to about 17 nH from the previous 34 nH, and the short-circuit current pulsewidth was shortened to 85 ns. Pulsewidth of discharge plasma current was only about 110 ns. DPP EUV source was characterized in terms of EUV signals (7–16 nm) and images. The experimental results show that a shorter current pulse produces sharper EUV signals. Ultrashort current pulse discharge radiated a sharp EUV signal with a narrow pulsewidth [full-width at half-maximum (FWHM)] of only 10 ns. Axial and radial sizes (FWHM) of EUV-emitting plasma were 2 mm and $400~\mu \text{m}$ , respectively. EUV source resembles an ellipse differing from the jet shape driven by longer current pulses. Thus, a DPP EUV source driven by an ultrashort current pulse may suit high temporal and spatial resolutions required for EUV application. Corresponding plasma dynamics are observed and discussed. A comparison of time-resolved visible and EUV light images indicates that EUV emission radiates from two adjacent stagnated hot plasma columns and localizes along the central axis. This also differs from longer current driven plasma dynamics, in which EUV emission radiates from the neck part between two separate cooler plasma zones and moves with the current flow. This implies that ultrashort current pulse may inhibit axial development of EUV-emitting plasma, thus improving EUV source spatial stability and reducing EUV radiation size.

High-speed electrochemical discharge drilling (HSECDD) for micro-holes on C17200 beryllium copper alloy in deionized water

Beryllium copper alloys with excellent features are widely used in many engineering fields, and their fabrication requires high machining speed. However, the fabrication of beryllium copper alloys by traditional processes has serious problems. In this study, high-speed electrochemical discharge drilling (HSECDD), a hybrid process containing electrical discharge machining (EDM) and electrochemical machining (ECM) in deionized water, was used to machine micro-holes on C17200 beryllium copper alloy. The material removal mechanism of HSECDD was studied and compared with traditional EDM. The performance of the process was investigated under different conductivities of peak current and pulse width. The results show that HSECDD is a high-efficiency method to machine C17200 beryllium copper alloy. During HSECDD, the material removal depends mainly on EDM. And, the ECM occurs at the entrance region of micro-holes machined by EDM. The function of ECM is to expand the gap between the electrode and the hole. The machining speed and average diameter of micro-holes increase with the increasing of peak current and pulse width. Increasing the pulse width will reduce the electrode wear. However, the taper angle will increase. In addition, the results also show that a value of 0.34-A peak current and 10-μs pulse width can be considered an ideal parameter for HSECDD to machine micro-holes on C17200 beryllium copper alloy.

Combining an obstacle and electrically driven vortices to enhance heat transfer in a quasi-two-dimensional MHD duct flow

The design of vortex promoters in a heated-wall duct is often limited by the considerations of practicality, especially in complex systems such as fusion blankets. The present study investigates the use of current injection to invoke a street of vortices in quasi-two-dimensional high transverse magnetic field magnetohydrodynamic duct flows to enhance instability behind a cylinder. The intent is to generate intensive flow vorticity parallel to a magnetic field downstream of a field-aligned cylinder. Electric current enters the flow through an electrode embedded in one of the Hartmann walls, radiates outward, imparting a rotational forcing around the electrode due to the Lorentz force. The quasi-two-dimensional nature of these flows then promotes a vortical rotation across the interior of the duct with axis aligned to the magnetic field. The hot and cold walls are parallel to the magnetic field. Electric current amplitude and pulse width, excitation frequency and electrode position are systematically varied to explore their influences on the convective heat transport phenomenon. This investigation builds on a recommendation from previous work of Bühler (J. Fluid Mech., vol. 326, 1996, pp. 125–150) dedicated to understanding of the flow stability in a similar configuration. This study provides supportive evidence for the use of current injection as an alternative to the conventional mechanically actuated turbuliser, with heat transfer almost doubled for negligible additional pumping power requirements.

High-energy sub-nanosecond optical pulse generation with a semiconductor laser diode for pulsed TOF laser ranging utilizing the single photon detection approach

Bulk and quantum well laser diodes with a large equivalent spot size of d a /Γ a ≈ 3 µm and stripe width/cavity length of 30 µm/3 mm were realized and tested. They achieved a pulse energy and pulse length of the order of ~1 nJ and ~100 ps, respectively, with a peak pulse current of 6–8 A and a current pulse width of 1 ns. The 2D characteristics of the optical output power versus wavelength and time were also analyzed with a monochromator/streak camera set-up. The far-field characteristics were studied with respect to the time-homogeneity and energy distribution. The feasibility of a laser diode with a large equivalent spot size in single photon detection based laser ranging was demonstrated to a non-cooperative target at a distance of a few tens of meters.

Effects of Electric Barrier on Passage and Physical Condition of Juvenile and Adult Rainbow Trout

Abstract Electric barriers can inhibit passage and injure fish. Few data exist on electric barrier parameters that minimize these impacts and on how body size affects susceptibility, especially to nontarget fish species. The goal of this study was to determine electric barrier voltage and pulse-width settings that inhibit passage of larger bodied rainbow trout Oncorhynchus mykiss (215–410 mm fork length) while allowing passage of smaller bodied juvenile rainbow trout (52–126 mm) in a static laboratory setting. We exposed rainbow trout to 30-Hz pulsed-direct current voltage gradients (0.00–0.45 V cm−1) and pulse widths (0.0–0.7 ms) and recorded their movement, injury incidence, and mortality. No settings tested allowed all juveniles to pass while impeding all adult passage. Juvenile and adult rainbow trout avoided the barrier at higher pulse widths, and fewer rainbow trout passed the barrier at 0.7-ms pulse width compared to 0.1 ms and when the barrier was turned off. We found no effect of voltage gradient on fish passage. No mortality occurred, and we observed external bruising in 5 (7%) juvenile rainbow trout and 15 (21%) adult rainbow trout. This study may aid managers in selecting barrier settings that allow for increased juvenile passage.

A frequency and pulse-width co-modulation strategy for transcutaneous neuromuscular electrical stimulation based on sEMG time-domain features

Objective. Surface electromyography (sEMG) is often used as a control signal in neuromuscular electrical stimulation (NMES) systems to enhance the voluntary control and proprioceptive sensory feedback of paralyzed patients. Most sEMG-controlled NMES systems use the envelope of the sEMG signal to modulate the stimulation intensity (current amplitude or pulse width) with a constant frequency. The aims of this study were to develop a strategy that co-modulates frequency and pulse width based on features of the sEMG signal and to investigate the torque-reproduction performance and the level of fatigue resistance achieved with our strategy. Approach. We examined the relationships between wrist torque and two stimulation parameters (frequency and pulse width) and between wrist torque and two sEMG time-domain features (mean absolute value (MAV) and number of slope sign changes (NSS)) in eight healthy volunteers. By using wrist torque as an intermediate variable, customized and generalized transfer functions were constructed to convert the two features of the sEMG signal into the two stimulation parameters, thereby establishing a MAV/NSS dual-coding (MNDC) algorithm. Wrist torque reproduction performance was assessed by comparing the torque generated by the algorithms with that originally recorded during voluntary contractions. Muscle fatigue was assessed by measuring the decline percentage of the peak torque and by comparing the torque time integral of the response to test stimulation trains before and after fatigue sessions. Main Results. The MNDC approach could produce a wrist torque that closely matched the voluntary wrist torque. In addition, a smaller decay in the wrist torque was observed after the MNDC-coded fatigue stimulation was applied than after stimulation using pulse-width modulation alone. Significance. Compared with pulse-width modulation stimulation strategies that are based on sEMG detection, the MNDC strategy is more effective for both voluntary muscle force reproduction and muscle fatigue reduction.

Spatiotemporal dynamics of cortical perfusion in response to thalamic deep brain stimulation

Deep brain stimulation (DBS) has revolutionized the treatment of movement disorders. The parameters of electrical stimulation are important to its therapeutic effect and remain a source of clinical controversy. DBS exerts its actions not only locally at the site of stimulation but also remotely through afferent and efferent connections, which are vital to its clinical effects. Yet, only a few studies have examined how cortical activity changes in response to various electrical parameters. Here, we investigated how the parameters of thalamic DBS alter cortical perfusion in rats using intrinsic optical imaging. We hypothesized that thalamic DBS will increase perfusion in primary motor cortex (M1), proportional to amplitude, pulse width, or frequency of the stimulation applied. We applied 45 different combinations of amplitude, pulse width and frequency in the ventro-lateral (VL) nucleus of the thalamus in anesthetized rats while measuring perfusion in M1. VL thalamic DBS reduced cortical reflectance, which corresponds to an increase in cortical perfusion. We computed the maximum change in reflectance (MCR) as well as the spatial spread of MCR in each trial. Both MCR and spatial spread increased linearly with increases in current amplitude or pulse width of stimulation; however, the effect of frequency was non-linear. Stimulation at 20Hz was significantly different from that at higher frequencies while stimulation at higher frequencies did not differ significantly from each other. Moreover, the effect of pulse width on MCR was larger than the effect of amplitude. The proportional increase in M1 perfusion due to increase in amplitude or pulse width suggests that both activate more neural elements and increase the volume of tissue activated. These results should help clinicians set parameters of DBS. The use of optical imaging to monitor effects of DBS on M1 may not only help understand DBS mechanisms, but may also provide feedback for closed loop DBS devices.

In-plane current induced domain wall nucleation and its stochasticity in perpendicular magnetic anisotropy Hall cross structures

Hall cross structures in magnetic nanowires are commonly used for electrical detection of magnetization reversal in which a domain wall (DW) is conventionally nucleated by a local Oersted field. In this letter, we demonstrate DW nucleation in Co/Ni perpendicular magnetic anisotropy nanowire at the magnetic Hall cross junction. The DWs are nucleated by applying an in-plane pulsed current through the nanowire without the need of a local Oersted field. The change in Hall resistance, detected using anomalous Hall effect, is governed by the magnetic volume switched at the Hall junction, which can be tuned by varying the magnitude of the applied current density and pulse width. The nucleated DWs are driven simultaneously under the spin transfer torque effect when the applied current density is above a threshold. The possibility of multiple DW generation and variation in magnetic volume switched makes nucleation process stochastic in nature. The in-plane current induced stochastic nature of DW generation may find applications in random number generation.

Plasticity and microstructure evolution of W-CeO2 rods with different short-duration pulse currents

To improve the formability of W-rare earth electrode, the influence of high-energy pulse on the plasticity property of W-CeO2 rods was investigated. The effects of current density (J0), pulse width (tw), frequency (f), and strain rate on the plasticity of W-CeO2 rods were discussed in detail. Results of tensile tests show that the W-CeO2 rods applied with the electrical pulses obtain a maximum percentage total elongation at fracture (9.65 %), increased by 118.7 % compared to that without pulses. This is owing to both the heat effect and the interaction of current between dislocations and rare earth additions. Electron back scattered diffraction (EBSD)-generated grain boundary (GB) maps suggest that the length of low-angle grain boundaries composed of high-density dislocations decreases after deformation while applying the pulse current. This demonstrates that the short-duration pulsed current enhances the mobility of dislocations. Scanning electron microscopy (SEM) images of the rods after deformation with the pulse current show that the long fiber-shaped additions become discontinuous, which could reduce the stress concentration and hinder the crack propagation.

Characterization of evoked tactile sensation in forearm amputees with transcutaneous electrical nerve stimulation

Objective. The goal of this study is to characterize the phenomenon of evoked tactile sensation (ETS) on the stump skin of forearm amputees using transcutaneous electrical nerve stimulation (TENS). Approach. We identified the projected finger map (PFM) of ETS on the stump skin in 11 forearm amputees, and compared perceptual attributes of the ETS in nine forearm amputees and eight able-bodied subjects using TENS. The profile of perceptual thresholds at the most sensitive points (MSPs) in each finger-projected area was obtained by modulating current amplitude, pulse width, and frequency of the biphasic, rectangular current stimulus. The long-term stability of the PFM and the perceptual threshold of the ETS were monitored in five forearm amputees for a period of 11 months. Main results. Five finger-specific projection areas can be independently identified on the stump skin of forearm amputees with a relatively long residual stump length. The shape of the PFM was progressively similar to that of the hand with more distal amputation. Similar sensory modalities of touch, pressure, buzz, vibration, and numb below pain sensation could be evoked both in the PFM of the stump skin of amputees and in the normal skin of able-bodied subjects. Sensory thresholds in the normal skin of able-bodied subjects were generally lower than those in the stump skin of forearm amputees, however, both were linearly modulated by current amplitude and pulse width. The variation of the MSPs in the PFM was confined to a small elliptical area with 95% confidence. The perceptual thresholds of thumb-projected areas were found to vary less than 0.99 × 10−2 mA cm−2. Significance. The stable PFM and sensory thresholds of ETS are desirable for a non-invasive neural interface that can feed back finger-specific tactile information from the prosthetic hand to forearm amputees.

Spin-orbit torque induced magnetization switching in nano-scale Ta/CoFeB/MgO

We study the device size dependence of spin-orbit torque induced magnetization switching in a Ta/CoFeB/MgO structure with perpendicular easy axis. The miniaturization of the device from micrometer-sized wire to 80-nm dot results in the increase of the threshold current density Jth by one order, whereas Jth increases only slightly with further reducing the device size down to 30 nm. No significant increase in Jth is seen, as the current pulse width decreases from 100 ms down to 3 ns. We reveal that the switching in devices at reduced size is reasonably well explained by the macrospin model, in which the effects of both the Slonczewski-like torque and field-like torque are included.

Electrical nerve stimulation method for intraoperative localization of the inferior alveolar nerve within the mandible: a pilot study in rabbits

The efficacy of the electrical nerve stimulation method for localizing the inferior alveolar nerve (IAN) within the mandibular bone was evaluated. Six New Zealand rabbits were used (both sides of the mandible). The IAN was stimulated through the mandibular bone and compound action potentials (CAPs) were recorded proximally from the main trunk of the nerve. Stimulation current pulse widths were set at 0.05, 0.1, 0.3, 0.5, and 1ms. The minimum current magnitude that generated a CAP with a criterion level (300mV peak-to-peak amplitude) was measured in the range of 0.05–5mA. Correlations between the distance of the IAN from the active electrode site and the minimum current magnitudes were studied for each pulse width. The correlation coefficients were 0.678, 0.807, 0.893, 0.851, and 0.890 for the pulse widths of 0.05, 0.1, 0.3, 0.5, and 1ms, respectively. The minimum current producing the criterion CAP response in the IAN was significantly (P<0.0001 for all pulse widths) and highly correlated with the distance between the stimulation site and the nerve. The results suggest that electrical nerve stimulation is a promising method that can be used for the localization of the IAN, especially during mandibular implant surgery.