Small DC Voltage Research Articles

Optoelectronic Transimpedance Converter Based on MOS Photovaricap for High Resistive Gas Sensors

The gas detectors consist of two parts: metal-oxides gas sensor and transducer. The sensing material is made of a thin semiconductor layer. The transducer is responsible for converting the change in the several physical parameters of the thin sensitive layer into a measurable signal. Due to the high output resistance of high resistive gas sensors and the low input currents of amplifiers, electrometric cascades are employed, followed by the conversion of the gas sensors small direct current into an active current signal using a mechanical modulator (dynamic capacitor) to enhance sensitivity and stability. The aim of this research is to analyze the main characteristics of a novel type of dynamic capacitor that utilizes a surface metal-oxide-semiconductor (MOS) photovaricap (PV) as the regulating element when detecting signals from high resistive gas sensors. For the creation of surface MOS PVs, samples of p-Si with varying resistivity were chosen. A thin layer of SiO2 was deposited on these samples, onto which a translucent metallic electrode was applied. Modulation of the PV capacitance was achieved by illuminating it with a gallium arsenide LED. As a result, the capacitance of the PV is changed, producing a variable voltage across the load resistor, which was then amplified and recorded. It was observed that the settling time of the useful signal is determined by two factors. The first is the RC chain composed of the load resistance of the gas sensor and the input capacitance of the PV, and the second is slow relaxation phenomena in the structure of the MOS PV that lead to the screening of the induced charge. Characteristics of the MOS PV as a dynamic capacitor and the features of the photo capacitance as a semiconductor element, in turn, determine the transimpedance conversion coefficient. The conducted research showed that MOS PVs can be applied to register small DC currents and voltages from high resistive gas sensors. In this case, ordinary narrowband or wideband amplifiers with relatively low input resistance can be used instead of electrometric amplifiers with mechanical dynamic capacitors. The considered circuit has been experimentally tested with commercial resistors.

Traceability Technology of DC Electric Energy Metering for On-Site Inspection of Chargers

The on-site inspection of high-power DC chargers results in new DC high-current measurement and DC energy traceability system requirements. This paper studies the traceability technology of electric energy value for automotive high-power DC chargers, including: (1) the traceability method of the built-in DC energy meter and shunt of the charger; (2) precision DC high current and small precision DC voltage output and measurement technology. This paper designs a 0.1 mA~600 A DC high current measurement system and proposes a 0.005 level DC power measurement traceability system. The uncertainty evaluation experiment of the DC power measurement calibration system and the high-power DC charger’s on-site calibration experiment results verify the method’s effectiveness and feasibility in this paper. The experimental results show that the combined standard uncertainty of the DC power metering verification system can be 0.0451%.

Economic cost analysis of air-cooling process using different numbers of Peltier modules; Experimental case study

Generally speaking, a Peltier module obtains a high value of COP only for a small range of applied DC voltage. Indeed, increment of DC voltage sharply reduces its COP. Hence, to get a high total COP for a large-scale commercial Peltier air cooler (for example input power of 1000 W) each individual Peltier module should work with a small input DC voltage. This means, a greater number of Peltier modules should be employed in a real cooler to reduce the allocate DC voltage for any individual Peltier module. However, this means higher capital, maintenance, operating and maybe final cooling cost. Hence, a size related cost economic analysis is required for cooling process using Peltier module which is experimentally presented in this research. Three Peltier air coolers with different sizes (but in the same range of total input power) are investigated from efficiency and economic cost viewpoints. Findings show that despite the higher capital and maintenance cost for case “c” (6 TEM), it still provides cheaper cooling compared to the other cases. However, it is noted that case “b” (4 modules) provides 100% lower cooling cost compared to the case “a” (2 modules) while case “c” (6 modules) provides only 35% lower cooling cost compared to the case “b”. This means, although increasing module number enhances the total COP of the cooler (for a given input power) and reduces the cooling cost, further increment of module number will finally augment the cooling cost of the cooler. Hence, an optimized number of modules can be selected for a large-scale cooling by simultaneous multi economic and cooling optimization. The quantitative and qualitative findings of this research can be useful for future marketing, and commercialization purposes of large-scale air-cooling process using Peltier module.

(Digital Presentation) Degradation and Recovery of Low Temperature Poly-Si Thin Film Transistors Under DC and AC Bias Stresses

The low temperature poly-Si thin-film transistors (LTPS TFTs) have been extensively applied in the AMLCD and AMOLED due to their high carrier’s mobility and driving currents, and the ability to integrate the driving circuits onto the same substrate. The main mechanisms causing the degradation of the LTPS TFTs under bias stress are: hot carrier effect and self-heating effect. In this study, the degradation and recovery phenomena of the LTPS TFTs stressed by the hot carrier effect conditions would be systematically investigated. The device structures used in this study are n-channel LTPS TFTs with different lengths of lightly doped drain (LDD).First, we simultaneously apply a small positive DC voltage, approximately the threshold voltage plus 1V (Vth+1= +3 V), to the gate terminal and a large positive DC voltage (+12 V) to the drain terminal of the LTPS TFTs with three different LDD’s lengths. These stressing conditions would cause the TFTs operated in the saturation region, so that the channel is pinched off. And the electrons would be accelerated by a large transverse electric field when they drift from the source terminal to the drain one. The energetic electrons would impact the lattices of the channel and the interface between the gate dielectric and the channel near the drain terminal, causing the defect states and electron-hole pair generation. Few of the carriers with enough energy to overcome the energy barrier of gate dielectric would be trapped by the defects in it. The hot carrier effect causes the degradation of the TFTs devices, including the decrease of ON current and carrier mobility and the increase of OFF current, but less degradation of the threshold voltage and subthreshold swing. After the bias stressing, the resting time is added to investigate the recovery phenomena. The difference in the amount of degradation and the location of defects would cause the different recovery ratio. After the end of bias stressing, all of the terminals are not applied with any voltages in the resting periods. The electrons and holes generated in the channel near the drain terminal would recombine, and the defect states generated by the hot carrier impact slightly reduce, which causes the recovery phenomena of the degraded transistors.Then, we apply a small AC voltage (0 ~ +3 V) to the gate terminal and a large positive DC voltage (+12 V) to the drain one at the same time. This mode of bias stressing conditions is closer to the real operating mode of the TFTs in the driving circuits. From the experimental data, it could be found that there is no significant difference in the degradation of the TFTs under different frequency of AC signals applied on the gate. But the recovery ratio tends to gradually increase as the frequency increasing.Finally, a small positive DC voltage (+3 V) is applied to the gate terminal, and a large AC voltage (0 ~ +12 V) to the drain one at the same time. From the experimental data, it could be found that with the increase of AC signal frequency, the degradation of the TFTs decreases, but the recovery ratio of the TFTs increases due to the reduction of the effective stressing time in one period. As compared to the results of all stressing conditions, the TFTs, both of the gate and drain terminals applied with DC voltages, exhibit the largest degradation ratio but the least recovery one. However, the TFTs, as the gate terminal applied with DC voltages and drain one with AC voltage, exhibit the less degradation ratio but the largest recovery one.

Optimal Virtual Inertia Design for VSG-based Motor Starting Systems to Improve Motor Loading Capacity

Virtual synchronous generator (VSG)-based control approaches for AC machine drivers have attracted much attention in recent years. The contradiction between the strong motor loading capacity and the small DC voltage fluctuation is disregarded in previous studies. A larger virtual inertia is required to raise the torque gain and drive the motor with heavier loads, thus resulting in larger DC voltage variations. A systematic method is proposed for the optimal design of the virtual inertia for VSG-based motor starting systems to achieve the maximal motor loading capacity and the low DC voltage fluctuation in this paper. Firstly, the relationship between the virtual inertia and the loading capacity is revealed on the basis of the closed-loop analysis. Considering the DC voltage variation, the constraint on the maximal value of the virtual inertia is proposed from the energy-balance perspective despite the unknown contribution of the DC capacitors to the virtual inertia. To fully exploit the energy storage capacity of the DC capacitors and raise the upper limit of the virtual inertia under the same permitted DC voltage variation, a modified DC voltage reference is introduced. Extensive simulation and experimental results are presented to validate the effectiveness of the proposed methods.

Versatile AC Current Control Technique for a Battery Using Power Converters

Although a battery is a DC device, AC current is often necessary for testing, preheating, impedance spectroscopy, and advanced charging. This paper presents a versatile control technique to inject AC current to a battery. Synchronous buck and H-bridge topologies are operated in bidirectional mode and controlled by uni-polar and bi-polar pulse width modulation techniques for the AC current injection. The input and output passive circuits are specially designed considering AC current and the properties of the battery. A controller is proposed considering a small internal impedance, small AC ripple voltage, and variable DC offset voltage of a battery. The controller is capable of maintaining stable operation of AC current injection in two power quadrant within a small DC voltage boundary of a battery. The controller is comprised of a feedback compensator, a feedforward term, and an estimator. The feedback gain is designed considering the internal impedance. The feedforward gain is designed based on estimated open circuit battery voltage and input voltage. The open circuit voltage estimator is designed based on filters and battery model. For validation, AC current is injected to a Valence U-12XP battery. The battery is rated for 40 Ah nominal capacity and 13.8 V nominal voltage The controller successfully injected AC current to a battery with +10 A, 0 A and −10 A DC currents. The magnitude and frequency of the AC current was up to 5 A and 2 kHz respectively.

Interference effects induced by a precessing easy-plane magnet coupled to a helical edge state

The interaction of a magnetic insulator with the helical electronic edge of a two-dimensional topological insulator has been shown to lead to many interesting phenomena. One of these is that for a suitable orientation of the magnetic anisotropy axis, the exchange coupling to an easy-plane magnet has no effect on DC electrical transport through a helical edge, despite the fact that it opens a gap in the spectrum of the helical edge [Meng {\em et al.}, Phys.\ Rev.\ B {\bf 90}, 205403 (2014)]. Here, we theoretically consider such a magnet embedded in an interferometer, consisting of a pair of helical edge states connected by two tunneling contacts, at which electrons can tunnel between the two edges. Using a scattering matrix approach, we show that the presence of the magnet in one of the interferometer arms gives rise to AC currents in response to an applied DC voltage. On the other hand, the DC Aharonov-Bohm effect is absent at zero temperature and small DC voltages, and only appears if the applied voltage or the temperature exceeds the magnet-induced excitation gap.

Design of a flyback high-efficiency switching power supply

Switching power supplies are widely used in automotive, aviation, and DC speed control fields. Its biggest requirement is stable output and high efficiency. It is usually realized by resonant converters, but its control circuit is complex and the output ripple is large. In this paper, a new type of flyback switching power supply is designed using a flyback conversion circuit and a single-tube self-excited conversion circuit. Experiments have shown that the designed switching power supply improves the efficiency and reliability of the power supply while obtaining a small ripple, continuously adjustable, and stable DC voltage.

Neural Networks Based Shunt Hybrid Active Power Filter for Harmonic Elimination

The growing use of nonlinear devices is introducing harmonics in power system networks that result in distortion of current and voltage signals causing damage to power distribution systems. Therefore, in power systems, the elimination of harmonics is of great significance. This paper presents an efficient techno-economical approach to suppress harmonics and improve the power factor in power distribution networks using Shunt Hybrid Active Power Filters (SHAPF) based on neural network algorithms like Artificial Neural Network (ANN), Adaptive Neuro-Fuzzy Inference System (ANFIS), and Recurrent Neural Network (RNN). The objective of the proposed algorithms for SHAPF is to enhance system performance by reducing Total Harmonic Distortion (THD). In our filter design approach, we tested and compared conventional pq0 theory and neural networks to detect the harmonics present in the power system. Moreover, for the regulation of DC supply to the inverter of the SHAPF, the conventional PI controller and neural networks-based controllers are used and compared. The applicability of the proposed filter is tested for three different nonlinear load cases. The simulation results show that the neural networks-based filter control techniques satisfy all international standards with minimum current THD, neutral wire current elimination, and small DC voltage fluctuations for voltage regulation current. Furthermore, the three neural network architectures are tested and compared based on accuracy and computational complexity, with RNN outperforming the rest.

A Novel Step-Up Single Source Multilevel Inverter: Topology, Operating Principle, and Modulation

This paper presents a novel step-up dc to ac converter with only one power supply. These types of converters are suitable for renewable and sustainable energy applications with low input dc sources. The proposed topology has the ability of self-voltage balancing and does not apply end side H-bridge to produce a bipolar staircase waveform. Consequently, switching losses and voltage stress of semiconductor components are reduced to a great extent. A small dc voltage source can be used to achieve a high voltage high quality ac waveform through switching the precharged capacitors in series and in parallel. Circuit configuration and its operation principle, capacitors’ charging process, thermal model, capacitances, and losses calculations are discussed in details. Moreover, the comparison of the proposed circuit with the other single source multilevel converters shows that the proposed topology reduces the number of circuit elements. Finally, a laboratory nine-level prototype is built to verify the theoretical analyses and feasibility of the proposed topology. The experimental results show that the converter efficiency at 1 KW output power is 92.75%.

Local nonlinear dynamics of MEMS arches actuated by fringing-field electrostatic actuation

The nonlinear dynamic behavior of a resonant MEMS arch microbeam actuated by fringing electric actuation is investigated in this paper. The arch microbeam is loaded with DC and AC harmonic electric load and the ground electrodes placed at either side of the beam. The curvature caused imbalance distribution of field lines and results in a resultant force. Euler–Bernoulli beam equation was used in accordance with the shallow beam theory to get the equation of motion. Method of multiple scales (MMS) perturbation technique was used to perturb the beam near the fundamental frequency of the microbeam to study its resonant behavior in the local vicinity of the considered frequency. Different midpoint elevations were investigated to study the effect of curvature on the resonance frequency of the beam. The MMS reveals that a beam with low initial midpoint elevation shows initially a softening behavior for small DC voltage excitation. Then, the beam undergoes a hardening when the DC voltage is increased. Finally, the beam returns back to softening behavior when the DC load is further increased to higher values with a curling in the frequency response graph. When the midpoint elevation is increased, the beam is known to undergo symmetry breaking when the DC load is increased before regaining symmetry at even further higher DC load. The MMS shows that there is softening behavior in the initial region prior to symmetry breaking. The effective nonlinearity even drops further to more negative values making the beam more softened in the region of symmetry breaking. After the beam regains symmetry, the effective nonlinearity experiences a more significant drop now causing the beam to be highly softened in this region of high DC load.

Research and Construction of DC Energy Measurement Traceability Technology

With the implementation of energy saving and emission reduction policies, DC energy metering has been widely used in many fields. In view of the lack of a DC energy measurementtraceability system, in combination with the process of downward measurement transfer in relation to the DC charger-based field calibration technology and DC energy meter and shunt calibration technologies, the paper proposed DC fast charging, high DC, small DC voltage output and measuring technologies, and built a time-based plan by converting high DC voltage into low voltage and high current into low current and then into low voltage, leaving DC energy traceable to national standards in terms of voltage, current and time and thus filling in the gap in DC energy measurement traceability.

Phase-pure BiFeO3 produced by reaction flash-sintering of Bi2O3 and Fe2O3

Nanostructured, highly-insulating, single-phase BiFeO3 is obtained by applying a small DC voltage to a mixture of Bi2O3 and Fe2O3 at 625 °C in seconds.

Nonlocal vibration and pull-in instability analysis of electrostatic carbon-nanotube based NEMS devices

The objective of this paper is to investigate dynamical pull-in behavior of an electrostatic actuated nano-device based on Eringen's nonlocal elasticity theory. The Euler–Bernoulli beam model is used to establish the dynamic equation of motion of the nano-device subjected to both electrostatic and intermolecular forces. The nanobeam is considered with axially immovable ends and the geometrically nonlinearity due to mid-plane stretching is incorporated to the model as well. A new intermolecular attractive force model based on the macroscopic interactions of a circular cross section nanobeam and a flat surface is presented for the carbon nanotube based nano-device. The nonlinear static equation and the linear dynamic equation are treated by the Differential Quadrature Method (DQM) and through a comprehensive survey, the effect of small scale parameter, DC voltage, intermolecular force, residual stress and geometrical nonlinearity on the fundamental natural frequency and pull-in phenomenon are studied. The results are verified with the literature and a good agreement is achieved.

Self-Assembly of Organic Ferroelectrics by Evaporative Dewetting: A Case of β-Glycine.

Self-assembly of ferroelectric materials attracts significant interest because it offers a promising fabrication route to novel structures useful for microelectronic devices such as nonvolatile memories, integrated sensors/actuators, or energy harvesters. In this work, we demonstrate a novel approach for self-assembly of organic ferroelectrics (as exemplified by ferroelectric β-glycine) using evaporative dewetting, which allows forming quasi-regular arrays of nano- and microislands with preferred orientation of polarization axes. Surprisingly, self-assembled islands are crystallographically oriented in a radial direction from the center of organic "grains" formed during dewetting process. The kinetics of dewetting process follows the t-1/2 law, which is responsible for the observed polygon shape of the grain boundaries and island coverage as a function of radial position. The polarization in ferroelectric islands of β-glycine is parallel to the substrate and switchable under a relatively small dc voltage applied by the conducting tip of piezoresponse force microscope. Significant size effect on polarization is observed and explained within the Landau-Ginzburg-Devonshire phenomenological formalism.

PLZT-Based Shutters for Free-Space Optical Fiber Switching

With the increasing demand for optical fiber switching technologies from data center networks, shutter-based free-space optical fiber switching technology is promising for such network applications as the major advantages of this switching technology are that multicast switching, which is a vital functionality required in data center networks, can be easily achieved through its optical fan-out mechanism and that the switching performance can also be significantly strengthened while new materials with a faster response time are used as a spatial light modulator (SLM) to act as shutters. In this paper, the characteristics of ferroelectric liquid crystals and lead lanthanum zirconate titanate EO ceramic (PLZT) materials used as an SLM to act as shutters based on a type of strips for free-space optical fiber switching technology have been investigated. Although the PLZT-based shutters have a fundamental characteristic that a higher driving voltage might be required in order to provide a fast switching time less than a subnanosecond, with the use of a simple push–pull amplifier circuit design that can make a small input signal ride on a large dc voltage, the driving of a PLZT device in an optical switch can easily be achieved. Although the power consumption problem of this PLZT device resulting from a high driving voltage was not investigated in this paper, it can be effectively improved through a general boost converter that can be used to raise a small input dc voltage to a required higher driving voltage for the PLZT device. A proof of concept $1\times N$ , i.e., a 1 $\times$ 6 free-space optical fiber ribbon switching architecture capable of scaling to an $N\times N$ switching architecture for data center network application, was experimentally implemented to investigate the fiber array switching properties of PLZT-based shutters based on a type of strip. The experimental results show that the bit error rates estimated from the $Q$ -factor were all less than $10^{-9}$ and that the jitters were all less than 7.35% under a variety of shutter driving voltages at a link speed of 1 Gb/s and above.

Research on Shoot-Through Zero Vector of Impedance Source Linearization Control Strategy

Z-source inverter takes advantage of a distinctive impedance source network and modulation method of shoot-through vector, and achieves the function of buck/boost DC - AC inverter in the single stage system at the same time, which is suitable for grid-connected PV systems with large input voltage variations. The purpose of this study is to draw a unified method of shoot-through vector and grid inverter of the z-source inverter, apply the method of state-space averaging for the modeling analysis of the z-source inverter and give a complete mathematical model. Based on which and according to the nonlinear control theory and making use of the linearization of affine nonlinear model of the z-source inverter, we can get the specific derivation of equation. The results of the simulation and experiment show that according to the linearization of the shoot-through vector with affine nonlinear model for the z-source, we can make the system have the characteristics of fast and accurate tracking, small overshoot, small DC voltage, AC current ripple and small THD, and it has a certain practical value.

A Simple GHz Resonator for Superconducting Materials Characterization

This work examines the design and operation of a longitudinal resonant cavity, paired with monopole send and reciprocal patch receive antennae, that couples radio-frequency energy to a superconducting thin film carrying high current densities (~10 5 A/cm 2 ). The dielectric substrate supporting the film penetrates the waveguide, which operates in an evanescent mode below the design cutoff frequency of 18 GHz. Oscillatory vortex motion in the thin film is found to produce a small (~0.1 mV) dc voltage. When the niobium film is patterned to form an aperture that permits resonant conditions within the waveguide volume, the measured voltage increases by an order of magnitude. The increase is explained in the framework of the Larkin-Ovchinnikov model for quasiparticle behavior inside a moving normal vortex core. Operated near the superconducting transition, this device is useful for materials characterization, including the possibility to extract parameters including the pinning force. The authors suggest that the device could be used to characterize the pinning potential or to explore quasiparticle dynamics in superconducting thin films.

A Generic Model of Memristors With Parasitic Components

In this paper, a generic model of memristive systems, which can emulate the behavior of real memristive devices is proposed. Non-ideal pinched hysteresis loops are sometimes observed in real memristive devices. For example, the hysteresis loops may deviate from the origin over a broad range of amplitude A and frequency f of the input signal. This deviation from the ideal case is often caused by parasitic circuit elements exhibited by real memristive devices. In this paper, we propose a generic memristive circuit model by adding four parasitic circuit elements, namely, a small capacitance, a small inductance, a small DC current source, and a small DC voltage source, to the memristive device. The adequacy of this model is verified experimentally and numerically with two thermistors (NTC and PTC) memristors.

Development of Fluxgate Magnetometers Based on Fe<sub>61</sub>Co<sub>19</sub>Si<sub>5</sub>B<sub>15</sub> Amorphous Ribbons

This paper deals with the characterization of fluxgate magnetometers that adopt a Fe61Co19Si5B15 ribbons as magnetic core. The experimental characterization concerned the dependence of Δt and ΔV according to the magnetic field Hdc. The change of the field (variable input) held by changing the offset, adding a small dc voltage to ac, taking in extremely important results. Still, examined the dependence of ΔV on the frequency for two different types of coils, a circular and an oval coil, made of the same material, Fe61Co19Si5B15.