Open-circuit Conditions Research Articles

Comprehensive Comparison of Two Fault Tolerant Axial Field Modular Flux-Switching Permanent Magnet Machines with Different Stator and Rotor Pole-Pairs Combinations

This paper gives a comprehensive comparison among two fault-tolerant axial field modular flux-switching (AFFSPM) machines with different stator modular segments (U- and E-core) and stator-slots/pole-pairs combinations. The topologies of two AFFSPM machines are introduced, each with two feasible stator slots and rotor pole-pairs combinations with high winding factors based on the slot-conductor back-EMF star vectors theory. Then, the static performance including the air-gap flux density, flux linkage, back-electromagnetic force (back-EMF), and electromagnetic torque are analyzed and compared. Moreover, the fault-tolerant capability is then investigated by the torque performance under one- and two-phase open-circuit conditions in which the corresponding fault-tolerant control strategies are applied. The predicted results confirm that the 6-stator slot/11-rotor-pole-pair E-core AFFSPM machine exhibits the best performance of the four candidates.

Targeted enhancement of electrochromic memory in Fe(II) based metallo-supramolecular polymer using molybdenum disulfide quantum dots

Bistable electrochromic (EC) display with long EC memory has been a much-anticipated goal owing to its zero-energy consumption when maintaining the colored or bleached state when used in smart windows. However, it is very challenging to engineer the structure of the materials to accomplish a long EC memory along with high optical contrast, durability, switching fastness, and coloration efficiency which are of significance for fabricating the electrochromic devices with essentially power efficiency. Herein, we have judiciously incorporated the charge trapping MoS2 quantum dots (QDs) to prepare an electrochromic nanocomposite (polyFe-QD-10) of an Fe2+-based metallo-supramolecular EC polymer (polyFe) for the targeted enhancement of EC memory than the pristine polyFe polymer. The polyFe-QD-10 based electrochromic device (ECD) exhibits more cycle durability as it produced no loss in ΔT after the measurement of 100 cycle, while pristine polyFe-based ECD produced 14% loss in similar 100 cycle. The prototype ECD with polyFe-QD-10 film is also demonstrated with fast switching time (3.3 s for bleaching and 0.78 s for coloring), and good coloration efficiency (242.2 cm2 C−1). Remarkably, the ECD based on polyFe-QD-10 composite displays higher EC memory in open circuit condition as it takes 32 min for 90% reappearance of the original purple color after complete bleaching, while the pristine polyFe based ECD regains 90% of the transmittance of the color state only in 15 min. The strategy reported here presents the polyFe-MoS2 QD composite thin film an encouraging candidate for developing power efficient electrochromic information displays and smart windows.

Corrosion resistance of pulsed laser modified AZ31 Mg alloy surfaces

The effect of laser surface melting on the corrosion resistance of AZ31 Mg alloy in 0.1 M NaCl solution was investigated using different laser processing conditions (energy densities of 14 and 17 J cm−2). Laser treatment induced rough surfaces primarily composed of oxidized species of Mg. XPS analysis revealed that the surface concentration of Al increased significantly as a consequence of LSM. Electrochemical impedance spectroscopy showed that the laser treatment remarkably increased the polarization resistance of the AZ31 Mg alloy and induced a passive-like region of about 100 mV, as determined by potentiodynamic polarization. Analysis of the results obtained provide solid evidence that within the immersion times used in this study, LSM treatment increased the corrosion resistance of AZ31 Mg alloy under open circuit conditions and anodic polarization.

Improved Fault-Tolerant Model Predictive Torque Control of Five-Phase PMSM by Using Deadbeat Solution

This paper proposes an improved fault-tolerant model predictive torque control (MPTC) for a five-phase permanent magnet synchronous motor based on deadbeat solution, which offers the reduced computation burden, good steady-state performance and simple control structure. Under the open-circuit fault condition, the virtual voltage vectors (VVV) which can restrain the harmonics work as the candidate vectors. The deadbeat solution is adopted to predict the reference voltage vector. The optimal VVV can be selected directly and rapidly according to the sector of the reference voltage vector. Hence the computation burden can be reduced largely because the process of testing all candidate VVVs is avoided. In order to reduce the error between the reference voltage vector and the selected VVV, a null vector is introduced by a simple geometric principle. Then, the duration of the selected VVV can be obtained. Therefore, the steady-state performance is enhanced because of the deadbeat solution and the multi-vectors in each control period. The experiments are presented to verify the proposed fault-tolerant MPTC.

Developing an electroanalytical procedure for the determination of caffeic acid phenethyl ester at a boron-doped diamond electrode by the use of cationic surfactant media

The aim of the present work is to describe voltammetric analysis of caffeic acid phenethyl ester (CAPE) by using a boron-doped diamond (BDD) electrode in the presence of the cationic surfactant. Using cyclic voltammetry, CAPE demonstrated a single well-defined, quasi-reversible, adsorption-controlled by oxidation and reduction peak at approximately +0.44 V & +0.22 V respectively, (vs. Ag/AgCl) in the Britton-Robinson buffer (BR, 0.04 mol L−1, pH 5.0). The obtained results showed that the oxidation peaks of CAPE are pH dependent (ranging from 2.0 to 6.0). The oxidation peak currents of CAPE were significantly increased by using cetyltrimethylammonium bromide (CTAB, cationic surfactant) in the selected supporting electrolyte. Under the optimum parameters of experiment, the linear relationship was found for CAPE determination in 0.04 mol L−1 BR buffer solution (pH 5.0) including 1 × 10−4 mol L−1 CTAB at +0.41 V (vs. Ag/AgCl) (after 30 s accumulation at the open-circuit condition). The linear range was found with 0.01 to 1.0 μg mL−1 (3.5 × 10−8–3.5 × 10−6 mol L−1) via the detection limit 0.0028 μg mL−1 (9.8 × 10−9 mol L−1). The developed approach was used successfully to detect CAPE concentration in the model urine samples. To our knowledge, this is the first approach for electrochemically analyzing of CAPE.

Fast locating method of MMC lower tube IGBT open-circuit fault based median error between the actual and the predicted value of the capacitor voltage

Modular multilevel converters have found a large number of applications in high-voltage and high-power DC transmission due to their modularity, scalability, multi-equality and other advantages. The two typical topologies in MMC systems are half-bridge sub-module structure and full-bridge sub-module structure. Half-bridge sub-module is widely used in MMC systems by virtue of its simple control structure, high conversion efficiency and low cost. Insulated gate bipolar transistor (IGBT) failures, especially open-circuit failures, are a major factor in the reliable operation of MMC systems. Fast and accurate positioning of the open circuit fault location and removal of the fault submodule is of great significance for handling MMC system faults. Aiming at the current situation of the fault location of the MMC system, this paper compares the error of the predicted median capacitance voltage with the actual value , and proposes an accurate diagnosis method for MMC lower IGBT tube open circuit faults. This method is suitable for one or more IGBT lower tube open-circuit fault conditions, and can quickly locate the faulty submodule within 5ms. Finally, an MMC simulation system with 8 sub-modules is built based on MATLAB/Simulink, which effectively verifies the accuracy of the proposed method.

Sodiation Of Hard Carbon: How Separating Enthalpy And Entropy Contributions Can Find Transitions Hidden In The Voltage Profile.

Sodium-ion batteries (NIBs) utilize cheaper materials than lithium-ion batteries (LIBs) and can thus be used in larger scale applications. The preferred anode material is hard carbon, because sodium cannot be inserted into graphite. We apply experimental entropy profiling (EP), where the cell temperature is changed under open circuit conditions. EP has been used to characterize LIBs; here, we demonstrate the first application of EP to any NIB material. The voltage versus sodiation fraction curves (voltage profiles) of hard carbon lack clear features, consisting only of a slope and a plateau, making it difficult to clarify the structural features of hard carbon that could optimize cell performance. We find additional features through EP that are masked in the voltage profiles. We fit lattice gas models of hard carbon sodiation to experimental EP and system enthalpy, obtaining: 1. a theoretical maximum capacity, 2. interlayer versus pore filled sodium with state of charge.

Equilibration processes in alkaline Cu | Cu(II), glycine system

The nature and kinetics of the equilibrium processes at the interface between the copper electrode and the alkaline solution containing glycine complexes of Cu(II) have been studied. The material balance equations that consider the formation of Сu(I) complexes were used to calculate the composition of the equilibrium system. It was found that the amount of Сu(I) compounds increases with increasing the pH and ligand concentration. Using the EQCM method it was found that the electrochemical dissolution of Cu electrode proceeds under open circuit conditions at potentials 60–70 mV higher than their equilibrium values. The generation of Cu+ ions obeys the laws of pseudo-first order processes at a rate constant of ~2 × 10–4 s–1. It is assumed that the final product of the equilibration is a monoligand complex of CuL (L– is a glycinate anion). Besides, there is a thermodynamic probability of the formation of cuprous oxide in the system.

Bacterial Competition for the Anode Colonization under Different External Resistances in Microbial Fuel Cells

This study investigated the effect of external resistance (Rext) on the dynamic evolution of microbial communities in anodic biofilms of single-chamber microbial fuel cells fueled with acetate and inoculated with municipal wastewater. Anodic biofilms developed under different Rext (0, 330 and 1000 ohms, and open circuit condition) were characterized as a function of time during two weeks of growth using 16S rRNA gene sequencing, cyclic voltammetry (CV) and fluorescence microscopy. The results showed a drastic difference in power output of MFCs operated with an open circuit and those operated with Rext from 0 to 1000 ohms. Two steps during the bacterial community development of the anodic biofilms were identified. During the first four days, nonspecific electroactive bacteria (non-specific EAB), dominated by Pseudomonas, Acinetobacter, and Comamonas, grew fast whatever the value of Rext. During the second step, specific EAB, dominated by Geobacter and Desulfuromonas, took over and increased over time, except in open circuit MFCs. The relative abundance of specific EAB decreased with increasing Rext. In addition, the richness and diversity of the microbial community in the anodic biofilms decreased with decreasing Rext. These results help one to understand the bacterial competition during biofilm formation and suggest that an inhibition of the attachment of non-specific electroactive bacteria to the anode surface during the first step of biofilm formation should improve electricity production.

A new Approach for the Voltammetric Sensing of the Phytoestrogen Genistein at a Non‐modified Boron‐doped Diamond Electrode

AbstractAn effective electrochemical sensor was constructed using an unmodified boron‐doped diamond electrode for determination of genistein by square‐wave voltammetry. Cyclic voltammetric investigations of genistein with HClO4 solution indicated that irreversible behavior, adsorption‐controlled and well‐defined two oxidation peaks at about +0.92 (PA1) & +1.27 V (PA2). pH, as well as supporting electrolytes, are important in genistein oxidations. Quantification analyses of genistein were conducted using its two oxidation peaks. Using optimized experiments as well as instrumental conditions, the current response with genistein was proportionately linear in the concentrations range of 0.1 to 50.0 μg mL−1 (3.7×10−7−1.9×10−4 mol L−1), by the detection limit of 0.023 μg mL−1 (8.5×10−8 mol L−1) for PA1 and 0.028 μg mL−1 (1.1×10−7 mol L−1) for PA2 in 0.1 mol L−1 HClO4 solution (in the open circuit condition at 30 s accumulation time). Ultimately, the developed method was effectively applied to detect genistein in model human urine samples by using its second oxidation peak (PA2).

Photon-induced degradation of InGaN-based LED in open-circuit conditions investigated by steady-state photocapacitance and photoluminescence

Degradation of InGaN–GaN LEDs has been the subject of intense investigations in the past few years. While current- and temperature-induced degradation processes have been described, the impact of photon-induced degradation has not been investigated in detail in the literature. This paper aims at improving the understanding of the mechanisms responsible for the degradation of the InGaN subject to high photon densities by stressing the devices under a high-intensity laser beam in open-circuit conditions (i.e., in the absence of external current). We analyzed the degradation by means of electrical, optical, and deep-level characterization techniques. First, we demonstrate the existence of optically induced degradation processes in GaN LEDs: from photoluminescence measurements, we observed a decrease in the luminescence after stress, more prominent in the region irradiated during stress. Second, we ascribe this effect to a decrease in internal quantum efficiency due to the generation of non-radiative defects within the active region. Third, by steady-state photocapacitance measurements, we reveal the presence of a shallow level with an energy of EC–2.2 eV, which can be ascribed to gallium vacancies and its complexes with oxygen and nitrogen and can be related to the increase in yellow luminescence.

Nonlinear Potential Scanning as a Novel Approach to Calculation of the Time Variable Galvanic Displacement Reaction Rate

AbstractA novel approach to estimate the rate of galvanic displacement reaction was proposed, which allowed the most accurate calculation of the displacement process rate at each moment of time by exact reproducing the open‐circuit conditions. We applied the method for mild steel samples immersed in pyrophosphate‐citrate electrolyte for Cu−Zn alloy electrodeposition. The time dependences of parameters of steel‐electrolyte interaction are obtained. The rate of steel dissolution in open circuit conditions increases by 1.6–2.9 times as compared with corrosion in pyrophosphate‐citrate medium. The results of our approach were verified by an independent experiment using anodic stripping of the obtained deposits.

Electroanalytical investigation and voltammetric quantification of antiviral drug favipiravir in the pharmaceutical formulation and urine sample using a glassy carbon electrode in anionic surfactant media.

This work describes the electrochemical investigation of a promising antiviral agent, favipiravir (FAV) utilizing a nonmodified glassy carbon (GC) electrode, along with a unique voltammetric approach that can determine FAV with a good degree of accuracy, speed, and cost-effectiveness. Using cyclic voltammetry, the compound demonstrated a single well-defined and an irreversible oxidation peak at approximately +1.12 V (vs. Ag/AgCl) in Britton-Robinson (BR) buffer at pH 10.0. The synergistic effect of anionic surfactant, sodium dodecyl sulfate (SDS) on the adsorption ability of GC electrode remarkably increased the sensitivity of the stripping voltammetric measurements of FAV. Employing square-wave adsorptive stripping voltammetry at +1.17 V (vs. Ag/AgCl) (after 60 s accumulation at open-circuit condition) in BR buffer (pH 10.0) containing 3 × 10-4 M SDS, the linear relationship is found for FAV quantification in the concentration from 1.0 to 100.0 μg mL-1 (6.4 × 10-6-6.4 × 10-4 M) with a detection limit of 0.26 μg mL-1 (1.7 × 10-6 M). The proposed approach was used successfully to determine FAV in pharmaceutical formulations and model human urine samples.

Influence of the Magnetic Field on the Diffusion Capacitance of a Serial Vertical Junction Silicon Solar Cell in Frequency Modulation

In this work, a theoretical study of the effect of the magnetic field on the minority charge carrier density and the diffusion capacity of a silicon solar cell with vertical junction in series in dynamic frequency regime, is done. From the relative continuity equation of the minority charge carriers’ density we establish the boundary condition at the junction and the base medium. The expression of the density of minority carriers of charges in the base, allows us to determine the capacity of diffusion of the solar cell according to the magnetic field, the frequency of modulation, the wavelength of illumination and a junction recombination velocity. The profile of the diffusion coefficient allowed us to make a choice on the values of the magnetic field. These values of the magnetic field intensity will be fixed throughout this article. Each value of the magnetic field strength corresponds to a well-defined value of the resonance frequency. We obtained two ranges of illumination wavelengths from the minority charge carrier’ density profile. The influence of the magnetic field on the diffusion coefficient, of the density of minority charge carriers in short-circuit and open-circuit conditions and of the diffusion capacity, for a specific wavelength, is theoretically studied.

Diode Open-Circuit Fault Research on the Parallel-Connected 24-Pulse Rectifier With DC-Side Passive Harmonic Reduction Circuit

Multipulse rectifiers (MPRs) with dc side passive harmonic reduction circuits often have lower input current total harmonic distortion (THD) values and power losses, that fulfill power requirements for many industrial occasions. In addition to normal operation properties, fault tolerance is another aspect closely related to overall performance of MPRs. This article takes a common parallel-connected 24-pulse rectifier as an example, researches its operation characteristics and fault tolerance under diode open-circuit fault conditions. Operation modes under single or double diodes open-circuit fault in the main circuit, as well as diode open-circuit fault in the dc side harmonic reduction circuit are discussed in details. It can be determined that load voltage is the characteristic parameter that directly reflects the fault information. Related simulation and experimental verifications are performed, all results are consistence with theoretical waveforms. This article provides useful guidance for fault handling and clarifies factors related to the reliability of MPRs, which are helpful for novel MPRs design.

Modelling the electrochemical transients during repassivation under open-circuit conditions in a neutral solution

The responses of the current and the coupled potential to rapid depassivation have been studied on a three-electrode system under open-circuit conditions. Passivated AISI 304 stainless steel in low- and high-conductivity solutions of Na2SO4 has been depassivated with a single, rapid scratch over the small fraction of surface of the working electrode (WE). Single- and dual-WE configurations have been implemented. Once the surface is scratched, the current and potential transients exhibit a delayed maximum and minimum, respectively, in contrast to the outcome of more common potentiostatic scratching experiments. A simple model based on the equivalent circuit has been developed to predict the observed transients and provides clear relations between the features of the transient and the parameters of the electrolyte and the electrodes. The interfacial capacitance of the electrodes’ passive surfaces proves crucial for the shapes of the observed potential and current transients. It is shown that this capacitance temporarily provides the majority of the charge for repassivation under open-circuit conditions. Possible sources of specific discrepancies between the model and the measured transients are indicated.

Developing Shunt-Current Minimized Soluble-Lead-Redox-Flow-Batteries

Shunt currents in membrane-less soluble-lead-redox-flow-batteries (SLRFB) are observed in open-circuit condition and found to depend on size of the stack, manifolds, flow rates and charge/discharge parameters. Ramifications of shunt currents on the performance of membrane-less SLRFB stacks with internal and external manifolds are reported. In the case of stacks with 3, 5 and 7-cells and internal manifold design, the charge current for the middle cell decreases by 3.3%, 6%, and 8.5%, while the discharge current increases by 2.6%, 5.5%, and 6.6%, respectively, for 3 A charge/discharge current. By contrast, no such adverse effect is observed for external manifold design. The current—potential studies show that while the stacks comprising 3 and 5-cells deliver a maximum power density of 35 mW cm−2, which declines to 15 mW cm−2 for the 7-cell stack with internal manifold design, while the power density remains invariant at 50 mW cm−2 for stacks with external manifold design. An 8-cell stack of 12 V, 50 mAh/cm2 specific capacity and 273 Wh energy storage capacity with 64% energy efficiency is also reported which shows good cyclability over 100 cycles with 95% coulombic efficiency when cycled at 20 mA cm−2 current density for 1 h duration.

An explicit solution for the design of a target-frequency-customized, piezoelectric-defect-introduced phononic crystal for elastic wave energy harvesting

This paper proposes an explicit solution for the design of a target-frequency-customized, one-dimensional phononic crystal (PNC) with a defect for piezoelectric energy harvesting under longitudinal waves. Due to the innate narrow bandwidth nature of the defect modes of a PNC at the target frequency, there is a great need to generate an electromechanically coupled defect band of a piezoelectric-defect-introduced PNC. This work considers the transfer matrix method which has been widely used in analytical approaches. The need for defect bands to be included in a bandgap inspires the use of a quarter-wave stack as a unit cell to match the bandgap's central frequency with the target frequency. In band structure analysis, considering that the electromechanically coupled defect band corresponds to a set of real wavenumbers despite being within the bandgap, several possible solutions for the piezoelectric defect's length are derived in an explicit fashion. Since switching from a short- to an open-circuit condition causes defect bands to slightly increase due to piezoelectric effects, an explicit solution that reflects the piezoelectric defect's electrical characteristics is finally proposed. Finite-element-based numerical validation studies are conducted to study two aspects, specifically parametric studies (i.e., the natural numbers in the solution to the piezoelectric defect's length, the supercell sizes, and the defect locations) and supporting studies (i.e., the electrical boundary conditions and unit cell designs). At the target frequency, it is demonstrated that the proposed PNC design actualizes the formation of one defect band and the representation of the peak output voltage.

Investigation of noise and vibration characteristics of an IPMSM with modular‐type winding arrangements having three‐phase sub‐modules for fault‐tolerant applications

The noise and vibration level in modular-type permanent magnet synchronous machines with fractional slot concentrated windings (FSCW) is considered to be an important design consideration, particularly for applications requiring fault tolerance. In this work, an interior permanent magnet synchronous machine (IPMSM) with FSCW is designed in a modular manner by dividing its stator windings into different arrangements having independent three-phase sub-modules with separate neutral points. First, the modular concentrated winding arrangement is studied to investigate the radial forces, vibration, and the associated noise level in the prototype machine having three-phase sub-modules under open-circuit fault conditions. Then, another type of distributed three-phase sub-module winding arrangement is analysed to further investigate the vibration and noise level in the same prototype machine under the same operating conditions. A detailed two-dimensional (2D) fast Fourier transform analysis is performed to investigate and compare the machine radial forces, induced harmonics, and sub-harmonics for the two analysed winding arrangements. Considering the advantages and disadvantages of both the winding arrangements, the third type of mixed concentrated and distributed three-phase sub-modules winding arrangement is introduced in this work, combining the first two winding design approaches. A comprehensive harmonic (3D) structure, along with the vibration and noise analysis, is performed using a multi-physics model analysis for all the winding arrangements under different three-phase sub-modules open-circuit fault conditions. Lastly, the vibration levels of all the machine prototype models under different winding arrangements are experimentally validated. Moreover, the different modular types of winding arrangements are deeply investigated in this work to suggest the best winding arrangement approach that enables the machine to work in a wide range of applications requiring lower power levels or under critical, faulty, and hostile conditions. The proposed winding arrangement has reduced stator deformation with a reduced vibration and noise level under three-phase sub-modules open-circuit fault-tolerant conditions that can be used according to process requirements.

Operando Infrared Spectroscopy Reveals the Dynamic Nature of Semiconductor-Electrolyte Interface in Multinary Metal Oxide Photoelectrodes.

Detailed knowledge about the semiconductor/electrolyte interface in photoelectrochemical (PEC) systems has been lacking because of the inherent difficulty of studying such interfaces, especially during operation. Current understandings of these interfaces are mostly from the extrapolation of ex situ data or from modeling approaches. Hence, there is a need for operando techniques to study such interfaces to develop a better understanding of PEC systems. Here, we use operando photoelectrochemical attenuated total reflection Fourier transform infrared (PEC-ATR-FTIR) spectroscopy to study the metal oxide/electrolyte interface, choosing BiVO4 as a model photoanode. We demonstrate that preferential dissolution of vanadium occurs from the BiVO4/water interface, upon illumination in open-circuit conditions, while both bismuth and vanadium dissolution occurs when an anodic potential is applied under illumination. This dynamic dissolution alters the surface Bi:V ratio over time, which subsequently alters the band bending in the space charge region. This further impacts the overall PEC performance of the photoelectrode, at a time scale very relevant for most lab-scale studies, and therefore has serious implications on the performance analysis and fundamental studies performed on this and other similar photoelectrodes.