DC Method Research Articles

Interfacial Synthesis of Layer-Oriented 2D Conjugated Metal-Organic Framework Films toward Directional Charge Transport.

The development of layer-oriented two-dimensional conjugated metal-organic frameworks (2D c-MOFs) enables access to direct charge transport, dial-in lateral/vertical electronic devices, and the unveiling of transport mechanisms but remains a significant synthetic challenge. Here we report the novel synthesis of metal-phthalocyanine-based p-type semiconducting 2D c-MOF films (Cu2[PcM-O8], M = Cu or Fe) with an unprecedented edge-on layer orientation at the air/water interface. The edge-on structure formation is guided by the preorganization of metal-phthalocyanine ligands, whose basal plane is perpendicular to the water surface due to their π-π interaction and hydrophobicity. Benefiting from the unique layer orientation, we are able to investigate the lateral and vertical conductivities by DC methods and thus demonstrate an anisotropic charge transport in the resulting Cu2[PcCu-O8] film. The directional conductivity studies combined with theoretical calculation identify that the intrinsic conductivity is dominated by charge transfer along the interlayer pathway. Moreover, a macroscopic (cm2 size) Hall-effect measurement reveals a Hall mobility of ∼4.4 cm2 V-1 s-1 for the obtained Cu2[PcCu-O8] film. The orientation control in semiconducting 2D c-MOFs will enable the development of various optoelectronic applications and the exploration of unique transport properties.

Advanced remediation using nanosized zero-valent iron and electrical current in situ − A comparison with conventional remediation using nanosized zero-valent iron alone

This study presents an advance on the standard in situ reductive remediation technique using nanosized zero valent iron (NZVI). The initial process used a conventional form of NZVI, NANOFER 25S (NANO IRON, s.r.o.), at a site contaminated with chlorinated hydrocarbons (CHC) in 2014. In 2018, levels of contamination at the site were still too high; hence, a second remediation intervention was performed using a cheaper form of NZVI, NANOFER STAR DC (NANO IRON, s.r.o.), accompanied with application of an electrical current (DC). The physical-chemical parameters at the site showed moderate reductive conditions for both techniques. While remediation with NANOFER 25S showed a continuous decrease in NZVI activity over time, application of NANOFER STAR DC + DC resulted in a long-term reductive effect, observable as a persistent decrease in CHC concentration and evolution of ethene and ethane dechlorination products. NZVI in the STAR DC + DC was still active after around 200 days. Final efficiency of the STAR DC + DC method was calculated at 3.7 times higher than the conventional technique using NANOFER 25S only. Laboratory-scale experiments confirmed the field observations, indicating the significantly elevated effectivity of STAR DC + DC.

An adaptive hybrid dynamic state estimation method of the medium-voltage DC integrated power system with pulse load

When a great change periodically takes place in power of the periodic pulse load in the medium-voltage DC integrated power system in a short time, it will lead the system to stay in a periodic electromagnetic (EM) transient state. Its time constant is far less than that of the traditional land power system which is in an electromechanical transient state, so the convergence of the filter and accuracy of the estimation will be affected. This problem is similar to the estimation of a maneuvering target in tracking, but the methods used for estimating the maneuvering target cannot be directly applied to estimate the EM transient of the system. For this reason this paper proposes an adaptive estimation method. Based on the high accuracy of unscented Kalman filter and reliability of Hybrid extended Kalman filter under EM transient conditions, the method can ensure the accuracy of estimation and reliability of the algorithm by adaptively adjusting the estimation method according to changes in the system operating conditions. The method is proved to be better than the existing method in terms of estimative effect through experiment and also proved to be reliable by the consistency test on the filter.

Electrochemical impedance in ac diagnostics of weakly conducting media

Impedance ac diagnostics is regularly used to study the transport phenomena in conducting systems of differrent dimensionalities. A common reason for using ac methods that are more complex than dc methods is the possibility to exclude the influence on the current-voltage (I−V) characteristic of contact phenomena accompanying dc measurements. In some cases (2d electron systems over helium) dc transport measurements are impossible. In weakly doped semiconductors (diluted electrolytes), the situation is less critical, but problems with the ohmic properties of the conducting contacts remain. The analysis of the details of the formalism that determines the reaction of a conducting medium to an external disturbance depends largely on the form of Ohm’s law for a conductor introduced into the impedance circuit. If there is a reason to define this law by the formula j = σΕ, where j, σ, E correspond to local values of current density, conductivity, and transport electric field, the structure of complex resistance Z^F(ω) is considered as a force one. If there is a diffusion component in Ohm’s law then the structure of complex resistance Z^μ(ω) is considered as an electrochemical one. We describe a standard electrolytic capacitor in series RC with a step load in terms of force or complex electrochemical impedance. Comparison with experiment shows the electrochemical structure of the complex resistance.

Investigation of Electrode Kinetics of Porous La-Sr-Co-Fe-oxide (LSCF) Electrodes on Yttria-Stabilized Zirconia (YSZ) Electrolyte Using Alternating Current (AC) and Direct Current (DC) Methods

Lanthanum strontium cobalt iron oxide (LSCF) is commonly used as a cathode in solid oxide fuel cells (SOFCs), because it is a mixed ionic-electronic conductor with reasonable oxygen ion conductivity and high electronic conductivity. Yttria stabilized zirconia (YSZ) is used as an electrolyte in SOFCs with good oxygen ion conductivity. AC techniques are used to test the performance of SOFCs. But electrode processes at the cathode and the anode cannot be studied separately using two-electrode electrical impedance spectroscopy (EIS). To overcome this problem, two-electrode EIS with three probes and DC tests were conducted. An LSCF/8YSZ/LSCF symmetrical bar-shaped cell was made, and platinum strip electrodes were applied as probes for EIS and DC measurements. Impedance spectra across the cathode and the platinum strip electrode and across the anode and the platinum strip electrode were measured separately. The sum was evaluated to see if it matches the EIS spectra across the cathode and the anode. The polarity was switched to study how it affects the electrode processes. The polarization resistances of the electrodes were also measured by a DC method separately. EIS and DC measurements are in good agreement. Results indicate the two electrodes need not be identical.

Topology Derivation of Multiple-Port DC–DC Converters Based on Voltage-Type Ports

Multiple-port dc–dc converters are characterized by a variety of kinds and a large number of circuit topologies. In this article, we aim to reveal the intrinsic relationship among the topologies of multiple-port dc–dc converters and propose the topology derivation method. First, the voltage- and current-type ports are summarized from basic dc–dc converters, and the approach of converting current-type ports into voltage-type ports is discussed. Then, according to Kirchhoff's law, four types of multiple-input multiple-output converters named input-port-series output-port-series, input-port-series output-port-parallel, input-port-parallel output-port-series, and input-port-parallel output-port-parallel are presented. Second, the topology derivation method of multiple-port bidirectional dc–dc converters based on the voltage-type ports is studied in terms of power flow paths in various operation modes, and then the topology optimization method is proposed. Particularly, a flow diagram for the optimal design procedure is given to guide the topology derivation for some specific requirements. Based on the proposed approach, a family of multiple-port dc–dc converters can be derived, which provides lots of viable candidates for practical engineering. Furthermore, one derived converter named the parallel-type three-port bidirectional buck converter is analyzed in three operation modes to demonstrate the topology derivation. Finally, the effectiveness of the above theoretical analysis is verified by those experimental results.

Flexible Power Distribution Technology Based on Modular DC Charging Pile

With the rapid development of electric vehicle industry in China, the contradiction between the increasing users' demand for real-time charging and the unbalanced planning and design of charging piles is increasingly apparent. DC charging pile on the market is developed rapidly, but its structure is with multi-gun to one-pile. It is difficult to meet the demand of different kinds of electric vehicle battery charging, different battery capacity and the user expected charging time. To solve the problems, a flexible power distribution method of DC charging pile is proposed in this paper. When multiple EV in different types and states are charged at the same time, and the actual charging demands of each user and the charging battery are considered, the power module can be dynamically switched to realize the flexible power distribution, the idea of flexible power distribution is described. Then the algorithm steps of power distribution were presented. Finally, the Matlab/Simulink was used for example analysis to simulate the power distribution process when different initial SOC batteries were charged simultaneously.

A comparative analysis of generation and transmission expansion planning models for power loss minimization

In modern power systems, renewable energy resources are becoming more relevant due to their eco-friendly nature and sustainable electrification. Therefore, it is important to consider the effects of the renewable energy resources (RERs) on the generation expansion planning and transmission expansion planning (GTEP) simultaneously. The proper assessment of power losses is essential in order to adequately evaluate the consequence of renewable energy resources in power systems. This paper presents multi-objective optimization problems that are solved using DC, modified DC and AC modelling methods in order to accurately and efficiently compute electrical losses and its impacts on the expansion planning procedure. This paper develops a Mixed Integer Non-linear Programming (MINLP) problem and was solved using CONOPT and CPLEX solvers embedded in Algebraic Modelling Language. The proposed methods are evaluated and validated on three case studies: IEEE Garver’s 6 bus system, IEEE 24 bus test system and a real-world Nigeria Power System. A comparative analysis of the three modelling approaches and a sensitivity analysis of the simulation results indicate that AC solution method provide an accurate computation of power losses and efficient optimal planning strategy as compared to the modified DC method.

Effect of Thermal Annealing on the Electrical Properties and Gas Sensing for Pulsed Laser Deposition Cr2O3 Thin Films

In this study, a double frequency Nd: YAG deposited by Pulsed Laser Deposition (laser beam 1064 nm, 6 Hz repetition rate and 10 ns pulse duration) were used for a thin Cr2O3 deposit on glass substrate. Many growth parameters have been considered to specify the optimum condition, namely substrate temperature at room temperature, oxygen pressure (2.8×10-4 mbar), laser energy (600) mJ and the number of laser shots was 500 pulses. The thickness was of about 160 nm and annealing temperature at (300, 400 and 500) °C. Using DC method, the conductivity and Hall coefficient of Cr2O3 films were measured. The sensing properties of the p-type (Hall coefficient was positive) films for NO2 gas have been studied, and the result revealed that the Cr2O3 films have low sensitivity at room temperature, and it’s improved by increasing the annealing temperature to 500° C.

Steady-State and Transient DC Magnetic Flux Bias Suppression Methods for a Dual Active Bridge Converter

This article presents dc magnetic flux bias suppression methods for a dual active bridge (DAB) converter in both steady state and transient process. The steady-state dc offset is caused by asymmetries of the circuit and power switches in practice, while the transient offset is caused by the sudden update of phase shift ratio. This dc bias will increase the conduction losses, lead to loss of zero voltage switching (ZVS), and even saturate the magnetic components. To prevent this risk, this article proposes methods to suppress the dc bias both in steady state and transient process. For steady-state dc bias suppression, the duty cycles of square voltages generated by the primary and secondary side H-bridges are regulated according to the dc bias current. The conditions to achieve zero dc bias and the small-signal model to regulate the dc bias current are derived. For transient dc bias suppression, the phase shift ratio variation is limited to ensure the peak inductor current within the safe operating range. Tunnel magnetoresistance (TMR) is employed to sense the currents, and an analog integration and sampling method is proposed to detect dc bias. Finally, the proposed method is verified through experimental results on a 3200-W DAB prototype.

Determination of Diagnostic Reference Level (DRL) in Common Computed Tomography Examinations with the Modified Quality Control-Based Dose Survey Method in Four University Centers: A Comparison of Methods.

Background: The diagnostic reference level (DRL) is measured with different methods in the common Computed tomography (CT) exams, but it has not been measured through the size-specific dose estimate (SSDE) method in Iran, yet.Objective: This study aimed to calculate the local DRL (LDRL) using the new quality control-based dose survey method (QC) and patients’ effective diameter (MQC) and compare them with a data collection method (DC) as well as local national DRLs (NDRL).Material and Methods: In this cross-sectional study, LDRL, based on the third quartile of volumetric computed tomography dose index (CTDIvol) and dose length product (DLP) values, was calculated for the four common CT examinations in four CT scan centers affiliated with Shiraz University of Medical Sciences by DC, QC and MQC methods. The CTDIvol of each patient for each CT exam calculated with three methods was compared with paired t-test. Also, the LDRL using MQC method was compared with other national DRL studies.Results: There was a significant difference between the CTDIvol values calculated with MQC and QC in all four examinations (P <0.001). The LDRL based on CTDIvol obtained by the MQC method for head, sinus, chest, abdomen, and pelvis were (50, 18, 15, 19) mGy, respectively, and the calculated DLP values were also (735, 232, 519, 984) mGy.cm. Conclusion: In MQC, LDRL based on CTDIvol was calculated with a mean difference percentage of (19.2 ± 11.6)% and (27.1 ± 8.1)% as compared to the QC and DC methods, respectively. This difference resulted from the use of the SSDE method and dose accuracy in the QC dose survey

IR Measurement of an LFP/C Battery: A Different Perspective

Energy security and green energy are paving way for entire globe to adopt battery based ESS and EV. Online monitoring of battery parameters namely capacity and impedance are crucial to get better performance and life from the system. Impedance is a complex parameter comprises of ohmic, charge transfer and diffusion components. The effective impedance value differs depending on the measurement methodology and data accusation speed. DC method is generally used in the field due to simplicity and cost effectiveness. The present study adopts DC current interruption method for measuring impedance of 12.8 V/10 Ah, LFP/C battery. The voltage recovery and relaxation segment were used to derive impedance value at various SoC’s. First using electrochemical theory, it was proved that only diffusion is operating after current interruption when data is monitored at 1 s interval. The diffusion resistance changes not only with SoC but also with mode of operation i.e., charge vs. discharge. An empirical model was proposed taking care of three forces namely voltage gradient, repulsive force between lithium atom in graphene layer and Van der Waal’s force between graphene layers. The impact of the diffusion resistance on BMS is highlighted. It is suggested that the study can be used for monitoring ageing and calendaring life of battery, deducing the relationship between raw material and design parameter to performance of the battery.

Synthesis and Characterization of Sm-Ho-CeO2 Compounds Produced by Different Synthesis Methods

The most important part of a solid oxide fuel cell is the ceramic electrolyte. In this study, cerium oxide (CeO2) was used as the ceramic electrolyte, and different dopant types were used to increase total conductivity. In this study, the most commonly used Sm, and the less frequently used Ho elements were doped simultaneously. As a result, the effect of dope and different synthesis methods on electrolyte properties was evaluated. Three rates were studied with the total amount of Sm-Ho being 20%. The effect of the dopant types on conductivity with critical radius effect was investigated. These dope types were placed in a CeO2 crystal lattice by using the sol-gel and hydrothermal methods. After synthesis, the stable phase was obtained at room temperature. X-ray powder diffraction (XRD) was used for phase determination. The thermogravimetry (TG) determined mass change. Scanning electron microscopy (SEM) was used in the analysis of surface morphology. Total conductivity measurements were measured by the four-probe dc method. After synthesis processes, cubic compounds were obtained. The total conductivity values of the cubic phases samples obtained by two different synthesis methods were compared. The highest conductivity was observed in the sol-gel compounds. The highest electrical conductivity Ce0.80Sm0.10Ho0.10O2 system sol- gel; 6.92x10-3(Ωcm)1- at 655 oC. It was found that the compound obtained as a result of the evaluations could be used ceramic electrolyte application.

Investigation of Electrical and Thermoelectric Properties of ZnO/rGO Composites Prepared by Conventional Solid-state Reaction Method

ZnO/rGO composites are prepared by the conventional solid-state reaction method. Structural properties of prepared compounds were studied using XRD technique and it is observed that all the samples are crystallized in wurtzite structure. Electrical resistivity measurements were carried out using four probe method employing a closed cycle refrigerator. With addition of rGO, colossal reduction in the resistivity is observed which is about three orders of magnitude smaller than that of the pure sample of ZnO. Room temperature Hall measurements were performed to estimate the bulk concentration and results show that addition of rGO into ZnO matrix enhances the number of charge carriers. Thermopower measurements were carried out using differential dc method and a large reduction in Seebeck coefficient is observed.

Synthesis and Characterization of Sm-Ho-CeO2 Compounds Produced by Different Synthesis Methods

The most important part of a solid oxide fuel cell is the ceramic electrolyte. In this study, cerium oxide (CeO2) was used as the ceramic electrolyte, and different dopant types were used to increase total conductivity. In this study, the most commonly used Sm, and the less frequently used Ho elements were doped simultaneously. As a result, the effect of dope and different synthesis methods on electrolyte properties was evaluated. Three rates were studied with the total amount of Sm-Ho being 20%. The effect of the dopant types on conductivity with critical radius effect was investigated. These dope types were placed in a CeO2 crystal lattice by using the sol-gel and hydrothermal methods. After synthesis, the stable phase was obtained at room temperature. X-ray powder diffraction (XRD) was used for phase determination. The thermogravimetry (TG) determined mass change. Scanning electron microscopy (SEM) was used in the analysis of surface morphology. Total conductivity measurements were measured by the four-probe dc method. After synthesis processes, cubic compounds were obtained. The total conductivity values of the cubic phases samples obtained by two different synthesis methods were compared. The highest conductivity was observed in the sol-gel compounds. The highest electrical conductivity Ce0.80Sm0.10Ho0.10O2 system sol- gel; 6.92x10-3(Ωcm)1- at 655 oC. It was found that the compound obtained as a result of the evaluations could be used ceramic electrolyte application.

An Overview and Comprehensive Comparative Evaluation of Constant-Frequency Voltage Buck Control Methods for Series Resonant DC–DC Converters

The paper focuses on galvanically isolated series-resonant dc-dc converters with a low quality factor of a magnetically integrated resonant tank. These converters can be controlled at a constant switching frequency to achieve the input voltage buck regulation. The paper compares various buck control methods, such as conventional pulse-width modulation, hybrid pulse-width modulation, shifted pulse-width modulation, hybrid shifted pulse-width modulation, improved shifted pulse-width modulation, asymmetrical pulse-width modulation, pulse-width modulation, and hybrid pulse-width modulation applied to the series-resonant dc-dc converter. The study considers step-up implementation of the series-resonant dc-dc converter topology with the voltage doubler rectifier, which makes it suitable as a front-end dc-dc converter for the integration of renewable energy sources in dc microgrids. The voltage buck control methods considered were compared analytically in terms of the cumulative power losses calculated theoretically. The theoretical results were compared with the experimental measurements to confirm the calculations and benchmark the voltage buck control methods. The experimental validation was performed using a 250 W prototype that demonstrated the hybrid PSM achieves the best performance. The experimental results were found in good agreement with analytically predicted values of the power loss.

BLDC Motor Drives: A Single Hall Sensor Method and a 160° Commutation Strategy

The application of Hall-based BLDC motors ranges from automotive accessory components such as oil and water pumps to high speed compressors. This paper proposes a new twelve-step unsymmetrical 160° commutation strategy using a single Hall-effect sensor method for brushless DC (BLDC) motor drives. The signal from the Hall-effect sensor is used to generate a number of pseudo Hall signals via a proposed speed-position estimator. The pseudo signals are then employed to control switching logic of a voltage source inverter (VSI). The effectiveness of the single Hall sensor method is examined on the unconventional 160° strategy, and on conventional 120°, 150° and 180° strategies with promising results. The paper presents a detailed comparison of the twelve-step unsymmetrical 160° commutation strategy with six-step voltage space vector that is used in conventional 120° and 180° strategies, and twelve-step symmetrical voltage space vector that is used in 150° strategy. Simulation results are validated via experimental measurements on a laboratory set-up using a real time dSPACE control environment, a representative BLDC motor prototype, a VSI and associated control components.

Lyapunov function‐based improved switching command for a boost converter with an inductor–capacitor input filter

This study presents a control method for DC–DC switching power converters to avoid the instability caused by the interaction between a tightly controlled switching converter and an input low-pass filter. The proposed method is based on the Lyapunov stability criterion. A non-linearised model is established, and the instantaneous quantities of the state variables are considered. The switching command is formulated by calculating the stability of the system. The inductor current and voltage across the filter capacitor, along with the state variables in the switching converter, follow the corresponding references. A boost converter is considered to demonstrate the associated effectiveness. The results of several simulations and experiments pertaining to the start-up, tracking, and regulation stages validate the proposed control approach. Moreover, the robustness of the approach against variations in the parameters of the controlled system is examined experimentally. To demonstrate the superiority of the proposed method, the method is compared with the proportional–integral, fuzzy, and flatness-based controllers.

Incipient fault diagnosis method for DC–DC converters based on sensitive fault features

DC–DC converters play an important role in electrical systems. The fault state of a DC–DC converter has a major impact on the operation of the back-end components and the entire electrical system. Therefore, the fault diagnosis is very necessary when the fault state of DC–DC is in the early stage. It can decrease the likelihood of happening the serious faults that may result in the enormous economic loss. To effectively diagnose the incipient fault in DC–DC converters, an incipient fault diagnosis method based on sensitive fault features is proposed. Firstly, for each type of the incipient fault, this study obtains the statistical features in time domain and the wavelet analysis local energy values in the frequency domain of the output. Then to further improve the incipient fault diagnosis accuracy, this study removes the redundant fault features based on overlap calculation, the unique fault features for each type of incipient fault will be selected. Finally, these sensitive fault features are used to build support vector data description models, which can diagnose the incipient faults. Simulation and hardware experimental results validate the practicability and effectiveness of the proposed method.

Recycling electrochemical processing of Ag(I) species dispersed in polypyrrole towards Ag0 nanoparticles

Silver(I) hexafluorophosphate was dispersed in electrosynthezed polypyrrole hexafluorophosphate by precipitation, using an aqueous Ag(I) nitrate solution. The electrochemistry of the resulting composite was studied in aqueous hexafluorophosphate. The examined potential window encompassed the reversible redox process of the polymer and the redox transformations of the inorganic components, i.e. silver species, taking place within this window. The electrocrystallization of silver nanoparticles was controlled by dc potential. The Ag nanoparticles entrapped in polypyrrole, generated at reduction potentials of the composite, were 101 nm in diameter. The slightly larger AgNP of a mixed chemical nature was formed by a spontaneous discharge of the oxidized polypyrrole - salt composite towards the open circuit potential. Electrochemical processing and characterization of the composite were done using the dc and ac methods. Several other methods of chemical and structural identification were employed. The influence of oxygen for the processing of the composite towards metallic nanoparticles was shown. Electrochemical chemically irreversible oxidation of Ag2O to AgO in the polypyrrole matrix was found.