DC Mode Research Articles

Electromagnetic effects and accurate wall-temperature measurement method under directly electric heating mode

By directly imposed electrical energy on metal materials with low voltage but high current to generate Joule heat is an effective energy conversion method. The corresponding temperature will quickly reach the predetermined value. It is also an effective way to achieve homogeneous heating or local non-uniform heating in the heterogeneous conductive elements, thus directly electric heating is widely used in scientific experiments and industrial practices. However, direct electrical heating method may effect by electromagnetic effect (skin effect or proximity effect) and interfere on the sensor, results in inconsistent temperature distribution or inaccurate temperature, even under the condition with power frequency (f = 50 Hz or 60 Hz). In the present paper, a comparative experimental investigation on temperature distribution of multiple parallel blocks at steady and transient process under DC and AC heating mode have been measured by infrared camera and thermocouples. It is found that the temperature measured by AC heating is always lower than that measured by DC heating under the same apparent power applied effected by electromagnetic effect. Three different sensor installations used for temperature measurement is also discussed and found an effective installation method. The electric field and temperature field in parallel blocks is further analyzed by electromagnetic-thermal coupling multiphysics solver after model verification. Moreover, another experiment discovered that the imposed external DC potential will generate a non-linear interference to the measured temperature, the temperature sensor with a good insulation can get more accurate result. These result can provide a technical guidance for direct electrical heating scientific researches and industrial application.

PHOTOSENSITIVE FIELD-EFFECT TRANSISTOR BASED ON REDUCED GRAPHENE OXIDE FILM

A photosensitive graphene field-effect transistor was created by depositing a reduced graphene oxide (rGO) film on the surface of the SiO2 layer on a silicon substrate, which serves as both a photosensitive medium and the field-effect transistor gate. The electrical and photoelectric properties of the field-effect transistor based on the rGO film were studied in DC and AC modes. Linear sections of the drain current on the gate voltage dependence and significant dependence of the electronic component of the rGO film conductivity on the irradiation with white light were revealed based on the analysis of the switching characteristics of the obtained field-effect transistor. A photoinduced decrease in the internal resistance and an increase in the capacitance of the conducting channel of the graphene field-effect transistor in the range of 102–105 Hz were revealed. It has been established that the photoresponse time of the obtained field-effect transistor to light pulses of IR, visible, and UV radiation is about 1.5 ms. The obtained results can be used to simplify the technology of manufacturing photodetectors based on graphene.

Characterization and corrosion behaviour of a phosphate-based plasma electrolytic oxidation coating on extruded EV31 magnesium alloy

Abstract This paper is focused on evaluating the surface properties of protective coating prepared by plasma electrolytic oxidation on magnesium alloy EV31. Plasma electrolytic oxidation was performed in DC mode with a constant current density of 0.05 A cm−2 for 14 min. Evolution of voltage was measured and depicted graphically in order to describe the growth of the plasma electrolytic oxidation coating. Morphology and thickness of the plasma electrolytic oxidation coating were examined together with corrosion resistance of the coating by measurements of electrochemical characteristics using electrochemical impedance spectroscopy and potentiodynamic polarization after 1 h in 0.1 M NaCl. Results from potentiodynamic polarization showed decrease in corrosion current density i corr from 10.50 μA cm−2 (substrate) to 1.02 μA cm−2 (plasma electrolytic oxidation coated) and results from electrochemical impedance spectroscopy showed increase in R p by one order of magnitude for plasma electrolytic oxidation coated sample after both 1 h and 168 h exposure times.

Research on the Formation, Microstructure, and Properties of 304 Stainless Steel AC-DC Hybrid TIG Welding

In this work, a new welding method, AC-DC hybrid TIG welding, is used to weld 304 stainless steel. Research on the formation, microstructure, and properties of 304 stainless-steel welded joints are studied by using optical microscope and microhardness. The results show that the weld with AC/DC hybrid welding is a fish-scale pattern, and the density of the fish-scale pattern increases with the increase of AC proportion. Both the weld penetration and the ratio of weld penetration to weld width are the highest when AC accounts for 30%. At this point, the weld penetration is 0.83 mm larger than DC mode, an increase of 93.26%, and the ratio of weld penetration to weld width is 1.6, which is 76.19% higher than DC mode. When the proportion of AC is increased, the microstructure of the weld is equiaxed or columnar, and the microstructure of the heat-affected zone is ferrite in the form of lath. The hardness of the weld is greater than that of the base metal, and the hardness of the heat-affected zone is the lowest. The microhardness distribution of the weld with AC 50% is the most uniform. When AC accounts for 20% and 30%, the average weld hardness is the highest, which are 196.7 HV and 198.1 HV, respectively.

AC Excitation to Mitigate Drift in AlGaN/GaN HEMT-Based Sensors

AlGaN/GaN high electron mobility transistor (HEMT) based sensors hold promise as small solid-state physical and chemical sensors because they can operate without a reference electrode and can be integrated into miniaturized sensor arrays. However, over extended time periods, low frequency noise causes anomalous variations (drift) in sensor signal, especially in liquid environments. These effects occur despite electromagnetic interference mitigation. To understand the low frequency noise, 1/ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> noise measurements between 0.1 and 100 kHz were undertaken, in both air and water, under constant pH and normal laboratory pressure conditions. The 1/ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">γ</sup> noise for the device in water was larger in magnitude than in air, and estimates for the γ-parameter in air and water were approximately 1 and 1.5, respectively. The corner frequency was observed between 100 and 1000 Hz. Based on this analysis, AC excitation at 1 kHz was applied to the conduction channel to compare the sensor stability in de-ionized water with DC operation. In this controlled test, introduction of AC excitation resulted in a strong correlation of sensor signal with the ambient temperature variations over nearly 90 hours of testing (effectively acting as a temperature sensor with a high degree of stability) while operation in DC mode resulted in largely no correlation with temperature. This indicates that AC excitation above the corner frequency is a potentially effective method to mitigate long-term sensor instability, a critical limitation for any AlGaN/GaN transistor-based physical or chemical sensors in aqueous environments.

Nanocomposites based on porous silicon and reduced graphene oxide for ionizing radiation sensing

In this study, the field-effect transistor (FET) based on the oxidized porous silicon (PS) – reduced graphene oxide (rGO) sandwich-like composite has been created. The electrical characteristics of the obtained FET were studied in both DC and AC modes. I-V curves and switching characteristics of the PS–rGO-based FET were analyzed. An increase in resistance and a decrease in capacitance of the experimental structures have been found in the 25 Hz − 1 MHz frequency range due to the joint action of α-, β-, and γ-radiation. The parameters of the equivalent circuit model of the PS–rGO-based FET before and after irradiation with 226Ra isotope have been determined using the impedance spectra. The formation of radiation-induced defects and the charge accumulation in the PS layer is considered a possible mechanism of the ionizing radiation influence on the graphene FET conductivity. The FET based on the PS–rGO structures has a high potential for application in ionizing radiation sensors due to the linear dependencies of resistance and capacitance on the irradiation duration.

Optical monitoring of DC/RF plasma sputtering for copper oxide film growth at low temperature

DC/RF plasma sputtering process for the growth of copper oxide thin film was studied by optical emission spectroscopy. The films were produced by a balanced magnetron sputtering system nearly at room temperature. The influence of applied power in DC and RF mode and Ar/O2 flow ratio on the film properties was investigated as well as their relationship to the plasma species and the main chemical reactions during the film growth. It was found that the concentration of active species in the plasma and their abundance ratio is very effective in the reactions related to the film growth process and the properties of the deposited film. It was shown that copper oxide film with CuO phase owing low energy band gap can be synthesized at low temperatures by controlling the ionization rate, the energy of the active species, the film growth rate, and finally the relative concentration of copper to oxygen species in the plasma. CuO thin films (Eg=1.28 eV) were achieved in DC mode at the lowest applied power (50 W) and in the lowest Ar/O2 flow ratio (2/1). This oxide phase was also observed for two both the synthesized films in RF mode, at 50 W (Eg=1.39 eV) and 100 W (Eg=1.23 eV) in an Ar/O2 flow ratio of 2/1.

ITBC Controlled IPWM for Solar Based Wide Range Voltage Conversion System

This paper presents an isolated tiny or micro-bidirectional DC–AC converter (ITBC) that operates in a single-phase, single-stage, bidirectional, and isolated configuration. The converter utilises a voltage-in-phase PWM (IPWM) control scheme to regulate the potential conversion ratio of the converter, enabling it to handle a wide voltage range. The converter also enables smooth power flow direction changes and can achieve soft switching, resulting in high efficiency. A unidirectional current controller can be used for both DC–AC and AC–DC modes. The paper provides detailed information about the micro-inverter's working principles, design procedure, characteristics, and control strategy. The proposed solution is verified by a 500-watt test bench model with a voltage input range of 30 volts to 50 volts.

МОДЕЛИРОВАНИЕ СИСТЕМЫ ТЯГОВОГО ЭЛЕКТРОСНАБЖЕНИЯ ПОСТОЯННОГО ТОКА С 6-ТИ ПУЛЬСНЫМИ ПРЕОБРАЗОВАТЕЛЯМИ

The technique of computer modeling of DC traction power supply system’s modes in phase coordinates implemented in Fazonord software package is considered. The developed computer models can be used to determine the parameters of the DC and AC current subsystems mode and also to determine the mode at higher harmonics

Long pulse operation of neutral beam injector on EAST tokamak

The Experimental Advanced Superconducting Tokamak (EAST) is one of the fully superconducting tokamak. A powerful neutral beam injection system, which consists of two injectors (EAST-NBI), was employed on EAST for plasma heating and current driving. The designed parameters for each injector are as follows: deuterium beam energy is 50–80 keV, beam power is 2–4MW and the beam duration is 10–100 s with modulation.In order to support the planned physics research on EAST, the NBI system was expected to work with long pulse on DC mode. So, the NBI system was optimized, including the cooling channels optimization of high power ion source and high heating flux parts, and the feedback control for stable beam extraction. The characteristics of the NBI system after optimization was studied in the lasted EAST campaign. The NBI system can work well with arc power feedback regulation and the temperature rise of high heating flux parts was decreased after upgrade, hence it can be operated with 100 s. Long pulse operation with 100 s will be tested in the next campaign of EAST experiment.

Large- and Small-Signal Modeling and Control Strategy for Multi-Output Welding Power Supply

Welding technology is a key aspect of the manufacturing industry. With the application of aluminum alloy expanding to more applications, the demand for advanced welding technology for aluminum alloy is constantly increasing. The aluminum alloy welding process requires a multi-output welding power supply to improve aluminum alloy welding quality. In this paper, we design a novel type of multi-output converter that outputs dual DC or single AC according to different welding process requirements and analyze its working principles in detail. Considering the influence of load current variation on the circuit’s performance, we established small-signal models of the DC and AC working modes and large-signal models of the system. Based on these models, we designed a control algorithm for the proposed multi-electrode arc welding power supply. Finally, we constructed an experimental prototype and demonstrated the feasibility of the control strategy. Based on the welding power supply designed in this paper, the welding process control of aluminum alloy can be more accurate, resulting in better welding quality.

Hardware Architecture for Realtime HEVC Intra Prediction

Researchers have, in recent times, achieved excellent compression efficiency by implementing a more complicated compression algorithm due to the rapid development of video compression. As a result, the next model of video compression, High-Efficiency Video Coding (HEVC), provides high-quality video output while requiring less bandwidth. However, implementing the intra-prediction technique in HEVC requires significant processing complexity. This research provides a completely pipelined hardware architecture solution capable of real-time compression to minimize computing complexity. All prediction unit sizes of 4×4, 8×8, 16×16, and 32×32, and all planar, angular, and DC modes are supported by the proposed solution. The synthesis results mapped to Xilinx Virtex 7 reveal that our solution can do real-time output with 210 frames per second (FPS) at 1920×1080 resolution, called Full High Definition (FHD), or 52 FPS at 3840×2160 resolution, called 4K, while operating at 232 Mhz maximum frequency.

Comparative Evaluation of Common-Ground Converters for Dual-Purpose Application

The focus of this paper is to provide a comparative analysis of various common-ground converters that serve as dual-purpose power electronic interfaces. These interfaces are designed to be used in both DC and single-phase AC grids, utilizing the same terminals for both modes of operation. The idea lies in the utilization of the same semiconductors in the DC-DC and DC-AC configurations, resulting in minimal redundancy. Particular attention is focused on the comparative evaluation approach. A novel Flying Inductor (FI)-based converter was selected for experimental verification. The design example and experimental prototype of a dual-purpose DC-DC/AC power electronic converter is capable of providing 2 kVA of power in AC mode and 4 kW in DC mode. The experimental results indicate that the converter can operate in both AC and DC grids according to their respective modes. The conclusion of the study highlights the potential applications and main benefits of this technology.

Fast modeling approach of large-scale non-inductive HTS coils under different current supply

This paper presents a fast-integral modeling approach for the design and characterization of large-scale non-inductive high temperature superconducting (HTS) coils made of first-generation HTS tape. The integral modeling is combined with a strategy of far tape approximation allowing to model a reduced set of consecutive tapes instead of the entire coil. It makes it possible to estimate the losses and the current density distribution in the coil, under different current supply. This leads to a considerable reduction in the computation time. The calculated AC losses show a good agreement with the Norris ellipse formula and measurements, highlighting the importance of considering the elliptical section of the superconductor in the tape, in the modeling. The developed modeling approach is in particular useful in the AC + DC mode, where Norris’s formulas cannot be used to determine the losses. Besides, some interesting phenomena have been observed, related to the current distribution in the tapes at different AC and DC current values.

Impact of electric mobility on the design of renewable energy collective self-consumers

European countries aim to reach important targets in the energy field through the increase of energy efficiency in final uses, the exploitation of renewable energy sources, and the implementation of energy communities. In the aforesaid framework, renewable energy self-consumers represent a smart solution to foster the adoption of renewable energy power plants and storage systems in the residential and tertiary sectors. The goal of the paper is to propose an optimisation-based methodology to evaluate the impact of electric mobility on the optimal design of renewable energy collective self-consumers. The integration of renewable sources and storage systems with charging infrastructures for electric vehicles is analyzed and discussed by running a stochastic optimization model, developed in Matlab/Yalmip, to evaluate different scenarios with different electric mobility penetration levels. The paper shows how the presence of electric vehicles increases the optimal installed size of the RES plants significantly, from 15% up to more than 25%. Moreover, it underlines how the optimal charging system, in terms of type, number, and size of charging stations, is affected by the considered number of electric vehicles but also by the model and thus the characteristics of the electric vehicles such as the maximum accepted charging power in AC and DC modes.

Comparative Analysis of Inter-Inverter Interactions in Emerging Hierarchical-Infeed and Conventional Multi-infeed LCC-HVDC Systems

The emerging hierarchical-infeed LCC-HVDC (HIDC) system has been recently commissioned for the long distance bulk power transmission in China. Compared to the conventional multi-infeed LCC-HVDC (MIDC) system with inverters coupling only in the ac-side, different inter-inverter interactions exist in the HIDC system where inverters couple in both the ac- and dc- sides. It is beneficial to reveal the underlying difference of the inter-inverter interactions in the HIDC and MIDC systems for determining which system should be adopted in the planning study. However, this difference has not been clearly revealed yet in earlier works. Thus in this paper, the inter-inverter voltage interaction factor (IVIF) index is firstly introduced to quantitatively assess the inter-inverter interactions. The analytical calculation methods of the IVIF for the HIDC and MIDC systems are also presented for the satisfactory accuracy and efficiency. Moreover, these methods are further used for comparative analysis of parametric dependence of the IVIF in the HIDC and MIDC systems considering various system parameters, operation variables and dc control modes. The analysis results clearly reveal the underlying difference of the inter-inverter interactions in the HIDC and MIDC systems. Finally, the effectiveness of the theoretical assertions is verified by experiments based on the hardware-in-the-loop platform.

Improvement of microstructure and mechanical properties of stainless steel TIG based wire arc additive manufacturing by using AC/DC mix current waveform

In this work, a new current waveform, the AC/DC mix current waveform was employed to improve the microstructure and mechanical properties of 307Si stainless steel component during the TIG based wire arc additive manufacturing (TIG-WAAM). The results showed that the morphology of γ-austenite is changed from the columnar dendrites (with DC mode) to the equiaxed dendrites (with AC/DC mix mode). The grain size was refined due to the reduction of the temperature gradient in the AC/DC mix mode. The degree of refinement grain is increased with the increase of AC ratio. The tensile strength of the 70%DC+30%AC-sample in the traveling and building directions are respectively increased by about 60 MPa and 41 MPa compared with that of the 100%DC-sample. The grain refinement is the mainly reason of the improvement of mechanical properties of the TIG-WAAM component with the AC/DC mix mode.

Solution processed low operating voltage SnO2 thin film transistor by using Li2SnO3/TiO2 stacked gate dielectric

A thin layer of sol–gel derived lithium stannate (Li2SnO3) was deposited by a spin coating method that shows high areal capacitance with low DC conductivity which originated due to the mobile lithium ion (Li+) and low carrier concentration. The DC conductivity of this Li2SnO3 thin film has been reduced further by adding a sol–gel derived titanium-oxide (TiO2) layer. Moreover, bilayer thin film effective areal capacitance also increases due to the higher relative permittivity of TiO2 layer. The measured areal capacitance of such Li2SnO3 /TiO2 bilayer thin films is 518 nF/cm2 with a low current density of 3.8 X 10-5 A/cm2 under 5 V external bias, can fulfil the requirement as gate dielectric of a low operating voltage (≤3V) thin film transistor (TFT). For identifying its applicability as gate insulator, a solution-processed tin oxide (SnO2) thin film transistor (TFT) was fabricated with Li2SnO3/TiO2 stacked gate dielectric. In this TFT structure, thin film of TiO2, SnO2 and Li2SnO3 are all polycrystalline in nature. The electrical characterization of TFT has been done under DC mode operation in ambient atmosphere measurement which remain almost unaltered under 11 cyclic measurements. The optimized TFT required only 3.0 V external bias that shows an electron mobility of 3.47 cm2 V−1 s−1 with on/off ratio of 50.

Aerogel-Based Single-Ion Magnets: A Case Study of a Cobalt(II) Complex Immobilized in Silica

The chemical immobilization of cobalt(II) ions in a silica aerogel matrix enabled the synthesis of the first representative example of aerogel-based single-ion magnets. For the synthesis of the lyogels, methyl-trimethoxysilane and N-3-(trimethoxysilyl)propyl ethylenediamine were co-hydrolyzed, then the ethylenediamine groups that were immobilized on the silica matrix enabled the subsequent binding of cobalt(II) ions. Lyogels with various amounts of ethylenediamine moieties (0.1-15 mol %) were soaked in isopropanol solutions of cobalt(II) nitrate and further supercritically dried in carbon dioxide to obtain aerogels with a specific surface area of 210-596 m2·g-1, an apparent density of 0.403-0.740 cm3·g-1 and a porosity of 60-78%. The actual cobalt content in the aerogels was 0.01-1.50 mmol per 1 g of SiO2, which could easily be tuned by the concentration of ethylenediamine moieties in the silica matrix. The introduction of cobalt(II) ions into the ethylenediamine-modified silica aerogel promoted the stability of the diamine moieties at the supercritical drying stage. The molecular prototype of the immobilized cobalt(II) complex, bearing one ethylenediamine ligand [Co(en)(MeCN)(NO3)2], was synthesized and structurally characterized. Using magnetometry in the DC mode, it was shown that cobalt(II)-modified silica aerogels exhibited slow magnetic relaxation in a nonzero field. A decrease in cobalt(II) concentration in aerogels from 1.5 mmol to 0.14 mmol per 1 g of SiO2 resulted in a weakening of inter-ion interactions; the magnetization reversal energy barrier likewise increased from 4 to 18 K.

Realization of Outstanding Stable 1S1R Behavior Based on Al-Doped NbOx

In this study, we proposed a remarkable one-selector one-resistor (1S1R) device with a single Al-doped NbOx layer, which performed reasonable resistance and switching voltages without degeneration, implying robust stability and outstanding uniformity. The measurements of dc and ac modes were applied to confirm the nonvolatility and effective storage performance. Besides that, a conduction model based on the results of the first principles calculations was proposed to explain the reason for the oxygen vacancies were generated more and tended to the cluster. Meanwhile, they were easier to migrate in Al-doped due to a lower barrier. These contributed to achieving stable conductive filaments as well as the switching process and improve uniformity and stability. Consequently, we developed an excellent 1S1R without an independent rectified cell, which has the potential for 3-D architecture.