Direct Current Research Articles

Effects of Degassing Treatment on the Dielectric Properties of XLPE Insulation Used in High-Voltage DC Power Cables

Cross-linked polyethylene power cables are widely used in high-voltage DC transmission lines, owing to their good dielectric and physical–chemical properties. However, the production process of XLPE involves cross-linking and degassing, in which the cross-linking process produces a variety of cross-linking by-products, and the changes in the properties of the cable insulation caused by the degassing process are not well understood. XLPE samples were degassed at 90 °C for 7 and 14 days in this paper, and the main by-products were found to be α-methylstyrene, acetophenone, and cumyl alcohol, the contents of which all declined after the degassing treatment. The results show that the space charge density, the leakage current under a high electric field at different temperatures, and the breakdown strength of the XLPE samples all decreased after the degassing treatment. On the other hand, the XLPE sample after 7 days’ degassing had the lowest conductivity and the highest conductance activation, and the space charge density and the charge decay rate as well as the breakdown strength after 7 days’ degassing differed little from the 14-day treated sample, demonstrating that the 7-day degassing treatment at 90 °C would be enough to achieve superior performance.

Study of low-profile near-field electromagnetic energy harvesting

Abstract In order to recover the magnetic energy that leaks from an induction cooktop, this study suggests a straightforward and cost-effective magnetic-field energy harvester (MFEH) circuit. With the aid of the intended circuitry, the acquired magnetic energy is transformed into DC electrical energy. We harvested the magnetic-field energy (MFE) from the induction cooktop at various heights and locations of the energy harvesting coil. With a load resister of 46.6 Ω and a capacitance of 1 mF, the developed MFEH circuit, when positioned 2 cm beneath the cooktop, can capture an average DC power of 1936 mW. Placing the energy-harvesting coil 7.5 cm beneath the induction cooktop lowers the power output to 142 mW. For a range of load resister values, the MFE gathered at various locations along the energy harvesting coils is examined. Batteries can be used to store the gathered energy for later use. Additionally, the suggested device is shown to be capable of wirelessly powering low-power Internet of things devices and charging mobile devices. The suggested device differs from the previously published magnetic harvesting circuits due to the induction cooktop’s superior performance and capacity to gather MFE.

Excellent Tribological Properties of WS2 Films in Air by Doping Copper

WS2 films exhibit excellent tribological properties in a vacuum, but they are prone to failure due to oxidation in air, which severely limits their application. Cu has great potential to improve the tribological properties of WS2, similar to that of Au and Ag. Thus, to clarify the contribution of Cu to the tribological properties of WS2 films and provide new insight for the development of new multi-environmentally adaptable films, this study deposited WS2-Cu composite films under different sputtering powers of the Cu target by magnetron sputtering systems, and the Cu target was supplied by DC power. Then, the structure of films was analyzed by FESEM, EDS and XPS. The results show that Cu is difficult to uniformly dope on the WS2 film at a high sputtering power of Cu target, showing possibly low solubility of Cu in WS2 film. However, a uniform and dense WS2-Cu composite film was deposited under the lower sputtering power of Cu target. Furthermore, the results of the nanoindentation test demonstrated that the WS2-Cu composite films exhibited high hardness (6.6 GPa). Finally, the tribological properties of the WS2-Cu films were examined, and their friction interface was characterized by SEM, EDS and TEM. The WS2-Cu film demonstrated superior tribological behavior in air (the average friction coefficient is 0.09), based on a special sliding interface, low oxidation levels of WS2 and Cu-rich transfer film. This study provides a new insight and a new method for improving the environmental adaptation ability of WS2 film.

Development and laboratory assessment of a subsea particle image velocimetry system for bubble and turbulence measurements in marine seeps

AbstractWe present the development and laboratory evaluation of RPiPIV, an underwater particle image velocimetry (PIV) system controlled by a Raspberry Pi. Designed specifically to measure bubble characteristics and bubble‐induced flow in natural hydrocarbon seeps, RPiPIV comprises three primary pressure enclosures, housing a consumer‐grade laser for particle illumination, a Gig‐E camera for image capture, a Raspberry Pi for system control, and essential supporting electronics for voltage conversion, battery management, and remote connection. Operating on 24–36 V DC power, the RPiPIV system can be deployed tethered onto a remotely operated vehicle or self‐contained for extended duration measurements. Comparing the RPiPIV and a laboratory high‐speed camera system, we conducted assessments of bubble imaging in a bubble stream and PIV measurements in a water jet, bubble‐chain flow, and single‐orifice bubble plume. Laboratory assessments revealed that bubble diameter estimates differed by approximately 5%. In PIV measurements, mean axial velocities exhibited differences of approximately 5%, while turbulent normal and shear stresses showed variances within 10–30%. Dissipation rates of turbulence kinetic energy differed by approximately 60%. These findings underscore the system's potential for reliably quantifying complex multiphase flow characteristics in deep‐sea environments.

Adaptive Controller Approach for a Three-Axis Helmholtz Magnetic Test-Bed to Test Detumbling Simulations in the GWSAT Satellite

Abstract The paper introduces the design and simulation of the IS501NMTB magnetic test-bed, which utilizes three Helmholtz coils controlled by three independent ITECH IT6433 DC power sources and a MAG649L magnetometer. The goal is to perform in-the-loop simulations to test detumbling and nadir-pointing attitude control algorithms for the GWSAT mission, as well as to assess the capability of the IS501NMTB to characterize the magnetic dipole of small satellites using perturbation observers. A mathematical model based on RL circuits and the Biot–Savart law is employed and validated with experimental data measured in 2021 and 2024, demonstrating parameter variations over time. Additionally, closed-loop PID, adaptive PID, and MRAC control algorithms were tested for canceling Earth’s magnetic field and simulating Earth’s magnetic field at the GWSAT orbit using the IGRF-13 model. The results obtained from these simulations are analyzed and compared using error integration and control integration metrics to determine whether the use of adaptive controllers is advantageous in this application.

Supraharmonic Distortion at the Grid Connection Point of a Network Comprising a Photovoltaic System

Grid-connected photovoltaic (PV) systems inject nonsinusoidal currents into the grid at the point of their connection. The technology of the inverter utilized for the conversion of DC power into AC is directly associated with distortion characteristics. Even though pulse-width-modulated (PWM) converters generate considerably lower harmonic distortion than their predecessors, they are responsible for the emergence of a new power quality issue in distribution grids known as supraharmonics, which can cause problems such as overheating and malfunctions of equipment. PV systems are known sources of supraharmonics, but their impact has not yet been thoroughly researched. Due to the multitude of parameters affecting their performance, a more rigorous treatment is required compared to more common nonlinear devices. In this paper, emissions from a three-phase grid-connected PV system are examined by means of a dedicated simulation tool taking into account the specifics of inverter switching action without overly increasing computational cost. The impact of environmental parameters as well as factors affecting the switch control of the converter is investigated. The dependence of the supraharmonic emission of the PV system on the converter characteristics rather than environmental conditions is demonstrated. Furthermore, simulation studies on a network comprising the PV system and an additional supraharmonic-emitting system in simultaneous operation are conducted. Their combined effect on the distortion at the connection point of the network to the grid is assessed by means of a power flow-based approach, capable of quantifying interactions within this network. From the viewpoint of the grid, an increase of supraharmonic-related disturbance at low irradiance conditions is revealed.

Decoration of Silver Nanoparticles on WS2-WO3 Nanosheets: Implications for Surface-Enhanced Resonance Raman Spectroscopy Detection and Material Characteristics

This study investigates the chemical and structural modifications of vertically aligned tungsten disulfide–tungsten trioxide (WS2-WO3) nanosheets decorated with silver nanoparticles (Ag(NPs)) under nitrogen plasma conditions. The synthesized vertically aligned WS2-WO3 nanosheets were functionalized through direct-current (DC) magnetron sputtering, forming silver-decorated samples. Structural changes, as well as the size and distribution of Ag(NPs), were characterized using scanning electron microscopy (SEM). Chemical state analysis was conducted via X-ray photoelectron spectroscopy (XPS), while Raman spectroscopy was employed to investigate vibrational modes. The findings confirmed the successful decoration of Ag(NPs) and identified unexpected compound transformations that were dependent on the duration of functionalization. The synthesized and functionalized samples were evaluated for their sensing capabilities towards Rhodamine B (RhB) through surface-enhanced resonance Raman scattering (SERRS). This study discusses the impact of substrate morphology and the shape and size of nanoparticles on the enhancement of SERRS mechanisms, achieving an enhancement factor (EF) of approximately 1.6 × 106 and a limit of detection (LOD) of 10−9 M.

Full-bridge DC-DC Converter based on Linear Active Disturbance Rejection Control

Dual Active Bridge (DAB) converter has been a research hotspot in recent years. It is widely used in distributed power generation system, DC microgrid system and power management system. Traditional PI controllers do not perform well in the face of nonlinear loads and external disturbances, so a more advanced control method is needed to improve the stability and performance of the system. In this paper, a control strategy based on active disturbance rejection control (ADRC) is proposed to improve the control performance of full-bridge DC-DC converter. First of all, the small signal mathematical model of full-bridge DC-DC converter is established, and the function relationship between input, output, control quantity and disturbance quantity in the system is obtained. Then, the extended state observer of ADRC core module is designed, and its parameters are adjusted and simulated, compared with the traditional PI controller. The simulation results show that the full-bridge DC-DC converter based on LADRC has faster dynamic response and better disturbance immunity, which can effectively improve the stability and robustness of the system.

Topology and Control Strategy of Multi-Port DC Power Electronic Transformer Based on Soft Switching

Multi-port DC power electronic transformer (PET) is a core equipment for achieving transformation of different voltage levels and flexible interconnection of different DC buses in a DC distribution system. It is capable of bidirectional energy flow, flexible regulation of power flow, port fault isolation, and other functions. A new five-port DC transformer topology based on soft switching technology is proposed in this paper. In this topology, different DC voltage levels can be interconnected efficiently, such as 20 kV, 750 V, ±375 V, and 300 to 500 V adjustable. The control of each port is simple and flexible. The output voltage is stable, and they are independent of each other, which can improve the system reliability. The topology of the proposed multi-port DC transformer is introduced in detail. The working principle, control strategy, and parameter design method of the transformer are analyzed. Simulations and experimental results are provided to validate the theoretical analysis.

A Novel IGBT-Based Silicone Carbide Rectifier Design for Improved Energy Efficiency in Telco Data Centers

This study presents a novel topology designed to enhance the energy efficiency and quality of IGBT-based high-frequency rectifiers, which are commonly used to supply the high DC power required in industrial applications. In the proposed design, traditional silicon semiconductors are replaced with advanced SiC semiconductors, resulting in reduced switching losses and improved energy quality due to higher frequency switching. The new topology also offers solutions to challenges such as inrush current, reverse energy flow, and high DC output voltage issues typically encountered in IGBT-based rectifiers. The goal is for this topology to maximize efficiency and applicability. The proposed design is simulated in the Simulink environment, with the results presented in the findings section. To highlight the advantages of the new topology, the electrical parameters of the widely used three-phase full-bridge IGBT rectifier topology are employed for comparison.

Application of Active Components such as DC Generators and Operational Amplifiers in Mechanical Design

DC generators and operational amplifiers have become increasingly important as the need for automation and precise control in mechanical engineering continues to grow. Since their invention in the 19th century, DC generators have played an important role in power systems, especially in applications that require a stable DC power supply. Meanwhile, since the 1960s, operational amplifiers have played an important role in analog circuits, and their applications cover a wide range of fields such as audio processing, signal conditioning, data acquisition and control systems. This paper explores the multiple applications of DC motors and operational amplifiers in mechanical systems and their integration through a literature review approach. It is found that these components not only improve the efficiency and performance of mechanical systems, but also provide higher control accuracy in areas such as robotics and industrial automation. In addition, with the continuous advancement of technology, the combination of the two is expected to realize innovations and breakthroughs in more fields. The research in this paper provides an important reference for the future innovation and development of mechanical engineering

State of Charge Estimation for Lithium Battery in Shipboard DC Power Grid Based on Differential Evolutionary Algorithm

More and more attention has been paid to ships with a DC power grid. State-of-charge (SOC) estimation is a pivotal and challenging assignment for lithium-ion batteries in such ships. However, the precision of SOC estimation is strongly connected with the system parameters. To better identify these parameters in lithium-ion batteries, a differential evolution (DE) algorithm was introduced into this paper as the optimizer. Initially, a first-order RC equivalent circuit model (ECM) was created to characterize the battery’s dynamic behavior. Following this, to estimate open-circuit voltage (OCV) throughout the entire dynamic process, a math model of optimization was established to minimize inaccuracies between the real and estimated terminal voltages. Moreover, estimated SOC values were obtained through OCV-SOC mappings and were contrasted against the true SOC values. The findings manifested the efficacy of the presented structure and technique in comparison with various frequently-cited DE variants.

Skin-Integrated Electrogenetic Regulation of Vasculature for Accelerated Wound Healing.

Neo-vascularization plays a key role in achieving long-term viability of engineered cells contained in medical implants used in precision medicine. Moreover, strategies to promote neo-vascularization around medical implants may also be useful to promote the healing of deep wounds. In this context, a biocompatible, electroconductive borophene-poly(ε-caprolactone) (PCL) 3D platform is developed, which is called VOLT, to support designer cells engineered with a direct-current (DC) voltage-controlled gene circuit that drives secretion of vascular endothelial growth factor A (VEGFA). The VOLT platform consists of a 3D-printed borophene-PCL honeycomb-shaped matrix decorated with borophene-PCL nanofibers by electrospinning. The honeycomb structure provides mechanical stability, while the nanofibers facilitate the adhesion, migration, and proliferation of the engineered cells. The cells incorporate a DC-powered reactive oxygen species (ROS)-sensing gene circuit wired to an engineered synthetic promoter that triggers secretion of VEGFA to promote vascularization in the adjacent extracellular matrix. Cells engineered with this gene circuit and enclosed in the VOLT matrix, termed the VOLTVEGFA system, can be simply triggered using off-the-shelf AA batteries, utilizing the established ability of a brief DC bias to generate non-cytotoxic levels of ROS. For proof-of-concept, a subcutaneous wound-healing model in rats is chosen. Electrostimulation of a VOLTVEGFA implant (5 V, 20 s per day) induced secretion of VEGFA, and significantly accelerated neovascularization and granulation tissue formation, resulting in faster wound closure compared with non-stimulated controls. Complete re-epithelialization and dermal regeneration are observed within 15 days of application.

Analysis of the persistent photoconductivity in composite nanocrystalline ZnO/Si films produced by co-sputtering at room temperature

AbstractThe persistent photoconductivity (PPC) behavior in composite nanocrystalline films ZnO(RF)/Si(DC) films grown by co-sputtering was studied. The studied films were produced by fixing the ZnO RF magnetron power at 120 Watts and varying the DC power for the Si target from 0 to 80 Watts. The produced films were structural, optical, and electrical characterized; n-type films were produced for all the composition range. The PPC behavior was studied in samples grown with the composition formed with the ZnO (RF = 120 W)/Si (DC = 20 W) power condition, and by exposing the sample surfaces under continuous or pulsed ultraviolet (UV) radiation (390–400 nm). After applying an extended cleansing period, the PPC characteristic time constants, τ.63, were obtained; the turn-off time constant varied from 16.8 to 22.8 s, while the turn-on time constant changed from 24 to 30 s. These periods are linked to the UV light lattice absorption and the corresponding energy relaxation mechanisms. Graphical abstract

Rapid electrothermal upcycling hexachlorobutadiene (HCBD) polluted distillation residue into turbostratic graphene for enhanced electromagnetic wave absorption.

The trichloroethylene production industry generates high-boiling-point solid residues during rectification, which contain high concentrations of chlorinated contaminants, particularly hexachlorobutadiene (HCBD). Traditionally, these distillation residues are managed through co-incineration or landfilling, leading to environmental and economic challenges. In this study, we present a rapid and environmentally friendly electrothermal approach for both detoxifying and upcycling distillation residue into graphene-based electromagnetic wave (EMW) absorbing materials. By employing a DC power pulse discharge with a 10 s duration, we achieved over 99 % HCBD degradation efficiency. Characterization results indicate that the thermal shock transforms the distillation residue into high-value turbostratic pulse graphene (tPG). This tPG, featuring a unique structure, demonstrates substantial potential as an EMW absorber, with an effective absorption bandwidth of 3.9 GHz and a reflection loss of -42.0 dB at a minimal matching thickness of 1.6 mm. The method offers a sustainable, cost-effective solution for hazardous waste management, combining rapid processing with high-value material production.

Wideband rectifying metasurface with enhanced efficiency for wireless power transmission via harmonic feedback design.

We present a wideband rectifying metasurface (RMS) with enhanced system efficiency for wireless power transmission and energy harvesting. The RMS consists of periodic arrays with integrated diodes, with a high input impedance matched with the diodes, thus eliminating the matching network between metasurface (MS) and rectifier. Besides, a unique harmonic feedback network is embedded in each unit cell, rectifying the high-order harmonic generated by the diode repeatedly, improving the total efficiency over a wide bandwidth. The converted DC power is channeled to one single load through the DC-paths formed by the branches of MS and a series of inductors, avoiding additional DC-combination networks. The MS can effectively capture EM energy at an operating band of 2-3.5 GHz, and the simulated radiation-AC efficiency is up to 99% at 2.8 GHz. A finite 8 × 8 array is fabricated and measured. The total conversion efficiency reaches a peak value of 60.5% at 2.7 GHz when the power density is 25dBm/m2, and is greater than 40% from 2.3 GHz to 2.9 GHz, exhibiting a wide bandwidth of 23.1% compared with existing state-of-the-art studies. The integrated MS-based RF energy harvester with the advantages of a simple structure is of great significance for wireless power transfer and energy harvesting applications.

Use of a virtual laboratory to improve the understanding of direct current electrical circuits

The purpose of this project was to analyze a way to improve the understanding of direct current electrical circuits in students of the fourth semester of High School of the College of Bachelors of the State of Hidalgo. The methodology used is based on the constructivist approach, based on problem-based learning. The results obtained show that a large percentage of the students improved their understanding of the topics when doing virtual practices. It is concluded that the teacher can use virtual simulators in institutions where, due to lack of infrastructure, there is no science laboratory

Electrochemically grafted molecular layers as on-chip energy storage molecular junctions.

Molecular junctions (MJs) are celebrated nanoelectronic devices for mimicking conventional electronic functions, including rectifiers, sensors, wires, switches, transistors, negative differential resistance, and memory, following an understanding of charge transport mechanisms. However, capacitive nanoscale molecular junctions are rarely seen. The present work describes electrochemically (E-Chem) grown covalently attached molecular thin films of 10, 14.3, and 18.6 nm thickness using benzimidazole (BENZ) diazonium salts on ITO electrodes on a quartz substrate upon which 50 nm of aluminum (Al) top contact was deposited to fabricate large-scale (area = 500 × 500 μm2) molecular junctions. The capacitance of the molecular junctions decreases with increasing thickness of molecular layers, a behavior attributed to a classical dielectric role in which the geometric capacitance of the device within a uniform dielectric component is expected to decrease with increasing thickness. An electrical dipole moment in BENZ oligomers enhances polarizability; hence, the dielectric constant of the medium leads to an increase in the capacitance of MJs, which reaches a maximum value of ∼53 μF cm-2 for a junction of 10 nm molecular film thickness. In addition to direct-current (DC) electrical measurements, and computational studies, we performed alternating current (AC)-based electrical measurements to understand the frequency response of molecular junctions. Our present study demonstrates that BENZ-based molecular junctions behave as classical organic capacitors and could be a suitable building block for nanoscale on-chip energy storage devices.

DC power quality analysis: technical insights for LVDC networks and measurement systems

DC power quality analysis: technical insights for LVDC networks and measurement systems

Optimized design of solid state power controller (SSPC) operating circuit for unmanned aerial vehicles (UAV) DC power distribution systems

Optimized design of solid state power controller (SSPC) operating circuit for unmanned aerial vehicles (UAV) DC power distribution systems