Alternating Current Direct Current Research Articles

Wideband AC Voltage Standards

This article presents a critical review and comparison of constructions and metrological properties of contemporary wideband standards for AC voltage. It focuses on selected thermal voltage converters (TVCs) used in alternating current-direct current (AC-DC) transfer voltage standards and for the most precise measurements of AC voltages up to approximately 100 MHz. These devices serve as primary AC voltage standards at National Measurement Institutes (NMIs).

Effect of AC/DC mixed current waveform on surface oxidation, microstructure and mechanical properties of TIG welded TC4 titanium alloy

Coarse β-grains and severe surface oxidation are major factors plaguing the comprehensive properties of tungsten inert gas (TIG) welded joints of titanium alloy. To improve the performance of welded joints, a novel current waveform, alternating current/direct current (AC/DC) mixed current waveform which was named Mix-TIG was proposed. In Mix-TIG, the oxide film on the weld surface is broken up by the cathodic crushing effect. Cyclic variations of the current waveform produce stronger arc stirring and more intense oscillations in the molten pool which results in grain refinement. In addition, the lower temperature gradient in the melt pool due to the smaller heat input in Mix-TIG also contributes to grain refinement. The elongation and microhardness of the Mix-TIG were increased.

Hysteresis measurement and generic modeling of magnetostrictive materials under high-frequency excitation and high-intensity bias field

The applied DC (direct-current) bias fields can cause the changes of hysteresis and loss properties of magnetostrictive alloys materials, which further affect the output characteristics of electromagnetic devices. This study investigates the impact of high-frequency AC (alternating-current) excitation and high intensity DC bias magnetic field on hysteresis characterization for different magnetostrictive materials. To obtain the hysteresis properties of materials, a generic dynamic magnetic measured system is established, which can test the low-permeability magnetic materials with a DC bias strength range of 0–20000 A/m at AC excitation frequency range of 1–9 kHz. The tested results show that the Terfenol-D, Fe83Ga17, and Fe30Co70 exhibit different DC bias sensitivities, which cause the largest deviation (31.68 %) of losses compared with unapplied DC bias field. To better predict these changes, a generic high-frequency dynamic Jiles-Atherton (J-A) model with the coupling AC excitation and DC bias field is proposed. The AC excitation and DC bias related terms are introduced to characterize distortion and ellipticity phenomenon for these hysteresis loops. A combined method of Simulated Annealing Particle Swarm Optimization-Linear Decreasing Inertia Weight (SA-PSO-LDIW) algorithm and Neural Network (NN) are proposed to identify the introduced relevant parameters. This paper solves the problem of high-frequency hysteresis measurement and loss calculation for low permeability and high electrical impedance magnetostrictive rods-shaped material which can help guide the high frequency application for magnetostrictive materials.

Relay demonstration on board for final year student

The present invention relates to a relay demonstration board, characterized by a microcontroller, numbers of relays are connected to the microcontroller by a plurality of switches, wherein the first relay is connected to a light bulb for controlling the lighting of the bulb and the second and third relay are connected to a DC motor for controlling the rotational direction of the motor. Accordingly, these objectives may be achieved by following the teachings of the present invention. This invention relates to a relay demonstration board for teaching and learning purpose. An electrical relay is an electromagnetic switch operated by a relatively small electric current that can control a much bigger current and thus enable both circuits to be electrically isolated from each other. Relays have been used in wide variety of applications such as home appliances, digital computers and automation system due to its simplicity, long life and high reliability. The project present invention relates to a relay demonstration board. It is developed to allow students to understand the function of relay and how to connect relay in circuit. The major components include three relays, one light bulb and one direct current (DC) motor. The relays are used for control purpose while the light bulb and DC motor are used as the output. Furthermore, the light can be connected in alternating current (AC) or DC circuit to show students how to connect AC circuit and DC circuit. Besides, this tool are invention can be connected to an external microcontroller such as an Arduino board to provide input and or signal to the circuit.

The Impact of Solar Intermittency on the Concentration Polarization Factor, Water Quality and Specific Energy Consumption in the Reverse Osmosis Process

Water scarcity has prompted the use of desalination technologies such as reverse osmosis (RO) due to its low energy requirement and high production rate. In the present article, the concentration polarization factor (β) was evaluated in RO processes, in batch and continuous systems and with an alternating current (AC) and direct current (DC) to desalinate water with 10,000 mg L−1 of total dissolved solids (TDS). In DC, the power variation and its effect on β was evaluated by simulating intermittent solar photovoltaic radiation. The specific energy consumption (SEC) in kWh m−3, the water quality in mg L−1 of TDS and β were evaluated. In a batch process, 3.98 and 3.85 kWh m−3 were required for AC and DC, respectively. In a continuous process with AC, 3.79 kWh m−3 was required, and for DC, it decreased by 17.93%. The permeate water quality was evaluated with reference to the Mexican standard of 1000 mg L−1 in TDS. A TDS concentration of 1631 mg L−1 was found in batch–AC processes, and a TDS concentration of 747 mg L−1 was found in batch–DC processes. In continuous AC–DC processes, the TDS concentration did not exceed 1000 mg L−1. The permitted β limit was 1.2. The result of the batch process when using DC was 1.007, while for AC, it was 1.022. In continuous processes with AC, the β was 1.008, and in DC, it was 1.012. The results prove that the intermittency due to power variation is an alternative way to reduce the concentration polarization factor, with effects that include a reduction in the specific energy consumption and an improvement in the permeate water quality.

A Self-Powered VDJT AC–DC Conversion Circuit for Piezoelectric Energy Harvesting Systems

A comprehensive model for micro-powered piezoelectric generator (PG), analysis of operation, and control of voltage doubler joule thief (VDJT) circuit to find the piezoelectric devices (PD’s) optimum functioning points are discussed in the present article. The proposed model demonstrates the power dependence of the PG on mechanical excitation, frequency, and acceleration, as well as outlines the load behaviour for optimal operation. The proposed VDJT circuit integrates the combination of voltage doubler (VD) and joule thief circuit, whereas the VD circuit works in Stage 1 for AC (alternating current)–DC (direct current) conversion, while a joule thief circuit works in Stage 2 for DC–DC conversion. The proposed circuit functions as an efficient power converter, which converts power from AC–DC and boosts the voltage from low to high without employing any additional electronic components and generating duty cycles. The electrical nature of the input (i.e., PD) of a VDJT circuit is in perfect arrangement with the investigated optimisation needs when using the proposed control circuit. The effectiveness of the proposed VDJT circuit is examined in terms of both simulation and experiment, and the results are presented. The proposed circuit’s performance was validated with available results of power electronics interfaces in the literature. The proposed circuit’s flexibility and controllability can be used for various applications, including mobile battery charging and power harvesting.

Self‐Powered Piezoelectric Actuation Systems Based on Triboelectric Nanogenerator

AbstractSustainable power supply via triboelectric nanogenerator (TENG) is attractive for self‐powered actuation systems in the era of the Internet of Things (IoTs). Herein, a low‐power actuation scheme enabled by the multilayered TENG for piezoelectric actuators, including the stack, unimorph, and micro‐fiber composite (MFC) actuator, is reported. The working principles of TENG‐powered piezoelectric actuators and their displacement characteristics in direct current (DC) and alternating current (AC) modes are theoretically investigated. Compared with conventional high‐voltage power sources, the multilayered TENG delivers a maximum power of only 10.17 mW, providing a low‐power alternative for piezoelectric actuator with self‐powered capability and operational safety. Meanwhile, the hysteresis of the stack actuator that is critical in precise positioning control is reduced by 58.1%. A precise positioning system is demonstrated by utilizing the TENG‐powered stack actuator as an object stage for microscope focusing applications. The feasibility of vibration control with a 76.7% reduction in vibration amplitude is also verified via two TENG‐powered MFC actuators. A rectifying control circuit comprising the rectifier and gas discharging tube is established to implement AC–DC conversion and discharging control, achieving a larger displacement of the unimorph actuator. The TENG‐powered piezoelectric micropump demonstrates its potential application in liquid transport through straightforward operation.

Modelling and simulation for energy management of a hybrid microgrid with droop controller

<span lang="EN-US">The most efficient and connected alternative for increasing the use of local renewable energy sources is a hybrid microgrid, these systems face additional challenges due to the integration of power electronics, energy storage technologies and traditional power plants. The hybrid <a name="_Hlk120713679"></a>alternating current-direct current (AC-DC) microgrid that is the subject of this research uses a primary-droop control system to regulate state variables and auxiliary services, thus, it is composed of batteries, solar panels and a miniature wind turbine (PDC) and controls how each energy source in a microgrid contributes to the final product. To achieve the given objectives, this paper will create appropriate models for each part of the microgrid design and define, among them, the energy storage batteries and power electronic converters required for each level of each of these systems. Finally, the dynamic nature of the system will be critically evaluated and characterized, to distribute the load and reduce imbalances, modify the primary drop of the resulting microgrid using MATLAB simulation.</span>

Design and Optimization of Multi-Stage TMR Sensors for Power Equipment AC/DC Leakage Current Detection

Tunnel magnetoresistance (TMR) can measure weak magnetic fields and has significant advantages for use in alternating current/direct current (AC/DC ) leakage current sensors for power equipment; however, TMR current sensors are easily perturbed by external magnetic fields, and their measurement accuracy and measurement stability are limited in complex engineering application environments. To enhance the TMR sensor measurement performance, this paper proposes a new multi-stage TMR weak AC/DC sensor structure with high measurement sensitivity and anti-magnetic interference capability. The front-end magnetic measurement characteristics and interference immunity of the multi-stage TMR sensor are found to be closely related to the multi-stage ring size design via finite element simulation. The optimal size of the multipole magnetic ring is determined using an improved non-dominated ranking genetic algorithm (ACGWO-BP-NSGA-II) to derive the optimal sensor structure. Experimental results demonstrate that the newly designed multi-stage TMR current sensor has a measurement range of 60 mA, a fitting nonlinearity error of less than 1%, a measurement bandwidth of 0–80 kHz, a minimum AC measurement value of 85 μA and a minimum DC measurement value of 50 μA, as well as a strong external electromagnetic interference. The TMR sensor can effectively enhance measurement precision and stability in the presence of intense external electromagnetic interference.

Structural Design and Analysis of New Electromagnetic Actuator

active vibration control can effectively restrain low-frequency line spectrum vibration. As an output end of control force, an electromagnetic actuator has the problem of low precision of output force and zero drift. Therefore, a new type of electromagnetic actuator is designed in this paper. The parametric modeling of the magnetic circuit structure is carried out, and it is verified that the magnetostatic attraction in direct current (DC) magnetic circuit is zero. Then, a calculation method of electromagnetic force in alternating current/direct current (AC/DC) magnetic circuit is deduced. The mechanical-electrical-magnetic-thermal multi-physical coupling field simulation of the electromagnetic actuator is carried out, which shows that the improved magnetic circuit structure effectively solves the zero drift, improves the precision of output force of the actuator, and allows the actuator to have lower electromagnetic heat output and electromagnetic loss.

Comprehensive review of battery charger structures of EVs and HEVs for levels 1–3

SummaryAs battery electric vehicles (BEVs), plug‐in hybrid electric vehicles (PHEVs), and hybrid electric vehicles (HEVs) gain popularity among the consumers, current research initiatives are targeted at developing battery charger structures that can exploit utility power to charge vehicle batteries and thus less dependent on fuel usage. This paper reviews the state of the art and implementation of battery charger structures, charger power levels, and the evolution of publications on electric vehicles in the digital libraries and Espacenet patent base. Charger systems addressed are categorized as a structure with a non‐isolated alternating current (AC)–direct current (DC) stage, structure with an isolated AC–DC stage, and structure with two non‐isolated stages. Advantages and disadvantages of each conductive battery charging structure have been discussed due to weight, volume, cost, necessary equipment, the complexity of topologies, and other factors. In addition, both off‐board and on‐board charger systems with unidirectional or bidirectional power flow are presented. Several electronic converters for power‐level chargers are being developed to allow plug‐in vehicles to be capable of vehicle to grid (V2G), where they can function as distributed resources and power can be returned to the grid.

Ancillary Ligand Coordination Directed Modes of Aggregation in Mixed-Valence Tetranuclear Cobalt Complexes: Synthesis, Structure, Field-Induced SIM Behavior, and Theoretical Insights

The contrasting metal–ion coordination reactivity behavior for the multisite ligand H3L ([2,6-bis-{(2-hydroxymethyl-phenylimino)methyl}-4-methylphenol]) with Co(ClO4)2·6H2O in the presence of ancillary ligands NaPiv (Piv = (CH3)3CCO2–) and NH4SCN afforded two different types of mixed-valence tetranuclear cobalt complexes, [CoIII3CoII(HL)(L)(μ4-O)(μ-OH)((CH3)3CCOO)2]ClO4·H2O (1) and [CoIII2CoII2(L)2(NCS)4(CH3CN)2]·CH3CN (2). In the first case, the presence of bridging pivalate anions triggered the oxido-hydroxido-bridged dual control for aggregation, whereas in the second case, terminal thiocyanate coordination forced the dicubane type of aggregation. The connectivity for different numbers of CoIII and CoII ions are achieved through contrasting bridges by ancillary water-molecule-derived HO– plus O2– linkers and ligand-anion-based double phenolato bridges, where terminal monodentate coordinations finally fulfill the octahedral geometries around the CoII ions. Alternating current/direct current (AC/DC) magnetic studies revealed field-induced slow magnetic relaxation for complex 1 that arises from the single octahedral CoII ion connected to three other diamagnetic CoIII ions. Whereas in complex 2, having a tetranuclear CoIII2CoII2 structure, the two CoII centers showed an antiferromagnetic interaction (J = −0.39 cm–1). The structural distortions in these two types of aggregates lead to different magnitudes of easy-axis magnetic anisotropy (D = −51.31 cm–1 for 1 and −31.9 cm–1 for 2) and a small but non-negligible transverse component (E/D = 0.263 for 1 and 0.255 for 2). The static and dynamic magnetic data were analyzed using DFT and CASSCF-based calculations.

Terminal Node of Active Distribution Network Correlation Compactness Model and Application Based on Complex Network Topology Graph

Multiple nodes (such as distributed generation (DG), electric vehicles (EV), energy storage (ES), flexible loads (FL), etc.) are connected to the active distribution network (ADN), which changes its original operational mode. According to the bidirectional current and low-voltage transmission mode, this study proposed a multi voltage and multi electricity flat loop network, AC/DC (Alternating Current/ Direct Current) hybrid network, unified interface and flexible self-organizing network based on Complex network theory. First, the ADN complex network topology of various nodes is established based on the actual grid connected terminal nodes and power flow sensitivity algorithm. Second, using the TOPSIS model, the influence factor matrix of weighted directed network is established. The matrix can be used to guide the formulation of the distribution network operation mode, and the robustness and reliability of this paper are verified by using the standard multi voltage level main distribution hybrid model provided by the Panda Power website as the verification method. Finally, using the influence maximization calculation model of the New Creedy algorithm, the node correlation matrix is expanded to form a super family region set of active distribution network. The results show that the seven nodes in this paper have high correlation, while the other nodes have low correlation. In addition, the change of reactive power has little impact on other nodes, for a node with a change rate of 0, it is obviously not in the same power supply family as node 1, and theoretically it may not have a topological relationship, be a power generation node, or be completely independent. Analyzing the relationship between nodes has a guiding significance for power supply recovery and interaction in distribution network reconfiguration.

Thermal Aging Properties of 500 kV AC and DC XLPE Cable Insulation Materials.

Despite similar material composition and insulation application, the alternating current (AC) cross-linked polyethylene (XLPE) and direct current (DC) XLPE materials cannot replace each other due to different voltage forms. Herein, this work presents a systematical investigation into the effects of thermal aging on the material composition and properties of 500 kV-level commercial AC XLPE and DC XLPE materials. A higher content of antioxidants in the AC XLPE than in the DC XLPE was experimentally demonstrated via thermal analysis technologies, such as oxidation-induced time and oxidation-induced temperature. Retarded thermal oxidation and suppression of space charge effects were observed in thermally aged AC XLPE samples. On the other hand, the carbonyl index of DC XLPE dramatically rose when thermal aging was up to 168 h. The newly generated oxygen-containing groups provided deep trapping sites (~0.95 eV) for space charges and caused severe electric field distortion (120%) under -50 kV/mm at room temperature in the aged DC XLPE samples. For the unaged XLPE materials, the positive space charge packets were attributed to the residue crosslinking byproducts, even after being treated in vacuum at 70 °C for 24 h. Thus, it was reasoned that the DC XLPE material had a lower crosslinking degree to guarantee fewer crosslinking byproducts. This work offers a simple but accurate method for evaluating thermal oxidation resistance and space charge properties crucial for developing high-performance HVDC cable insulation materials.

Measurement-Based Nonlinear SPICE-Compatible Photovoltaic Models for Simulating the Effects of Surges and Electromagnetic Interference within Installations

An emerging area of interest within photovoltaic (PV) centred research is the simulation of the propagation of electromagnetic interference (EMI) and surges within PV installations. An overarching constraint in all simulation-based research is the accuracy of the models employed. In general, for PV-focussed simulations, nonlinear models are utilised for direct current (DC) analyses, whilst linearised models are employed for analyses involving surges or conducted electromagnetic interference. For large-signal electromagnetic interference and surges, the following two problems arise: (1) the aforementioned linearisation is only valid for the small-signal case, and (2) as they are constructed using only DC measurements, traditional large-signal PV models are generally only valid for DC conditions. Therefore, neither of these approaches can properly represent real-world PV behaviour under dynamic conditions. To overcome this limitation, this article proposes a more suitable model, compatible with Simulation Program with Integrated Circuit Emphasis (SPICE), and which results from the combination of two sub-models: one for large-signal DC cases, and one for small-signal alternating current (AC) cases. Consequently, the combined model enables improved modelling of the effects of large-signal transient perturbations to be performed, as well as cases involving small-signal AC and large-signal DC perturbations. The model parameters are extracted using data from two different classes of measurement setups: the first utilised a vector network analyser (VNA) to produce small-signal AC impedance results (covering a frequency range between 1 Hz and 50 MHz), and the second produces DC current-voltage curves. Both classes of measurement setup consider the device under test at multiple operating points. Key results include: (1) an improved SPICE-compatible PV model which caters for large-signal transient simulations, as well as for small-signal AC and large-signal DC cases, (2) improvements in the modelling of reverse bias behaviour when compared to the standard SPICE diode implementation, (3) the correct implementation of a voltage-dependent total capacitance (suitable for large-signal simulations), (4) modelling parameters for both a small (10 W) and a large (310 W) PV module, (5) measurement results which de-embedded the parasitic effects of the test setups employed, and (6) above 1 MHz, the physical layouts of the cells within the PV modules begin to influence the observed impedances.

Predictive Commutation Failure Suppression Strategy for High Voltage Direct Current System Considering Harmonic Components of Commutation Voltage

The commutation failure of high voltage direct current (HVDC) systems could lead to unstable operation of the alternating current/direct current (AC/DC) hybrid power grid. The commutation voltage distortion caused by harmonics is a considerable but unclear factor of commutation failure. According to the control switching process of HVDC systems, the commutation voltage-time area method is employed to analyze and reveal the influence mechanism of harmonic components of commutation voltage on first and subsequent commutation failures. Considering the distortion characteristics of AC voltage, a predictive commutation failure suppression strategy considering multiple harmonics of commutation voltage is proposed. In this strategy, the new extinction angle and the zero-crossing offset angle after voltage distortion are calculated considering the harmonic components so as to obtain the compensation margin of the lag trigger angle by combining the correction margin with the voltage change rate. Moreover, the tuning method of parameters of extinction angle and voltage prediction variables are provided. Finally, a case study based on CIGRE standard HVDC system is performed and analyzed by using power systems computer-aided design (PSCAD) software. Compared with the International Council on Large Electric systems (CIGRE) standard test model and traditional commutation failure prevention (CFPREV) control model, the results verify that the proposed strategy can effectively reduce the risk of first and subsequent commutation failures and improve the sensitivity of CFPREV control.

Graftable voltage stabilizer for enhancing insulation performance of crosslinked polyethylene

AbstractWith the popular application of alternating current/direct current (AC/DC) hybrid power grid, ultra‐high‐voltage (UHV) AC/DC cables of long‐distance and large‐capacity transmission systems have been strongly demanded. Voltage stabilizers are widely used to resist AC electrical tree of cross‐linked polyethylene (XLPE) insulation materials, but poor compatibility with polymer matrix limited improvement of DC insulation performance. In this research, the maleic anhydride‐modified 2,4‐dihydroxybenzophenone as a novel voltage stabilizer 4‐(4‐benzoyl‐3‐hydroxyphenoxy)‐4‐oxobut‐2‐enoic acid (MDVS) was synthesized to improve the electrical properties of XLPE. The XLPE‐g‐MDVS with different contents of MDVS was prepared, and both AC electrical properties and DC electrical properties were tested. The results indicate that the modified XLPE retain the characteristic of voltage stabilizer to resist AC electrical tree and improve breakdown strength, and to exhibit excellent DC insulation performance in a wide temperature range. In the comparison with the pristine XLPE, the graft of MDVS can significantly suppress space charge accumulation and decrease DC conductivity. At 70°C, the maximum amount of space charge density of XLPE‐g‐1.2wt%MDVS is 56.2% lower than that of XLPE, and the DC conductivity decreases by nearly two orders of magnitude. Furthermore, the DC breakdown strength of XLPE‐g‐1.2wt%MDVS materials exhibit higher than that of the pristine XLPE. In addition to the self‐excited energy dissipation of the voltage stabilizer, quantum chemical calculations demonstrated that the improvement of DC performance attributed to the deep traps introduced by MDVS.

Detachable all-carbon-linked 3D covalent organic framework films for semiconductor/COF heterojunctions by continuous flow synthesis

Detachable all-carbon-linked 3D covalent organic framework films for semiconductor/COF heterojunctions by continuous flow synthesis

Harmonic Mitigation in VFD Controlled Chiller Compressor Using AC Line Reactor and DC Link Choke Combination

With the goals of a better power factor and reduction in energy use, variable frequency drives (VFDs) have been standardized in various industrial applications including Heating, Ventilation, and Air-conditioning (HVAC) systems. However, key issues related to the deterioration in the power quality associated parameters (voltage harmonic distortion and current harmonic distortion) due to the growing number of VFDs demand a wholesome analysis of the problems faced by the users. In this present work, an analysis has been performed to investigate the potential impact of using alternating current (AC) line reactor and direct current (DC) link choke combination on harmonic mitigation in a VFD driven water-cooled centrifugal chiller compressor. Using a combination of AC line reactor and DC link choke as one of the low cost solutions in harmonic mitigation of a VFD driven load in HVAC systems can be decided based on the investigation done in this research work.

Phase-Independent Reactive Power Compensation Based on Four-Wire Power Converter in the Presence of Angular Asymmetry between Voltage Vectors

The paper presents the reactive power compensation method that allows for reducing the active power flow even in the presence of angular asymmetry between voltage vectors of the utility grid. Reactive power compensation ensures the reduction of power transmission losses and therefore brings significant economic benefits to electricity consumers. The concept of the alternating current/direct current (AC/DC) converter for prosumer applications operating as a local reactive power compensator has been proposed. The system is driven by a multi-resonant algorithm, allowing for independent control of the reactive power in each phase. The proposed method was validated experimentally by using a prototype of the converter, programmable AC source, and grid impedance model. The method made it possible to cover the reactive power demand without unnecessary active power generation and thus to improve the efficiency of the analyzed prototype. This solution can be implemented particularly in radial grids and non-urban areas.