DC Component Research Articles

Coil-Only High-Frequency Lamb Wave Generation in Nickel Sheets

This study presents a novel, coil-only magnetostrictive ultrasonic detection method that operates effectively without permanent magnets, introducing a simpler alternative to conventional designs. The system configuration is streamlined, consisting of a single meander coil, an excitation source, and a nickel sheet, with both the bias magnetic field and ultrasonic excitation achieved by a composite excitation containing both DC and AC components. This design offers significant advantages, enabling high-frequency Lamb wave generation in nickel sheets for ultrasonic detection while reducing device complexity. Experimental validation demonstrated that an S0-mode Lamb wave at a frequency of 2.625 MHz could be effectively excited in a 0.2 mm nickel sheet using a double-layer meander coil. The experimentally measured wave velocity was 4.9946 m/s, with a deviation of only 0.4985% from the theoretical value, confirming the accuracy of the method. Additionally, this work provides a theoretical basis for future development of flexible MEMS-based magnetostrictive ultrasonic transducers, expanding the potential for miniaturized magnetostrictive patch transducers.

An adaptive online monitoring system using NFSOGI-PLL for three-phase voltage unbalance in grids

The extensive utilization of unbalanced and nonlinear loads has significantly impacted power quality in modern grids. Among various metrics, the three-phase voltage unbalance factor (TPVUF) stands out as a crucial indicator. To mitigate the challenges posed by harmonics and DC components that interfere with accurate TPVUF measurements, this paper introduces the Notch Filter-based Second-Order Generalized Integrator Phase-Locked Loop (NFSOGI-PLL) for the first time and designs an adaptive online monitoring system for TPVUF based on NFSOGI-PLL. To validate its performance, the hardware design and rapid software development of the NFSOGI-PLL-based TPVUF online monitoring system are thoroughly implemented, and the system is tested under various conditions. The results indicate that the proposed system not only provides real-time performance and high accuracy, complying with the rigorous standards set by GB/T 15543-2008 and IEC 61000-4-27, but also demonstrates remarkable stability under diverse influences. These findings underscore the exceptional filtering and tracking abilities of the NFSOGI-PLL in power systems, as well as the accuracy and anti-interference capabilities of the NFSOGI-based TPVUF online monitoring system, which holds great potential for widespread application in power system control and research.

Leak detection in water supply pipeline with small-size leakage using deep learning networks

Pipeline transportation technology has witnessed remarkable development in recent years, while the issue of leakage poses a serious limitation to this technology’s progress, especially for the small-scale leakage in water pipelines that exhibits weaker leakage signals. To address those challenges, this study investigates leak detection in water supply pipeline with an inner pipe diameter of 100 mm in the operating range of volume flow Q = 40–80 m3/h, leakage flow Ql = 0.65–1.33 m3/h and pressure p = 130–220 kPa. The characteristics and propagation of leakage pressure signals are analyzed. An adaptive improved variational mode decomposition (VMD) based on the white shark optimizer (WSO) algorithm is proposed, utilizing sample entropy as the fitness function. Additionally, tent chaotic mapping is employed for parameter initialization, mean normalization is used to minimize the influence of the DC component, and signal relative energy serves as a boundary condition. The processed data is utilized to establish leakage detection models using long short-term memory network (LSTM), gated recurrent unit (GRU), convolutional neural network (CNN) and SqueezeNet framework. The performance of leakage detection models is evaluated and compared using 962 sets’ data using evaluation indicators and confusion matrix. The results indicate that SqueezeNet-GRU demonstrates superior performance in pipeline leak detection and localization applications, achieving 97.40 % accuracy for the total dataset.

Research on DC Component Suppression Method of Non-isolated Grid-Connected Inverter

Research on DC Component Suppression Method of Non-isolated Grid-Connected Inverter

Design and Implementation of Bridgeless Power Factor Corrector with Low Static Losses

Research and development of power factor corrector (PFC) for AC/DC converters of single-phase AC power supply network are discussed within this article. Two-channel bridgeless PFC is proposed in this paper. The proposed converter allows us to lower current DC component generation in the power network and to reduce static and dynamic losses of semiconductor devices. The suggested solution characteristic features are the absence of a diode bridge while using two identical converters operating in different power network voltage half periods. Due to cumulative chokes in each converter, the function setting the consumption current sinusoidal form is realized with the ability of wide-range output voltage regulation. A number of Simulink-models have been developed in order to study operating modes and to test control algorithms of the proposed bridgeless PFC. The input current harmonic content, efficiency coefficient, passive elements’ electrical parameters, and output voltage pulsation coefficient of the proposed bridgeless PFC were researched by Simulink-models. The results obtained show the efficiency of the proposed solutions regarding PFC. The THD value does not exceed 1.3% in steady state mode and is not over 4% during the voltage stabilization process; the minimal value of the output voltage pulsation coefficient is 3.1%. The suggested solutions can be applied in accumulator batteries’ charging sets and DC motors’ reduced-current start.

Dynamics of a horizontal magnetic pendulum in a repulsive magnetic field and driven by two coil magnets

We studied theoretically and experimentally in this work the nonlinear dynamics of a horizontal magnetic pendulum in a repulsive magnetic field controlled by two coil magnets. The mathematical equations of the system are derived using the magnetic charges interaction model. The system presents a single equilibrium point which is stable if the currents through the coils are positive. Considering the situation where the current through the coils is sinusoidal with a DC component, analytical calculations using the harmonic balance method and numerical simulations are also carried out. The results obtained are shown in terms of amplitude responses, time–displacement diagrams, and phase portraits. The two-parameter bifurcation diagrams are plotted showing the different dynamical behaviors considering the current amplitudes, frequency, angle between the coil magnets, and the modulation indexes as the control parameters. Amplitude jumps, hysteresis, and multistability are also observed. In the experimental part, the modulated current sources that can provide the required current in the coil magnets have been designed and implemented. The complete experimental setup of the magnetic pendulum is also presented. Good agreements are found between our theoretical results and experimental ones.

3D reconstruction with single-frame two-step phase-shift method based on orthogonal composite fringe pattern projection

Abstract In order to realize single-frame three-dimensional (3D) reconstruction, a single-frame two-step phase-shift method based on orthogonal composite pattern projection is proposed to solve the problem that the traditional N-step phase-shift profilometry needs multiple projections for 3D reconstruction. The orthogonal composite pattern uses only two carrier channels to reduce the spectrum overlapping influence on the demodulation accuracy of carrier and modulated fringes. A two-dimensional variational mode decomposition method is adopted to remove the background DC component of the sinusoidal fringe to overcome the mode overlap problem by controlling the size of the bandwidth. Thus, the two-step phase-shift method is applied to calculate the phases for 3D reconstruction. The experimental results show that, compared with the typical Fourier transform profilometry method, 3-step composite method and 2 + 1 composite method, the 3D reconstruction accuracy of the proposed method is improved by 49.1%,31.4% and 23.2% respectively according to mean absolute error, and by 73.0%, 58.4% and 56.8% respectively according to mean squared error as the evaluation index. Finally, the dynamic 3D reconstruction experiment demonstrates the good adaptability of dynamic 3D reconstruction.

Seismicity associated with hydraulic fracturing in Changning shale gas field, China: Constraints from source mechanisms, stress field and fluid overpressure thresholds

Source properties and stress fields are critical to understand fundamental mechanisms for fluid-induced earthquakes. In this study, we identify the focal mechanism solutions (FMSs) of 360 earthquakes with local magnitude ML ≥ 1.5 in the Changning shale gas field from January 2016 to May 2017 by fitting three-component waveforms. We then constrain the directions of the maximum horizontal stress (σHmax) for four dense earthquake clusters using the stress tensor inversion method. The stress drops of 121 earthquakes with ML ≥ 1.5 are calculated using the spectral ratio method. We examine the spatiotemporal heterogeneity of stress field, and discuss the cause of non-double-couple (non-DC) components in seismicity clusters. Following the Mohr-Coulomb criterion, we estimate the fluid overpressure thresholds from FMS for different seismic clusters, providing insights into potential physical mechanisms for induced seismicity. The FMS results indicate that shallow reverse earthquakes, with steep dip angles, characterize most events. The source mechanisms of earthquakes with ML ≥1.5 are dominated by DC components (> 70%), but several earthquakes with ML > 3.0 and the microseismic events nearby during injection period display significant non-DC components (> 30%). Stress inversion results reveal that the σHmax direction ranges from 120° to 128°. Stress drops of earthquakes range between 0.10 and 64.49 MPa, with high values occurring on reverse faults situated at a greater distance from the shale layer, accompanied by a moderate rotation (≤ 25°) in the trend of σHmax. The seismic clusters close to the shale layer exhibit low fluid overpressure thresholds, prone to being triggered by high pore-pressure fluid. The integrated results suggest that the diffusion of high pore pressures is likely to be the primary factor for observed earthquakes. The present results are expected to offer valuable insights into the origin of anomalous seismicity near the shale gas sites.

An average-phase calibration method for the sensing matrix of a Modulated Wideband Converter

As a sub-Nyquist sampling structure based on compressed sensing (CS), a modulated wideband converter (MWC) is used for spectral blind sampling and reconstruction of multiband sparse signals. Sinusoidal signals with known phases have been theoretically used to study the calibration of the sensing matrix of MWC, but in practice, the initial phase of sinusoidal signals is unfortunately difficult to know in advance. Consequently, phase error will exist in the calibrated sensing matrix, which reduces the reconstruction signal-to-noise ratio (RSNR) of the reconstructed signal.In this paper, we first analyze the phase error uncertainty caused by the DC component of the periodic pseudo-random sequence. In addition, an average-phase calibration method based on a 0/1 mixing sequence is proposed to calibrate the sensing matrix. Each column of the sensing matrix is calibrated according to its average phase, which avoids introducing phase error when using sinusoidal signals with arbitrary unknown phases. Comparative experiments are conducted to evaluate the performance of the proposed method in terms of the RSNR and the reconstruction mean squared error (RMSE). The results show that the RSNR obtained by the proposed method is 40 dB, which is close to the signal-to-noise (SNR) of the input RF signal.

AC ripple on DC voltage: Experimental and theoretical investigation of the impact on accelerated ageing in electrical insulation

AbstractWith the increasing penetration of DC systems into the high voltage and medium voltage power industry, DC voltage is becoming common for distribution/transmission and to supply different typologies of loads. The allowable extent of AC ripple superimposed to DC, and its effect on insulation ageing, is a long‐term discussed topic. The most harmful phenomenon causing extrinsic ageing acceleration and insulation system premature failure is partial discharges (PD); thus, the risk of incepting PD due to AC ripple could become a primary issue for electrical asset equipment reliability. In this work, the impact of AC sinusoidal ripple on insulation system life and reliability is dealt with, considering both intrinsic and extrinsic ageing but focusing on the latter, that is, the PD aspect. Experiments are performed to assess how the jump voltage (due to AC ripple) and the DC component impact on PD activity in terms of amplitude and repetition rate. For the first time, the correlation between the magnitude of jump voltage associated with ripple and PD inception is established, shedding a light on the allowable ripple extent which does not impact significantly on ageing and premature insulation failure. This approach can provide straightforward tools for design specification and ageing inference of insulation systems.

An advanced meta metrics-based approach to assess an appropriate optimization method for Wind/PV/Battery based hybrid AC-DC microgrid

This paper discusses the growing influence of renewable energy and distributed generation, emphasizing the need for smart control systems to maximize benefits and optimize network performance. However, the absence of a standardized evaluation framework makes it challenging to compare different control systems effectively, especially in large-scale hybrid networks with both AC and DC components. While hybrid energy systems show promise for greener and more reliable power networks, they introduce complexity to control methods. Researchers are exploring innovative approaches, including linear and nonlinear techniques, to leverage renewable energy sources effectively in hybrid grids. The paper provides an overview of heuristic evolutionary optimization methods for microgrids (AC, DC, and hybrid AC-DC), highlighting promising techniques such as Crow Search Algorithm, Modified Crow Search Algorithm, Particle Swarm Optimization, and Genetic Algorithms. Comparative analysis suggests that the Modified Crow Search Algorithm performs best across various evaluation criteria, indicating its potential for optimizing microgrids effectively.

Electric-field-induced assists fabrication of micro-SiC/Epoxy coating with low additive amount to improve surface insulating performance of HVDC insulator

The micro-SiC/Epoxy composite coating has huge potential for application in the insulator of high voltage direct current (HVDC) gas insulated switchgear (GIS) since it can effectively suppress charge accumulation at gas–solid interface and adaptively regulate resistive electric field distribution. However, achieving stable and fruitful properties often requires high filler concentrations, which can compromise processability and long-term stability. Thus, a new method is proposed for preparing SiC/Epoxy composite coatings based on in-situ electric-field-induced assist (EFIA). The alignment process of SiC induced by the in-situ electric field, the effects of in-situ field on the physical and chemical properties of cured composites were studied. Even at concentrations far below the percolation threshold, the alignment of SiC particles along the in-situ electric field direction can induce significant non-linear conductive properties along that specific direction in the composite. Furthermore, the EFIA-coating leads to a 59.43% reduction in surface charge accumulation, more than a 50% decrease in charge dissipation time, and a 17.3% increase in surface flashover voltage. The coating discussed in this paper will be helpful in insulation design of DC components.

AC Loss Estimation Method for REBCO Superconducting Tapes in AC+DC Fields for Field Windings in Fully Superconducting Synchronous Machine for Electric Aircraft

Abstract The estimation of AC loss in REBa2Cu3O y (REBCO; RE = rare earth, such as Y, Eu, and Gd) superconducting tapes within superconducting synchronous motors and generators for electric aircraft is imperative during the design stage phase to optimize efficiency and cooling considerations. Our previous studies clarified the AC loss characteristics, focusing on estimating the AC loss in armature windings. While the magnetic field applied to the armature windings is exclusively as an AC field, the field windings are subject to a composite field comprising both AC and DC components. Notably, the amplitude of the AC component is markedly smaller than the magnitude of DC component. This study experimentally investigated to consider the AC loss properties in field windings. The experimental results were as follows: When subjected to operational conditions of field windings within synchronous motor and generator, the AC loss increased with the DC field strength. This property is attributed to a reduction in the critical current induced by the external field. Hence, we modified the method for estimating AC loss. Subsequently, we validated the effectiveness of the modified method.

Failure mechanism of metallized film capacitors under DC field superimposed AC harmonic: From equipment to material

AbstractThis study focuses on the degradation behaviour of metallised film capacitors, which are the essential components for the stability of converter valves in flexible ultra‐high voltage direct current (HVDC) transmission systems. Through systematic experimentation, we investigated the failure mechanisms of MFCs under HVDC fields with superimposed harmonics, considering both equipment and material perspectives. The experiments subjected capacitors to 500 h of ageing under two conditions: a DC/AC‐superimposed field with a constant DC component of 290 kV/mm and an AC ripple rate varying from 12% to 28%, and a control group aged solely under a DC field. Our findings indicate that capacitors aged under the DC/AC‐superimposed field exhibited shorter lifespans and more significant capacitance loss than those aged under only the DC field. This difference in performance is primarily attributed to the distinct electrode loss behaviours observed under each ageing condition, which are key factors in the capacitors' capacitance decay. Moreover, the biaxially oriented polypropylene films in the DC‐aged samples showed more severe deterioration, characterised by more noticeable molecular chain scission and reduced breakdown strength, compared to those aged under the DC/AC superimposed field. This difference is partly due to the moderate temperature increase caused by harmonics, which benefits the aggregation structure, and partly to the reduced molecular structure damage from the AC field.

High voltage gain minimum‐phase isolated DC‐DC converter with improved transformer utilization

AbstractThe standard structure of an isolated SEPIC (iSEPIC) does not have a minimum‐phase nature, which signifies no additional support for the output capacitor during ON‐time conditions. Consequently, it has high voltage stress, right half plane (RHP) zeros presence, DC component in the transformer core, and less transformer utilization. This paper presents a modification in a iSEPIC converter having higher voltage gain over a conventional iSEPIC converter. This work analyzes a modified iSEPIC structure by providing additional support to the output capacitor during ON‐time conditions. As a result, the nonminimum‐phase nature will be transformed into the minimum‐phase nature. Consequently, all the mentioned demerits of the standard iSEPIC structure are eliminated The derived discrete‐time modeling analyzes the RHP zeros dependence on the load variation. This modification also leads to improvement in dynamic performance to accommodate the load variation. Finally, a 60 W modified iSEPIC prototype is developed to validate the proposed analysis.

Limitations of mean-field approximations in describing shift-current and injection-current in materials

We theoretically and computationally investigate bulk photovoltaic effects, with a specific focus on shift-current and injection-current. Initially, we perform a numerical analysis of the direct current (dc) induced by a laser pulse with a one-dimensional model, utilizing mean-field theories such as time-dependent Hartree–Fock and time-dependent Hartree methods. Our numerical results, obtained with mean-field theories, reveal that the dc component of the current, as a second-order nonlinear effect, exists even after irradiation with linearly polarized light as a second-order nonlinear effect, indicating the generation of injection-current. Conversely, when we employ the independent-particle approximation, no injection-current is generated by linearly polarized light. To develop the microscopic understanding of injection-current within the mean-field approximation, we further analyze the dc component of the current with the perturbation theory, employing the mean-field approximations, the independent-particle approximation, and the exact solution of the many-body Schrödinger equation. The perturbation analysis clarifies that the injection-current induced by linearly polarized light under the mean-field approximations is an artifact caused by population imbalance, created through quantum interference from unphysical self-excitation pathways. Therefore, investigation of many-body effects on the bulk photovoltaic effects have to be carefully conducted in mean-field schemes due to potential contamination by unphysical dc current. Additionally, we perform the first-principles electron dynamics calculation for BaTiO3 based on the time-dependent density functional theory, and we confirm that the above findings from the one-dimensional model calculation and the perturbation analysis apply to realistic systems. Published by the American Physical Society 2024

A novel measurement‐protection‐integrated current transformer based on hybrid core and magnetic field sensor

AbstractCurrent transformers (CTs) are widely used for energy metering, relay protection, condition monitoring and control circuits. However, CT saturation may lead to non‐negligible measurement errors and relay malfunctions, posing a threat to the stability and security of the power grid. In order to address the problem of CT saturation, a novel measurement‐protection‐integrated current transformer (MPICT) is proposed. First, the working states of the MPICT are summarised and the approximate expressions for the steady‐state measuring characteristics, the transient response characteristics, and the measurement errors are derived from the equivalent circuit model. Then, the feasibility of the MPICT and the theoretical analyses are verified by the 3D FEM simulation imitating the presented MPICT excited by diverse currents. Finally, a down‐scale prototype is fabricated and a series of tests are conducted in the laboratory to validate the effectiveness of the equipment. The simulation and experimental results suggest that the output of the MPICT can accurately reconstruct the primary current waveform, even if the primary current contains decaying or constant DC component.

Modulated step-heating thermography for coating thickness measurement

In this paper, the modulated step-heating thermography is proposed for opaque coating thickness measurement. The surface is heated by a modulated heating flux at a frequency that the thermal wave is confined within the coating layer. The DC component of the thermal signal is normalized by the amplitude of the AC component to cancel out the influences from the variations in heating intensity, surface absorptivity and emissivity, resulting in a linear correlation to the coating thickness. Meanwhile, it eliminates the need for tedious frequency trail and the issue of the nonmonotonicity as suffered in conventional thermography. Both theoretical and experimental results confirmed the effectiveness. Specimens with thickness ranging from 100 to 400 μm are measured with a relative error within ±7.9 %.

A boosted DC algorithm for non-differentiable DC components with non-monotone line search

A boosted DC algorithm for non-differentiable DC components with non-monotone line search

Compensation characterization of the UPQC system under an improved nonlinear controller based on the MSTOGI-PLL device

To solve the delay problem of a unified power quality conditioner (UPQC) system during the separation of the fundamental positive-order components and to better filter out the DC and harmonic components to realize accurate phase locking, a mixed second- and third-order generalized integrator phase-locked loop (MSTOGI-PLL) has been designed to replace the traditional synchronous reference frame phase-locked loop (SRF-PLL). Under the premise of adopting the new phase-locking device of MSTOGI-PLL, the active disturbance rejection control (ADRC) controller or the super-twisting algorithm (STA) sliding mode controller is used in the DC voltage control module instead of the traditional PI controller, and the suitability of the two nonlinear controllers with the MSTOGI-PLL device is investigated. First, the new MSTOGI-PLL device is designed, and the new phase-locking method is applied to make the UPQC realize accurate phase locking under the non-ideal situation of the grid voltage containing unbalance, DC component, harmonics, and so on. Based on the above foundation, the ADRC or STA controller is independently adopted to replace the PI controller to construct the UPQC system with the ADRC + MSTOGI phase-locking device and the second-order STA + MSTOGI phase-locking device. Finally, a simulation comparison is carried out in a Simulink simulation platform regarding the UPQC system under different phase-locking devices, and the simulation results demonstrate that MSTOGI-PLL can successfully filter out the DC component and resolve the phase-locking process delay issue. Additionally, the UPQC system with ADRC + MSTOGI-PLL exhibits superior immunity and response speed to the PI controller and the second-order STA controller.