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To address the challenge of accurately determining the saturation state induced by transformer DC bias, we propose a combined method for analyzing the DC bias of the transformer using vibration signals. This method employs the complementary ensemble empirical mode decomposition (CEEMD) to preprocess the vibration signals and fuzzy entropy (FuzzyEn) to assess the degree of DC bias. The optimal measurement point of the transformer is determined through transformer mechanical analysis. Subsequently, a vibration test. experimental platform is established to capture vibration signals at five distinct points on the transformer shell and core. These signals are then subjected to CEEMD for reconstruction, enabling the determination of the degree of DC bias. This assessment is based on fuzzy entropy values and difference curve analysis. The results demonstrate that the FuzzyEn value, serving as an indicator of the iron core's saturation due to DC bias, effectively detects the level of DC bias. Upon reaching its maximum value, the FuzzyEn of the vibration signal signifies the core's entry into the saturation zone. Specifically, the maximum FuzzyEn value is approximately 1.5 A on both sides of the core, about 1 A on the left and right sides of the shell, and 2 A in the middle of the shell. These findings confirm the efficacy of the combined CEEMD and FuzzyEn method. [ABSTRACT FROM AUTHOR]

Global energy and environmental issues are becoming increasingly problematic, and the vibration and noise problem of 110 kV transformers, which are the most widely distributed, have attracted widespread attention from both inside and outside the industry. DC bias is one of the main contributing factors to vibration noise during the normal operation of transformers. To clarify the vibration and noise mechanism of a 110 kV transformer under a DC bias, a multi-field coupling model of a 110 kV transformer was established using the finite element method. The electromagnetic, vibration, and noise characteristics during the DC bias process were compared and quantified through field circuit coupling in parallel with the power frequency of AC, harmonic, and DC power sources. It was found that a DC bias can cause significant distortions in the magnetic flux density, force, and displacement distributions of the core and winding. The contributions of the DC bias effect to the core and winding are different at Kdc = 0.85. At this point, the core approached saturation, and the increase in the core force and displacement slowed. However, the saturation of the core increased the leakage flux, and the stress and displacement of the winding increased faster. The sound field distribution characteristics of the 110 kV transformer under a DC bias are related to the force characteristics. When the DC bias coefficient was 1.25, the noise sound pressure level reached 73.6 dB.

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract Power transformer is widely used in the power system with the rapid development of the power converters connected to the grid. When a transformer operates under DC bias conditions, its iron core loss increases significantly, causing local overheating and threatening the proper operation of the transformer. However, there are persistent difficulties in accurately assessing the core loss when the induction waveform is influenced by a DC bias. This paper first proposes improvements to the J–A and Preisach models to evaluate the core loss of the iron core under DC bias. Additionally, we incorporate the hysteresis models into the finite element method (FEM) by modifying the fundamental constitutive equations in the FEM model in order to perform a precise core loss/distribution calculation. To verify the accuracy of prediction, a transformer prototype with a laminated core is developed. The improved J–A-FEM and Preisach-FEM models were directly compared in terms of calculation accuracy, numerical implementation, and computational burden.

Modulation efficiency and mechanisms of repetitively pulsed streamer discharge in humid air are ambiguous with dramatic variations in free electron availability, residual ion mobility, enhanced heat release, etc, caused by water molecules intentionally supplemented or existing in the surrounding environment. The inception and propagation patterns of repetitively pulsed streamer discharge modulated by superimposed DC bias are experimentally investigated in the needle-plane electrode configuration. The inception voltage decreases due to negative ion drift under positive DC bias. The secondary streamer with a bright glowing cloud prolongs towards the plane electrode and the diameter decreases under positive DC bias. The primary streamer tends to propagate along the off-axis direction under negative DC bias. The number of applied pulses before breakdown decreases with the increase in positive DC bias and illustrates an insignificant dependence on the negative DC bias. The effect of air humidity is more pronounced than the DC bias. The streamer inception, propagation, and morphological transition are explained by residual space charge distributions and drift velocity. [ABSTRACT FROM AUTHOR]

Summary: In the context of the dual active bridge (DAB) bidirectional DC‐DC converter using the traditional dual‐phase‐shift (DPS) control method, a transient DC bias occurs during power co‐direction and commutation conversion. This bias negatively impacts the converter's transient performance and can lead to harsh effects, such as hard switching problems, resulting in power loss and excessive current stress. In a closed‐loop control system, poor transient response may destroy the stability of the converter. In this paper, the transient‐optimized‐dual‐phase‐shift (TODPS) control strategy is proposed to eliminate the transient DC bias and to maintain soft switching during transient states. It reduces power loss, eliminates excessive current stress, and allows for smooth transitions between single‐phase‐shift (SPS) and DPS control strategies without introducing DC bias. A closed‐loop control system based on TODPS control is established with feed‐forward compensation to adjust the primary‐side current and modify transmission power. This adjustment enhances the transient performance of the DAB converter. The proposed strategy is versatile and applicable to various power conversion scenarios involving DAB converters. It enables quick switching of the magnitude and direction of the primary‐side current during transient states, resulting in a smooth transient effect without noticeable overshoot or oscillation. The experiment results verify the effectiveness of the proposed transient optimization strategy. [ABSTRACT FROM AUTHOR]

This paper investigates an indoor hybrid visible light communication (VLC) and radio frequency (RF) scenario with two-hop downlink transmission. A light emitting diode (LED) transmits both data and energy via VLC to an energy-harvesting relay node, which then uses the harvested energy to retransmit the decoded information to an RF user in the second phase. The design parameters include the direct current (DC) bias and the time allocation for VLC transmission. We formulate an optimization problem to maximize the data rate under decode-and-forward relaying with fixed receiver orientation. The non-convex problem is decomposed into two sub-problems, solved iteratively by fixing one parameter while optimizing the other. Additionally, we analyze the impact of random receiver orientation on the data rate, deriving closed-form expressions for both VLC and RF rates. An exhaustive search approach is employed to solve the optimization, demonstrating that joint optimization of DC bias and time allocation significantly enhances the data rate compared to optimizing DC bias alone.

The large-scale application of flexible DC power transmission technology leads to DC bias in transformer cores, and the vibration analysis of transformers under the influence of DC bias is becoming a hot topic. In this paper, based on the "electromagnetic-mechanical" coupling model, we propose a bias vibration analysis method for large power transformers. The electromagnetic forces calculated in the electromagnetic field are mapped to the surfaces of structural members and tanks in the structural force field by means of a grid mapping method, facilitating the direct calculation of transformer vibration displacements under DC bias conditions. Finally, based on the coupled magnetic-structural analysis, the maximum deformation of different structures of the transformer under different DC bias magnetism is studied. The vibration response band of the transformer is above 100Hz, where the DC input of 25A per phase causes the maximum displacement deformation of 39.06mm in the transformer tank, which provides the analysis basis for the safe operation of the transformer.

Dual-phase composite magnetic materials have magnetic and permanent magnetic properties. They can realize the dual-phase conversion of soft magnetic and permanent magnetic composites with a small amount of excitation energy. They have the advantages of good control and conversion characteristics and save energy, and they have a wide range of application scenarios in regard to power equipment. In this paper, the magnetization modeling of dual-phase composite magnetic materials is carried out based on micromagnetic theory, and a specific mathematical expression is given. Secondly, the preparation process of the dual-phase composite magnetic material is studied, the dual-phase composite magnetic material is prepared, and the demagnetization curve of the dual-phase composite magnetic material is measured. Finally, the application of dual-phase composite magnetic materials in power equipment is carried out. Using the soft magnetic and permanent magnetic characteristics of dual-phase composite magnetic materials, their impact on DC bias suppression in transformers is assessed. Magnetic circuit reluctance theory is used to develop the structure and electromagnetic design of a transformer. A transformer prototype with DC bias suppression ability based on dual-phase composite magnetic materials is manufactured, and simulation and experimental research are carried out. The simulation and experimental results verify the correctness of the proposed scheme. Although this scheme requires a more complex core structure, the energy-saving effect is remarkable without changing the transformer's neutral grounding. The indicators meet the actual requirements of the project. [ABSTRACT FROM AUTHOR]

Aging in dielectrics manifests as a reduction in capacitance over time owing to the applied electric field. This study revisits the aging mechanism in multi-layer ceramic capacitors (MLCCs), specifically considering DC-bias voltage and temperature variables. The findings indicate that aging is intensified by higher DC-bias voltages (electric field strength) and elevated temperatures, ultimately leading to capacitance saturation. A poling–depoling experiment confirms the rapid assessment of saturation capacitance. Consequently, we propose a straightforward method involving electric field manipulation to quantitatively evaluate the saturated capacitance of MLCCs under aging conditions. The estimated capacitance aligns closely with the measured capacitance after 2000 h, with an error rate not exceeding 4 %. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Although a high permittivity (ε′>104) of rutile TiO 2 can easily be obtained by doping with Ta5+, the low loss tangent (tanδ<0.05) cannot be achieved. Furthermore, ε′ of giant dielectric oxides is usually dependent on environmental factors (temperature and humidity) and operation factors (frequency and DC bias). In this study, greatly reduced tanδ and enhanced ε′–stabilities were obtained in TiO 2 by doping with Ta 2 O 5 and indium tin oxides (ISO). Dense ceramics with homogeneously dispersion of doping elements were obtained by sintering at 1400 °C for 3 h. The rutile phase was detected with expanded lattice parameters as ISO increased, while the average grain size decreased slightly with a narrow size distribution. According to the Raman spectroscopy, oxygen vacancies in Ta 2 O 5 –doped TiO 2 tended to slightly increase by doping with ISO. Besides a high ε′ of ∼2–4 × 104, low tanδ values of 0.007–0.04 (103 Hz) were achieved in the temperature range of −80 to 200 °C. The temperature coefficient of ε′ at 1 kHz from −120 to 200 °C was lower than ±10% compared to that of 25 °C. Furthermore, the ε′ was also nearly independent on the DC bias even at 300 V/cm (∼2.6%). Surprisingly, the ε′ was nearly independent on humidity over the range of 25–90%RH. Thereas, this giant dielectric material may have a great potential for capacitor applications. Impedance and dielectric spectroscopies revealed that the giant dielectric properties were caused by the interfacial polarization, while the effect of defect dipoles cannot be ignored, which could have a primary contribution in a low–temperature range. [ABSTRACT FROM AUTHOR]

A bias current in the power system will cause saturation of the measuring current transformer (CT), leading to an increase in measurement error. Therefore, in this paper, we first conducted measurements of the direct current component in a 10 kV distribution system. Subsequently, a reverse extraction method for the CT distorted current under direct current bias conditions based on Random Forest Classification (RFC) and Long Short-Term Memory (LSTM) was proposed. This method involves two stages for the reverse extraction of CT distorted currents under direct current bias conditions. In the offline stage, data samples were generated by changing the operating environment of the CT. The RFC classification algorithm was used to divide the saturation levels of the CT, and for each sub-class, Particle Swarm Optimization–Long Short-Term Memory Network (PSO-LSTM) models were trained to establish the mapping relationship between the secondary distorted current and the primary current fundamental component. In the online stage, the saturated data segments were extracted from the secondary current waveform using wavelet transform, and these segments were input into the offline model for current reverse extraction. The simulation results show that the proposed method exhibited strong robustness under various CT conditions, and achieved high reconstruction accuracy for the primary current. [ABSTRACT FROM AUTHOR]

High-voltage flexible power systems, with their intrinsic characteristics, play an increasingly important role in electronic power systems. Synchronization between the inverter and the grid needs to be achieved by a phase-locked loop (PLL), the performance of which determines the quality of power transmission. This paper proposes a PLL adapted to extremely harsh grid conditions. Firstly, the traditional synchronous reference frame PLL and the dual second-order generalized integrator (DSOGI-PLL) are analyzed, and the errors in phase-locking and the shortcomings of these two methods in the presence of DC components in the grid are pointed out. Secondly, based on the harmonic grid voltage, a repetitive control internal model is introduced by DSOGI to realize the real-time tracking and regulation of the harmonic signals in order to suppress the harmonic voltage disturbance. In addition, a DC bias elimination and frequency adaptive method is proposed to solve the problems of DC bias and grid voltage frequency fluctuation in order to achieve adaptive tracking of the grid phase. Finally, the superiority of the proposed strategy is verified through simulations and experiments. [ABSTRACT FROM AUTHOR]

During the operation of the urban subway, there will be stray current leaking into the ground, which may invade the neutral point of the transformer along the subway line, causing the working magnetization curve of the transformer core to shift, thereby causing the direct-current (DC) bias effect of the transformer. Since there are unknown parameters in the equivalent circuit model of the stray current of the subway, in order to simplify the process of the influence of the subway operation on the neutral current, based on the analysis of the formation mechanism of stray current, a real subway line has been selected and a monitoring platform in the nearby high-voltage (HV) substation has been built to record the neutral current. Meanwhile, through the on-site recording of the entry and exit time of subway trains at four consecutive stations, the running trajectories of the subway trains can be reversed. According to the trajectory of the subway train, the recorded neutral current was re-divided into time periods, and the synergistic analysis of the neutral current and the train trajectory in the corresponding time period was carried out. The neutral current measurement results for 4 consecutive days indicate that the influence of the subway train on the neutral current of the substation is mainly the influence of the unbalanced load, and the degree of the unbalance mainly comes from the distance and the acceleration and braking of the subway train. The trajectory of the subway train is related to the amplitude of the neutral current. The closer the subway train is to the substation, the greater the impact on the neutral current.

When a transformer is in the DC bias state, a series of consequences will occur. Mainly including excitation current distortion, losses increase, hot spot temperature rise and vibration and noise increase, these consequences are not conducive to the safe operation of the power grid. The relevant DC bias studies mainly focus on the case of several hundred amps of DC. In some special conditions like the HEMP E3 period, the bias DC is about several thousand amps. So, it is important to get the changing trend of relevant physical quantities when the transformer is at severe DC bias saturation. To obtain the excitation characteristics of transformers in the case of severe DC bias up to several thousand amperes, this paper established 3D finite element models of a single-phase three-limb transformer, a three-phase three-limb transformer, and a three-phase five-limb transformer. The graph of the variation of the harmonics within the 10th order of the excitation current with the direct current is obtained. And through the magnetic field distribution change of the iron core in the DC bias simulation, the reasons for the changing trend of the excitation current distortion characteristics can be analyzed.

Transformers, reactors and other electrical equipment often work under harmonics and DC-bias working conditions. It is necessary to quickly and accurately simulate the hysteresis characteristics of soft magnetic materials under various excitation conditions in order to achieve accurate calculations of core loss and the optimal design of electrical equipment. Based on Preisach hysteresis model, a parameter identification method for asymmetric hysteresis loop simulation is designed and applied to the simulation of hysteresis characteristics under bias conditions of oriented silicon steel sheets. In this paper, the limiting hysteresis loops of oriented silicon steel sheets are obtained through experiments under different working conditions. The first-order reversal curves(FORCs) with asymmetric characteristics is generated numerically, and then the Everett function is established under different DC bias conditions. The hysteresis characteristics of the oriented silicon steel sheets under harmonics and DC bias are simulated by improving FORCs identification method of the Preisach model. By comparing the results of simulation and experiment, the effectiveness of the proposed method is verified, so as to provide an important reference for material production and application. [ABSTRACT FROM AUTHOR]

Direct current (DC) bias leads to increased vibration and noise in transformers. One of the main causes is the magnetostrictive effect of the transformer core. To address this phenomenon of magnetostriction, firstly, a transmission line model (TLM) of a single-phase transformer under DC bias is developed using transmission line theory and Jiles–Atherton (J–A) ferromagnetic hysteresis theory, taking into account the winding copper loss, core eddy current loss, and leakage effect. Secondly, the time-domain simulation of the single-phase transformer based on the Newton–Raphson iterative method is carried out, and the magnetostriction characteristics of the transformer under different DC and its variation law are analyzed. Finally, the results show that the DC bias results in magnetostrictive distortion and vibration acceleration curve distortion, the left and right wings of the magnetostrictive butterfly curve are no longer symmetrical, the slope of the vibration acceleration image increases significantly, and the degree of distortion is positively correlated with the magnitude of the DC. In addition, the peak values of the magnetostrictive deformation and vibration acceleration become larger under DC bias, leading to an increase in the vibration and noise of the transformer. The research object of this paper is the single-phase transformer, and the research method can also be applied to the study of three-phase transformers. [ABSTRACT FROM AUTHOR]

A novel Performance Optimized Carrier Stored Trench Gate Bipolar Transistor (CSTBT) with Low Switching Loss has been proposed. By applying a positive DC voltage to the shield gate, the carrier storage effect is enhanced, the hole blocking capability is improved and the conduction loss is reduced. The DC biased shield gate naturally forms inverse conduction channel to speed up turn-on period. Excess holes are conducted away from the device through the hole path to reduce turn-off loss (Eoff). In addition, other parameters including ON-state voltage (Von), blocking characteristic and short circuit performance are also improved. Simulation results demonstrate that our device exhibits a 35.1% and 35.9% decrease in Eoff and turn-on loss (Eon), respectively, in comparison with the conventional shield CSTBT (Con-SGCSTBT). Additionally, our device achieves a short-circuit duration time that is 2.48 times longer. In high-frequency switching applications, device power loss can be reduced by 35%. It should be noted that the additional DC voltage bias is equivalent to the output voltage of the driving circuit, enabling an effective and feasible approach towards high-performance power electronics applications. [ABSTRACT FROM AUTHOR]

Dual-phase composite magnetic materials have magnetic and permanent magnetic properties. They can realize the dual-phase conversion of soft magnetic and permanent magnetic composites with a small amount of excitation energy. They have the advantages of good control and conversion characteristics and save energy, and they have a wide range of application scenarios in regard to power equipment. In this paper, the magnetization modeling of dual-phase composite magnetic materials is carried out based on micromagnetic theory, and a specific mathematical expression is given. Secondly, the preparation process of the dual-phase composite magnetic material is studied, the dual-phase composite magnetic material is prepared, and the demagnetization curve of the dual-phase composite magnetic material is measured. Finally, the application of dual-phase composite magnetic materials in power equipment is carried out. Using the soft magnetic and permanent magnetic characteristics of dual-phase composite magnetic materials, their impact on DC bias suppression in transformers is assessed. Magnetic circuit reluctance theory is used to develop the structure and electromagnetic design of a transformer. A transformer prototype with DC bias suppression ability based on dual-phase composite magnetic materials is manufactured, and simulation and experimental research are carried out. The simulation and experimental results verify the correctness of the proposed scheme. Although this scheme requires a more complex core structure, the energy-saving effect is remarkable without changing the transformer’s neutral grounding. The indicators meet the actual requirements of the project.

When the transformer is running, the vibration which is generated in the core and winding will spread outward through the medium of metal, oil, and air. The magnetic field of the core changes with the variation of the transformer excitation source and the state of the core, so the corresponding vibration and noise change. Therefore, the vibration and noise of the transformer contain a lot of information. If the information can be associated with the fault characteristics of the transformer, it is significant to evaluate the running state of the transformer through the vibration and noise signal, which improve the intelligence, safety, and stability of the transformer operation. Based on this, modeling and simulation of transformer multi-point grounding, DC bias, and short-circuit between silicon steel sheets fault are first carried out in this paper, and vibration and noise distribution of transformer under different faults are given. Second, a fault diagnosis method based on transformer vibration and noise characteristics is proposed. In the process of implementation, vibration and noise signals under multi-point grounding, DC bias, and short-circuit between silicon steel sheets are taken as the sample data, and the probabilistic neural network algorithm is used to effectively predict the transformer fault. Finally, the effectiveness of the proposed scheme is verified by identifying the simulation faults-the proposed fault diagnosis method based on PNN can be effectively applied to transformer.

Due to their excellent capabilities to generate and sense ultrasound signals in an efficient and well-controlled way at the microscale, piezoelectric micromechanical ultrasonic transducers (PMUTs) are being widely used in specific systems, such as medical imaging, biometric identification, and acoustic wireless communication systems. The ongoing demand for high-performance and adjustable PMUTs has inspired the idea of manipulating PMUTs by voltage. Here, PMUTs based on AlN thin films protected by a SiO2 layer of 200 nm were fabricated using a standard MEMS process with a resonant frequency of 505.94 kHz, a −6 dB bandwidth (BW) of 6.59 kHz, and an electromechanical coupling coefficient of 0.97%. A modification of 4.08 kHz for the resonant frequency and a bandwidth enlargement of 60.2% could be obtained when a DC bias voltage of −30 to 30 V was applied, corresponding to a maximum resonant frequency sensitivity of 83 Hz/V, which was attributed to the stress on the surface of the piezoelectric film induced by the external DC bias. These findings provide the possibility of receiving ultrasonic signals within a wider frequency range, which will play an important role in underwater three-dimensional imaging and nondestructive testing. [ABSTRACT FROM AUTHOR]

[Introduction] The paper aims to effectively suppress the disturbance of non characteristic harmonics to the power grid in the tokamak power supply system, the paper studies the mechanism of low-frequency harmonics in the tokamak power supply system. [Method] By introducing an improved switching function model, selected ITER fusion device as an example and established its corresponding AC/DC equivalent circuit model combined with its corresponding parameters, the corresponding output second harmonic was obtained through calculation and simulation. [Result] The ratio of output to input is calculated, and the stability factor value almost tends to zero. [Conclusion] It is determined that the DC bias of rectifier transformer do not cause harmonic instability of the system.

• Accurate transformer equivalent circuit for PDP simulation under DC bias is proposed in this study. The main contributions of this paper include: • The proposed π equivalent circuit is derived from the principle of duality. The two excitation branches correspond to the two magnetic circuits of the core. In the PDP circuit simulation, the operation and restraint currents have a specific physical meaning. • The three-segment component saturation inductance is proposed. The non-uniform deep saturation phenomenon of the transformer core under DC bias can be accurately simulated by the excitation inductances of the two excitation branches, respectively. Percentage differential protection (PDP) is one of the main protections of the transformer. The traditional transformer T equivalent circuit is insufficient to simulate the uneven saturation characteristics of the core for PDP under DC bias. Therefore, the transformer π equivalent circuit with three-segment component saturation is proposed for transformer PDP circuit simulation. FEM simulation is carried out to analyze the performance of transformer. The simulation and the experiment on PDP operation and restraint currents are conducted. Compared to the experiment, the errors of operation and restraint currents are significantly reduced using the proposed circuit under DC bias. The circuit simulations of transformer internal and external faults are implemented. The electromagnetic field analysis verifies the limitation of T equivalent circuit for PDP. The proposed method can achieve better performance in both transformer internal and external fault circuit simulation than the traditional method. [ABSTRACT FROM AUTHOR]

A bias current in the power system will cause saturation of the measuring current transformer (CT), leading to an increase in measurement error. Therefore, in this paper, we first conducted measurements of the direct current component in a 10 kV distribution system. Subsequently, a reverse extraction method for the CT distorted current under direct current bias conditions based on Random Forest Classification (RFC) and Long Short-Term Memory (LSTM) was proposed. This method involves two stages for the reverse extraction of CT distorted currents under direct current bias conditions. In the offline stage, data samples were generated by changing the operating environment of the CT. The RFC classification algorithm was used to divide the saturation levels of the CT, and for each sub-class, Particle Swarm Optimization–Long Short-Term Memory Network (PSO-LSTM) models were trained to establish the mapping relationship between the secondary distorted current and the primary current fundamental component. In the online stage, the saturated data segments were extracted from the secondary current waveform using wavelet transform, and these segments were input into the offline model for current reverse extraction. The simulation results show that the proposed method exhibited strong robustness under various CT conditions, and achieved high reconstruction accuracy for the primary current.

In this article, the sources of DC bias and its effects on power transformers are first summarized. Secondly, the article classifies and summarizes the current DC bias calculation problems of power transformers, and puts forward some interesting viewpoints on the research logic of related calculations. The current processing methods of DC bias effect are classified and discussed, their advantages and disadvantages are compared, and the logic flow of DC bias effect processing is proposed. Finally, the current research on DC bias voltage of power transformers is summarized, and the progress and deficiencies of current research are pointed out, which has certain reference value for future research on DC bias voltage and its suppression. [ABSTRACT FROM AUTHOR]

DC bias in a transformer is a threat to the safe and efficient operation of dual active bridge (DAB) converters. Detecting a dc component in milliamperes mixed with a large ac current is difficult. This article proposes a current sensor based on ac magnetic flux (MF) cancellation. The proposed sensor utilizes a current transformer (CT) to extract the ac component in the measured current. Then, a power op-amp copies the CT signal to an additional winding to generate an ac MF opposite to that of the main ac current. Hence, the sensor range required to measure the dc is greatly reduced for a much smaller absolute measurement error. Using only a CT and a simple op-amp circuit, the proposed solution features low complexity and power consumption. The relative error in a range of 15-A ac current is 0.038%, showing a five-fold improvement compared to off-the-shelf sensors. The proposed sensor is verified on a 1-kW DAB prototype, where the dc bias is suppressed to nearly null owing to the proposed sensor. [ABSTRACT FROM AUTHOR]

Magnetic components have become one of the primary barriers to high power density converters, especially to current-source converters (CSCs). In CSCs, the inductors/transformers have a predominantly dc flux to store energy, which can be offset by standard permanent magnets (PMs). However, eddy currents in standard PMs induce significant losses and thermal stress for medium-frequency applications. This article proposes using laminated PMs to offset the dc flux while reducing eddy currents, leading to significant reductions in the size, cost, and losses of inductors/transformers. Furthermore, the laminated PMs’ optimal location, orientation, and distribution are investigated to generalize this approach for maximum benefits. Three-dimensional finite-element analysis simulation and hardware experiments are presented to validate the effectiveness of the proposed approach in a medium-frequency transformer (MFT) for CSCs. Compared with standard PMs, the proposed use of laminated PMs reduces aggregate core-plus-PM losses by 85% in experiments, and thus, relaxes the MFT thermal design. Finally, the proposed approach is experimentally validated in a $\text{40}\,\text{kVA}$ flyback-type MFT for a soft-switching solid-state transformer. Compared to the traditional design without any PMs, the proposed design increases the saturation current by 46% while inducing only 5% more losses, leading to significant savings in magnetics cost and size. [ABSTRACT FROM AUTHOR]

The receive sensitivity of lead zirconate titanate (PZT) piezoelectric micromachined ultrasound transducers (PMUTs) was improved by applying a DC bias during operation. The PMUT receive sensitivity is governed by the voltage piezoelectric coefficient, h31,f. With applied DC biases (up to 15 V) on a 2 μm PbZr0.52Ti0.48O3 film, e31,f increased 1.6 times, permittivity decreased by a factor of 0.6, and the voltage coefficient increased by ~2.5 times. For released PMUT devices, the ultrasound receive sensitivity improved by 2.5 times and the photoacoustic signal improved 1.9 times with 15 V applied DC bias. B-mode photoacoustic imaging experiments showed that with DC bias, the PMUT received clearer photoacoustic signals from pencil leads at 4.3 cm, compared to 3.7 cm without DC bias. [ABSTRACT FROM AUTHOR]

Fast and accurate acquisition of current components is a key factor for an active power filter to realize transient control under unbalanced conditions. In this letter, a robust real-time algorithm, which rapidly separates the positive-sequence component (PSC) from multiple decaying dc (DDC) components, dc bias component, negative-sequence component, and harmonics, is proposed. To this end, first, the multiple DDC components are detected in the multiple disturbance and unbalanced grid context, by making use of the periodicity of remaining components. The dc bias can be obtained accordingly, followed by the detection of a compound signal encompassing the positive-sequence component, negative-sequence component, and harmonics. Specifically, the compound signal can be extracted precisely, based on the detected DDC and dc bias components, with one grid cycle response time, or approximately, within half grid cycle. A switching logic of the two approaches is designed to shorten the overall convergence time and improve steady-state accuracy. The PSC is then effectively extracted by constructing the virtual orthogonal signal of the compound signal and using dq-frame filtering. Compared with the existing transient control techniques, the proposed scheme guarantees one grid cycle response time and simultaneously suppresses multiple disturbances. Finally, experimental results verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In order to solve the problems of direct current (DC) bias of potential transformers in distribution networks without grounding at neutral points during single-phase grounding, resulting in distortion of excitation current overcurrent, increase of harmonic, vibrations, losses and heat generation, etc., resulting in potential transformer failures, frequent fuses of primary-side fuses and hazards to the distribution system. The excitation current expression of the potential transformer during the fault period was solved by the instantaneous symmetrical component method, the generation mechanism of the DC bias of the potential transformer was analyzed, and a DC bias suppression measure considering arc extinguishing was proposed. Based on PSCAD/ EMTDC simulation software, the neutral point ungrounded distribution network was built, and the influence factors of the DC bias of the potential transformer caused by the single-phase grounding and the effectiveness of the suppression measures were simulated. The results show that core saturation and fault phase angle are important factors affecting the DC bias of the potential transformer, and the proposed measures can effectively suppress the occurrence of DC bias overcurrent. [ABSTRACT FROM AUTHOR]

With the wide application of high voltage/ultra-high voltage (HV/UHV) DC transmission technology, the impact of DC grounding electrode location selection on the surrounding power grid has become increasingly prominent, especially the problem of DC bias hazard caused by DC grounding electrodes at provincial grid boundaries needs to be solved urgently. This paper studies the assessment and prevention of trans-regional DC bias risk, and proposes an inversion method of earth resistivity model based on the measured data of neutral current in the provincial boundary area. Firstly, the DC bias risk of provincial boundary power grid is simulated and calculated, and the influence of reasonable selection of earth model on the accuracy of risk assessment results is explained. Based on the classical Fletcher-Reeves conjugate gradient method and the measured neutral current data, a reduced-order inversion method for the earth resistivity parameters of the provincial boundary power grid is proposed. On this basis, a set of DC bias risk control scheme is formulated for the actual project of Gannan power grid. Finally, the feasibility of the scheme is verified by simulation and measured data. [ABSTRACT FROM AUTHOR]

A significant transition towards low-carbon, renewable energy sources and technological adaptation is mandatory in the present scenario to address climate change and achieve a sustainable energy system. Aligned with the upgradation in technology, as the need for efficient and smart energy grows, power electronics are being extensively used in power systems. Various factors can affect the pervasive use of power electronics associated with power transformers, thereby introducing the DC bias in the system. DC bias in the transformer leads to a shift in operating point, a rise in excitation current and a generation of harmonics. This causes an increase in core losses and temperature, resulting in exceeding the thermal limits and leading to transformer failure. Consequently, there is an emergency need to understand the DC bias capability of power transformers that aims at optimal transformer selection without being overrated. This research employs Ansys maxwell software to model and simulate a 500 kVA, 11kV/420V three-phase power transformer. The experimental investigation is carried out through a scale-down value of a 5 kVA laboratory prototype. The research findings revealed a significant negative impact of DC bias on power transformer capabilities that could be detrimental to its performance, health and lifespan. The analysis results provide valuable insights for the design engineer during the initial stages of designing a high-performance, cost-effective transformer with a low failure rate. • Electromagnetic and thermal analysis of dc biased power transformer. • DC bias withstand capability of the power transformer. • Impact on the power transformer rating and failure risks in concern with the DC bias. • Improve existing dc capabilities for sustainability. [ABSTRACT FROM AUTHOR]

Direct current (DC) bias leads to increased vibration and noise in transformers. One of the main causes is the magnetostrictive effect of the transformer core. To address this phenomenon of magnetostriction, firstly, a transmission line model (TLM) of a single-phase transformer under DC bias is developed using transmission line theory and Jiles–Atherton (J–A) ferromagnetic hysteresis theory, taking into account the winding copper loss, core eddy current loss, and leakage effect. Secondly, the time-domain simulation of the single-phase transformer based on the Newton–Raphson iterative method is carried out, and the magnetostriction characteristics of the transformer under different DC and its variation law are analyzed. Finally, the results show that the DC bias results in magnetostrictive distortion and vibration acceleration curve distortion, the left and right wings of the magnetostrictive butterfly curve are no longer symmetrical, the slope of the vibration acceleration image increases significantly, and the degree of distortion is positively correlated with the magnitude of the DC. In addition, the peak values of the magnetostrictive deformation and vibration acceleration become larger under DC bias, leading to an increase in the vibration and noise of the transformer. The research object of this paper is the single-phase transformer, and the research method can also be applied to the study of three-phase transformers.