Effect Of DC Bias Research Articles

Vibration and noise mechanism of a 110 kV transformer under DC bias based on finite element method

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.

MCML-BF: A Metal-Column Embedded Microstrip Line Transmission Structure with Bias Feeders for Beam-Scanning Leakage Antenna Design.

This article proposes a novel fixed-frequency beam scanning leakage antenna based on a liquid crystal metamaterial (LCM) and adopting a metal column embedded microstrip line (MCML) transmission structure. Based on the microstrip line (ML) transmission structure, it was observed that by adding two rows of metal columns in the dielectric substrate, electromagnetic waves can be more effectively transmitted to reduce dissipation, and attenuation loss can be lowered to improve energy radiation efficiency. This antenna couples TEM mode electromagnetic waves into free space by periodically arranging 72 complementary split ring resonators (CSRRs). The LC layer is encapsulated in the transmission medium between the ML and the metal grounding plate. The simulation results show that the antenna can achieve a 106° continuous beam turning from reverse -52° to forward 54° at a frequency of 38 GHz with the holographic principle. In practical applications, beam scanning is achieved by applying a DC bias voltage to the LC layer to adjust the LC dielectric constant. We designed a sector-blocking bias feeder structure to minimize the impact of RF signals on the DC source and avoid the effect of DC bias on antenna radiation. Further comparative experiments revealed that the bias feeder can significantly diminish the influence between the two sources, thereby reducing the impact of bias voltage introduced by LC layer feeding on antenna performance. Compared with existing approaches, the antenna array simultaneously combines the advantages of high frequency band, high gain, wide beam scanning range, and low loss.

Effect of a negative DC bias on a capacitively coupled Ar plasma operated at different radiofrequency voltages and gas pressures

The effect of a negative DC bias, |V dc|, on the electrical parameters and discharge mode is investigated experimentally in a radiofrequency (RF) capacitively coupled Ar plasma operated at different RF voltage amplitudes and gas pressures. The electron density is measured using a hairpin probe and the spatio-temporal distribution of the electron-impact excitation rate is determined by phase-resolved optical emission spectroscopy. The electrical parameters are obtained based on the waveforms of the electrode voltage and plasma current measured by a voltage probe and a current probe. It was found that at a low |V dc|, i.e. in α-mode, the electron density and RF current decline with increasing |V dc|; meanwhile, the plasma impedance becomes more capacitive due to a widened sheath. Therefore, RF power deposition is suppressed. When |V dc| exceeds a certain value, the plasma changes to α–γ hybrid mode (or the discharge becomes dominated by the γ-mode), manifesting a drastically growing electron density and a moderately increasing RF current. Meanwhile, the plasma impedance becomes more resistive, so RF power deposition is enhanced with |V dc|. We also found that the electrical parameters show similar dependence on |V dc| at different RF voltages, and α–γ mode transition occurs at a lower |V dc| at a higher RF voltage. By increasing the pressure, plasma impedance becomes more resistive, so RF power deposition and electron density are enhanced. In particular, the α–γ mode transition tends to occur at a lower |V dc| with increase in pressure.

Effects of DC bias on evolutions of repetitively pulsed streamer discharge in humid air

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.

Enhanced Wear and Corrosion Resistance of AZ91 Magnesium Alloy via Adherent Si-DLC Coating with Si-Interlayer: Impact of Biasing Voltage

Magnesium alloys are the lowest-density structural metals with a wide range of applications, such as aircraft skins, engine casings and automobile hubs. However, its low surface hardness and non-corrosion resistance in natural environments limit its wide range of applications. In this work, Si-DLC coatings (Si: 15 at.%) are fabricated on AZ91 alloy using a hollow cathode discharge combined with a DC bias voltage from 0 to −300 V to increase the deposition rate and modulate the structure and properties of the coatings. The Si interlayer with a thickness of around 0.6 µm is deposited first to enhance the adhesion. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy are used to investigate the effect of DC bias on the microstructure evolution of Si-DLC coatings. Meanwhile, corrosion and wear resistance of the coatings at various bias voltages have been investigated using electrochemical workstations and pin-on-desk wear testers. It is shown that the bias-free coating has a loose structure and is less resistant to corrosion and wear. The bias coating has a compact structure, small carbon cluster size, high chloride ion corrosion resistance, and high wear resistance against Al2O3 spheres. The corrosion potential of the coating bias at −300 V is −0.98 V, the corrosion current density is 1.35 × 10−6 A·cm−2, the friction coefficient is 0.08, and the wear rate is 10−8 orders of magnitude. The formation of SiC nanocrystals and high sp3-C, as well as the formation of transfer films on the surface of their counterparts, are the main reasons for the ultra-high wear resistance of the bias coatings. The wear rate, coefficient of friction, and corrosion rate of the coating are 0.0069 times, 0.2 times, and 0.0088 times that of the AZ91 alloy, respectively. However, the bias coating has only short to medium-term protection against the magnesium alloy and no long-term protection due to cracks caused by its high internal stress.

Measurement and calculation for high frequency magnetic losses of Terfenol-D alloy rod under coupled stress and DC bias fields

Compressive stress, a DC bias magnetic field, and an AC excitation field significantly affect hysteresis characteristics and magnetic energy losses of magnetostrictive materials. Therefore, studying high frequency magnetic losses of magnetostrictive materials under coupling of these three conditions is of great importance for improving the output performance of high power magnetostrictive transducers. In this paper, a magnetic property testing system for magnetostrictive materials has been constructed. It enables the magnetic property testing of Terfenol-D alloy rods under the simultaneous application of stress and DC bias at high frequency excitation (a maximum AC magnetic flux density of 0.5 T at an excitation frequency of 9 kHz). Based on Bertotti separation theory and experimental data, considering the coupling effect of stress and DC bias, a computational model for the high frequency magnetic losses of Terfenol-D materials is proposed. The model incorporates relevant parameters of stress and DC bias to modify loss coefficients, and the expressions for loss coefficients are identified using the symbolic regression method. A comparative analysis between experimental data and model calculation shows good agreement, with the maximum and average errors of 4.68% and 1.74%, respectively.

A 4:1 Switched Capacitor Converter With Low Flying Capacitors Voltage and High Efficiency

In this paper, a 4:1 switched capacitor converter (SCC) is derived. Compared with the Dickson 4:1 converter, the voltage of flying capacitors is lower and thus the effect of dc bias on multi-layer ceramic capacitor (MLCC) is reduced. With a limited number of MLCCs, the proposed converter achieves a higher efficiency, and it is suitable for the applications with limited volume such as mobile phone fast charging. A 20-V to 5-V prototype is built with 24 X7R MLCCs in 0805 package, and its efficiency is 1.7% higher than the Dickson 4:1 and 1.1% higher than the Series-parallel 4:1 at 16-A output current.

Effect of DC bias on dipolar response of yttrium iron garnet

Yttrium iron garnet (YIG) is a prominent magnetic (ferrimagnetic) insulator and an excellent material for wide ranging microwave and millimeter-wave applications. In polycrystalline form it exhibits high dielectric loss due to contributions coming from grain & grain boundaries, and Fe heterovalency. We have investigated the effect of dc bias voltage on the dielectric properties of YIG in a wide range of temperature (100 - 600 K) and frequencies (100 Hz - 1 MHz). Consistent with previous observations, without bias a dominant frequency dispersion due to hopping of the Fe2＋ & Fe3＋ is observed in low temperature region and a wider frequency dispersion is observed at higher temperatures arising due to grain-grain boundary contributions. Application of a small dc bias voltage increases the dielectric constant and reduces the dielectric loss significantly at higher frequencies. The DC bias-induced improvements are much more dramatic at higher temperatures, where grain boundary contributions dominate. Our detailed analysis of dc and ac conductivity data show that the dc bias suppresses the grain boundary contributions significantly and at the same time it boosts the polarizability due to the Fe2＋/Fe3＋ hopping.

Structure and dielectric properties of Lu-doped SrBi2Ta2O9 synthesized by the molten salt method

Lu-doped SrBi2Ta2O9 (SrBi2-xLuxTa2O9 where x = 0, 0.025, 0.05, 0.75 and 0.1) powders were synthesized by combination of molten salt method and solid-state route. FTIR, Raman and XRD techniques were performed to follow the transformation of reactants into the desired products. Characterization of all samples shows pure and single-phase orthorhombic structured materials obtained with plate-like morphology that is composed of fine and coarse-grained particles. The prepared powders were pressed and sintered at different temperatures up to 1200?C. Microstructure of the sintered samples is also likely to be affected by doping. The first study of dielectric measurements describes the effect of the application of DC bias, at roomtemperature, on the undoped and Lu-doped ceramics and shows that there is little or no effect of DC bias. The sample SrBi1.95Lu0.05Ta2O9 had maximal dielectric constant (??) and minimal dielectric loss (tan?). In the second part of this work, the temperature dependence of ?? and tan_ was considered. It was concluded that Lu-doping not only reduces the Curie temperature, but also brings a diffused phase transition, showing a crossover between displacive and diffusive behaviour.

Overview of Research Status of DC Bias and Its Suppression in Power Transformers

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.

Effect of external electric potential on the mechanical resonance of MEMS cantilever resonator

This work presents an analytical model to predict the natural frequency of electrostatically actuated micromachined cantilever beam under the application of DC voltage. The analytical modelling uses an energy based method with a sinusoidal vibration assumption. The electric field between the cantilever electrodes is assumed to be vertical and fringing field effects are neglected. The behaviour of natural frequency and a closed-form expression for pull-in voltage are evaluated. The electrostatic spring softening effect of DC bias on the resonant natural frequency is studied in particular. Results are compared with simulation in ANSYS.

Direct current (dc) bias effect on the dielectric constant of Dy and Ho-doped BaTiO3-based ceramic and MLCCs

With the increasing demand for the miniaturization, high capacitance and high reliability of the Multilayer Ceramic Capacitor (MLCC), the thickness of single dielectric layer is less than 1 μm and the original partical size of the powder has reached the scale less than 300 nm. In this paper, BaTiO3 powder of various partical sizes (150–500 nm) was modified with Dy and Ho through a chemical coating method. The dense and uniform ceramics in accordance with EIA X7R-type temperature stability were sintered under low oxygen partial pressure and good dielectric properties of dielectric constant >2000 and dielectric loss <1% were obtained. The grain size effect on the dielectric properties under various dc-bias field were systematically investigated. It is found that the fine-grain ceramic exhibits a lower absolute change of the dielectric constant and a higher dc-bias stability. Furthermore, the modified 150 nm BaTiO3 powders was made into 1210-type MLCCs, and the dielectric behavior of the MLCCs with different dc-fields and ac-fields were study over −55 °C–125 °C. It is found that the ac electric field had a greater influence on the dielectric properties at room temperature and below, and the dielectric constant variation under a dc-bias field was also greatly advanced for the modified fine-grain MLCCs. The results provide a reference for the design of the next generation of BME-MLCCs.

(Invited) DC-Bias and Temperature Effect on the Dielectric Properties of a Polyimide Thin Layer

Photo-processable Polyimide is widely used as a thin sensitive layer (less than 4µm) for relative humidity or as a passivation layer (higher than 4µm) for power semiconductor devices (Si, SiC, GaN, etc.). In this work, an interdigitated transducer (IDT) was produced by standard photolithography on glass substrate. Each IDT consists of two interdigitated gold electrodes with filling area of 2×2 mm2 and two wires around the interdigitated electrodes, one to heat the sensor and the other to measure the local temperature. Then the polyimide material was spin coated homogeneously on top of the planar electrodes to obtain different layer thicknesses ranging from 1 to 11 µm.The electrical properties of the sensors (coated IDT with polyimide) were monitored by impedance spectroscopy using a HP4192 4192A LF impedance analysis controlled by a PC, permitting automated data collection. The advantage of our sensor is the possibility to carry out the impedance measurements at different temperatures (from RT to 350°C) by locally heating up the sensor using the integrated heater around the electrodes. The design of the realized sensor is adequate to study the sensitivity of the polyimide layer to relative humidity as well as the DC-bias and temperature effect on its dielectric properties.First, impedance measurements were performed from 1 MHz to 100 Hz to obtain the optimum frequency at which the sensor capacitance changes linearly with relative humidity. Next, capacitive measurements of the sensor were recorded at 100 kHz under different relative humidity levels. The detected signal, the capacitance, follows a linear dependence on the relative humidity once it is varied from 5 to 80%. The coating of the sensor with an optimal thickness of polyimide allows the best performance of the humidity sensor in terms of response and recovery times.Second, we studied the effect of temperature and DC bias on the change in sensor capacitance at a constant frequency of 100 kHz and under a constant flux of 250 sccm N2. The temperature and DC bias were increased from 20 to 350°C and from 0 to 35 V, respectively. Only when the sensor temperature exceeds 280°C does the DC bias begin to have an effect on the measured capacitance. The sharp increase in capacitance is due to the increase in charge carriers. This peak immediately decreases exponentially even before the bias is removed. The decrease can be referred to the loss of energy, due to the transport of charge carriers. Since electromigration is active at temperatures above 200 °C, this could explain why an effect starts to occur when sensors are heated above this threshold. The large increase in capacitance at higher temperature and higher DC current is generally reproducible in terms of shape but not in terms of magnitude. At higher temperature and under higher DC bias, a sharp increase in capacitance usually appears and then followed by an exponential decrease to a constant value even though the sensor is still under the same DC bias.Finally, we performed impedance measurements of our sensors over the frequency range 100 to 1MHz. From these measurements, we deduced the complex electric modulus, which corresponds to the dielectric relaxation processes inside a medium, if an electric field is applied and which is inversely proportional to the complex permittivity. This gives an alternative approach to analyze the electrical response of the Polyimide material and allows to study the relaxation phenomena, to study the long-range conductivities, as well as to identify the localized dielectric relaxation phenomena. The real part of the electrical modulus shows a decrease with the increase of the DC bias (from 0 to 35V) for frequencies below 30 kHz. Its value tends to zero for low frequencies and reaches a plateau for high frequencies. But not affected by the applied bias. This suggests a decrease in relaxation processes by an applied electric field, especially for low frequencies. At frequencies below a few kHz, space charge polarizations are the most dominant mechanism. In the case of a strong electric field obtained by a higher DC polarization, the relaxation process may be prohibited, resulting in a lower value of the electric modulus. It reaches a constant plateau at high frequencies, suggesting that the relaxation mechanism is mainly frequency dependent rather than DC bias dependent, which is in good agreement with the literature. The measurement of the electrical modulus suggests that the relaxation mechanisms are mainly frequency dependent, rather than dependent on the applied DC bias.

Investigation of the Effects of DC Bias on Single-Phase Shell Type Transformers Using Frequency-Dependent Reluctance-Based Model

In this article, a reluctance-based model is developed for time-efficient analysis of shell type single-phase power transformers under the direct current (dc) bias conditions. Unlike other reluctance-based transformer models in the literature, the developed one considers frequency dependent nature of the winding resistances. This is important especially for accurate determination of losses and maximum loading capability (MLC) of the transformers under dc bias and non-sinusoidal conditions. In addition to that, by using the developed model, three different MLC determination approaches, which are based on the rated primary side current, rated total loss and rated primary winding loss, are examined for dc bias conditions. These novel examination results clearly point out that among three approaches the rated primary winding loss-based one should be preferred for the safe operation of the transformers in the systems with dc bias.

Quantum model considers the effect of laser wavelength, intensity, and DC bias on photoemission

Calculations demonstrate the importance of laser electron heating, which can increase the quantum efficiency of photoemission.

Analysis on the Influence of Remote 110kV Substation on Transformer DC Bias

High voltage direct current (HVDC) transmission system has the advantages of large capacity, long distance and low loss. Relying on the advantages of HVDC transmission, China has established a large-scale energy transmission channel in the west, effectively solving the problem of uneven local energy distribution. However, HVDC transmission will generate ground current when it is operating in a single pole, which will cause the DC bias effect of the transformer. At this time, the core magnetic circuit of the transformer is saturated. Transformers will experience increased vibration, increased noise, local overheating, and surge in harmonics. This paper, based on the Jinhua HVDC transmission project as a background, established a power grid topology model in Zhejiang area based on the field-circuit coupling method. The focus is on calculating the DC bias of Shenze transformers in Jinhua area, and proposing treatment measures based on the calculation results. According to the actual measurement of the project, the accuracy of the calculation result is verified, which reflects the effectiveness of the governance measures.

Effect of DC Bias on Dielectric Properties of NdFeO3

The solid-state synthesis method was used to prepare polycrystalline samples of NdFeO3. The effect of dc bias was observed on the dielectric properties of prepared NdFeO3 samples. Impedance was found to be comprised of three contributions corresponding to grains, grain boundaries, and sample-electrode contact. Temperature and frequency-dependent dielectric measurements revealed that the sample electrode contact and grain boundary responses get modified, while grain response remains unaltered under dc bias. Large dielectric permittivity (of the order of ∼103) in the entire studied temperature range (100 K–450 K) and at high frequencies (∼5 MHz) was found to remain unaffected under dc bias, suggesting that the large dielectric constant is an intrinsic property of NdFeO3.

Four‐phase interleaved TCM DC‐DC buck converter with matrix inductor in battery charging application

In this paper, a 1-kW DC-DC buck converter with a four-phase interleaved matrix inductor is proposed for battery charging applications. It is well-known that the DC bias on the inductor will cause high core loss as it changes the B–H characteristic. Typically, the transient conduction mode employed in high voltage applications for zero-voltage-switching of devices would cause higher inductor current ripple. The conventional approach to reduce the effect of DC bias and inductor current ripple is employing multi-phases. However, the cost and size of the converter will increase significantly. This paper proposes the matrix inductor which has a small volume and reduces the effect of the DC bias by flux sharing and flux cancellation at the same time, results in low inductor core loss. With the interleaved operations the output current ripple can be lower which is suitable for battery charging application. Besides, the comparison of the synchronous and interleaved operation is presented. A 1-kW prototype is built and the experimental results show that the peak efficiency is 99.1% and 99.2% for synchronous and interleaved control, respectively. Additionally, the output current ripple of the interleaved operation is reduced by 85% in comparison with the synchronous operation.

A Dynamic Hysteresis Model for Loss Estimation of GO Silicon Steel Under DC-Biased Magnetization

A new algorithm for numerical identification of the static Preisach hysteresis model is proposed for more accurate estimation of dc-biasing hysteresis curves and hysteresis loss of the grain-oriented silicon steel sheet. Based on the experimental asymmetric major hysteresis loop under dc-biased magnetization, two sets of first-order reversal curves corresponding to ascending and descending branches, respectively, are numerically generated for construction of the Everett function. According to the equivalent field separation technique, a dynamic hysteresis model is established by parameter extraction of excess loss, and then used for simulation of dc-biasing dynamic hysteretic behaviors. The consistency between the simulated results and the measured ones demonstrates the effectiveness of the proposed method. The effect of dc bias on iron loss is analyzed as well.

AC and DC bias effect on capacitance–voltage nonlinearities in Au/HfO2/M (M = Pt, TiN, W, and AlCu) MIM capacitors: effect of the bottom electrode material

Metal–Insulator–Metal (MIM) capacitors based on high-k oxides require stability with the applied electric field. However, experiment reveals a nonlinear behavior of capacitance with ac or dc bias. In this work, we measure capacitance–voltage nonlinearities for Au/10-nm HfO2/M (where M = TiN, Pt, W, and AlCu alloys). It is observed that ac capacitance is strongly dependent on the bottom electrode material. This dependency is discussed through the correlated barrier hopping (CBH) model. Accordingly, the ac nonlinearity is ascribed to the polarization of isolated defect pairs, which in turn increase as the maximum barrier height decreases. This induces higher nonlinearity as compared to the dc one. For the dc bias, oxygen affinity of active metal electrode may describe the origin of dc nonlinearities.