DC Bias Excitation Research Articles

A magnetic-mechanical strong coupling FEM model and vibration characteristic analysis of transformer core under DC bias

The vibration of a transformer core induced by magnetostriction is closely related to the environment and safety of devices. The DC bias excitation leads to the over saturation of the transformer core and causes more severe vibration. In this paper, a magnetic-mechanical strong coupling model based on a fixed-point time-periodic 2D finite element method with excitation voltage and DC bias current as the input is established in which the vector magnetic potential A, winding current I, and displacement in the core u are simultaneously taken as solution variables, and the fixed-point reluctivity is introduced to deal with the nonlinear problem of the core. In this model, the magnetic field and mechanical field are associated with the piezomagnetic equations and variational principle, and the circuit and magnetic fields are connected through the law of electromagnetic induction. The equivalent thickness of the core model and the determination of the initial value are discussed. A test transformer with a laminated core is made for experimental measurement. The accuracy and efficiency of the model proposed are verified by comparing the calculated results with the experimental results, and the influence of DC bias components on the magnetic characteristics and vibration of the transformer core is analyzed.

High-Frequency Losses Calculating Model for Magnetostrictive Materials Considering Variable DC Bias

According to the actual operation conditions, a kind of high frequency losses testing system of magnetostrictive materials under DC bias is built. The dynamic hysteresis loops for Terfenol-D samples at different AC driving frequencies and magnetic densities are studied experimentally under variable DC bias excitation. The magnetic energy losses are obtained from these dynamic hysteresis loops. The three-variable magnetic energy loss matrix is established by these measured data. On the basis of Bertotti loss separation theory, the high frequency losses calculating model of magnetostrictive materials considering variable DC bias excitation is proposed by using the algorithm of Levebverg-Marquard and the method of matrix transformation. In this model, according to the multivariate parametric regression, the loss coefficients are modified by introducing DC bias-related terms. The loss comparison at different operating conditions shows that the computed results in this proposed model are in good agreement with the experimental ones.

Power conversion efficiency prioritized AC filter inductor design for three-phase PWM inverter

This study was conducted to develop a design method of power density and efficiency maximization for three-phase pulse-width modulated (PWM) inverters that include AC filter. A tradeoff relationship exists between power density and efficiency. In general, increasing the switching frequency is known to increase the switching device loss and decrease the volume of the passive components. A three-phase PWM inverters design should consider the balance between conversion efficiency and inverter volume. However, best of our knowledge, no practical study has focused on the optimal design of a three-phase PWM inverter that includes an AC filter. This is because the iron loss of the AC filter inductor changes in complicated ways depending on the DC-bias excitation, amplitude of switching ripple current, etc. Therefore, the present authors clarified this iron loss mechanism and realized a highly accurate iron loss calculation method in previous studies. In this paper, the relationship between efficiency and volume for the switching frequency was analyzed when the AC filter inductor was designed for minimal loss by adjusting the core diameter, height, and number of winding turns. The efficiency and volume optimization achieved by designing a proper inductor was verified via comparison with a base design.

Noise Suppression in Parallel Fluxgate Magnetometers by DC-Biased Excitation Method

Noise Suppression in Parallel Fluxgate Magnetometers by DC-Biased Excitation Method

Modeling and Performances of the Orthogonal Fluxgate Sensor Operated in Fundamental Mode

Fluxgate magnetometer is an important device for weak magnetic-field measurements. By adding a large dc bias excitation current, the performances of fluxgate can be highly improved. In this article, based on the assumption of the single-domain state within the probe core wire, the quasi-static Stoner–Wohlfarth model (SW model) was used to construct a mathematic model for the output signal of the orthogonal fluxgate probe operated in fundamental mode (FM-OFG). The dynamic hysteresis loop characteristics were also considered here, and the expected first-harmonic output signal corresponding to the theoretical analysis was obtained from our model. A prototype FM-OFG probe was fabricated by using a 20 mm-long Co–Fe–Nb–Si–B amorphous microwire as core wire and a 1500-turn solenoid as pickup coils. Output performances were analyzed at different external fields, ac excitation currents, and dc bias currents. A good agreement between the modeling results and the experimental ones was found. The noise level was reduced down to 9.01 pT/rt (Hz).@.1 Hz. The simulation method and experiment results provide theoretical guidance for the subsequent design and improvement of the FM-OFG.

Electromagnetic Vibration Analysis of Magnetically Controlled Reactor Considering DC Magnetic Flux

The main factors of stress distribution in MCRs are the magnetostriction effect of the core materials and the magnetic force between gaps under DC bias excitation. This article developed a coupling model for MCRs considering Maxwell magnetic force and magnetostriction under DC flux density biases. The constitutive equations of the magnetic field and strain field are constructed based on the magnetic property curves with a new measured and analyzed method to consider DC magnetic flux biases, which is the key contributions of this study. Then, the electromagnetic vibration properties of the MCR model are calculated and analyzed. To prove the validity of the proposed method, the vibration of a 4.4 kVar-220 V MCR is tested and analyzed.

Study on Dynamic Hysteretic and Loss Properties of Silicon Steel Sheet Under Hybrid Harmonic and DC Bias Excitation

The dynamic and static hysteresis properties as well as loss properties of grain oriented (GO) silicon steel sheet are measured under the AC-DC hybrid excitation containing both DC bias and harmonic components. The influence of the DC-biasing magnetic field, harmonic orders and phase shift angles on the iron loss is analyzed in depth based on the experimental data under different excitations. A dynamic hysteresis model and the parameter identification method is presented to simulate the asymmetrical hysteresis curve with minor loops. According to the equivalence between loss separation and field separation, the static part of magnetic field intensity are calculated by an improved Preisach model, while the dynamic parts are obtained by fitting the classical loss as well as excess loss. The consistency between simulation and measurement verifies the effectiveness and accuracy of the proposed method.

Core loss separation model under square voltage considering DC bias excitation

There are many magnetic inductors, such as filter inductors used in power electronic devices, being subjected in square waveform excitation together with DC bias. This paper proposes an improved core loss separation model to calculate the core loss of the magnetic materials under square waveform excitation together with DC bias. The core loss of the magnetic material with such excitation is calculated, and compare with the results using other models. The comparison shows that the improved model is more accurate than the other model. The discussion also shows that the improved model can identify the hysteresis loss and eddy loss. The results demonstrate that the improved model can optimize the design of inductors to improve the performance of the power electronic applications.

The FEM Calculation Considering Vector Magnetic Properties of Electrical Steel Sheet Under DC-Biased Field

This article proposes an enhanced dynamic vector magnetic hysteresis model for describing the effect of dc-biased field and eddy current on vector magnetic quantities. A governing equation combining the proposed model is derived for finite-element analysis of magnetic characteristics distribution of transformer core under dc-biased excitation. The numerical results of the transformer core by using the enhanced model with consideration of dc-biased excitation and eddy current are compared with the numerical results obtained by using the magnetizing curve. It proves that the proposed model can consider vector magnetic properties and iron loss of electrical steel sheet under both dc-biased and rotating magnetic fields during numerical analysis.

Research on excitation current and vibration characteristics of DC biased transformer

In practical engineering, DC disturbance will lead to excitation saturation and vibration intensification on transformer core, as well as affecting the normal operation of equipment and power grid. According to the problem, a new idea is proposed in this paper. Based on the electromagnetic characteristics of DC biased transformer, excitation saturation and core vibration are studied by using excitation-vibration harmonic response analysis method. Excitation current is identified through electromagnetic coupling to characterize the excitation saturation degree. Then, vibration harmonic response model is established to analyze core vibration. Electromagnetic characteristics of DC biased Y/Δ transformer are simulated. The variation of excitation current and core vibration at different DC levels are studied. Excitation-vibration characteristics of three-phase group transformer and three-phase three-limb transformer are compared and summarized. With experimental platform built, the correctness of simulation results is verified by experimental data, and the effectiveness of the proposed method can be proved.

B-periodic oscillations in the Hall-resistance induced by a dc-current-bias under combined microwave-excitation and dc-current bias in the GaAs/AlGaAs 2D system

We report the observation of dc-current-bias-induced B-periodic Hall resistance oscillations and Hall plateaus in the GaAs/AlGaAs 2D system under combined microwave radiation- and dc bias excitation at liquid helium temperatures. The Hall resistance oscillations and plateaus appear together with concomitant oscillations also in the diagonal magnetoresistance. The periods of Hall and diagonal resistance oscillations are nearly identical, and source power (P) dependent measurements demonstrate sub-linear relationship of the oscillation amplitude with P over the span 0 < P ≤ 20 mW.

An Optimization and Comparative Study of Air-Coupled CMUT Cells With Circular and Annular Geometries.

Air-coupled capacitive micromachined ultrasonic transducers (CMUTs) with annular cell geometry have recently been reported to have a promising transmit sensitivity. This paper reports three optimization schemes, which further improve the transmit sensitivity and also help achieve a reasonable comparison between the novel annular and conventional circular cells. Lumped element models of both cell types with laminate plate structures are presented. Based on these models, a design optimization flowchart was constructed to facilitate analytical optimization on the three schemes. Circular and annular CMUTs with a common 97-kHz natural resonance frequency were fabricated and characterized to verify the efficacy of the optimization principle. Using the optimization flowchart, annular and circular cells with frequencies ranging from 100 to 300 kHz were analytically optimized and then compared. The comparison results demonstrate that, given the same dc bias and ac excitation voltage, the output power density at the plate surface of the optimized annular cell is double that of the optimized circular cell. Additionally, when generating the same surface power density, an optimized annular cell requires either half the dc bias or half the ac excitation voltage of an optimized circular cell. This paper provides a practical optimization framework for CMUT cell design and demonstrates the superiority of annular cells for air-coupled applications.

Iron Loss Estimation Method for a General Hysteresis Loop With Minor Loops

In order to design highly-efficient electrical machines, it is necessary to estimate their iron losses accurately. The conventional iron loss estimation method [1], [2] estimates iron loss based on the assumption that eddy current loss coefficient (k e ) and hysteresis loss coefficient (k h ) under non-sinusoidal excitation are equal to k e and k h under sinusoidal excitation. However, these coefficients are not identical because minor loops are not centered but on ascending and descending major hysteretic curves. In this paper, we verify whether k e under dc-biased excitation is equal to k e under sinusoidal excitation. In addition, the method of analyzing iron loss under non-sinusoidal excitation using dc-biased magnetic properties is proposed.

Performance Analysis of Synchronous Reluctance Machines Having Nonoverlapping Concentrated Winding and Sinusoidal Bipolar With DC Bias Excitation

This paper describes the operation principle and analyzes the electromagnetic performance of synchronous reluctance (SynR) machines having the structure of switched reluctance machines but excited by an ac sinusoidal current with dc bias, i.e., salient-pole SynR with nonoverlapping concentrated windings and a dc bias excitation. Under such excitation, these machines become similar to permanent magnet (PM) counterparts. The dc bias, which is equivalent to the PM excitation, produces back electromotive force (EMF) in the ac coils as well as cogging torque. Thus, injecting the ac coils by sinusoidal currents results in output torque on the machine shaft. The produced back EMF and cogging torque, and torque ripple magnitudes and periods, as well as the optimal ac current angle and the ac/dc current density ratio, strongly depend on the winding connection configuration. The maximum average torque can be achieved when the ac/dc current density ratio is 2 and the symmetrical winding connection, which results in a lower torque ripple, is employed. A prototype machine is built and tested to confirm the analyses and conclusions.

Beat Interferences in Fundamental Mode Orthogonal Fluxgates

Fundamental mode orthogonal fluxgates (FM-OFGs) can be made very thin so that one can assemble them in an array to image magnetic field distributions. The dc-biased ac excitation current is fed to the U-shaped wire core of the sensor head; therefore, one can enclose the area by the excitation of the current path, which is made small. Due to the high sensitivity of FM-OFG, tiny but substantial (several hundreds pT) sinusoidal oscillations are visible in the output when two FM-OFGs are placed close to one another. The frequencies of such oscillations are found to be exactly the difference of two ac excitation frequencies independently operated upon the sensor head and higher harmonics of the difference frequency. The interference can be described as a beat of the excitation magnetic fields. We will show that interferences are mainly caused by the inductive coupling of the excitation magnetic field and that, although interferences decay quickly in intensity with increased distance between the sensor heads, they remain at the level of several hundreds pT at 5.8 cm apart. A solution to the problem is to use the same excitation frequency for all the sensor heads, which will suppress beat interferences where they are converted to tiny dc components.

Experiment and Simulation of Eddy-Current Loss inside Copper Shielding of Transformers under DC Biasing Condition

With the advent of power electronic technology, the excitation conditions applied to transformers, motors, etc. could be very atypical. DC bias excitation is an undesired working condition of AC power transformers, the asymmetrical saturation of the transformer core, the heavy noise, the serious vibration, and the local loss concentration can all potentially occurred in dc-biased transformers. The effect of the exciting current under different dc-biased magnetization on eddy-current loss in copper plate based on a reduced engineering-oriented benchmark model (TEAM Problem 21) is investigated. Experiment scheme for dc biasing is presented and the distribution of the eddy current loss under different dc-biased excitation conditions was studied in detail. The engineering applicability of three dimensional eddy current analysis methods for dc-biased magnetization field computation and the practical loss modeling are examined, which has been demonstrated via the numerical modeling results and the measured data.

Modeling Magnetic Hysteresis Under DC-Biased Magnetization Using the Neural Network

The excitation conditions of electrical steel are generally sinusoidal but, with the advent of power electronics in recent years, dc-biased excitation is sometimes experienced. The use of an iron core under dc-biased magnetization gives rise to asymmetrical hysteresis loops and the hysteresis loss in the iron core also increases with the value of dc excitation. For iron cores working with dc-biased excitation, accurate modeling of the nonlinear characteristics for the iron core that includes the dc-bias is very important for the computation of the exciting current and the iron loss. In this paper, an efficient approach for simulating the hysteresis loop of iron core under dc-biased excitation using neural-network theory is presented. The proposed method has the merits that a specific hysteresis loop can be identified conveniently and effectively to ensure that accurate electromagnetic-field analysis can be realized.

低オフセット基本波型直交フラックスゲート

A method is presented for canceling offset of an orthogonal fluxgate operating in the fundamental mode with dc biased excitation. Offset occurs under the influence of the magnetic anisotropy that is inherent in a wire core. When both the excitation current and dc bias polarities are either positive or negative, the absolute value of the offset is the same but the signs are contrary. The offset can therefore be removed by changing polarities of both excitation current and dc bias periodically to take the mean value. This method can also reduce the input-output hysteresis. Experimental results are shown for a sensor head consisting of a 15-mm-long cobalt-based amorphous wire of 120 μm in diameter and a 300-turn sensing coil formed on the wire.

Orthogonal fluxgate mechanism operated with dc biased excitation

A mode of operation is presented for an orthogonal fluxgate built with a thin magnetic wire. By adding a proper dc bias to the wire excitation, the new mode is easily established. In this case, the fundamental component of the induced voltage at the sensing coil (secondary voltage) is made sensitive to the axial magnetic field, compared to the second harmonic in a conventional orthogonal fluxgate. The operating principle is explained using a magnetization rotation model. A method is proposed to cancel the offset that is inevitable when the magnetic anisotropy is present in a magnetic wire at an angle to its circumference. Experimental results are shown for a sensor head consisting of a 2-cm-long Co-based amorphous wire 120 μm in diameter with a 220-turn sensing coil. The sensitivity obtained is higher than that obtained using a conventional type of the orthogonal fluxgate built with the same sensor head. It is also demonstrated that the proposed method for canceling the offset works well.

Chaos in superconducting tunnel junctions

All currents through a superconducting tunnel junction, including quasiparticle tunneling current and Josephson current, are modeled on an electronic simulator. The current–voltage (I–V) curves of a rf-driven superconducting tunnel junction are generated using this simulator so that the ranges of dc bias and rf excitation, over which chaotic behavior occurs, can be found for a given rf frequency. It turns out that the ranges are roughly the same as those for the resistively shunted junction model, although some differences exist. Contributions of either quasiparticle current or Josephson current to chaos in the junction are evaluated briefly.