Magnetic Flux Density Waveform Research Articles

Time‐harmonic field‐circuit model for brushless doubly fed induction machine

AbstractA computationally efficient time‐harmonic finite element model for the steady‐state analysis of a brushless doubly fed induction machine (BDFIM) is proposed. In the model, the electromagnetic couplings of the BDFIM are described by means of the sum of two complex magnetic vector potentials that represent the two fundamental harmonic time components of the magnetic flux density distribution in the rotor frame of reference. As in an ordinary induction motor, the non‐linearity of the magnetisation characteristic is accounted for using an effective magnetic permeability. For the BDFIM, this is derived by considering the features of modulated magnetic flux density waveform. The accuracy of the approach has been validated by comparing the characteristics of a D270 machine operating in the double‐feed mode with ones obtained from the experimentally verified time‐stepping model at various operating conditions. High accuracy of the results coming from the proposed model is demonstrated even under deep saturation conditions within the magnetic circuit.

Design optimization with genetic algorithm of open slotted axial flux permanent magnet generator for wind turbines

ABSTRACT In this study, the design parameters of Open Slotted Axial Flux Permanent Magnet (OSAFPM) Generator for wind turbines are presented using Genetic Algorithms (GA), an optimization algorithm based on natural selection and genetic mechanisms. Electromagnetic analysis of Open Slotted Axial Flux Permanent Magnet generator has been performed by using parameters optimized with Genetic Algorithms. The ANSYS Maxwell program, which uses the finite element method (FEM), has been used for electromagnetic analysis. Compared to ANSYS Maxwell, it is observed that the genetic algorithm significantly reduces the computational time required for design optimization. However, initial design and optimization with Genetic Algorithms have resulted by 8.94% increase in power densities. In addition, 12.71%, 38.62%, 62.02%, and 56.39% improvements have been obtained for air gap magnetic flux density, flux linkage, induced voltage, and current waveforms, respectively. This suggests that optimization with a Genetic algorithm improves the Open Slotted Axial Flux Permanent Magnet generator parameters.

Static magnetic field analysis of hollow-cup motor model and bow-shaped permanent magnet design

The hollow-cup Permanent Magnet (PM) motors have the characteristics of low power consumption, and are widely used in the aerospace field. At present, the tile-shaped PMs used by hollow-cup PM motors have poor sinusoidal characteristics of the air gap magnetic flux density waveform, which will cause torque ripple. The existing method for improving the air gap magnetic flux density waveform is not very effective when applied to hollow cup, a special motor with no stator core and large air gap. A bow-shaped PMs structure is designed for the hollow-cup motor in this paper. First, the equivalent surface current method is used to calculate the analytical formula of the static magnetic field of the model. Then, the Finite Element (FE) method is used to calculate the static air gap flux density waveform of conventional tile-shaped PMs and bow-shaped PMs with different bow heights, and the corresponding harmonics and sine distortion are obtained by Fourier decomposition. The simulation results show that the bow-shaped PMs can effectively improve the sinusoidal characteristics of the static air gap flux density waveform. And the suitable bow height is determined. Finally, a prototype is made based on the suitable bow height for experiments, and compared with the analytical result and the FE result, and the accuracy and effectiveness of the bow-shaped PMs with the suitable bow height are verified.

Calculation and Analysis of Eddy-Current Loss in Switched Reluctance Motor

The eddy-current loss of switched reluctance motor (SRM) is studied and analyzed in this paper. As a significant part of core loss, eddy-current loss has a great influence on motor performance. First, the average magnetic flux waveforms in every distributed region are derived from the magnetic equivalent circuit (MEC) model. Based on this, each harmonic of magnetic density is obtained by adopting the fast Fourier transform (FFT) method for further calculation. Then, each harmonic eddy-current loss is computed by sinusoidal magnetic density and the total eddy-current loss in different region of motor is derived by superposing of them. Therefore, the calculated results at different speed and conduction angles of each region are analyzed. Finally, the 3D finite element (FE) model is established in software FLUX and the experimental platform of the SRM prototype is built.

Study on Control Method of Magnetic Flux Density Waveform in AC Magnetic Measurement

To estimate the magnetic properties of the magnetic material, magnetic flux density waveform (B waveform) must be sinusoidal wave. However, it is necessary to control the exciting waveform in consideration of the distortion, because voltage waveform induced by B-coil is distorted due to the magnetic properties. As a result, the IBCM can make B waveform sinusoidal wave with the least number of feedbacks than any control method. Because the IBCM performs noise cancelling for measured waveform and make accurate exciting waveform from measured waveform.

Core-Loss Analysis of Linear Magnetic Gears Using the Analytical Method

In this study, analysis of core-loss occurring in the magnetic flux modulation core of a linear magnetic gear and the core of each mover is presented, using an analytical method. Losses in electric machines were generally calculated and analyzed using the finite element method (FEM). However, in the case of core-loss, the exact loss value could not be calculated using FEM data. Therefore, we considered the harmonic component of the air-gap magnetic flux density waveform with the modified Steinmetz equation, and performed a more accurate core-loss analysis with magnetic behavior analysis. Thus, we performed a calculated core-loss characteristic comparison with the FEM and the modified Steinmetz equation.

Influence of Driving Mode on Loss Characteristics of Doubly Salient Brushless Motor With Rectangular Wire Armature Winding

The loss of a doubly salient brushless motor (DSBLM) with rectangular wire armature winding mainly includes ac copper loss, iron loss, and converter loss. The driving mode has a certain influence on motor loss. Therefore, the loss characteristics of a DSBLM with rectangular wire armature winding driven by brushless dc (BLDC) and brushless ac (BLAC) are comparatively studied in this article. First, the magnetic flux density waveforms of armature winding and stator under ideal currents drive are compared, and the waveform changes of ac copper loss and iron loss are analyzed. Second, the effect of pulsewidth modulation (PWM) on motor loss for actual operation in two driving modes is studied. Third, the converter loss of different driving modes is also considered. Finally, the theoretical analysis and simulation results are verified by the experimental results of a DSBLM. In the BLAC driving mode, a DSBLM with rectangular wire armature winding has better loss characteristics.

Electromagnetic Vibration-Prediction Process in Interior Permanent Magnet Synchronous Motors Using an Air Gap Relative Permeance Formula

Interior permanent magnet synchronous motors have the advantage of being applicable to various fields owing to their high torque density and wide operating range but have the disadvantage of large electromagnetic vibrations. To calculate the electromagnetic vibration, analysis of the magnetic flux density of the air gap using the finite element method (FEM) is essential. This process requires a significant amount of time because of the use of many analysis models. The radial force, which is the source of vibration, is expressed as the square of the air gap magnetic flux density, the vibration can be predicted in advance by calculating the waveform of the air gap magnetic flux density using a formula. In this paper, a new air gap relative permeance formula is proposed when an offset is applied to the outer diameter of the rotor to reduce electromagnetic vibration. By calculating the waveform of the air gap magnetic flux density using the proposed air gap relative permeance formula, a model with a minimum total harmonic distortion is selected. The validity of the formula was confirmed by comparing the FEM result with the waveform of the air gap magnetic flux density calculated using the proposed formula. The proposed model minimized the vibration and was confirmed using FEM. Using the proposed formula, vibration can be easily and quickly predicted in analytic way. The prototype of the final model was developed and compared using FEM, and the validity of the analysis result was confirmed.

Analysis and Modeling of Instantaneous Magnetizing Power of Ferromagnetic Cores in the Time Domain

This letter presents an approach to the analysis and modeling of instantaneous magnetizing power of ferromagnetic samples in a uniaxial magnetic field. The analysis is based on the calculation of constitutive components (absorbed and oscillatory) of this power using harmonic components of the sample's magnetic field strength. The modeling is based on Bertotti's model of power loss separation, completely in the time domain. The approach was applied to the experimental results obtained for a toroidal sample made of grain-oriented electrical steel for controlled shape of the magnetic flux density waveform at frequencies of 1 and 50 Hz. In addition to the introduction of the approach, this letter presents measured waveforms of the magnetic field and flux density to which the approach has been applied. The waveforms of the corresponding instantaneous magnetizing powers and its components as well as instantaneous power loss components are presented. The main features of the approach are also discussed.

GaN-Half-Bridge for Core Loss Measurements Under Rectangular AC Voltage and DC Bias of the Magnetic Flux Density

An accurate calculation of core losses is essential for the design of switched-mode power supplies. However, such predictions remain a challenge as core losses depend on various parameters, e.g., the waveform of the magnetic flux density, including its fundamental frequency and dc bias. To investigate the influence of dc bias, core loss measurements usually impose a dc current and, thus, dc bias of the magnetic field strength on ungapped toroid samples. However, hardware designers require the ac and dc excitation of the magnetic flux density. Therefore, this article proposes a half-bridge configuration to impose rectangular ac voltages on the core under test (CUT). By performing a pulsed operation in combination with an iteration method, the desired ac and dc excitation of the magnetic flux density can be obtained. GaN-HEMTs have been applied as they allow a printed circuit board design with low parasitic inductances and thus avoid ringing. The measurement setup is able to characterize magnetic materials at high frequencies for triangular magnetic flux density waveforms, including dc bias and different duty cycles. In addition, the influence of magnetic history on core losses can be studied, an issue usually not addressed in the literature. Moreover, the relationship between the dc bias of the magnetic field strength and the dc bias of the magnetic flux density is investigated. A simple functional approach, e.g., by using the initial magnetization curve, does not suffice to describe this relationship. Accordingly, core losses should be derived as a function of dc bias of the magnetic flux density for the results to be of practical use to hardware designers.

Acceleration technique of flux waveform control with FPGA

The magnetic flux density waveform is controlled to a sinusoidal wave for quantitative measurement in AC magnetic property measurement. The magnetic characteristics are nonlinear and it is difficult to make the magnetic flux density waveform sinusoidal. Therefore, the magnetic flux density waveform is made into a sinusoidal wave by feedback control (Kaido et al., 1998). Feedback control is performed by differential control, but in the non-linear region of high magnetic flux density, the convergence of the waveform is deteriorated and measurement time is increased.In this research, we succeeded in shortening the control time by using FPGA (Field-Programmable Gate Array) as the magnetic flux density waveform control method. The waveform control method sets various initial conditions in the PC, and is sent to the FPGA together with the target voltage waveform data. The FPGA starts feedback control from the information.The magnetic flux density was measured from 0.1 T to 2.0 T by using a single sheet tester and setting the amplitude ratio and the strain ratio to 0.5% or less using 50A1300 and 50A470. As a result, it has succeeded in significantly speeding up compared with the device which controls the waveform only with the conventional software.

Modeling of Rotating Magnetic Properties of Electrical Steel Sheet Under DC-Biased Field

As the core material of an electrical device, the electrical steel sheet is often under ac and dc-biased magnetizing conditions due to the wide utilization of power electronics. For an accurate description of rotating magnetic properties of electrical steel sheet under the dc-biased field, an improved model considering magnetic hysteresis and nonlinear magnetization characteristics is established. The reluctivity coefficients and hysteresis coefficients of the improved model are calculated from magnetic flux density and magnetic field intensity waveforms measured by the feedback control system. The accuracy and reliability of the improved model are verified by the comparison of the measured and calculated hysteresis loops of electrical steel sheet under the dc-biased field.

Iron Loss Estimation Method for Silicon Steel Sheet Taking Account of DC-Biased Conditions

One of the issues of an iron loss estimation is the modeling of an excess loss. This paper investigates the modeling method for the excess loss under dc-biased conditions. The proposed approach is based on the 1-D finite-element analysis for the silicon steel sheet in the thickness direction considering hysteretic property and skin effect. In addition, the magnetic flux density waveform is divided into the outline loop and minor loops and estimate the excess loss of each loop using the eddy current loss correction factor $\kappa $ taking account of dc-biased conditions. To demonstrate the effectiveness of the proposed method, we compare the estimated loss with measured one for the harmonic wave in single sheet tester.

Performance Comparison and Applicability Analysis of Different Armature Structures for a Small-Scale HTS Linear Synchronous Motor

High-temperature superconducting (HTS) coils could bear larger current density and produce higher magnetic field compared to permanent magnets. An HTS linear synchronous motor (LSM) with its secondary excitation system made of HTS coils can provide larger thrust force but unavoidable larger normal force. This paper focuses on the analysis and comparison of different armature structures in an HTS LSM to improve the magnetic flux waveform quality, decrease the normal force, and simultaneously maintain the thrust force. Five alternative armature structures are proposed and investigated, i.e., coreless double layer lap winding (DLLW), yokeless DLLW, coreless and yokeless DLLW, and flat winding with and without iron yoke. Three dimensional models of HTS LSMs are built and verified to compare the magnetic field and force performances of various armature structures using the finite element method. Results indicate that armatures without iron components perform better. Furthermore, the yokeless flat winding is recommended for its 81% reduction of magnetic flux harmonic component and 52% increase of thrust force compared with DLLW.

Impact of Modulator Designs and Materials on Efficiency and Losses in Radial Passive Magnetic Gear

This paper presents an analysis of efficiency for passive magnetic gear resulting from the selection of materials and structures in the magnetic circuit. A particular attention is paid to the structure of modulator, which forms the crucial element of the system, and which can be designed in a variety of ways. In this paper, the considered alternatives include a modulator design manufactured from soft magnetic composite material and from circumferentially and axially stacked lamination. Based on the experimentally determined efficiency versus load curves, the study demonstrates that the soft magnetic modulator has similar performance as for the case of a circumferentially and axially stacked lamination. The physical reasons of this result are explained by means of the finite element analysis of magnetic flux waveforms in the crucial parts of the systems.

New compensation ferrometer design

Abstract The compensation ferrometer is an instrument for the measurement of open specimen soft magnetic materials parameters at AC magnetization based on the magnetomotive force compensation method. New magnetizing process regulator that controls voltage induced in measuring winding (magnetic flux density waveform) and the voltage induced across Rogowski-Chattock potentiometer (compensation) was developed recently. This paper deals with a new compensation ferrometer design that allows taking the full advantage of the new regulator. New ferrometer based on STEMlab platform improves precision and speed of the measurement.

Core Loss Calculation in a Variable Flux Permanent Magnet Machine for Electrified Transportation

The paper is focused on the modeling and measurement of core losses in an AlNiCo-based variable flux permanent magnet machine. The application of AlNiCo as a low coercivity magnet provides the ability of the magnet flux control using short-time $d$ -axis current pulses. This allows a reduction in the machine core losses under high-speed conditions, thus improving the machine efficiency. In order to identify the machine efficiency gains, the core losses have to be accurately modeled at different magnetization levels. An advanced core loss model for the variable flux machine (VFM) is first presented. This model is based on the calculation of an equivalent sinusoidal waveform of nonsinusoidal magnetic flux density. The model is then utilized to calculate the core losses in a tangentially magnetized VFM using finite-element simulation. In order to validate the developed model experimentally, a measurement method is developed to segregate the mechanical losses and the no-load core losses at different speeds and magnetization levels for a 5-hp VFM. Finally, the proposed model accuracy is verified through a comparison with the experimentally measured core losses under a no-load condition.

Closed-Loop Control for a Rotational Core Loss Tester

In this paper, a flux density waveform controller is proposed for core loss measurements under rotating magnetic fields in the electrical steel. It is based on a vector control scheme in the synchronous dq reference frame. The proposed dq vector controller eliminates the need of commonly used harmonic compensation techniques; improving the execution and convergence times of the controller. Furthermore, it eliminates the need of filters and transformer isolators, which further reduces delays, thus improving the system's dynamic response. The performance of the controller is analyzed using simulations and validated experimentally. The proposed controller is experimentally shown to control the magnetic flux waveforms within 2% of the reference flux density signals at very high densities (up to 1.9 T) under sinusoidal conditions, and up to 1.2 T under nonsinusoidal conditions.

Tunable one-dimensional assembly of magnetic nanoparticles using oscillating magnetic fields at low frequencies for polymer nanocomposite fabrication

Tunable, one-dimensional (1D) nanofiller assembly using oscillating magnetic fields in the low frequency range (<5 Hz) is studied as a scalable and energy-efficient method to structure nanofillers within viscous matrices to deliver anisotropic, multi-functional polymer nanocomposites (PNCs). In this work 1D assembly tailoring was first experimentally studied and demonstrated using the model system of superparamagnetic iron oxide nanoparticles (SPIONs, 15 nm, 0.02–0.08 vol%) in DI water using varying magnetic fields (0–5 Hz frequency, 10–100 G magnetic flux density, and square and sinusoidal waveforms). In addition to lateral assembly of nanofillers, when the field oscillation is turned on, transverse assembly can be introduced as the magnetic moments of the particles respond to the changing fields by Brownian rotation. The degree of transverse assembly, in balance with lateral assembly and the resulting nanofiller patterns, was observed to be determined by the magnetic field parameters, magnetic responsiveness of the nanofillers, and the matrix viscosity. Based on this assembly study, PNCs consisting of ferrimagnetic iron oxide nanofillers in a thermoset polymer, with two different linear nanoparticle patterning, were successfully fabricated using small magnetic fields (<100 G) even in a viscous matrix (70 cP) with a short assembly time of 30 min. This work can contribute to scalable manufacturing and thus bulk application of multi-functional PNCs enabled by more precise nanofiller and interface structuring.

Magnetic flux waveform estimation for fast efficiency map calculation in permanent magnet synchronous motors

Magnetic flux waveform estimation for fast efficiency map calculation in permanent magnet synchronous motors