Harmonic Magnetic Field Research Articles

Analysis of Eddy Current Loss of 120-kW High-Speed Permanent Magnet Synchronous Motor

Pulse width modulation current harmonics and space harmonics are some of the major factors affecting the rotor eddy current loss of the high-speed permanent magnet motor. In this study, based on the principle of the equivalent current sheet, a two-dimensional motor model in a rectangular coordinate system was established. Considering the armature reaction, the end effect, and the current harmonics generated by variable frequency power supply, the eddy current loss of the rotor at different frequencies was analyzed and calculated using the analytical and finite element methods (FEM). When the frequency is between 200 Hz and 600 Hz, the variation trend of the rotor eddy current loss with a frequency obtained by analytical calculation and FEM analysis is roughly the same, and the error is still within a reasonable range. However, as the frequency continues to increase, the error between the two becomes larger and larger. Furthermore, based on the two-dimensional FE model, the influence of the sleeve material, the thickness, and the composite structure on the rotor eddy current loss were studied and analyzed. It was found that adding a graphene shielding layer between the permanent magnet and the sleeve can effectively shield the harmonic magnetic field, greatly reduce the eddy current loss of the permanent magnet, and effectively prevent the temperature of the permanent magnet from being too high, which is conducive to the continuous and stable operation of the high-speed permanent magnet motor.

Effects of the mechanical vibrations on the thrust force characteristics for the PMLM driven motion system

In the permanent magnet linear motor (PMLM) driven system, the unique zero-transmission structure intensifies the coupling between servo system and mechanical system. This paper presents the effects of the mechanical vibrations on the characteristics of the thrust force for the PMLM driven motion system. Firstly, the mechanical dynamic model of the direct drive system is established using Lagrange equation, and the main mechanical vibration forms are analyzed. Then, the influences of different mechanical vibrations on the distribution of air–gap magnetic field and the drive current are studied. Finally, the thrust spectrum characteristics of PMLM considering the mechanical vibrations are analyzed and verified by experiments. The results show that the mechanical vibrations will directly affect the amplitudes of the nominal thrust and the original thrust harmonics of PMLM. In addition, it will be coupled with the magnetic field harmonics and the drive circuit harmonics, which generates a large number of new thrust harmonics and worsen the thrust fluctuation and dynamic precision of the motion system.

Nonlinear amplification of the magnetic induction signal in a magnetomodulation sensor with an amorphous ferromagnetic core

The purpose of this work is to show the possibility of using a magnetic field-controlled nonlinearity of the amplitude change in an oscillatory LC-circuit containing a core made of an amorphous ferromagnetic alloy with compensated longitudinal magnetostriction, which makes it possible to obtain a high conversion coefficient of weak magnetic field sensors operating at room temperature. Methods. A practical method for constructing magnetomodulation sensors of magnetic induction with a fixed magnetic displacement field, which corresponds to the maximum steepness of the nonlinear characteristic of an oscillatory circuit with an amorphous ferromagnetic core in the region of autoparametric resonance, is considered. Results. It has been shown that the stable conversion factor of a 35 mm long sensor based on an oscillatory circuit with autoparametric amplification at a modulation frequency of 256 kHz can reach 10 mV/nT, which allows, with the available element base, to record signals of a weak alternating magnetic field with an amplitude of 0.03 pT/Hz1/2 in the frequency range 10...1000 Hz. It is noted that the excitation of the sensor by a weak harmonic magnetic field of a high frequency and the constant presence of the amorphous ferromagnetic core near the state of technical saturation significantly reduces the level of intrinsic magnetic noise of the magnetomodulation sensor. Conclusion. Magnetomodulation sensors with autoparametric amplification of the magnetic induction signal can find application in geophysics, magnetobiology and biomedicine.

Possible solution for the integer resonance crossing problem of GeV-class isochronous Fixed-Field Alternating Gradient accelerators

Fixed-Field Alternating Gradient accelerators (FFAG, also known as FFA) are promising candidates for next-generation GeV-class proton driver with average beam power of several megawatts. In isochronous accelerators, radial tunes are approximately increasing with beam energy in a linear way, and thus the integer resonance crossing problem becomes the major bottleneck of GeV-class isochronous FFAG design. In 2019, China Institute of Atomic Energy (CIAE) proposed an isochronous FFAG conceptual design with capability of producing 2GeV/6MW continuous wave (CW) proton beam. However, this conceptual design shows that the beam size is blown up at high energy region due to the third harmonic magnetic field caused by imperfections. The reason is that the integer resonance vr=3 causes a large coherent oscillation, and this large amplitude is not compatible with the following third order intrinsic resonance 3vr=10. In order to correct the large coherent motion before reaching the 3vr=10 resonance, we propose an idea of integer resonance suppressor (IRS) which intentionally introduces the third harmonic magnetic field. Our calculation shows that third harmonic field of 10Gs is acceptable with proper IRS settings, meaning that the requirements of magnet manufacture and installation can be relaxed. The increased imperfection tolerances will make magnet manufacture and installation much easier.

Mechanism Analysis of Output Fluctuation in a Three-Phase Dynamic Wireless Charging System

In a dynamic wireless charging (DWC) system, the mutual inductance between the transmitter and receiver coils may vary with the position of the receiver, resulting in a fluctuation of the output voltage. Although a three-phase DWC system can reduce output fluctuation by traveling wave magnetic field, the existing three-phase systems still cannot achieve a uniform output voltage. In order to further improve the output stability, this article analyzes the cause of output voltage fluctuation. The magnetic field generated by the three-phase transmitter coils is decomposed into the fundamental and the harmonic traveling wave magnetic fields for analysis in this article. And a new calculation method of induced voltage is proposed from the perspective of dynamic electromotive force. Then, the voltages induced by the fundamental and the harmonic magnetic fields in the receiver coil are compared, revealing that the fifth and above harmonic magnetic fields are the ultimate cause of the output fluctuation. Subsequently, two fundamental methods to reduce the output fluctuation are proposed, and the effect of the output fluctuation on the efficiency is analyzed. Finally, a prototype was built to verify the correctness of the theoretical analysis and the feasibility of the proposed output fluctuation reduction methods.

Design and Performance Analysis of Axial Flux Permanent Magnet Machines with Double-Stator Dislocation Using a Combined Wye-Delta Connection

Conventional fractional slot concentrated winding three-phase axial flux permanent magnet machines have an abundance of armature reaction magnetic field harmonics which deteriorate the torque performance of the machine. This paper presents a double-stator dislocated axial flux permanent magnet machine with combined wye-delta winding. A wye-delta (Y-△) winding connection method is designed to eliminate the 6th ripple torque generated by air gap magnetic field harmonics. Then, the accurate subdomain method is adopted to acquire the no-load and armature magnetic fields of the machine, respectively, and the magnetic field harmonics and torque performance of the designed machine are analyzed. Finally, a 6kW, 4000r/min, 18-slot/16-pole axial flux permanent magnet machine is designed. The finite element simulation results show that the proposed machine can effectively eliminate the 6th ripple torque and greatly reduce the torque ripple while the average torque is essentially identical to that of the conventional three-phase machines with wye-winding connection.

A Novel Parallel Hybrid Excitation Field Modulated Machine With Efficient Utilization of Multiworking Harmonics

In this article, a novel parallel hybrid excitation field modulated machine with efficient utilization of multiworking harmonics is proposed. The key of the proposed machine is to efficiently integrate the parallel hybrid excitation and multiworking harmonics to enhance average output torque and flux regulation capability. First, operation principle and air-gap magnetic field harmonics of the machine are investigated by using field modulated principle, which reveals the contribution of each working harmonic to flux linkage and torque. Then, performances of the machine are analyzed, such as open-circuit back-EMF, flux regulation capability, torque-speed characteristics, etc. Also, the proposed machine is compared to conventional ones for evaluation. Finally, a prototype is manufactured and tested to validate the theoretical and simulated results.

Brushless Excitation Principle and Experimental Verification of Hybrid Excitation Synchronous Generator Based on Harmonic Magnetic Field

It is well known that the air-gap magnetic field of the permanent magnet synchronous generator (PMSG) is difficult to adjust. To overcome this challenge while maintaining the brushless feature of PMSGs, a hybrid excitation synchronous generator (HESG) based on inherent third harmonic field induction is proposed in this paper. The HESG adds a set of third harmonic windings with a pitch of 1/3 of the armature winding in the stator core and a set of harmonic windings with the same pitch as the third harmonic winding in the rotor core. Due to electromagnetic induction, the third harmonic field established by third harmonic windings in the stator induces the harmonic electromotive force (EMF) of six times the frequency in the rotor harmonic winding. This harmonic EMF is directly provided to the rotor excitation winding after rectifying by the diode rotating rectifier. The HESG has armature windings and third harmonic windings in the stator, and excitation windings, harmonic windings and permanent magnets in the rotor. In this article, the mechanism of stator third harmonic winding EMF, rotor harmonic EMF, and the brushless excitation are elaborated. The experimental results of adjustable armature winding voltages with controlling the stator third harmonic winding current have proven the feasibility of the proposed brushless excitation principle based on the third harmonic.

Modelling the fluid flow, solidification and segregation behavior in electromagnetic DC casting of magnesium alloy

Making clear the metallurgical transport behaviors during direct chill (DC) casting is of great significance to control the solidified structure and reduce the casting defects, but it still remains difficult because the high temperature and the opaque of melt make them hard to observe and detect directly. Numerical modelling provides a way to reveal the physical fields involved during DC casting. The present research used a two-dimensional axisymmetric model which coupled the heat transfer, fluid flow, solidification and species transfer in order to study the effect of different magnetic fields (harmonic magnetic field (HMF), pulsed magnetic field (PMF) and out-of-phase pulsed magnetic field (OPMF)) on the flow pattern, solidification characteristic and solute distribution in the electromagnetic DC casting of magnesium alloy billet having the diameter of 500 mm. The results show that when the magnetic field is on, there are the desirable variations including the homogenous temperature profile and faster solidification rate, as well as the alleviated central negative segregation and the reduced whole segregation level on the cross section of the billet. For the different magnetic fields, OPMF shows the strongest stirring effect, leading to the highest solidification rate at the initial solidification stage. Furthermore, the central negative segregation and the segregation level along the cross section are alleviated most as compared to other magnetic fields.

High-Frequency Motor Modeling by Harmonic Magnetic Field Analysis Considering Magnetic Saturation and DC Bias Magnetic Field

High-Frequency Motor Modeling by Harmonic Magnetic Field Analysis Considering Magnetic Saturation and DC Bias Magnetic Field

Towards Understanding the Interconnection between Celestial Pole Motion and Earth's Magnetic Field Using Space Geodetic Techniques.

The understanding of forced temporal variations in celestial pole motion (CPM) could bring us significantly closer to meeting the accuracy goals pursued by the Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG), i.e., 1 mm accuracy and 0.1 mm/year stability on global scales in terms of the Earth orientation parameters. Besides astronomical forcing, CPM excitation depends on the processes in the fluid core and the core–mantle boundary. The same processes are responsible for the variations in the geomagnetic field (GMF). Several investigations were conducted during the last decade to find a possible interconnection of GMF changes with the length of day (LOD) variations. However, less attention was paid to the interdependence of the GMF changes and the CPM variations. This study uses the celestial pole offsets (CPO) time series obtained from very long baseline interferometry (VLBI) observations and data such as spherical harmonic coefficients, geomagnetic jerk, and magnetic field dipole moment from a state-of-the-art geomagnetic field model to explore the correlation between them. In this study, we use wavelet coherence analysis to compute the correspondence between the two non-stationary time series in the time–frequency domain. Our preliminary results reveal interesting common features in the CPM and GMF variations, which show the potential to improve the understanding of the GMF’s contribution to the Earth’s rotation. Special attention is given to the corresponding signal between FCN and GMF and potential time lags between geomagnetic jerks and rotational variations.

Torque ripple optimization for synchronous reluctance motors based on a virtual permanent magnet harmonic machine model

The torque ripple is affected by both the stator and the rotor magnetic field harmonics. In synchronous reluctance motors (SynRM), there are only rotor permeance harmonics existing on the rotor side for the absence of the rotor windings. Since the asymmetric rotor flux barriers are widely applied in the SynRM rotor, it is difficult to calculate the rotor permeance accurately by the analytical method. In this article, the effects of the rotor permeance harmonics on the air-gap magnetic field are studied by a virtual permanent magnet harmonic machine (VPMHM), which is a finite-element (FE) based magnetostatic analysis model. The air-gap flux density harmonics produced by the SynRM rotor are extracted from the VPMHM model and used as the intermediate variables for the torque ripple optimization. The proposed method does not need to solve the transient process of motor motion. Hence, the time of the optimization process can be significantly shortened. Finally, a full electric cycle is simulated by dynamic FE simulation, and the torque ripple is proved to be effectively reduced.

Magnetic Field Optimization and Tolerance Study of a Medical Superconducting Cyclotron

SC200 cyclotron is a compact superconducting cyclotron for proton therapy developed by the ASIPP (Hefei, China)-JINR (Dubna, Russia) collaboration. In this paper, some beam dynamics simulations are done to evaluate the magnetic field of SC200 measured by mapping system. Magnetic field is optimized by shimming bars and coils to make sure beam can be accelerated to the entrance of extraction system. The optimization of isochronism of magnetic field, beam radial oscillation caused by imperfect first harmonic of magnetic field, magnetic vertical focusing force and radial magnetic field at median plane are presented. The tolerance of imperfect average magnetic field bump and radial magnetic field are studied by beam dynamics simulation.

Experimental Investigation of Nonlinear Standing Waves in DC/VHF Hybrid Capacitive Discharges

It is recognized that in very-high-frequency capacitively coupled plasma (VHF CCP) reactors, the standing wave effects can be enhanced by the presence of nonlinear higher harmonics self-excited by the plasma series resonance (PSR). In this work, we investigated the influence of the dc bias on the excitation of the nonlinear standing waves in a parallel-plate capacitively coupled dc/VHF (60 MHz) hybrid discharge sustained in argon, with both the dc source and the VHF source applied to the top electrode. A hairpin probe was employed to determine the axial/radial distribution of the electron density, while a high-frequency B-dot probe was used to measure the radial distributions of the harmonic magnetic field and the harmonic current density. With no dc bias applied, the nonlinear standing wave excitation was observed to be predominant; the high-order harmonic current density exhibited a main peak at the electrode center and one or more minor peaks between the electrode center and the edge, leading to a center-high electron density profile. With the addition of the dc source, the harmonic excitations and the corresponding nonlinear standing wave effect tend to be suppressed with the increase of dc bias, resulting in improved plasma uniformities. Underlying mechanisms of the suppression effect of the dc bias on the nonlinear standing wave excitation were analyzed.

Analysis and Compensation of Hall Sensor-Based Position Detection Errors in TPMSLM

The air gap flux density in tubular permanent magnet synchronous linear motor can be approximated as a sine function related to mover position. Therefore, analog hall sensors are used to measure flux density and detect motor position. This technique exhibits the advantages of low cost and small installation volume. The major drawback of this technique is that many interference factors (e.g., magnetic field harmonics and assembling tolerances) degrade position detection accuracy. To compensate for position detection errors, the influences of interference factors on the magnetic field model are analyzed, and a unified formula for position estimation error is derived. A compensation algorithm based on the Luenberger observer and an Adaline neural network (ANN) is further proposed. The Luenberger observer is utilized to estimate raw position, and ANN is used for error compensation. In the experiments performed on a prototype motor, the proposed method is compared with typical algorithms under different operating conditions. Experimental results validate the effectiveness and robustness of the proposed method. The position estimation error of the proposed method is within 120 $\mu \text{m}$ under different operating conditions.

Reversal of domain walls drift direction in a low-frequency magnetic field in iron garnet crystals

The reversal of domain walls (DWs) drift direction in (110) iron garnet plate with shape anisotropy with an increase of the amplitude of an alternating harmonic magnetic field was established experimentally. The harmonic magnetic field H = H0sin(2πft) (f = 3–1000 Hz, H0 up to 2.2⋅104 A/m) was applied perpendicular to the plane of the sample. The DW drift velocities and intensities of nucleation centers of magnetic dislocations (MDs) were measured. It is proposed that the reason for the reversal of direction of the DW drift is a change of direction of the gradient of demagnetizing fields in the sample with an increase of the external field amplitude. The change in configuration of an internal magnetic field is indicated by the experimentally established change in the activity of MD nucleation centers with the increase of the external field amplitude. A model is proposed in which direction and speed of DW drift are determined by magnetic field gradient in the sample.

Zonal harmonics of solar magnetic field for solar cycle forecast

According to the scheme of action of the solar dynamo, the poloidal magnetic field can be considered a source of production of the toroidal magnetic field by the solar differential rotation. From the polar magnetic field proxies, it is natural to expect that solar Cycle 25 will be weak as recorded in sunspot data. We suggest that there are parameters of the zonal harmonics of the solar surface magnetic field, such as the magnitude of the l=3 harmonic or the effective multipole index, that can be used as a reasonable addition to the polar magnetic field proxies. We discuss also some specific features of solar activity indices in Cycles 23 and 24.

Magnetoactive Soft Drivers with Radial-Chain Iron Microparticles.

Magnetoactive elastomers (MAEs), one kind of typical novel magnetoactive driver applied in the soft robotic area, have become one of the research hotspots as they can provide biologically friendly driving methods with safe, preprogrammed, and easy-to-implement properties. In this study, novel MAEs embedding soft magnetic iron microparticles with radial chains, which can be molded in one piece, achieve 3D deformation, and co-work between multiple MAEs under single homogeneous stimuli, are proposed. Then, two kinds of novel magnetoactive drivers are established based on the proposed MAEs, which can achieve the synchronous pumping behavior of heart and the extension behavior of muscle under applied homogeneous magnetic fields. The experimental data show that (1) for the pumping behavior, the maximum instantaneous flow rate and total pumping volume can reach 200.1 and 52.3 mL/min, respectively, under 120 BPM applied harmonic magnetic field with 0-300 mT amplitude; (2) the muscle extension behavior can achieve a strain of 0.925 without a loading mass and carry a load of 40 times its own weight with a pronounced dynamic movement. It should be emphasized that the behavior of the proposed magnetoactive drivers can be excited by remote homogeneous magnetic fields, and it has great application potential in biomimetic or bioinspired soft driving systems.

Modulating the polarization of broadband terahertz pulses from a spintronic emitter at rates up to 10 kHz

Reliable modulation of terahertz electromagnetic waveforms is important for many applications. Here, we rapidly modulate the direction of the electric field of linearly polarized terahertz electromagnetic pulses with 1–30 THz bandwidth by applying time-dependent magnetic fields to a spintronic terahertz emitter. Polarity modulation of the terahertz field with more than 99% contrast at a rate of 10 kHz is achieved using a harmonic magnetic field. By adding a static magnetic field, we modulate the direction of the terahertz field between angles of, for instance, −53° and 53° at kilohertz rates. We believe our approach makes spintronic terahertz emitters a promising source for low-noise modulation spectroscopy and polarization-sensitive techniques such as ellipsometry at 1–30 THz.

Development of a high precision small aperture quadrupole magnet with copper plate coils

Using the conventional coil manufacturing method, the iron core of a small aperture quadrupole magnet needs to be divided into four or more segments to install the excitation coils, which brings assembly errors and generates high-order magnetic field harmonics. In this paper, the development of a high-precision small-aperture quadrupole magnet named HQ22 using copper plate coils is described. The magnet has a bore aperture of 22 mm, a gradient of 90 T/m, and an effective length of 0.36 m. Its coil is mainly composed of a number of U-shaped copper plates, electrical connection sheets, and insulating sheets, which are directly assembled and connected on the pole. Outside the coil, water box with cooling water channel inside is installed to provide indirect cooling to the coil. Using copper plate coil, one-piece or two-piece structure can be adopted for the iron core, so the assembly error is reduced and magnetic field quality can be improved. The research provides an attractive technical scheme for small aperture quadrupole magnets in future light sources. The detailed magnet design, magnetic field calculation and measurement results of HQ22 are presented, and the application prospect of copper plate coil is discussed.