The 50 most-cited articles in IEEE Transactions on Magnetics, 2020

Oil and gas pipelines transport and distribute large quantities of oil products and natural gas to industrial and residential customers over a long distance. However, pipeline failures could lead to enormous hazards and safety issues. Metal loss, due to corrosion, is a significant cause for pipeline failures. To detect and quantify metal loss, in-line inspection (ILI) is carried out periodically to assess the integrity of the pipeline. Among all the ILI techniques, magnetic-flux leakage (MFL) is the most popular one due to its high efficiency, robustness, and good applicability to both oil and gas pipelines. This article provides a comprehensive review of the pipeline corrosion assessment with the MFL technique from the data analytic perspective. The analyses of the MFL signal and data contribute to both corrosion quantification and prediction. In this article, the state of the art for the MFL measurement technique is briefly reviewed first. For corrosion quantification, the signal processing methods together with the characterization models, which aim to enhance the measurement and…

Rare-earth permanent magnets (RE-PMs) are widely used in high-efficiency and high-torque density electrical machines. However, in recent years, the exclusive and unstable supply of rare-earth elements (REEs) is a major concern to substitute RE-based electrical machines by less or even no RE alternatives. Ferrite (Fe) PMs as the least expensive PMs show promising opportunities for designing low-cost non-RE electrical machines. This article reviews some relevant works on Fe-based machines, which generally have been conducted to replace RE-based machines. Fe-based machines, including PM brushless, PM-assisted synchronous reluctance, PM flux switching, and PM Vernier machines, are introduced and their main design challenges, such as low PM energy product and vulnerability to irreversible demagnetization, are addressed. In addition, a comparison of RE- and Fe-based machines reveals that when both cost and efficiency are the major concerns, Fe-based machines can be a good successor to RE-based machines.

The commutation torque ripple of a brushless dc motor (BLDCM) in a six-step driving mode generates vibration noise. To minimize the commutation torque ripple of the BLDCM, this article analyzes the cause of torque ripple and establishes the model of torque ripple suppression by using the phase current predictive method based on the trapezoidal back electromotive force (EMF). In addition, based on the prediction model of the non-commutation phase current, the pulsewidth modulation model predictive control (PWM-MPC) algorithm is proposed. By changing the duty cycle with prior evaluation, the predictive control avoids commutation current hopping, thereby reducing torque ripple during commutation. This control approach is more accessible to be implemented, because it does not require changing the topology of the motor driving circuit. Simulation models of the proposed control scheme constructed in the MATLAB/Simulink environment are given, compared with the conventional square-wave driving method. Moreover, experiments are performed to verify the feasibility. The output torque during…

This article proposes the use of transfer learning for the deep neural network to reduce the computing cost of the topology optimization of electric motors based on a genetic algorithm (GA). The average torque and torque ripple values are shown to be accurately inferred by the transfer learning with small learning data. The individuals on the Pareto front are only evaluated by the finite-element method, while others are fast evaluated only by convolutional neural networks (CNNs). The proposed method makes it possible to reduce the computing cost to less than 15% of the conventional topology optimization method.

Because the synchronous reluctance motor (SynRM) does not require a rare-metal-based permanent magnet (PM), the demand for SynRMs is progressively increasing because of the inexpensive design. However, due to the disuse of the PM, the average torque of the SynRM is much lower than that of an interior PM synchronous motor. Although many shapes of the flux barrier have been reported for the improvement of the torque characteristics, most of them are derived from the shape optimization method. Since the topology of the rotor and stator core is fixed during shape optimization, there is the possibility of further improving the torque performance using topology optimization (TO). Furthermore, it is very important to reduce the iron loss as well as to improve the torque characteristics to improve the SynRM efficiency. In this article, a sensitivity analysis of the iron loss using the adjoint variable method is proposed. The procedure is successfully implemented for a TO based on a level-set method, and design optimization of the SynRM for reducing iron loss as well as improving the torque…

Reduction of the cogging torque is preferred during the design process of a permanent magnet (PM) synchronous machine (PMSM), especially in the low-speed traction applications. This article presents a dual-skew magnet technique to minimize the cogging torque in the axial-flux permanent-magnet (AFPM) motor with a yokeless and segmented armature (YASA). The theoretical expression of the cogging torque of the AFPM machine is deduced, and the advantages of the dual-skew magnet are verified by comparing with a sector shape magnet and a conventional skew magnet using the 3-D finite-element method (FEM). The simulation results show that, compared with the other two magnet topologies, the machine equipped with the dual-skew magnet shows its advantages in the reduction of cogging torque, torque ripple, and magnet eddy current loss.

In this article, a novel exterior-rotor multiple teeth enhanced-torque switched reluctance motor (SRM) is proposed, which exploits permanent magnets (PMs) inside the end teeth of the neighboring stator poles. First, the topology of the proposed motor, namely PM-SRM, is introduced and its working principle is illustrated. Then, based on the magnetic equivalent circuit (MEC) of the motor, it is proven that the PMs contribute to increase the air-gap flux density and regulate the stator poles flux density. As a result, the output torque of the motor is increased as well. The electromagnetic analyses of the proposed PM-SRM are performed using 3-D finite-element analysis. To validate the improved performance of the proposed PM-SRM, it is compared with its PMless counterpart and a classical 12/10-pole SRM in terms of the output torque and power, losses, and efficiency. It is shown that the proposed motor outperforms the two compared motors in terms of the output power and torque, and efficiency. Finally, a prototype of the motor is fabricated and tested to evaluate the predicted results.…

In this article, a new method for predicting efficiency maps of electric motor drives is proposed using deep learning (DL). Since many operating points need to be simulated using finite-element (FE) analysis to estimate the efficiency map of a single motor drive topology with certain geometry dimensions and materials, incorporating the whole efficiency map into the design optimization process is an overwhelmingly time-consuming task and may be impossible, depending on the availability of computational resources. Therefore, two DL network architectures are employed in this work to quickly and accurately predict efficiency maps. In the first architecture, the two important stages of efficiency map calculations, i.e., the flux linkage maps and the torque-speed envelopes, are replaced by a combination of recurrent and feedforward neural networks to account for geometric and operating point variations. For the second architecture, an end-to-end DL model was trained to predict the same efficiency maps. The output of the proposed methods has a good match with that of the FE solution,…

The computational cost of topology optimization based on the binary particle swarm optimization is greatly reduced by the use of deep neural networks (DNNs). A first convolutional neural network (CNN) is trained with data coming from finite-element analysis (FEA) with the aim of correctly estimating the output quantity (a motor torque in the proposed case study). A second CNN is trained to give as output the boundary conditions [(BCs), expressed in terms of fields or potentials] to be used as BC of a reduced finite-element method (FEM) model, created in order to still be able to give the correct value of the output quantity. In the optimization phase, the torque properties are evaluated by the trained CNN, and only a reduced percentage of cases are reevaluated by either the full FEM model or the reduced FEM model. The overall computational time of the optimization procedure is significantly reduced.

This article reviews the ferromagnetic hysteresis, magnetomechanical, and Barkhausen properties of magnetic materials and presents an integrated model to describe these effects and the underlying mechanisms that cause these effects. Hysteretic properties of ferromagnets, such as permeability, coercivity, remanence, and hysteresis loss are known to be sensitive to external factors including applied stress, temperature, and heat treatment, and internal factors like residual strain, microstructure, grain size, and anisotropy and the presence of precipitates of a second phase, such as iron carbide in steels. It thus becomes imperative to characterize the effect of these factors on the hysteresis parameters. Currently, several models such as Preisach, Stoner-Wohlfarth, and Jiles-Atherton are used to describe the magnetic hysteresis of ferromagnetic materials. We review here the quasistatic Jiles-Atherton hysteresis model which describes hysteresis in terms of domain wall motion enabling a connection to be made to the physical response of the magnetic material. This model has been…

This article proposes an optimal scheme for an interior permanent-magnet synchronous motor (IPMSM) in electric vehicle drive system using novel model predictive torque control (MPTC) algorithm. A single optimal voltage space vector (VSV) is applied with a two-level voltage source inverter in the conventional MPTC. An improved MPTC is presented to reduce the drawbacks with satisfied torque reaction performance without adding the sampling time. First, set switching table to alleviate the calculated complexity which decreasing the selection of the appropriate VSVs. Second, optimize the duty cycle to restrain the torque ripple. Finally, the conventional MPTC and the proposed MPTC are compared in the aspects of torque and flux ripples, current harmonics, and computational level in the experiment using dSPACE.

An approach for optimizing the rotor shape of a variable reluctance (VR) resolver is presented. In the optimization, the shape of the rotor is described with Fourier series. The Taguchi optimization method, combined with a finite-element method (FEM), is used to calculate the value of the objective function of the VR resolver and make the error of the angular position of the VR resolver to be minimum. The VR resolver with three-pole pairs is used as an example to show the effectiveness of the optimization approach.

This article presents the simultaneous magnetic and structural topology optimization of a transverse laminated synchronous reluctance machine rotor using a solid isotropic with material penalization (SIMP)-based approach with the globally convergent method of moving asymptotes (GCMMA) optimization algorithm. Magneto-structural single and multi-objective optimization formulations are presented. The single objective formulation maximizes the average torque subject to constraints on torque ripple, Von Mises stress, and compliance. The multiobjective formulation simultaneously maximizes average torque and minimizes compliance subject to constraints on torque ripple and Von Mises stress. In both optimization formulations, the electrical steel densities in the rotor mesh elements are the control variables. Including stress and compliance in the optimization formulation ensures a structurally feasible design. The design-dependent centripetal force contributed by each element in the rotor mesh is considered dependent on its density and mass. An intermediate density material issue is…

Smaller and lighter motors are needed to be used for cooperative robots, which are becoming a recent issue among articulated robots. In order to make the motor small, the axial length must be reduced within a limited diameter, so a reduction in the length of the core lamination and the winding end length must be considered. However, loss and thermal analysis are essential in the design process, as loss increases to meet output with excessive volume reduction and may consequently increase temperature severely. In this article, the magnetic performance for various analytical models studied to reduce the axial length is invested, and the thermal behavior is predicted by the analytical lumped-circuit method. A model with the tradeoff between the low temperature rise and high magnetic performance among several analytical models is selected. The magnetic characteristics and predicted temperature rise are compared to the measured results and found to be quite consistent.

Developing a permanent magnet synchronous machine (PMSM) for direct-drive electric vehicle (EV) has challenges such as obtaining high torque density and low torque ripple. The PMSM should have high pole numbers owing to low-speed operation, thereby increasing the use of rare earth magnets and cost. Therefore, in this article a consequent pole (CP) rotor topology is proposed in which the permanent magnet (PM) volume is reduced when compared with conventional surface PMSM (SPMSM). However, replacing south poles in an SPMSM with induced steel poles can increase torque ripple and reduce torque density. In order to improve torque density in a CP PMSM, structural modifications such as multilayer windings and non-ferromagnetic barriers have been proposed in the literature. These modifications increased the torque density while increasing the torque ripple. Therefore, this article proposes a novel two-level optimization method based on gradient descent algorithm, to address the challenges of improving torque density and reducing torque ripple simultaneously in a CP PMSM. Initially, an…

Spinel ferrite nanoparticles are widely studied to evaluate their suitability in many applications. Magnetic, electrical, optical, and catalytic properties of spinel ferrites nanoparticles depend on: i) intrinsic property such as cation distribution among tetrahedral (A-site) and octahedral ligand (B-site) sublattices in spinel structure and ii) extrinsic properties such as specific surface area and particle size distribution of nanoparticles. To enhance the above properties by modifying both the intrinsic and extrinsic parameters, narrow size distributed Mg0.7Zn0.3Fe2O4 mixed spinel ferrite nanoparticles are synthesized by the solvothermal reflux method using high boiling point reflux solvents. The particles are crystallized in a cubic spinel structure and are single crystallites with an average particle diameter of 12 nm, measured from an electron micrograph. The temperature-dependent dielectric constant $(\varepsilon^{\prime})$ and dielectric loss $(\varepsilon^{\prime \prime})$ of the sample show no change below 290 °C and increase with temperature up to 450 °C. Both…

This article proposes a new equivalent magnetic network (EMN) model for predicting the performances of interior permanent magnet (IPM) machines. The proposed EMN model incorporates the features of high accuracy and low time consumption in the reluctance network model and the magnetic equivalent circuit model, respectively, to achieve a tradeoff between the time consumption and calculation accuracy. A new air-gap model is also presented to make the dynamic analysis of the machine more efficient and easier. Moreover, the modeling approach of the rotor provides a standard for the modeling of IPM machines with permanent magnets (PMs) at different locations and of different shapes. In addition, the proposed EMN model takes into consideration the influence of flux leakage and iron saturation. Finally, the example machine is chosen, and the effectiveness of the EMN model is verified by comparison with the finite-element analysis and experimental tests.

Large dc current is typically measured by an open-loop sensor without a magnetic core. The widely used configuration uses a differential magnetic sensor inserted into the busbar hole or a differential magnetic sensor placed on the upper and lower surfaces of the busbar. The use of a differential sensor has the advantage of being resistant to external magnetic fields. In this article, a new differential ultra-small magnetic sensor with the size of 23.2 mm × 16.5 mm × 7.2 mm is designed. The sensor is based on tunneling magnetoresistance (TMR) and is placed on the upper surface edge of the busbar. The supply voltage is 5 V, the rated current measurement range is ±150 A, and the peak current measurement range is ±250 A, corresponding to 2.5 ± 2 V output at ±250 A dc peak current. The relative accuracy is less than ±1% at 25 °C and is less than ±2% over the full temperature range from -40 °C to 105 °C.

In permanent-magnet synchronous motor (PMSM), the winding current consists of different orders of harmonics due to the manufacture error, deadtime, and disturbances. This article proposes a winding current harmonic suppression method for PMSM by reducing the dominant fifth- and seventh-order current ripples. First, with reference frame transformation, the fifth- and seventh-order current ripples convert to sixth-order ripples in the synchronous reference frame (SRF). Then, with further transformation, these sixth-order ripples turn to dc signals. Next, the type-II Chebyshev filter is designed to extract these dc signals. Also, the proportional-integral (PI) controller is adopted to generate the current harmonic control voltage, which is setting the dc current harmonic signals reference to be zero. Finally, the current harmonic control voltage is compensated to the voltage reference in the SRF. Both the simulation and experimental results are presented to verify the effectiveness of the proposed method.

Conventional coreless linear permanent-magnet (PM) synchronous motors have been used commonly in various applications in industry. In this article, coreless double-sided PM linear motor design alternatives are proposed with a novel track structure with less magnets. A linear motor design with conventional coreless PM linear synchronous motor (PMLSM) is provided as a benchmark. Detailed 3-D finite-element analysis simulations for the proposed new track structures are presented with conventional linear motor design data. A thorough performance comparison is also presented. A prototype motor of a promising track design is built and tested. It is shown that the design data and test results are in good agreement, and the proposed alternative track design could be a decent low cost and relatively high force density solution for some applications.

The magnetic fluid seal is widely used in the high-speed mechanical devices. Also, the temperature of the seal increases with the viscous heating under the high shearing rate in the magnetic fluid. However, the influence of the temperature on the sealing performance has not been studied quantitatively in the available research. In this article, the change rule of magnetic fluid temperature and the influence on the sealing performance are researched through the simulation and experiment methods. The thermal field simulation is conducted with the heat generation in the fluid. To calculate the decrease of the magnetic properties quantitatively, the magnetization curves under different temperatures are measured to carry out the relationship between the saturation magnetization and temperature. Based on the magnetization curve result, the two-phase flow between air and magnetic fluid is solved under different shaft rotation speeds with the influence of temperature change. Besides, the sealing experiment is conducted with the highest rotation speed of 8000 rpm. The results of the…

Permanent-magnet synchronous hub motors (PMSHMs) have been investigated for electric vehicles. However, there are some challenges such as effective cooling and radial force. As PMSHMs are installed on the wheels, the radial force will directly affect the ride comfort of the vehicle. This article presents the analysis and optimization of the radial force for PMSHMs. The radial force densities of the symmetry and asymmetry PMSHMs are analyzed first. It is found that the symmetry PMSHMs have balanced force, while the asymmetry PMSHMs normally have big unbalanced radial force and vibration. To reduce the radial force of the asymmetry PMSHMs, an improved sequential Taguchi optimization method (ISTOM) with mixed orthogonal array is presented for an asymmetry PMSHM in this article. It can be found that the proposed method is efficient and can significantly reduce the radial force of the hub motor.

In the conventional flux reversal permanent magnet (FRPM) machine, half of the permanent magnets (PMs) produce the leakage flux at each operation moment, which results in poor utilization of magnets. In order to improve the magnetic flux utilization in the FRPM machine, this article proposes a novel consequent-pole FRPM machine topology with Halbach array magnets in the top of rotor slot, where Halbach array magnets in the rotor slot are employed to guide the flux into the rotor teeth to reduce the leakage flux. Therefore, compared with the conventional FRPM machine, the proposed counterpart exhibits larger back-electromotive force (back EMF) and torque density. In this article, the structure and operation principle of the proposed FRPM machine are investigated based on a classical 12-slot/17-pole FRPM machine topology. Furthermore, the electromagnetic performances of the proposed machine, including back EMF, electromagnetic torque, losses, flux-weakening, and overload capabilities are obtained and compared with the conventional machine by the finite-element method (FEM).

Permanent magnet Vernier machine (PMVM) has received more and more attention, due to its high torque density at low rotation speed. This article proposes a dual-stator hybrid excited PMVM with Halbach-array permanent magnets (PMs). The proposed machine can achieve high torque density with consequent-pole Halbach-array PMs in the rotor and has good flux regulation capability and high power factor. First, the basic principle of the proposed machine is discussed, and the proposed machine can be regarded as a combination of two machines. Finite-element analysis simulations are performed to verify the performance. Moreover, the influence of different parameters on the torque density, flux regulation capability, and power factor is analyzed. The results demonstrate the effectiveness of the proposed machine.

A large circular transmitter (power pad) is often utilized for inductively wireless charging so that the power receiver can position itself freely within the power pad. However, the uneven magnetic field distribution leads to the impedance mismatch and the variable transferred power due to the misalignment between a receiving coil and a relatively large transmitter coil. In this paper, the effects of the turn numbers, trace spacing, and coil size on the uniformity of magnetic field distribution over a planar spiral coil (PSC) are investigated based on an analytical model. Then, the genetic algorithm is used to optimize the trace width and spacing of a ten-turn PSC with the fixed outer and inner diameters, whereas the magnetic field is numerically calculated by HFSS software. The geometrically optimal PSC is obtained with the trace width approximately equal to trace spacing for each turn by minimizing the coefficient of variation (COV) of magnetic field within an effective charging area over the coil. The results showed that the simulated and measured COVs of magnetic field were…

Spin-transfer torque magnetic random-access memory (STT-MRAM) is the most promising next-generation memory technology that combines the advantages of mainstream memory technologies, such as SRAM, DRAM, and flash. In the STT-MRAM, a magnetic tunnel junction (MTJ) is used as a bit-cell to store the data, and its magnetic properties have a critical role in thermal noise-aware STT-switching operations. This work analyzes the impact of MTJ material and geometric parameter variations, such as saturation magnetization (MS), magnetic anisotropy (HK), damping factor (α), spin polarization efficiency factor (η), oxide thickness (tOX), free layer thickness (tF), tunnel magnetoresistance (TMR), and cross-sectional area of free layer (AF) variations on write error rate (WER) and read disturbance rate (RDR) for reliable write and read operations, respectively. To evaluate the scalability of MRAM devices, we investigate both WER and RDR with a wide range of MTJ diameters between 90 and 30 nm, which corresponds to mainstream technology nodes from 40 up to 14 nm advance node. In our work, the…

Due to the complex spatial magnetic field distribution and the variable motion mode, the torque analysis of spherical motors is usually carried out by the finite-element method (FEM) with a large amount of calculation and time consumption. In order to improve analysis efficiency, this article proposes a spherical motor torque calculation method based on the permanent-magnet surface current model and Lorentz force, aiming to replace the finite-element calculation. First, the equivalent surface current analytical expression of the rectangular permanent-magnet magnetic field is derived. Then, this expression is used to establish the 3-D magnetic field analytical model of Halbach array permanent magnets in the rotor. Based on this magnetic field, the Lorentz force of the energized stator coil is calculated. Then, the electromagnetic torque generated by the rotor is analyzed. Finally, the analytical results of the magnetic field and the motor torque are compared with those by the FEM and experiments, verified that, under the premise of ensuring the calculation accuracy, the proposed…

The development of traditional permanent magnet synchronous machines (PMSMs) in electric vehicle (EV) industry is limited by the unalterable permanent magnet (PM) excitation field. Variable-flux PMSMs are considered as a good candidate for EV propulsion for their ability to operate in a wide speed range with high efficiency by manipulating the magnetization state dynamically. A novel hybrid-PM variable-flux PMSM with series-parallel magnetic circuits is proposed in this article. The structure and operating principle of the proposed machine are introduced. The electromagnetic performances of the proposed machine are analyzed and compared with the series-connected and parallel-connected variable-flux machines, and the proposed machine combines the advantages of these two kinds of machines. The inductance characteristics of the proposed machine are analyzed by frozen permeability method (FPM), and the variation laws of inductance are quite different in different magnetization states and load conditions. The torque capacity of the proposed machine is analyzed. The torque ripple can be…

This work provides a new approach for modeling the electromagnets of the magnetic levitation (Maglev) vehicle Transrapid intending to effectively and efficiently represent the statics and the dynamics in a frequency range relevant for Maglev control design and for the use in mechatronic simulation models. It includes the effects of magnetic reluctances, fringing and leakage flux, magnetic saturation, and eddy currents. The modeling follows a systematic approach by setting up the equivalent magnetic and electric circuits, and coupling the equations using Ampère's circuital law and Faraday's law of induction resulting in a system of differential algebraic equations. It allows to study effects occurring in the magnet design process or different operating points, resulting, e.g., from aerodynamic uplift, for which an extended validity range is needed. Since the computational effort of such models is significant, additionally, a numerical procedure for model reduction is presented yielding a simplified version, which possesses a nearly identical input-output behavior and is usable for…

Magnetorheological fluid (MRF)-based rotating torque transmission devices are gaining popularity such as MR brake and MR clutch. The effectiveness of the developed devices reduces due to thermal thinning behavior such as a decrease in strength at high temperature of MRF. To design MR devices such as MR clutch and MR brakes, it is necessary to maintain the strength of MRF at the higher temperature. Since MRF is the main component of MR devices, the synthesis of good quality MRF is a prime concern. In this research article, the role of graphite flakes on the strength of MRF at high temperature and its rheology is investigated. In this article, the effectiveness of graphite flakes is tested on MRF by selecting different weight fractions. MRF and MRF with graphite flakes (MRFG) have been synthesized with carbonyl iron particles (80 wt%) and graphite flakes (0.5, 1, 2, 3, 4, and 5 wt%). MRF and MRFG are characterized or evaluated by the rheometer. The rheological properties of MRF and MRFG have been examined using rotational tests. Results show the effective use of graphite flakes in…

For continuous or spiral windings which feature multiple continuously transposed conductors (CTC) wound in parallel, the transposition structure is commonly used to suppress circulation between conductors. This introduces a local asymmetry in transformer windings. Fault analyses have shown that building an asymmetric structure in transformers increases deformation risk in these windings. Researchers have yet to fully investigate this asymmetric structure. This study was conducted to observe the influence of transposition structure in a 110 kV transformer. The conductor's relative position forms three patterns during the transposition process; two parameters are established to describe the position-changing process. A finite-element method (FEM) model is built to investigate the magnetic field and electromagnetic force distributions. The results indicate that the transposition structure distorts the magnetic field distribution. The maximum distortion factor of the axial component of magnetic flux density (Bz) along the axial direction caused by the transposition structure is 14.6%.…

Electromagnetic vibration is excited by the electromagnetic force waves generated by the air-gap magnetic field acting on the machine core. In this article, a fast and accurate calculation method of radial electromagnetic force density of surface-mounted permanent-magnet synchronous motors (SPMSMs) is proposed, and the radial force density including amplitude, frequency, and order is obtained. Comprehensively considering that the effect of the PM segmentation on electromagnetic force waves, cogging torque, and the no-load back electromotive force (back EMF), the optimal determination of the number of PM segmentation in different slot-pole combinations of SPMSMs is summarized, and six slot-pole combinations of SPMSMs with 6p36s, 4p36s, 6p9s, 8p9s, 8p12s, and 10p12s are calculated and analyzed to verify the universality of the conclusions, which lays a theoretical foundation for the weakening of the radial electromagnetic force.

In this article, a new low-cost small-scale three-phase brushless motor topology is proposed. This is a new topology for self-excitation of brushless wound rotor synchronous motor investigated initially for rated speed. For brushless excitation, the stator is designed to contain two windings, namely, three-phase armature winding and exciter winding. The rotor consists of two windings, that is, harmonic winding and field winding, and a diode rectifier. An inverter feeds the three-phase armature winding which is connected in series through an uncontrolled three-phase rectifier to a single exciter winding. When the current is supplied from the inverter, both the armature and exciter windings are energized eventually producing a flux in the air gap. Since the flux produced by the exciter winding is not synchronized with the field winding, it produces a harmonic to be intercepted by the harmonic winding on the rotor. Eventually, the voltage produced in the harmonic winding is used to feed dc current to the field winding for brushless operation. The results obtained by 2-D finite-element…

Multi-degree-of-freedom (MDOF) magnetic bearings have been widely investigated and designed for various applications. However, a new design magnetic bearing cannot be directly used without optimization due to the not relatively excellent performance. Besides, there may be a lack of consideration of the interaction of parameters in the design process. Hence, in this article, a three-degree-of-freedom hybrid magnetic bearing (THMB) is optimized as an example. First, a comprehensive sensitivity analysis is carried out to show the relationship between the parameters and optimization objectives in detail. Second, a cross-factor variance analysis is considered due to the possibility of parameter interaction. And then, a hierarchical multi-objective optimization structure is used with the Kriging model and the non-dominated Sorting Genetic Algorithm II (NSGA II). The simulation results verify the validity of the proposed method, and the prototype is under manufacture for further evaluation.

In this article, four novel approximate full-adder (AXFA) circuits based on the emerging magnetic tunnel junction (MTJ) device is proposed. The proposed magnetic FAs (MFAs) offer full nonvolatility, low area, and considerably lower energy consumption than their previous counterparts. Also, two of the proposed MFAs have the advantage of single event upset (SEU) tolerance. Simulation results reveal that the proposed designs offer over 50% energy efficiency in comparison with the considered previous fully nonvolatile MFAs. Using the proposed adders in the design of an approximate Gaussian filter, we showed that the filtered noisy images have almost the same results as the accurate Gaussian filter. The proposed MFAs have an accurate carry-out output and an approximate sum output with an error distance of 2.

In this article, a miniaturized ferrite Vivaldi antenna with tailored radiation performance in ultrahigh-frequency (UHF) band is presented. The novel magneto-dielectric NiZnCo ferrite materials were prepared, characterized, and adopted for the antenna application. A parametric study on the properties of the ferrite antenna is systematically implemented. Simulation results indicate that a significant size reduction for the antenna can be achieved by taking advantage of the relatively high permittivity and permeability of the ferrite material. Moreover, the inherent magnetic loss of the ferrite antenna substrates shows an effective suppression of the unwanted harmonic frequencies. The prototype of the ferrite Vivaldi antenna was fabricated with a relatively small dimension of 50×55×2 mm3, and antenna performances were tested to demonstrate the simulation. The measured lowest operating frequency (S11<; -10 dB) of the antenna is 0.82 GHz. Relatively high and flat gain is obtained in the frequency range of 0.8-0.95 GHz, while antenna gain is significantly suppressed above ~ 1.0 GHz. The…

The permanent-magnet Vernier (PMV) machine has been welcomed for direct-drive applications recently. Also, the fault tolerance is critical for special machine design in hostile conditions. This article proposes an efficient PMV machine with the modular winding configuration, which takes the fault-tolerant capability into account, especially the open-circuit fault. With the modular winding design, the better isolation between phases and modules can be obtained instead of dividing the stator core into segments. Meanwhile, the high efficiency needs to be guaranteed under both normal and partial-module operations. Therefore, the machine design, basic characteristics, and the fault-tolerant operation are performed and verified. Finally, the efficiency performances under normal and modular operations are analyzed and compared, which demonstrates the validity of the proposed idea and relevant considerations.

This article presents an analytical solution procedure to investigate the geometrical impact of the magnet and the rotor core on the performance of slotted, surface-mounted permanent magnet (PM) synchronous motors. In particular, four different motor configurations with loaf-shape/regular arc-shape magnets mounted on the octagon/circular rotor surface are investigated, and their no-load (i.e., PM flux density, back EMF, and the cogging torque) and on-load (i.e., armature flux density, winding inductance, and electromagnetic torque) performance metrics are compared. The analysis is carried out analytically by using the concept of the surface magnetization current (SMC) and the superposition theorem. First, the stator slots are nullified, and Poisson's equation is solved on a slot-less surface. The effect of the stator slots is then included by injecting equivalent SMC on the stator bore. For verification purposes, analytical results are validated via the finite element (FE) and experimental measurements on the motor prototype.

This article utilizes conductors with insulation of high thermal conductivity (ThC) combining suitable cooling methods to enhance the performance of traction motors for electric vehicles. The performance of a 10 kW interior permanent magnet (IPM) motor without forced cooling is considered as a benchmark. Then, the conductors with two conventional insulation materials and two with high ThC are applied to the IPM motor windings. Two cooling methods, finned housing (no forced cooling) and water cooling, are considered here. It is found that using conductors with high ThC insulation without forced cooling can only cool the windings by several degrees; however, the temperature can be considerably reduced by combining water cooling with an appropriate flow rate. The torque and power output of the IPM motor can also be significantly improved. This indicates that forced cooling can further enhance the effectiveness of conductors with insulation of high ThC. Two induction motors using conductors with two different insulation materials (0.1 and 3 W/m·K) are tested. The experimental results…

The axial-flux permanent magnet vernier machine (PMVM) is a competitive machine applied in the field of direct-drive which features on low speed and high torque. The rotor of axial-flux PMVM has a tendency to deflect to stator under the effect of the large and unbalanced axial electromagnetic force, which probably results in the collision between rotor and stator. Therefore, this article presents an analysis and optimization of the axial electromagnetic force of the axial-flux PMVM. First, the three-dimensional finite-element model (3-D FEM) is converted to equivalent two dimensional finite-element model (2-D FEM) for further axial electromagnetic force derivation and optimization. Subsequently, four design parameters that are sensitive to the axial electromagnetic force are selected and analyzed for further optimization, which aims to obtain an equal output torque, and reduce the axial electromagnetic force of entire rotor and peak force density of axial electromagnetic force as much as possible. Finally, a Kriging model between the objective functions and design parameters is…

This article presents an accurate analytical model to compute the magnetic field in a short moving-magnet linear motor with any pole and slot combinations. Two kinds of end effects caused by the finite length of the stator and mover are considered. The stator end effect is addressed by an equivalent slotting subdomain based on the subdomain analytical method. The mover end effect is analyzed with a virtual mover consisting of the mover and two additional virtual units. The length of virtual unit is given according to the effective motion stroke and magnetic circuit, and the remanence of permanent magnets in virtual units is specified as zero. A linear motor with 8 poles/6 slots and a Halbach array is used to verify the correctness of the proposed analytical model. Compared with the results from the finite-element analysis and previous subdomain analytical model, the proposed analytical model shows high accuracy on the calculations of the magnetic flux density, cogging force, and normal magnetic force.

The existence of direct current (dc) bias magnetic field changes the magnetostrictive properties of electrical steel sheets (ESSs) and intensifies the vibration and noise of transformers. In this article, the dynamic magnetostrictive properties of the ESSs under dc bias are measured and analyzed, and it is shown that the magnetostriction of the ESSs under dc bias has a complex dynamic anisotropy. An optimized backpropagation neural network (BPNN) is proposed to model the dynamic magnetostriction curves under the dc bias. In the construction of the BPNN, the topology is optimized by using the genetic algorithm and the parameters are optimally decided by using particle swarm optimization (PSO), respectively, to get a fast convergence and avoid the local optimal solution. The comparison of the proposed model with experimental measurements shows the accuracy of the proposed model is improved by 6%.

This article proposes an indirect method for predicting mechanical loss by considering the eddy current loss of permanent magnets (PMs) and conductors under the no-load condition. The mechanical loss has been conventionally predicted indirectly through experiments and numerical methods. The conventional method uses the no-load loss measured through experiments and the no-load iron loss calculated through a numerical method. With the increase in the demand for high-power-density motors, the PMs with high energy density and winding technology with high fill factor are required. Thus, the proportion of eddy current losses of PMs and conductors is increasing among the electromagnetic losses. Therefore, we propose an indirect method for predicting the mechanical loss considering the eddy current losses. The accuracy of the proposed method is higher than that of the conventional method. Moreover, the proposed method is verified by comparing the estimated efficiency of the specimen obtained by using this method with the measured efficiency.

In this article, two kinds of dual-layer segmented Halbach arrays have been proposed for permanent-magnet (PM) brushless machines. The analytical expressions of magnetic fields due to the inner-/outer-layer Halbach magnets have been separately obtained. For the maximal flux density in the air gap, the optimal magnet segment radian ratios or magnetization angles for each dual-layer Halbach array have been analytically determined separately. The induced back electromotive force and electromagnetic torque have been analytically obtained. The prediction results show that the optimized electromagnetic performances for each double-layer segmented Halbach array with different slot and pole combinations are better than those for the corresponding single-layer one. The proposed analytical model can also be applied for optimizing the multi-layer segmented Halbach array. The analytical prediction results of a PM machine with the double-layer segmented Halbach array have been compared with those obtained by a finite-element method.

The finite-element model is established to simulate electromagnetic forces of a permanent-magnet (PM) spherical motor using the commercial software from Ansoft. The Taguchi method is used to optimize the magnetic field density in the radial air gap and the maximum torque of the PM spherical motor. The final optimization parameters are determined by a response surface method (RSM). The simulation results of the optimized motor are compared with those of the original motor to show that the output performances of the optimized motor have improved greatly, which verifies the effectiveness and practicability of the Taguchi method on the optimization of the PM spherical motor.

The magnetostriction of an electrical steel sheet (ESS) is the main cause of the electromagnetically induced vibration of power transformers. In order to analyze the magnetostrictive hysteresis property of an ESS, a model is established based on the improved Jiles-Atherton (J-A) model by introducing the parameter k1, which considers the domain moment rotation. The magnetostrictive hysteretic loop of silicon steel would be obtained by combining the hysteretic loop with the model, in which the hysteretic loops can be more easily measured accurately than the magnetostriction loops. To verify the feasibility of the model, it is applied to Grain-oriented and non-oriented electrical steel, and the parameters in the model are extracted by using a particle swarm optimization algorithm. By comparing the measured data to calculate data obtained from the model, excellent agreement in the result is shown. The anisotropic properties of non-oriented silicon steel are also suitably shown. The results demonstrate the proposed model in the article is accurate for dynamic magnetic characteristics to…

A novel flux switching permanent magnet linear motor (FSPMLM), which has the advantages of high thrust density [the ratio of average thrust to permanent magnet (PM) volume] and low cost for long-stroke application, is proposed and investigated in this article. The topology of the novel FSPMLM with 12 slots is introduced and the basic operating principle is analyzed first. The optimal geometric parameters are selected by using the layered orthogonal optimization method. Then the electromagnetic performance of the motor is investigated by the analytical method based on the equivalent magnetic network model (MNM). Finally, a scheme of setting auxiliary teeth in the primary component is adopted to suppress the unbalance of the three phase flux linkages.

This article deals with electromagnetic forces of permanent magnet synchronous motors (PMSMs) with inclined and parallel rotor eccentricity. The electromagnetic forces have the spatial orders of the main components (multiples of pole numbers) and the sideband components when the rotor is eccentric. Although other studies have reported that each amplitude of an upper and a lower sideband is different, the causes of the asymmetry have not been fully investigated. The rotor eccentricity leads to changes in the gap permeance, the working point of the rotor magnets, and the distribution of gap magnetic flux density. By considering these effects in detail, we develop a new analytical expression of electromagnetic force, which expresses the asymmetry of a pairs of sidebands. The expression is compared with 3-D magnetic field analyses of PMSMs with inclined and parallel rotor eccentricity. As a result, it is found that upper sideband amplitudes are larger than lower sideband amplitudes, and the ratio of an upper sideband to the lower sideband of parallel eccentricity is larger than that of…

For high speed motors, smaller rotor diameters are required to make the surface speed less than 250 m/s. At the same time, dynamo motors for propulsion systems often require high torque. In such an environment, permanent magnet (PM) synchronous motors are more suitable than induction motors. In this work, a 270 kW dynamo motor is designed with a Halbach array using samarium-cobalt PMs. It utilizes the rotor back iron and carbon fiber sleeve on the rotor surface. Two design goals are set when the rotor inner and outer radii are fixed preferentially: minimization of PM usage and maximization of air gap field. A magnetic equivalent circuit is utilized to identify the saturation level of the rotor back iron and air gap field density. The Levenberg-Marquardt algorithm is applied to find the optimal coverage of radial magnet in a pole pitch and the optimal PM height. It is also observed that the resulting Halbach array motor is superior to surface-mounted PM motor in torque performance when the same amount of PM is used. A prototype motor was built on a real scale, but with a reduced…

The segmented-stator dual-rotor axial flux permanent magnet motor (AFPMM) in this article adopts two-segment Halbach permanent magnets (PMs) in the rotor and soft magnetic composite materials in the stator core, so it has the advantages of high torque density and high efficiency. This article proposes an optimization method for AFPMMs combining analytical optimization and nonlinear optimization, based on the analytical calculation of the magnetic field and electromagnetic performance. To realize analytical calculations, the AFPMM is regarded as the superposition of equivalent linear PM motor slices at different radii. The magnetic field is calculated using the slotless 2-D equivalent model and the slotted air gap relative permeability. Compared with finite-element analysis (FEA), the analytical calculation of the electromagnetic characteristics has acceptable accuracy and faster speed. The multiobjective optimization program for the AFPMM aims at lighter motor mass and lower loss. In analytical optimization, the expression of the optimal axial magnetization coefficient of the…