PM Array Research Articles

Comparative Analysis of Consequent-Pole Flux-Switching Machines with Different Permanent Magnet Arrangements for Outer-Rotor In-Wheel Direct-Drive Applications

Recently, the interest in consequent-pole flux-switching permanent magnet (CP-FSPM) machines has been increasing because of the flux-focusing PM arrangements and the removal of the flux-barrier effect. A simple and rigid outer-rotor salient pole rotor structure can be adopted in CP-FSPM machines, making them applicable for in-wheel direct-drive applications. In this study, three CP-FSPM machines with II-shaped (II-PM), V-shaped (V-PM), and straight U-shaped PM (SU-PM) arrays are analyzed and compared. Moreover, a CP-FSPM machine with inclined U-shaped PM (IU-PM) arrays is proposed to improve the flux-focusing effect and stator slot utilization. The working principles of CP-FSPM machines are analyzed by adopting a semi-analytical model. Combining the finite element analysis (FEA) results of air gap flux density and the analytical model of phase back electromotive force (EMF), the contributions of multiple working harmonics to the back EMF are quantitatively analyzed. Additionally, 6/16 and 6/17 CP-FSPM machines with different PM arrangements are globally optimized. Both the no-load and on-load performance of the optimized machines are included in the performance comparison. The results illustrate that the 6/16 and 6/17 machines exhibit their respective merits, and the IU-PM machine shows the best torque production ability in these CP-FSPM machines with the same design criteria.

3D Hybrid Segmented Layer Modeling of On-Load Magnetic Fields and Torques for Coreless Axial-Flux Permanent Magnet Synchronous Motor

This paper presents a novel 3-dimensional hybrid segmented layer model (3D HSLM) for coreless axial-flux permanent magnet synchronous motors (AFPMSMs). In the proposed 3D HSLM, the magnetic field sources are divided into the PM array and current-driven electro-magnets, which are captured by the combination of the magnetic scalar potential and vector potential models. This paper proposes a geometry function and cylindrical harmonic index modulation functions in order to correctly capture the curvature effect by the PMs and coils with arbitrary shapes and also the radial edge effect from the finite lengths of the rotor and the stator. The proposed modeling method also enables accurate estimation of the motor characteristics on the on-load conditions using the magnetic vector potential model. The fidelity of the proposed 3D HSLM is validated against the equivalent FEM models for various cases with different PM and coil shapes, in terms of the airgap magnetic fields, motor torque, and flux linkage. The comparison results show that the proposed 3D HSLM yields a modeling accuracy of more than 98% while significantly reducing the calculation time by two orders of magnitude as compared to the FEM models.

Design Criterion and Analysis of Hybrid-Excited Vernier Reluctance Linear Machine With Slot Halbach PM Arrays

This paper proposes a hybrid-excited vernier reluctance linear machine (HEVRLM) with slot halbach PM arrays. By utilizing halbach PM arrays, leakage flux that existing in the consequent pole structure can be greatly reduced. Besides, the dc excitation can enhance both the flux regulation capability and force density. First, the machine topology and working principle are introduced. Then, magnetomotive force (MMF)-permeance model is established to analytically calculate the air gap flux density under hybrid excitation. Moreover, the flux regulation capability, thrust force characteristic and PM demagnetization risk of the proposed machine are comparatively studied based on finite element method (FEM). It shows that halbach PM arrays can effectively reduce the leakage flux and further significantly improve the thrust force density by more than 30%. In addition, hybrid excitation is a feasible approach to further improve the thrust force density by distributing the optimal dc and ac currents. Moreover, the proposed HEVRLM exhibits high thrust force density compared with other three types of hybrid-excited linear machines. Finally, a prototype of HEVRLM is manufactured and tested for experimental validation.

3-D Analytical Model of Axial-Flux Permanent Magnet Machine With Segmented Multipole-Halbach Array

This paper presents a 3-D analytical model of an axial-flux permanent magnet (AFPM) machine with a segmented multipole-Halbach PM array. Closed-form solutions are self-consistently derived in terms of modified Bessel functions of the first- and the second-kind by solving analytically Laplace and Poisson equations by the method of magnetic scalar potential subject to the appropriate boundary conditions. In the preceding studies, their formulations are based on a 2-D or quasi 3-D geometry, and their discussions are often limited to the magnetic fields with low-poles of the regular PM. The proposed model successfully provides more rigorous and widely applicable expressions for magnetic fields, back-electromotive force, Lorentz torque and torque constant without limitations on the number of poles and the arrangements of the PM. Behavior of the torque constant is then shown against the number of poles ranging widely from low-poles to high-poles of the regular PM, the standard-Halbach PM and the multipole-Halbach PM for changeable geometrical parameters. The obtained results are of much use in understanding intrinsically the performance characteristics of the AFPM.

Constrained Multi-Objective Optimization for Double-Sided Tubular Machine With Hybrid Segmented PM

Double-sided tubular machines (DSTM) have greatly improved space utilization and power density, and are widely used in tidal power generation and high-power electric drives, while the thrust force ripple is also significant. To get the minimum cogging force with the maximum thrust force, hybrid segmented PM array topology is introduced to the DSTM and used as research object for multi-objective optimization. Due to the constraints among the parameters to be optimized, this paper proposes a new constrained multi-parameter multi-objective optimization method. In this method, a new optimal Latin hypercube(OLH) is put forward to solve the constrained parameter sampling problem. RReliefF is used to distinguish the importance of multi-parameter and divide them into three layers: strong, medium and weak, and surrogate models are established hierarchically to simplify the optimization complexity. In addition, an improved Gaussian process regression(GPR) algorithm is proposed to improve the optimization accuracy of strong significance parameters. The optimization results show that the average thrust force is increased by 4.7%, the cogging force is reduced by 28%, and total harmonic distortion rate of the voltage is reduced by 30.5% without loss of efficiency, which significantly improves the performance of the machine, and verifies the effectiveness of the proposed method, which is suitable for constrained multi-parameter multi-objective optimization.

Design and optimization of yokeless magnetic gear with asymmetric Halbach permanent magnet array for electric vehicle powertrain

In this paper, a novel 3/27/24 (pole pairs of inner rotor permanent magnet [PM]s/modulator/outer rotor PMs) high torque density yokeless magnetic gear with asymmetric Halbach PM array is presented and optimized for electric vehicle powertrain. The key is to improve the torque performance by replacing the magnetic steel with the light nonmagnetic material as the rotor core and employing the embedded magnetic steel bar as well as trapezoidal PM structure to form a low magnetic resistance in the magnetic circuit. The proposed machine has significant performance improvements in two aspects. Firstly, it has high torque density and low iron loss with the yokeless structure. Secondly, it has a high anti-saturation capability and low torque ripple with the asymmetric Halbach PM array and the embedded magnetic steel bar. The proposed structure is optimized by the co-simulation of the finite-element method and C++ optimization software. For a clear evaluation, the proposed structure is compared with generalized solutions in terms of performance and cost. Comparison results indicate that the proposed solution has the highest output torque, torque density, and torque per PM weight among solutions, reaching 214.1 N·m, 58.2 N·m/kg, and 95.6 N·m/kg, which greatly enhances the performance of the magnetic gear.

Combined optimization of a linear PM actuator with trapezoidal PMs and coils considering fringing effect for precision engineering

For precision engineering, a linear PM-moving actuator with trapezoidal PMs and trapezoidal coils considering the fringing effect is proposed. To take into account the effect of the finite-long trapezoidal PM array, an improved Fourier series expansion is developed to calculate the fringing-included magnetic field. Then the full-stroke thrust excited by the trapezoidal coils is accurately predicted and validated by the finite element method. Sensitivity of the trapezoidal parameters of PMs and coils is analyzed, and combined optimization is implemented by the genetic algorithm. Through the Pareto optimal solutions of thrust, the relation of the PM-coil parameter combination is described and formulated by curve fitting. Compared with the traditional rectangular PM actuators or other trapezoidal-typed actuators, the proposed actuator with trapezoidal PMs and coils further decreases the thrust ripple and largely increases the thrust magnitude simultaneously, and reaches an utmost-close effective stroke as well.

Power Oriented Design and Optimization of Dual Stator Linear-Rotary Generator With Halbach PM Array for Ocean Energy Conversion

In this paper, considering the oceanic multiple degree of freedom motion, a double stator linear-rotary permanent magnet (DSLRPM) generator with Halbach PM array is proposed for direct drive ocean energy conversion. It focuses on the power maximization generation resulting in a highly optimized DSLRPM generator to improve the generated power of the ocean energy conversion system in complex ocean condition. Based on the power-oriented design concept, the whole design process is divided into two steps. In the initial design procedure, the operating domain design is conducted, and the design point is selected. In the optimization design procedure, the non-dominated sorting genetic algorithm II (NSGA-II) coupled with response surface methodology (RSM) and sensitivity analysis is proposed to be as an optimization design technique. Finally, a prototype based on the optimized results is manufactured. The experimental results agree with the simulated result, and they both reveal that the proposed method can offer an effective design and optimization for the DSLRPM generator, where the multiple oceanic motions and complex operating conditions are considered.

Comparative study of partitioned stator flux-modulation motors with different permanent magnet arrays

By incorporating the merits of partitioned stator and flux modulation techniques, the partitioned stator flux modulation motors featuring high torque, have attracted much attention. This paper investigates four partitioned stator flux modulation motors with different types of PM arrays, including surface-mounted type, consequent-pole type, Halbach-array type, and half-Halbach type. The influences of key parameters on the average electromagnetic torque is conducted and compared. Then, based on the optimal designs, four motors are compared in terms of magnetic field distribution, back-electromotive force, torque characteristics, loss and overload ability. The result reveals that the half-Halbach motor is capable of utilizing more PM to improve electromagnetic torque. Also, the consequent-pole motor achieves the highest torque per PM usage. In addition, performance comparison under the same PM usage is carried out. The result shows that the half-Halbach motor not only exhibits the highest average torque but also achieves the highest PM utilization. Last, the prototype of half-Halbach motor is built for experimental verification.

Comparative Study of Electromagnetic Performance of Stator Slot PM Machines

This paper firstly explains how the stator slot PM (SSPM) machines have evolved from the conventional flux reversal PM machines (FRPMs), by placing the magnets over the tooth tips or between the tooth tips. The influence of tooth tips and PM configurations of five types of SSPM machines with various PM structures in stator slots, two with tooth tips and three without tooth tips, on the electromagnetic performance are then investigated and compared. It shows that, no matter what winding configurations (non-overlapping windings or overlapping windings), appropriate design of tooth tips can increase the average torque, the SSPM machines having flux focusing structures (i.e. Halbach array PM and spoke array PM) exhibit higher torque than those without flux focusing, and the SSPM machines with tooth tips have higher PM utilization rate than those without tooth tips. Non-overlapping windings can help provide higher torque density when the prototype machine length is less than around 125mm while overlapping windings are more advantageous if the machine length is over 125mm.

Analysis and Evaluation of a Linear Primary Permanent Magnet Vernier Machine With Multiharmonics

This article investigates a multiharmonics linear primary permanent magnet vernier machine. With the adoption of nonuniformly distributed PM arrays along the air gap, richer harmonics are achieved and make its performance superior to the conventional linear primary permanent magnet vernier machine. First, the structures are described and compared. Then, their operation principles are analyzed by the flux modulation theory. The electromagnetic performances of two machines are analyzed and compared through the finite element method and theoretical analysis. The results show that the multiharmonics linear primary permanent magnet vernier machine offers 15% higher thrust force density compared with the conventional linear primary permanent magnet vernier machine. Finally, the experiments on a prototype of the multiharmonics linear primary permanent magnet vernier machine are carried out for validation.

Frequency Domain Modeling of a Halbach PM Linear Generator Based Two-Body Point Absorber for Wave Energy Conversion

Point absorbers utilize the relative motion between the floating body and the submerged body to harvest the wave energy. This paper presents the parametric study of a two-body wave energy point absorber to investigate the influence of key design factors. The targeting point absorber employs a slotless Halbach linear generator as the power take-off system to improve the energy conversion efficiency. In this work, we have linearized our developed nonlinear time domain model and presented it in frequency domain to improve the simulation efficiency, where the results of the time domain model and the frequency domain model have been compared. The stochastic linearization method is employed for the first time to linearize the nonlinear dragging effect of a point absorber. The case study suggests that the stiffness of the power take-off system and viscous floater dragging coefficient should be as small as possible and the optimal mass of the bodies should be adopted to achieve the maximum power output. Under the irregular wave condition, the power matrix against the wind speed and the damping coefficient of the power take-off system shows that the optimal damping coefficient is determined by the local weather and geographic condition. Regarding the determinants of the damping coefficient, the factors that affect the power take-off system is investigated. The Halbach PM array length and the coil width should be specially optimized to obtain the desired damping coefficient of the power take-off system at a given point absorber dimension. Lastly, a test-rig has been developed to validate the magnetic domain model.

Research on Improved Permanent Magnet Linear Synchronous Motor for Direct-Drive Application

This paper takes a Halbach permanent magnet linear motor (PMLM) without a core as the research subject; based on the traditional structure of a single-layer PM array, an improved PMLM with an optimized double-layer Halbach PM array is proposed to reduce the harmonic components of the air gap magnetic flux density (AGMFD) for direct-drive applications in the feeding system of the machine tool which need high force capability. The 3-D models of PMLMs with single-layer and double-layer Halbach PM arrays are established by using finite element (FE) software; the air gap magnetic field, the back electromotive force (EMF), and the electromagnetic thrust of the two types of motors are analyzed. The simulated results show that the PMLM with an optimized double-layer Halbach PM array can achieve better performances of the motor and reduce the cost of the PMLM. Finally, the experimental results verify that the proposed double-layer Halbach PMLM is effective and practical.

Design and Analysis of a Novel Dual-Stator Cylindrical Linear Vernier Machine With LTS Field Windings

The cylindrical linear vernier machine (CLVM), in which the magnetic gearing effect is adopted, is a specific kind of the linear vernier machines (LVMs) and is suitable for the direct-drive applications that both low speed and high thrust are demanded at the same time. In order to further improve the thrust density of the LVMs, a novel dual-stator CLVM with low-temperature superconducting field windings (DCLVM-LTS) is proposed and analyzed in this paper. The operation principles of the DCLVM-LTS will be introduced in the paper by the analysis of the air-gap flux density. The superiorities of the proposed DCLVM-LTS are calculated by the finite element method. Compared to a DCLVM with PM arrays, the thrust density of the proposed DCLVM-LTS exhibits a considerable improvement in terms of thrust density, power factor, and economy efficiency.

Slotless tubular PM generator with dual quasi‐Halbach magnetized PM Array: Analytical and numerical magnetic field analysis

AbstractIn this paper, an initial design and analytical electromagnetic field solution for Slotless and Dual Quasi‐Halbach (DQH) Permanent Magnet mover is proposed for reciprocating free piston alternator application. Utilizing presented analytical magnetic field solution, Air‐Gap magnetic flux characteristic, and generated voltage are estimated. Using 3‐D finite‐element method (FEM) proposed structure numerically investigated and obtained numerical results employed to confirm the derived analytical models. The analytical results are compared with FEM and show excellent agreement. In order to determine output voltage and power characteristics, the load testing has been performed by a resistive variable load. The obtained results from FEM analysis and analytical magnetic field solution show an enhancement in the proposed alternator performance compared with the alternator with Halbach magnetized configuration, by improving provided power.

Characteristics of magnetic field distribution on the dual-cross layout cylinder PM type linear Halbach array

A strong magnetic field forming by Halbach PM array is an effective technical element for the developing of industrial magnetically actuators. In a brand new layout Halbach array using cylinder-shaped PMs, by synchronized rotation in the same direction with of all magnets, the slide of the magnetic field distribution has been confirmed. The proposal dual-cross layout Halbach array model using cylinder-shaped PMs, it can be expected multidimensional motion of the secondary conductor. However, the slide performance of magnetic field seems to depend on the forming of the magnetic flux density distribution. And, its magnetic flux density distribution is clearly dependent on the arrangement parameters of the cylinder-shaped PM of the array. In this paper, we would like to report that the forming of the magnetic field depending on arranged and layout parameters of the brand new dual-cross layout cylinder-shaped PM type linear Halbach arrays, by magnetic field simulation and measurement.

Gene expression analysis reveals chronic low level exposure to the pesticide diazinon affects psychological disorders gene sets in the adult rat

Chronic low level exposure to organophosphate (OPs) pesticides in adulthood has been linked to adverse neurobehavioural deficits and psychological disorder symptoms, although this remains a contentious issue. The OP-induced biological changes that could underlie these effects are unclear. We assessed gene expression changes following chronic low level exposure to diazinon, a pesticide with a high dietary exposure risk. Adult male rats were orally exposed to diazinon (0, 1, 2mg/kg, 5days a week for 12 weeks). After 4 weeks, marble burying behaviour was lower in diazinon exposed rats than vehicle exposed rats; this difference persisted for 8 weeks. Chronic diazinon exposure did not significantly inhibit acetylcholinesterase activity, the primary mechanism of action of high level OPs. Affymetrix GeneChip® HT RG-230 PM Arrays were used for gene profiling followed by Ingenuity Pathway analysis. In the hippocampus, the most significant gene expression changes caused by OP exposure were associated with Psychological Disorders, and Cell-To-Cell Signalling and Interaction functions. Genes encoding the AMPA3 glutamate receptor, glutaminase, dopamine transporter and tyrosine hydroxylase were up-regulated, whereas the gene encoding the GABAB1 receptor was down-regulated. In the dorsal raphe nucleus, genes associated with development and the Psychological Disorders function were significantly affected, including the up-regulation of the gene encoding the α1b-adrenoceptor, the major driver of serotoninergic (5-HT) neuronal activity. These data indicate that chronic exposure to diazinon in adulthood, below the threshold to inhibit acetylcholinesterase, stimulates glutamatergic, dopaminergic and serotonergic synaptic transmission which may underlie adverse neurological outcomes.

High‐torque‐density pseudo‐direct‐drive permanent‐magnet machine with less magnet

Magnetic gears, an alternative to conventional mechanical gearboxes, have been extensively studied in the last decade. By combining a magnetic gear and a conventional permanent-magnet machine into one frame, different magnetic-gear-integrated permanent-magnet machines with a high-torque density are obtained, among which the pseudo-direct-drive permanent-magnet machine features both a high-torque capability and a good power factor with an acceptable structural complexity. However, the stator PM array in the conventional pseudo-direct-drive permanent-magnet machine obstructs the magnetic path and reduces the excitation torque due to the coils. Another problem is the large permanent-magnet amount which increases the overall cost. The authors propose a novel topology which has an improved torque capability under the same excitation current with a reduced permanent-magnet amount. The working principles of the proposed machine are analysed theoretically using the linear-material assumption to decouple the permanent-magnet-machine part and the magnetic-gear part. Its performance is then validated by the finite-element method. A comparison study with the conventional topology is conducted to show its merits.

Design of An Electromagnetic Energy Harvesting System Applied to The Shock Absorber of A Sport Utility Vehicle : Part I. Single Permanent Magnet Layer Coreless Type

This paper deals with the design of an electromagnetic energy harvesting generator for the suspension system of a sport utility vehicle. The proposed generator is composed of a single coreless type permanent magnet layer, which increases flux density across the coil windings and eliminates flux leakage by using the Halbach PM array, thus improving the machine’s performance, including flux linkage and output power. The goal of the system is to regenerate energy from the kinetic energy of the suspension system of the sport utility vehicle. The proposed generator physically combines electrical and mechanical components, in which permanent magnets, coil windings, and back iron are attached to the body of the shock absorber. The design’s performance was investigated using the finite element method (FEM) and validated by comparison with experimental data.

Proposal and analysis of three closed double magnetic circuits to obtain a very long stroke for electrodynamic force generators

Electrodynamic force generators with a stroke of up to several hundred millimeters are in high demand in fields such as voice coil actuators and low frequency vibration metrology. The key is to extend the effective length of the long air gap (LAG) with required uniform magnetic flux density (MFD) and low magnetic flux leakage. This paper focuses on a proposal and comparative analysis of three closed double magnetic circuits (CDMCs) to obtain long/ultra-long strokes. Analyses are performed from the viewpoint of the magnetic line distribution, fringing effect, distribution of the MFD, and magnetic flux leakage in order to evaluate the stroke potential of three proposed CDMCs, while taking into account the vacuum annealing, material differences in permanent magnet pairs (PMs), and assembling errors in PM arrays. Analyses show that the CDMC with PMs assembled at the ends of the center yoke exhibits advantages over the other two schemes. An electrodynamic force generator with an air gap length of 200mm is constructed with this structure. Experimental results reveal an MFD of up to 233.5 mT, MFD non-uniformity of 0.2% in the LAG, and magnetic flux leakage of 3 mT, which meet the strict requirements in low frequency vibration metrology.