Magnet Skewing Research Articles

Performance Analysis of Slotless Axial Flux Permanent Magnet Machines with Skewed Magnets under Loading Condition

Performance Analysis of Slotless Axial Flux Permanent Magnet Machines with Skewed Magnets under Loading Condition

A study of rare-earth magnet profiles for torque ripple improvement of axial flux permanent magnet machine

Purpose The purpose of this study is to reduce the cogging torque in axial flux permanent magnet (AFPM) machine using optimal magnet shape. Design/methodology/approach This study analyzes different magnet shapes for AFPM machine performance enhancement. Three-dimensional (3D) finite element analysis is performed to see the effects of pole shaping on the cogging torque of the AFPM machine. Findings The magnetic pole shape has a significant effect on cogging torque and overall efficiency. The conventional model has the highest torque whereas the conventional skewing affected cogging torque positively and significantly reduced the cogging torque. The combination of skewing the pole along with face curving is more effective and decreases the cogging torque from 3.88 Nm to 1.5 Nm. Originality/value Rare-earth magnets are the most expensive and important part of AFPM machines. Shape and volume optimization of rare-earth magnets is crucial for the performance of AFPM machines. The research aims to analyze the different permanent magnet designs for performance improvement of the AFPM machine. Conventional flat top trapezoidal, curved-top and skewed-magnet shapes are analyzed and the performance of the AFPM machine is compared with different magnet shapes. Curved-top shape and skewed magnet significantly reduce the cogging torque. Furthermore, a combination of curved-top shape and skew magnet shape is proposed to reduce the cogging torque further and improve the AFPM machine’s overall performance. Newly proposed magnet profile gives skewed curve magnet shapes which reduce the cogging torque further. 3D finite element analysis has been used to analyze the single-sided AFPM with all four different magnet shapes. The research focuses on single-sided AFPM machines, but the results are also valid for double-sided AFPM machines and can be extended to other topologies of AFPM machines.

SSO-DRSS Axial Flux sensing in Switching Permanent Magnet Motor for cogging torque mitigation

This paper addresses the imperative requirements of high efficiency, power density, and speed in Axial Flux-Switching Permanent Magnet Motors (AxFSPM) for electric vehicles. Recognizing the limitations of conventional motor designs, especially their weight and size, hindering their universal applicability, this study proposes a novel approach. A Double Rotor Single Stator (DRSS) configuration is introduced, and its parameters are systematically optimized using the Shark Smell Optimization (SSO) algorithm. The SSO algorithm refines critical motor parameters, including axial length, turns per phase, and stator and rotor dimensions, resulting in a more compact AxFSPM motor with enhanced torque. Geometrical constraints are similarly optimized with SSO, and magnet skewing angles are employed for cogging torque reduction. The optimization process, implemented in MATLAB and ANSYS Maxwell, yields an average torque below 1.4 N m and cogging torque below 0.8 N m, demonstrating the effectiveness of the proposed approach. Comparative analyses against various motor models underscore the superiority of the SSO-optimized DRSS motor in terms of efficiency and compactness.

Cold-Spray Additive Manufacturing of a Petal-Shaped Surface Permanent Magnet Traction Motor

Several applications require low torque pulsations as they can lead to mechanical vibrations and acoustic noise in the electric motor. Optimization of the rotor permanent magnet (PM) shape is one of the effective methods for reducing torque pulsations. Unfortunately, the low versatility of the magnet fabrication technologies limits the development of new motor geometries. Cold spray additive manufacturing can be used for shaping permanent magnets for the direct fabrication of motor parts without the need for additional assembly steps. This fabrication technique allows an increase in the design flexibility of electric machine geometries targeting improved performance. This paper investigates the performance of permanent magnet rotors fabricated using a cold spray additive manufacturing technique for radial flux surface permanent magnet synchronous machines (SPMSM). The permanent magnet rotors considered are conventional rectangular-shaped with unskewed magnets (Model A), skewed magnets (Model B), and sinusoidal-petal shaped magnets (Model C) along the axial direction. The magnitude of magnetization current pulse required to magnetize these rotors is calculated and an impulse magnetizer setup is designed for in-situ magnetization. The performance of the shaped cold sprayed permanent magnet rotors and their effects on back EMF, electromagnetic torque, and cogging torque are analyzed experimentally and comparisons are made between the different rotor designs.

Investigation Effect of Magnet Skew on Thrust Force in Linear Brushless Direct Current Motor with FEM

This study is concerned with the reduction of ripple in the thrust force produced in a linear Brushless Direct Current Motor (BLDC). To reduce the ripples in the generated thrust force, different methods such as structural solutions are applied both in the control part and in the production phase of the motor. In this study, skew application, which is one of the mechanical methods, is proposed. For this reason, the changes in the thrust force of a BLDC motor with a surface magnet-placed translator are investigated by applying different levels of skew to the magnets. First, a 3D solid model of the motor was created. A pole on the translator of the linear BLDC motor is composed of 3 equal magnet groups. For each skew level, the magnets were shifted 3 mm independently of each other and the thrust force values were examined. For this process, a 3D magnetostatic analysis of the linear BLDC motor was performed. The results obtained show that the skewing process applied to the magnets reduces the ripples in the thrust curve up to a certain point, after which no significant improvement in the ripple is observed, while the average force value decreases significantly.

Fast Design Optimization and Comparative Analysis for Linear Permanent Magnet Motor with Magnet Skew, Auxiliary Tooth and Overhang Structure.

This paper presents a fast design optimization using an effective characteristic analysis for linear permanent magnet motors (LPMMs) with techniques for improving motor performance such as using an auxiliary tooth, permanent magnet (PM) skew, and overhang structures. These techniques have different effects on the characteristics of the LPMM depending on the combinations of each other, resulting in complexity in the design optimization process. In particular, the three-dimensional (3-D) effect of the PM skew and overhang structure takes a lot of time to be analyzed. To deal with this problem, an effective magnetic field analysis method and a novel optimization algorithm are proposed. Preferentially, the field reconstruction method is used for a fast and accurate evaluation of the magnetic field of the LPMM. In the proposed magnetic field analysis method, the change of magnetic field distribution due to the addition of an auxiliary tooth is predicted, and the 3-D magnetic field effect of PM skew and overhang structure is considered. By reducing the computational burden in the magnetic field analysis, the electromagnetic characteristics of LPMMs can be calculated quickly, such as detent force, end force, thrust force, and back-EMF. The effect of the auxiliary tooth and overhang structure on the optimal PM skew length is investigated with comparative study results. Subsequently, the proposed optimization algorithm has the advantage of reducing time cost by providing multimodal optimization and robustness evaluation of local peaks at the same time. The proposed method is verified via comparison with finite element analysis and experimental results.

Analysis of a Combined-Type Axial-Flux Permanent Magnet Machine

A combined-type axial-flux permanent magnet machine is proposed in this paper. The structure of the proposed machine is introduced. The torque density characteristics of the proposed combined-type axial-flux permanent magnet machine are studied, and the torque density advantages of this kind of machine are analyzed by comparing with radial-flux permanent magnet machines. The magnetic field analysis method of the machine is studied. In the process of magnetic field analysis, an air gap permeance element is proposed to improve the traditional magnetic equivalent circuit method, which can facilitate the establishment of magnetic equivalent circuit model at different times. The calculation results of the proposed method are verified by finite element method. The cogging torque optimization of this machine is investigated, which includes magnet skewing with different reference modes. The optimal magnet skewing angle is calculated and verified, and the characteristics of different cogging torque optimization methods are summarized.

Novel Quasi-Three-Dimensional Modeling of Axial Flux In-Wheel Motor With Permanent Magnet Skew

This paper presents a characteristic analysis of axial flux permanent magnet machines (AFPMMs) for in-wheel electric vehicles. Preferentially, a novel quasi-3-D model is developed for the fast and accurate design of AFPMMs. In electromagnetic field analysis, combined with field reconstruction method, the computation time of 2-D solutions is significantly reduced. With the use of time sweeping of the basis function, only the static finite element (FE) analysis is performed to calculate the air-gap flux distribution at the entire rotor position, whereas the conventional 2-D solutions require a transient FE analysis. In the shape sweeping process of the basis function, the virtual air-gap section method is introduced to take into account that the ratio of slot opening to slot pitch is different depending on the radius of analysis plane, which causes errors in the analysis results of the conventional quasi-3-D method. The virtual air-gap sections are obtained by interpolation of the spatial field between the mapped cylindrical planes. The proposed technique reduces the number of 2-D analysis planes required for high accuracy in the conventional quasi-3-D method, and it can also predict the air-gap magnetic flux distribution for skewed permanent magnets without additional FE analysis. Finally, using the magnetic fields calculated in the proposed method, the electromagnetic performances of the AFPMM are calculated, such as load torque, cogging torque, attraction force, and back-EMF. The analysis results were verified by comparison with the measurement results.

3D Characteristic Analysis of 3-Leg Linear Permanent Magnet Motor With Magnet Skew and Overhang Structure

This paper presents the 3-leg linear permanent magnet motor (TLPMM), which has a novel structure. It has an advantage of reducing the entire volume due to the attraction force cancellation. The TLPMM consists of stator and mover modules, simplifying the manufacturing process and maintenance. The TLPMM has a permanent magnet skew and overhang structure to improve motor performance. Therefore, the consideration of three dimension (3D) effects is required in the characteristic analysis. The proposed method is based on a field reconstruction method that provides a reduction in computational burden with high accuracy in analyzing 3D characteristics. For the evaluation of magnetic fields in non-uniform and complex air-gap in the TLPMM, the virtual air-gap section method is introduced. Using these proposed methods, the TLPMM with the magnet skew and overhang structure are effectively analyzed. This approach was verified by comparison with finite element analysis and experimental results.

Cogging Torque Reduction in Permanent Magnet Brushless DC Motor by using Various Design Modification Techniques

Cogging torque is a problem for continuous motion applications like scanning, contouring and mainly positioning applications that requires smooth and accurate motion. It degrades the performance and the life of the motor. Cogging torque cannot be completely omitted but can be reduced drastically using various design modification techniques. This paper focuses on reducing cogging torque in BLDC using three different techniques like stator slot modification, rotor magnet modification and skewing of stator slots and rotor magnets. The result obtained by combining these three techniques has yielded a new model with reduced cogging torque and trapezoidal Back Electromotive Force as compared to the conventional BLDC motor. Also, the cogging torque values for different rotor magnets and stator slots shapes are calculated and studied using Finite Element Analysis (FEA). A detailed thermal analysis of the same model presents the temperature and heat flow plots using Computer Aided Design (CAD).

Design and analysis of a high-performance surface inset permanent magnet motor with asymmetrical rotor

This paper presents a novel design strategy for surface inset permanent magnet (SIPM) motors to suppress torque pulsations and maintain the high output torque by integrating the magnet skewing and asymmetrical rotor configurations. The magnet skewing is implemented within one magnet pole pitch to reduce cogging torque by avoiding excessive torque degradation, and the asymmetrical rotor is designed to improve the utilization of the torque components, thus to compensate the decreased torque due to the magnet skewing. To highlight the advantages of the proposed motor, a conventional SIPM motor is adopted for performance comparison with the aid of the finite element method. As a result, the proposed SIPM motor highly reduced the cogging torque (−79.7%) and torque ripple (−54.7%) while maintaining a high average torque when compared to the conventional SIPM motor.

A New Asymmetric Planar V-Shaped Magnet Arrangement for A Linear PM Synchronous Motor

In this paper, a new asymmetric planar V-shaped magnet arrangement for a linear PM synchronous motor is proposed. Several magnet arrangements for the track of the proposed linear permanent magnet (PM) synchronous motor such as un-skewed magnets, conventional magnet skew, and V-shaped planar magnets have been investigated. The performance results of the linear motor with skewed magnets are compared to those of previously designed PM linear synchronous motor with conventional un-skewed rectangular-shaped (CuSRS) magnets. The forcer is kept the same for all track structures and a thorough comparison is provided for low detent force and low force ripple with the CuSRS and proposed planar V-shaped magnet skew approaches.

Fine-Tooth Iron-Core Linear Synchronous Motor for Low Acoustic Noise Applications

The design of a novel low-noise high-force linear motor for precision positioning applications, such as in semiconductor lithography, is presented in this paper. New magnetic designs achieve low noise and vibration by reducing high spatial-frequency magnetic field components, which cause harmonic vibrations of a moving stage. To reduce such force harmonic content, our new motor has fine teeth, narrow slots with high slot aspect ratio, five phases, and a moving skewed Halbach magnet array. As compared with a commercially available iron-core motor, in our new design, the acoustic noise level in Pascals is reduced by more than 90%, corresponding to a 20 dB reduction in sound pressure level, even with a nonskewed magnet array. Using a skewed magnet array, the cogging-driven and velocity-dependent noise is further reduced by 90% in Pascals. This new linear motor simultaneously is capable of very high shear force densities in order to support high-acceleration motions, and thus provides new options for high-performance and quiet linear motion devices.

Optimal Torque Ripple Reduction Technique for Outer Rotor Permanent Magnet Synchronous Reluctance Motors

Torque ripple reduction has been one of the main considerations in the optimal design of traction motors, such as permanent magnet assisted synchronous reluctance motors. Several design techniques including optimal slot/pole combination, stator slot and rotor magnet skewing, and shape optimization of rotor flux barriers have been studied intensively to reduce the torque pulsations in the internal rotor reluctance motors. However, internal rotor reluctance motors involve power train complexity and space constraints in the traction application. On the other hand, outer rotor motors can be designed optimally to eliminate these drawbacks and in addition, produce higher power density. In such outer rotor reluctance motor designs, torque ripple plays crucial role as the in-wheel motor is under duress of consistent rotational forces. Furthermore, optimization of outer rotor in-wheel motors needs to be thoroughly investigated to reduce the torque ripple and to generate higher torque density. In this paper, a rotor shape optimization based on design of notches and rotor flux barrier is presented. Detailed optimization process in adjunct to analytical and simulation results comparison is presented. Finally, optimal designs are fabricated and tests are conducted on the 3.7-kW prototypes to validate the proposed design-optimization theory.

Reduction of vibration and acoustic noise in permanent magnet synchronous motor by optimizing magnetic forces

Two methodologies are proposed in this paper to reduce electromagnetic vibration and noise of permanent magnet synchronous motor. A multiphysics model is firstly established to predict the vibration and noise. Experimental tests are conducted to validate the model. Then, the source of the vibration and noise peaks from calculated and tested results is located. Two methodologies are proposed to mitigate this source. One is by reducing its amplitude through adjusting slot opening width and magnet shape. The other is by changing the phase of the specific force harmonic along the axial direction through stepwise or continuous magnet skewing. The optimum skewing angle is analytically derived. Based on the validated multiphysics model, optimizations under different methods are compared. It is found that considerable reductions of noise can be achieved by reducing low space harmonics of radial force. In particular, to reduce the noise over a wide frequency band, magnet skewing is a better solution than optimizing slot opening width and magnet shape.

Axial Unbalanced Magnetic Force in a Permanent Magnet Motor Due to a Skewed Magnet and Rotor Eccentricities

We investigate the effect of a skewed permanent magnet (PM) with overhang on the axial unbalanced magnetic force (UMF) of a PM motor, especially in the presence of static and dynamic eccentricities of a rotor. We derive the mathematical equations of the axial UMF acting on PM motor due to the skewed PM with overhang and rotor eccentricities. We develop a 3-D finite-element model of the PM motor, not only to verify the frequency components of the proposed equations but also to determine the amplitude of the axial UMF. Further, we develop an experimental setup to measure the axial UMF caused by a skewed PM with overhang and rotor eccentricities. We confirm that the skewed PM with overhang generates an axial UMF with the harmonic of the least common multiple of pole and slot numbers. In addition, the static and dynamic eccentricities with the interaction of the skewed PM and overhang generate the axial UMF with the pole harmonics and slot harmonics, respectively.

Techniques for Reduction of the Cogging Torque in Claw Pole Machines with SMC Cores

As one of the main parasitic parameters in permanent magnet (PM) synchronous machines (PMSMs), cogging torque is the main component of the torque ripple, which has always been the handicap in the high-performance, low-speed drive systems. Over the last two decades, various methods have been proposed to decrease the cogging torque in both radial-flux and axial-flux PMSMs. Among these methods, stator slot skewing, stator tooth notching, permanent magnet (PM) skewing, PM shifting, and pole pairing are extensively investigated. However, little work has been done on reducing the cogging torque of the claw pole machine (CPM), whose cogging torque cannot be ignored. In this paper, the general methods that have been used to reduce the cogging torque in radial-flux and axial-flux PMSMs are developed and verified in a CPM with a soft magnetic composite (SMC) core. The 3-D finite element method (FEM) is used to calculate the cogging torque and PM flux linkage per turn. By comparing different cogging torque reduction technologies, it can be found that the magnet step skewing and unequal claw pole width are very suitable for CPM.

Minimization of Cogging Force in Fractional-Slot Permanent Magnet Linear Motors with Double-Layer Concentrated Windings

Permanent magnet linear motors (PMLMs) with double-layer concentrated windings generally show significant cogging forces due to the introduction of auxiliary teeth for eliminating the end-effect induced phase unbalance, even when the fractional-slot technology is applied. This paper presents a novel approach to reduce the cogging force by adjusting the armature core dimensions in fractional-slot PMLMs with double-layer concentrated windings, together with magnet skewing. It is shown that the proposed technique is capable of reducing the cogging force of the motor in an effective way, with the peak value minimized to less than 0.4% of the rated thrust force in the case study. Such a technique can also be applicable to other linear motors with appropriate changes.

Cogging torque reduction in axial-flux permanent magnet wind generators with yokeless and segmented armature by radially segmented and peripherally shifted magnet pieces

The inherent cogging torque component of the PM generators can cause problems at the start-up of wind turbines. To improve the operation of wind turbines, especially at low starting speeds, the wind generator cogging torque should be minimized. In this paper, an effective and practical approach is proposed for cogging torque reduction in the AFPM generators with yokeless and segmented armature (YASA). The proposed approach is based on the dividing magnets radially and shifting the magnet pieces peripherally with an appropriate shifting angle. Using a series of 3-D FEA simulations, the proposed approach is compared with the two conventional approaches, i.e. the magnet skewing approach and the selecting an appropriate magnet pole arc to pole pitch ratio, according to the cogging torque reduction and the negative impacts on the generator loadability. It is shown that using the proposed approach, the generator cogging torque can be greatly reduced (about 87%). Also, it is shown that compared with the other studied cogging torque reduction techniques, the proposed approach has less negative impact on the generator loadability. Some of the simulation results are verified using the experimental tests.

철심형 이동자와 고정자의 형상에 따른 영구자석 선형 동기전동기의 전자기력 특성 비교 및 피칭 모멘트 실험

This paper presents the characteristic analysis and experiment of force characteristics in permanent magnet linear synchronous motor for accuracy prediction of linear motion machine tools. In particular, the pitching moment resulting from attraction force ripple has been analysed and tested. Firstly, we analysed the characteristics of detent force, attraction force, and pitching moment in permanent magnet linear synchronous motor according to the design techniques such as auxiliary teeth, chamfering, and permanent magnet skewing. In addition, we suggested the experimental set for measurement of pitching moment. Finally, the results from measurement shows the good agreement with those obtained from finite element analysis results.