Spoke-type Permanent Magnet Synchronous Motor Research Articles

Study on Performance Improvement through Reducing Axial Force of Ferrite Double-Layer Spoke-Type Permanent Magnet Synchronous Motor with Core Skew

Recently, due to the price fluctuation and supply instability of rare earth mineral resources, there has been a lot of development of electric motors using non-rare-earth permanent magnets. As a result, motors using Dy-free permanent magnets and ferrite permanent magnets are being researched, and, in particular, ferrite permanent magnets often utilize spoke-type structures, which are magnetic flux concentrators, to compensate for their low coercivity and residual flux density. However, in general, spoke-type PMSMs do not use much reluctance torque, so double-layer spoke-type PMSMs have been studied for their more efficient design. Unlike general spoke-type PMSMs, double-layer spoke-type PMSMs can utilize high reluctance torque by increasing the difference between d-axis and q-axis reluctance. However, as the difference in magnetic resistance increases, vibration and noise are generated, which adversely affects the mechanical part and shortens the life of the motor. Although this problem seemed to be solved by applying core skew in the previous study, it was confirmed that the axial force caused by the axial leakage flux occurred in the maximum torque per ampere (MTPA) control section and the torque ripple was increased. Therefore, in this paper, a model that can apply symmetrical core skew and reduce axial force is proposed. First, the causes of the axial force generated in previous studies were analyzed. Based on the analysis of these causes, a new symmetrical core skew structure was proposed, and its justification was verified through FEA.

A Study on Magnetization Yoke Design for Post-Assembly Magnetization Performance Improvement of a Spoke-Type Permanent Magnet Synchronous Motor

Permanent magnet synchronous motors (PMSMs) are highly affected by magnetization, which determines the magnetization level in the permanent magnet (PM). There are three main magnetization methods: single-unit, stator coil, and post-assembly magnetization. Post-assembly magnetization is widely used in PMSM mass production due to its ability to achieve high magnetization performance using a separate magnetizing yoke. However, spoke-type PMSMs with ferrite PMs face challenges when using the post-assembly method. The structural configuration of two magnets located radially hampers effective magnetized field transmission to the rotor’s interior due to the narrow space between the magnets. Maximizing the magnetization rate becomes crucial, but the limited space in the spoke-type structure complicates this. This paper addresses the issue and analyzes factors influencing post-assembly magnetization characteristics. A novel yoke structure is proposed, reducing the distance between the coil and magnet, leading to more efficient magnetization. The parametric and performance comparative analysis shows an impressive 17.1%p increase in magnetization rate with the proposed yoke structure compared to the existing yoke. This outcome contributed to a solution for enhancing the magnetization performance of spoke-type ferrite PMSMs.

Analytical Method to Calculate Inductances of Spoke-Type Permanent-Magnet Synchronous Motors With Damping Bars

This paper proposes an analytical method to calculate inductances and resistances related to damping circuits of spoke-type permanent-magnet synchronous motor(PMSM) with damping bars. Harmonics of inductances are taken into account analytically in order to obtained performance of LSPMSM. Damping bars of spoke-type PMSM are divided into direct-axis and quadrature-axis damping circuits. The magnetic field, self-inductances and resistances of damping circuits and mutual inductances between damping circuits and stator winding are predicted analytically. The calculating results show that the inductances and resistances of spoke-type PMSM with damping bars by the proposed analytical method are well agreement with that predicted by finite-element method. The line-start process of spoke-type PMSM with multi-damping circuit model in which the inductances and resistances are calculated analytically is also similar with the experimental results. The finite-element and experimental results confirm that the developed analytical method has high accuracy for predicting inductances, resistances and performance of spoke-type PMSM.

Analysis and Modeling of Axial Leakage for Spoke-Type Hybrid Permanent Magnet Machines

In this study, we propose a novel analysis method for a spoke-type permanent magnet (PM) synchronous motor (PMSM) using two types of PMs that consider axial leakage flux using a magnetic equivalent circuit (MEC). Spoke-type ferrite PMSM have the advantage of concentrating magnetic flux; however owing to the shape in which the PMs are arranged along the radial direction, some magnetic flux leaks in the axial direction, which causes inconsistency between the 2D and 3D finite element analysis (FEA) results. Because 3D FEA requires considerable analysis time, using it in the initial design stage of the motor is inefficient. Therefore, we present a new analytical method combined with MEC to overcome the existing inefficient approach. To obtain analysis results equivalent to 3D FEA, the new residual magnetic flux density considering axial flux leakage was applied to 2D FEA PMs using MEC and 2D FEA. The validity of the proposed method was verified through 3D FEA and experiments conducted on the test models using two magnet types.

Swiveling Magnetization for Anisotropic Magnets for Variable Flux Spoke-Type Permanent Magnet Motor Applied to Electric Vehicles

This paper investigates the application of anisotropic low-coercive force (LCF) magnets to a novel variable-flux spoke-type permanent magnet synchronous motor (VFS-PMSM) for electrical vehicles with a wide speed range. In the VFS-PMSM, flux is regulated by swiveling the magnetization of the anisotropic LCF magnets instead of directly magnetizing or demagnetizing them. The previously proposed VFS-PMSM uses only isotropic LCF magnets for easily swiveling the magnetic pole direction, resulting in lower torque density. The challenge thus lies in the feasibility to swivel the magnetic pole direction of the anisotropic LCF magnet, and the impact of the different magnetization strengths of the anisotropic magnets on the motor performance. This paper first studies the feasibility to swivel the magnetization direction of anisotropic LCF magnets through experiments. It is confirmed that the magnetization direction can be successfully swiveled by 90 degrees with a reduced external magnetizing field. Then, two VFS-PMSM topologies and various rotor configurations are compared in terms of key performance indices to determine critical sizing factors for performance enhancement. Finite element analysis is used for simulations. In comparison with the VFS-PMSM equipped with isotropic LCF magnets, the maximum torque of the proposed topology can be improved for the same flux adjustment ability. Alternatively, the flux adjustment ability can also be enhanced by 37.43% for the same maximum torque.

A Novel Variable Flux Spoke Type Permanent Magnet Motor With Swiveling Magnetization for Electric Vehicles

This article proposes a novel variable-flux spoke-type permanent magnet synchronous motor (VFS-PMSM), whose air gap flux density can be adjusted by “swiveling” magnetic pole directions in permanent magnet (PM). This is distinctive from conventional methods that require a large magnetizing field to magnetize and demagnetize (or partially) rotor PM along the same axis for variable flux motors. This paper first compares the proposed VFS-PMSM with two other typical types, i.e., series and parallel arrangements combining high- and low-coercivity PMs to achieve variable flux. It is found that the magnetic circuit of the proposed motor is identical to that of the series type at flux enhancing and to that of the parallel type at flux weakening. Therefore, the wide flux regulation range of the parallel type motors and the excellent on-load demagnetization-resisting capability of the series type motors can both be achieved in the proposed design. Another benefit of the proposed design is that the flux produced by the low-coercivity magnet constantly or aligns with that produced by the high-coercivity one whether the motor is flux enhanced or weakened. This allows the low-coercivity magnet to maintain its operating point within a safe range. These features make the proposed design suitable for electric vehicle tractions. Finite element analysis is used to compare the performance of various types of motors and highlight the advantages of the proposed VFS-PMSM. Experiments are conducted to validate the feasibility of the low-coercivity magnet to be magnetized with the method proposed in this paper. It is found that the field strength to magnetize or demagnetize the rotor can be significantly reduced, which improves the feasibility of this design.

A Study on the Shape of the Rotor to Improve the Performance of the Spoke-Type Permanent Magnet Synchronous Motor

This paper describes a study on the improvement of the dehydration performance of the conventional washing machine model. Recently, as interest in improving the dehydration performance of washing machines has increased, the need for a study on a high-speed electric motor has emerged. However, this conventional spoke-type PMSM has difficulty in speeding up due to the following problems. First, field weakening control is indispensable for high-speed operation of an electric motor. This control method is a big problem in causing torque drop and irreversible demagnetization of the motor. Moreover, the centrifugal force increases during high-speed operation, which adversely affects the stiffness of the motor. Therefore, in this paper, a new rotor shape of spoke-type PMSM was proposed to solve the above problem.

A Study on Core Skew Considering Manufacturability of Double-Layer Spoke-Type PMSM

The spoke-type permanent magnet synchronous motor (PMSM), which is a general ferrite magnetic flux-concentrated motor, has a low portion of reluctance torque at the total torque magnitude. Therefore, as a way to increase the reluctance torque, there is a double-layer spoke-type PMSM that can maximize the difference in inductance between the d-axis and the q-axis. However, in the double-layer spoke-type PMSM, cogging torque, torque ripple, and total harmonic distortion (THD) increase with reluctance torque, which is the main cause of vibration and noise. In this paper, a method is proposed that provides the same effect as skew without dividing stages of the permanent magnet by dividing the core of the rotor into two types so that it is easy to manufacture according to the number of stages, unlike extant skew methods. Based on the method, the reduction in cogging torque and THD was verified by finite element analysis (FEA).

Design Process of Spoke-Type Permanent Magnet Synchronous Motor Considering Magnetization Performance

Demagnetization of permanent magnets (PMs) directly leads to deterioration of the performance characteristics of a permanent magnet synchronous motor (PMSM). Therefore, the design process of a PMSM generally considers the demagnetization of PMs. In this paper, we propose a design process of spoke-type PMSMs considering the demagnetization performance of PMs and magnetization performance directly related to mass production. Unlike other motors, it is difficult to obtain magnetization performance suitable for mass production using spoke-type PMSM unless magnetization performance is considered in the design stage. Therefore, the design process proposed in this paper would be a good guide for engineers designing spoke-type PMSMs in the industry. Finally, to verify the validity of the proposed design process, a real motor was fabricated, and its performance was evaluated experimentally.

Study on the Improvement of the Correction Coefficient Considering the 3-D Effect of Spoke-Type Permanent-Magnet Synchronous Motor

In this article, a correction coefficient is proposed to reduce the error between 2-D finite-element analysis (FEA) and 3-D FEA results. The 2-D FEA results of flux-concentrating machines, such as a spoke-type permanent-magnet synchronous motor (PMSM), show considerable error compared to 3-D FEA results because of 3-D effects. Therefore, 3-D FEA is required to predict the performances precisely for this kind of machine, but it is a time-consuming task. This article proposes the correction coefficient to get accurate results with 2-D FEA. Compared to previous studies, the proposed coefficient can consider the effect of both axial linkage flux and axial leakage flux. Furthermore, the proposed general-purpose correction coefficient could be easily applied to any complex-shaped spoke-type PMSM without complex mathematical calculations. In order to verify the proposed correction coefficient, 2-D and 3-D FEA were performed on various models. Finally, the validity was finally verified through comparison with actual experimental results for prototypes with particular specifications.

Design and Analysis of a Novel Rotor Shape to Improve Power Performance

This study proposes a novel rotor shape for the spoke-type permanent magnet synchronous motor (PMSM) to improve its power performance by changing permeance and increasing magnetic flux density strength in the air gap. Applying a wedge-shaped barrier to the rotor results in a reluctance change in areas of the rotor that have saturated magnetic flux density, which changes the permeance in the air gap. In addition, magnetic flux can be transmitted to the air gap to increase the air gap magnetic flux density strength. In this study, a wedge-shaped barrier was used to maximize air gap magnetic flux density and torque, thus eliminating the magnetic flux density saturation area that negatively affects torque. This wedge-shape barrier also changes the inductances. The results confirmed that average torque improves as magnetic flux density saturation area is removed.

Design of Power Density Improvement by Applying Novel Shape of Slit and Notch to Outer Rib of Rotor of Spoke-type Permanent Magnet Synchronous Motor

Objective:In this study, improvement of power density by applying novel shape of slit and notch to outer ribs of a rotor that reduces magnetic flux leakage in outer rib and increases air-gap magnetic flux density for spe PMSM for a washing machine, was investigated.Methods:It is important that motors for home appliance require lower manufacturing cost, high power and high efficiency. In order to increase power, rotor shape is re-designed. In the outer rib of the rotor, magnetic flux leakage occurs by permanent magnet and magnetic flux is saturated which is one of the factors that reduces the power and efficiency. However, if the outer rib is designed to be too thin, the permanent magnet may scatter during high-speed rotation. Therefore, a design considering permanent magnet scattering is necessary. Motor for a washing machine has two operating points that washing mode at constant torque point and dehydrating mode at high-speed point.Conclusion:For improvement of higher power density, 2-D finite elements analysis was performed to optimize the parameters of the shape of slit and notch to increase the torque. The torque increases by optimizing width and length of slit shape and notch shape. Finally, with the optimized parameters of shape of slit and notch, stack length was adjusted as per torque requirement for a washing machine motor and power density increases considering the safe factor from stiffness analysis.

A Study on the Design of an Outer Rotor and Spoke Type PMSM for Improving Power Density

Object: This paper proposes an outer rotor and spoke-type permanent magnet synchronous motor (outer rotor spoke-type PMSM) to increase the power density compared to the inner rotor spoke-type permanent magnet synchronous motor(inner rotor spoke-type PMSM) used in washing machines. Method: In order to investigate the output characteristics of the Outer Rotor Spoke-type PMSM, comparison and analysis were conducted on three models of 16-poles/9-slots, 20-pole/9-slots and 22-poles/9-slots. Compare models were conducted with the limited condition which applies the same current density, phase voltage limit, and stator. The final model was optimized based on the model with the best output characteristics among three compare models. Conclusion: Finally, output characteristics are compared between compare models and the final model.

Cross Saturation Inductance Analysis of a Permanent Magnet Synchronous Motor

This paper presents the cross saturation effect on a specially designed spoke type permanent magnet synchronous motor (PMSM) for the sensorless vector control. The cross saturation effect becomes very important where the sensorless control algorithm is used. Accurate flux linkage modeling is required to obtain a satisfactory position estimation and eventually minimum induced torque error. The magnetic saturation is the most impacting parameters affecting the position error. Since the Ld and Lq inductance difference is generally less than 5% in the spoke type PMSM, the accurate estimation of the cross saturation is critical for the sensorless vector control. In this paper, the designed PMSM has the Ld and Lq difference in 15% level even for the overload capacity. So it is even possible to operate the motor in the transient modes with the overload capacity by estimating right cross saturation effect with certain time limits. The mapping of the inductances and efficiency are obtained by using Finite element method and presented in the paper. Some experimental results are also given such as efficiency and power-speed variation at the constant torque.

A Study on the Maximum Flux Linkage and the Goodness Factor for the Spoke-Type PMSM

In this paper, we propose a goodness factor that shows how the output density of a Spoke-type permanent-magnet synchronous motor (PMSM) is improved than that of the conventional surface permanent-magnet synchronous motor (SPMSM). The application of the goodness factor, which is defined as the ratio of the total flux between different motor configurations, enables a comparison of the total flux between the SPMSM and spoke-type PMSM. A performance comparison analysis between the two motor configurations with the same rotor diameter, air gap length, stack length, permanent-magnet usage, and materials was performed using the proposed goodness factor. In order to improve the performance prediction accuracy, furthermore, the effect of both the bridge leakage and the axial leakage was included during the analysis process of the spoke-type PMSM. Finally, in order to verify the proposed method, SPMSM and Spoke-type PMSM with the same outer diameter size and permanent-magnet usage were fabricated and evaluated.

Design of 3-Times Magnetizer and Rotor of Spoke-Type PMSM Considering Post-Assembly Magnetization

Unlike the existing bar-type permanent magnets, it is difficult to magnetize the ferrite spoke-type permanent magnet synchronous motor (PMSM), because the permanent magnet is placed deep inside the shaft. In order to magnetize permanent magnet, a high magnetic field intensity is required. However, the high magnetic field intensity may cause demagnetization of surrounding permanent magnets. It has a bad effect on the magnetization of the permanent magnet and the performance of the spoke-type PMSM. In this paper, we proposed magnetizer models for magnetization of spoke-type 10 pole rotor and the inter-pole winding to reduce the demagnetization of surrounding permanent magnets. Finally, the optimally designed model was manufactured and the performance of the magnetizer was verified.

Analysis of Inductance According to the Applied Current in Spoke-Type PMSM and Suggestion of Driving Mode

The spoke-type permanent magnet synchronous motor (PMSM) is a motor built using nonrare earth elements, which feature low flux density. It has a flux concentrated structure of permanent magnet arrangement to improve power density. Further, the torque in the spoke-type PMSM is composed of a magnetic torque component from the permanent magnets and a reluctance torque arising from the inductance difference between the d - and q -axis. This paper analyzed the d - and q -axes inductances that affect the reluctance torque depending on the magnitude of the applied current and the current phase angle of the spoke-type PMSM at base speed. We also derived the variation of the d - and q - axis inductances, which is shown at the operation speed region. Accordingly, the variation of the current phase angle for generating the maximum output power is analyzed. Based on the above results, we predicted the variation in the driving mode of the spoke-type PMSM, and subsequently verified the prediction experimentally.

Design and analysis of a novel spoke‐type permanent magnet synchronous motor

This study presents a spoke-type permanent magnet synchronous motor (STPMSM) with a novel rotor which contains four individual iron core parts with flux barriers that are designed to realise a near-sinusoidal air gap flux density waveform. This novel type of rotor does not require thin bridges or retaining sleeves, the iron core parts of a rotor of this type are fixed to a non-magnetic sleeve by using dovetail slots, this structure can restrict flux leakage effectively and ensure sufficient mechanical strength. The initial design parameters of a 3 kW novel motor were obtained in the initial design process first, then several key parameters were optimised by using the Taguchi method, finally a comparative analysis of the novel motor structure and the conventional STPMSM structure was performed. The comparative analysis results reveal that the novel motor structure is superior to the conventional motor structure.

Computational Method of Effective Remanence Flux Density to Consider PM Overhang Effect for Spoke-Type PM Motor With 2-D Analysis Using Magnetic Energy

According to the conventional study, it is possible to perform 2-D finite-element analysis (FEA) to consider rotor overhang effect through the adjusted remanence flux density by employing an overhang parameter. The latest study addressed that the overhang parameter can be obtained using the variation of operating point of permanent magnet (PM). In this paper, we propose the novel computational method to calculate the effective remanence flux density directly to consider PM overhang effect making use of magnetic energy, which is applied for a spoke-type PM synchronous motor. The proposed method is validated through a comparison with the results of 3-D FEA.

비희토류 전동기의 효율 향상을 위한 Fan-shape type PMSM 설계 및 성능 분석

The rare earth output is concentrated in limited number of countries including China. Also the necessity for development of non-rare earth motor is getting signified due to the rapid increase of rare earth price and resource weaponizing policies. Non-rare earth motor is generally designed as spoke type PMSM (Permanent Magnet Synchronous Motor) in order to maximize the power density. Such spoke type PMSM has advantage in concentrating the flux but demonstrates lower efficiency compared to permanent magnet using Nd (Neodymium) permanent magnet. Therefore, applications with strong necessity for efficiency need rotor structure having improved efficiency compared to spoke type PMSM. Hence, this study suggested fan-shape type PMSM with somewhat lower power density but maximized efficiency. Fan-shape type PMSM is a rotor shape demonstrating outstanding reduction of iron loss compared to existing spoke type. Thus, this study analyzed the improvement of efficiency and reduction of loss arising from the suggested shape through parameter calculation.