Axial flux permanent magnet synchronous motors (AFPMSMs) have advantages over other motor types in terms of efficiency, vibration, and noise. However, torque ripple is an important problem for axial flux permanent magnet (AFPM) motors. One of the methods recommended as a solution to this problem is the skew operation. The skew can be applied to the magnets or the stator. However, for these motors, this process is mostly applied to magnets because the skew applied to the stator makes it difficult to manufacture. In this article, a solution to the torque ripple of an in-wheel AFPMSM for the electric vehicle is sought. For this purpose, designs, optimization, and 3-D analyzes have been carried out. This solution has been applied to magnets designed by skewing for ease of production. 3-D analyses have been carried out by applying skew of up to 40° with an angle of 5° to the magnets in the rotor. In light of the analysis, the most appropriate skew angle that does not affect motor performance has been determined. As a result of the analysis of the motor model obtained with the determined skew angle, it is observed that the torque ripple decreased by 86.71%. Finally, production has been carried out according to the analysis results obtained.

Performance Analysis and Reduction of Torque Ripple of Axial Flux Permanent Magnet Synchronous Motor Manufactured for Electric Vehicles

To accurately and quickly predict the open-circuit air-gap magnetic field in interior permanent magnet synchronous machines (IPMSMs), an analytical model based on magnetic equivalent circuit (MEC) method is proposed. The analytical model can provide radial and tangential components of open-circuit magnetic field in the slotless air gap. The radial component is obtained from the MEC model, and the tangential component is obtained from boundary conditions of macroscopic equations. Then, a complex relative air-gap permeance is applied to take the effect of slots into account. As a result, an accurate solution of both radial and tangential components of the flux density in the slotted air gap is obtained. Additionally, the no-load back electromotive force (EMF) and cogging torque are calculated based on the open-circuit air-gap magnetic field. All the analytical results are verified by the finite element (FE) analysis and they are well matched. In the end, a direct measurement experiment of open-circuit air-gap magnetic field is proposed to verify the validity of both radial and tangential open-circuit air-gap magnetic fields.

Analytical Model of Open-Circuit Air-Gap Field Distribution in Interior Permanent Magnet Machines Based on Magnetic Equivalent Circuit Method and Boundary Conditions of Macroscopic Equations

In an interior permanent magnet synchronous motor (IPMSM) with segmented skewed poles, the armature reaction magnetic field (AR-MF) changes nonlinearly due to the saturation of the rotor magnetic barrier. Meanwhile, this varies under different excitation currents. As a result, it is difficult to be calculated by means of analytical methods. In this paper, the calculation model of AR-MF of IPMSM is first established by vector superposition method, without considering the saturation effect of rotor and the slotting effect of stator. In the second step, the virtual magnetic field of the rotor is introduced to quantitatively calculate the influence of local inhomogeneous saturation on the AR-MF. The latter is derived by combining both the subdomain method and equivalent magnetic circuit method. The complex relative permeance is also introduced to establish the AR-MF accounting for the stator slotting effect. To validate the AR-MF calculation method proposed, an 8-pole 48-slot IPMSM with segmented skewed poles is considered as a case study, showing a comparison by both with finite element (FE) results and the electromagnetic torque measured on a test bench. The model proposed in this paper shows high accuracy and fast computation with respect to FE analysis. 

/pdf/calculation-model-of-armature-reaction-magnetic-field-of-1fcsx7v0.pdf

Calculation Model of Armature Reaction Magnetic Field of Interior Permanent Magnet Synchronous Motor With Segmented Skewed Poles

Due to the local inhomogeneous magnetic saturation of the core of the interior permanent magnet synchronous motor (IPMSM), the magnetic field changes nonlinearly, which makes the analytical calculation of the magnetic field difficult. Therefore, the calculation of the magnetic field mostly relies on the finite element method (FEM). However, the high computation cost of FEM restricts the efficiency of the design and analysis of IPMSM. In this article, an analytical model (AM) of slotless open-circuit air-gap magnetic field (OC-AG-MF) of IPMSM with V-shaped segmented skewed poles is derived by combining the subdomain method (SDM) and the magnetic equivalent circuit (MEC) method, and then, the AM of slotted OC-AG-MF of IPMSM with V-shaped segmented skewed poles is obtained by introducing the complex relative permeance. To show the effectiveness of the novel AM, the OC-AG-MF and cogging torque of an IPMSM with V-shaped segmented skewed poles for electric vehicles are calculated by the AM and FEM, respectively. The spatial order, amplitude–frequency characteristics, and the 3-D spatial distribution of the OC-AG-MF are analyzed. Finally, the accuracy of the AM is experimentally verified by direct measurement of OC-AG-MF and no-load back electromotive force (EMF) of the motor. The AM proposed in this article is shown to accurately calculate the radial and tangential components of OC-AG-MF of IPMSM with V-shaped segmented skewed poles considering rotor magnetic bridge saturation effect and stator slotting effect. Meanwhile, the efficiency of the design and analysis of the motor is expected to be improved due to the reduced computational effort compared to the prevalent FEM.

Open-Circuit Air-Gap Magnetic Field Calculation of Interior Permanent Magnet Synchronous Motor With V-Shaped Segmented Skewed Poles Using Hybrid Analytical Method

Permanent magnet synchronous motor (PMSM) for electric vehicles is developing higher frequency and speed but triggering a significant increase of eddy current loss. To resolve the eddy current loss issue, a novel flat wire transposed winding composed of double-row multiple parallel strands is proposed. Transposed winding techniques have been proved to be efficient in reducing eddy current loss by preventing the uneven leakage magnetic field induced by high frequency. The proposed transposition further improved this technique in reducing circulating current loss. Taking a 60-kW PMSM as an example, the novel flat wire transposed winding arrangement is carried out. The 3-D field-circuit coupled finite-element models of 360° complete transposed and incomplete transposed winding PMSM are established, and circulating current losses are compared. The analysis results show that incomplete transposed winding has a better performance in reducing the circulating current loss. The transposition method suitable for novel flat wire transposed winding is obtained, and the feasibility of PMSM with novel flat wire transposed winding to reduce winding losses is proven. 

Research on Novel Flat Wire Transposed Winding of PMSM for Electric Vehicle

A 3-D analytical model of armature reaction field (ARF) of interior permanent magnet synchronous motor (IPMSM) with multi-segmented skewed poles (MSP) and multi-layered flat wire winding (MFWW) considering current harmonics is proposed in this paper. Firstly, based on the MFWW distribution analysis and the coil magnetic field vector superposition method, the ideal ARF functions of the MFWW considering low-order current harmonics and high-order sideband current harmonics are derived. Secondly, 3-D relative permeance functions caused by the stator slotting effect and the multi-segmented rotor magnetic barriers are presented. Thirdly, 3-D analytical expressions of ARF are obtained by multiplying the ideal ARF functions and the 3-D relative permeance functions. Additionally, the effects of low-order current harmonics, high order sideband current harmonics, MSP, and stator slotting on the spatial orders and frequencies of ARF are analyzed. Finally, the proposed model is verified by finite element method (FEM) and experiment.

/pdf/3-d-analytical-model-of-armature-reaction-field-of-ipmsm-2pqlmannwq.pdf

3-D Analytical Model of Armature Reaction Field of IPMSM With Multi-Segmented Skewed Poles and Multi-Layered Flat Wire Winding Considering Current Harmonics

The invention relates to a rotary motor ultrathin air-gap field test device and method and relates to a motor magnetic-filed test device and method. A test platform and a teslameter are arranged, a rotary workbench is arranged on the test platform, a motor mounting base is arranged on the rotary workbench, a probe support is arranged on the test platform on one side of the rotary workbench, a testconnecting rod capable of horizontally rotating is arranged on the probe support, the probe of the teslameter is arranged on the lower end of the test connecting rod, a radial mark and a tangential mark are arranged on the test connecting rod, a reference mark is arranged on the probe support, when the radial mark is opposite to the reference mark, the test face of the probe of the teslameter isperpendicular to the radial direction of the rotary workbench, and when the tangential mark is opposite to the reference mark, the test face of the probe of the teslameter is perpendicular to the tangential direction of the rotary workbench. The device in the invention is simple in structure and convenient to use, the radial air-gap field and the tangential air-gap field can be accurately measured, the development cost of the product design stage is reduced, and quality inspection and fault diagnosis after product production are facilitated.

Rotary motor ultrathin air-gap field test device and method

3-D analytical model and direct measurement method (DMM) of ultra-thin open-circuit air-gap field (OCAGF) of interior permanent magnet synchronous motor (IPMSM) with multi-segmented skew poles (MSP) and multi-layered flat wire windings (MFWW) for electric vehicles (EV) are proposed. Basis functions of slotless OCAGF are derived through field reconstruction method (FRM). In order to consider MSP and slotting effects, a complex relative permeance function is extended from 2-D to 3-D. Based on the magnetic potential and permeance method, 3-D analytical model of OCAGF is obtained. Then the back electromotive force (BEF) is calculated through Faraday's Law and the cogging torque is obtained through Maxwell stress tensor method. Furthermore, spatial order and amplitude-frequency characteristics of OCAGF are revealed. Additionally, influence of local inhomogeneous saturation caused by PM materials on analytical accuracy is discussed. Finally, the proposed analytical model is verified through both the traditional indirect measurement methods (BEF measurement and cogging torque measurement) and a novel direct measurement method, in which ultra-thin OCAGF of 10−1 mm order of magnitude can be measured directly. Local microscopic characteristics of OCAGF in some important locations, such as tooth top and magnetic bridge, can be accurately detected by using of the direct measurement method.

3-D Analytical Model and Direct Measurement Method of Ultra-Thin Open-Circuit Air-Gap Field of Interior Permanent Magnet Synchronous Motor With Multi-Segmented Skew Poles and Multi-Layered Flat Wire Windings for Electric Vehicle

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3-D Analytical Model of Armature Reaction Field of IPMSM With Multi-Segmented Skewed Poles and Multi-Layered Flat Wire Winding Considering Current Harmonics

Rotary motor ultrathin air-gap field test device and method

3-D Analytical Model and Direct Measurement Method of Ultra-Thin Open-Circuit Air-Gap Field of Interior Permanent Magnet Synchronous Motor With Multi-Segmented Skew Poles and Multi-Layered Flat Wire Windings for Electric Vehicle