Flux-switching Permanent Magnet Machine Research Articles

Understanding Switched-Flux Machines: A MMF-Permeance Model and Magnetic Equivalent Circuit Approach

Due to their particular structure, switched-flux permanent magnet machines have become a very interesting alternative for many applications. This is why some recent studies have been focused in the understanding of the operating mechanism of these machines via the MMF-permeance modelling. However, the models that can be found in the literature make some simplifications that reduce their accuracy when predicting the performance of switched-flux machines. For example, the models that can be found in the literature are commonly not precise enough for machines with a wide slot, because the influence of the modulator of the primary side of the machine is neglected. In this article, a precise analytical model is developed for a 6/13 C-Core switched-flux machine via a combination of a magnetic equivalent circuit and a MMF-permeance model. The model is based on the magnetic field modulation principle. The analytical model is used to explain the flux focusing effect and the force generation mechanism of switched-flux machines. A new concept of PM field harmonic efficiency ratio is used to identify the most efficient PM field harmonics of 2 switched-flux machines. The precision of the model is validated via 2D and 3D Finite Element Method simulations, and experimental measurements that were obtained with a linear machine prototype. The results show that the model can predict the performance of switched-flux machines with a high accuracy level.

Optimization and Comparison of Dual-Armature Flux-Switching Permanent Magnet Machines With Different Stator Core Shapes

This article investigates the influence of design parameters on average torque and compares the electromagnetic performances of novel dual-armature flux-switching permanent magnet (DA-FSPM) machines with different stator core shapes. Firstly, the topology of novel E- and C-core DA-FSPM machines are proposed and their operating principles are introduced. Secondly, the influence of design parameters on average torque of U-, E- and C-core DA-FSPM machines are analyzed in detail, including the stator to rotor copper loss ratio, split ratio, magnet arc, stator tooth arc, stator yoke thickness, rotor tooth arc and rotor yoke thickness. Then, the key parameters of the machines are sequentially optimized to maximize the average torque. It shows that the optimal parameters of the DA-FSPM machines are no longer the same as their FSPM counterpart machines. Furthermore, the electromagnetic performances of the optimized DA-FSPM machines and their FSPM counterpart machines are compared, including the phase back-EMF, electromagnetic torque, overload capability, inductances, power factor, efficiency, and unbalanced magnetic force. Finally, the finite-element analyses are validated on two prototype machines.

Evaluation of the Skewing Effect on the Electromagnetic and Fluid Mechanics Performance of an Integrated Motor-Compressor

An integrated motor-compressor synergistically combines a flux-switching permanent magnet machine with an axial-flow compressor by shaping the rotor poles of the motor into airfoils. The airfoil-shaped rotor functions as the rotor of a motor as well as the rotor of an axial-flow compressor. The airfoil-shaped rotor poles need to be skewed by the proper blade stagger angle to obtain optimal fluid mechanics performance. The objective of this article is to investigate the effects of the stagger angle (skew) of the airfoil-shaped rotor on the thermodynamic and fluid mechanics performance of the integrated motor-compressor by mean line calculations and computational fluid dynamics (CFD). The skewing effects on the electromagnetic performance of the integrated motor-compressor with aligned and unaligned stator-rotor configurations are also investigated by analytical equations and three-dimensional finite-element analysis. A prototype is built for the integrated motor-compressor. Experimental results are also included to validate the simulations.

Torque Performance Enhancement of Flux-Switching Permanent Magnet Machines With Dual Sets of Magnet Arrangements

Torque performance, especially torque density, is a critical performance index for the flux-switching permanent magnet (FSPM) machine that is attractive for the propulsion system. In this article, a novel FSPM machine with dual sets of magnet arrangements is proposed. With the novel topology, the torque density of the proposed machine is significantly improved due to much increased working harmonic contents of magnetomotive force (MMF). Moreover, the cogging torque is also inherently reduced, which makes the proposed machine a promising candidate in the FSPM machine family. The operating principle of the proposed FSPM machine is revealed based on the MMF–permeance model and the numerical finite element analysis (FEA). The effect of geometric parameters, such as magnet thickness, auxiliary tooth width, and rotor tooth width on the average torque and cogging torque, is also investigated. Finally, a prototype has been manufactured to validate the analysis conclusion. With experimental test results, it is demonstrated that the proposed topology can achieve 30.8% higher torque density, 79.4% lower cogging torque, and 15.6% higher power factor than the conventional counterpart.

Improved Primary/Secondary Pole Number Combinations for Dual-Armature Linear Switched Flux Permanent Magnet Machines

Due to additional armature windings on the secondary, dual-armature linear switched flux permanent magnet machines (DALSFPMMs) exhibit higher force densities than conventional LSFPMMs. Nevertheless, the existing DALSFPMMs suffer from larger secondary phase numbers because of the prime secondary pole numbers. This article proposes more optional primary/secondary pole number combinations with fewer phase numbers for DALSFPMMs. The machine topology is introduced first, followed by the analysis of phase numbers, which indicates the DALSFPMMs with 8/9 primary/secondary poles (8p/9s) and 9p/8s have fewer phase numbers and need fewer power electronic devices. Then, the operation principle of DALSFPMM is analyzed from the perspective of air-gap field. After that, the electromagnetic performances of four DALSFPMMs with 8p/9s, 9p/8s, 6p/7s, and 6p/5s are investigated by 2-D finite element method, showing the 8p/9s and 9p/8s machines have higher average thrust forces, lower thrust force ripples, and higher thrust force to permanent magnet (PM) volume ratios than the 6p/7s and 6p/5s counterparts. Finally, a prototype machine is manufactured for the experimental validation.

A novel flux switching claw pole machine with soft magnetic composite cores

This paper proposes a novel flux switching claw pole machine (FSCPM) with soft magnetic composite (SMC) cores. The proposed FSCPM holds advantages of the conventional flux switching permanent magnet machine (FSPMM) and claw pole machine (CPM) with SMC cores. As permanent magnets are installed between the stator claw pole teeth, FSCPM has good flux concentrating ability, and the air gap flux density can be significantly improved. The torque coefficient of FSCPM is relatively high due to the applied claw pole teeth and global winding. FSCPM is mechanically robust because there are no windings or PMs on its rotor. Moreover, the core loss of FSCPM is relatively low for the SMC material has lower core loss at high frequency compared with silicon steels. The topology and operational principle of FSCPM are explained first. Several main dimensions of the machine are optimized to achieve better performance, based on 3D finite element method (FEM). Furthermore, the rotor skewing technology is adopted to reduce the cogging torque and torque ripple.

Analytical Model for Brushless Double Mechanical Port Flux-Switching Permanent Magnet Machines

In this article, a 2-D analytical model is presented for brushless double mechanical port flux-switching permanent magnet machines (BDMPFSPMMs). The BDMPFSPMM is an appropriate candidate to be employed as the electric motor in hybrid electric vehicles (HEVs) due to integrating two rotors and two stators into a compact structure. The radial and tangential components of the magnetic flux density are calculated due to permanent magnets and armature currents in each active region of the machine based on the subdomain method. The effects of the saliency on both the rotor and stator structures as well as their interactions are considered. The approach can be used for the magnetic field calculation in BDMPFSPMMs with any combination of rotor- and stator-pole numbers. Based on the computed magnetic flux density, electromagnetic torque, self and mutual inductances, flux linkage, induced voltage, local traction, and unbalanced magnetic force (UMF) are obtained. To validate the proposed model, the analytical results are compared with those obtained from the finite element method (FEM).

Leakage flux reduction of axial-flux switching PM machine by using HTS-disk

Nowadays, axial flux switching permanent magnet machines are attractive and widely used in direct drive applications because of their unique features. This paper proposes a high temperature superconductor (HTS) disk axial flux switching permanent magnet (AFSPM) machine with spoke type permanent magnets (PMs) and three-phase two layers concentrated windings. The novelty of the proposed machine is using HTS material on the rotor and stator as a disk, insignificant relative permeability of the HTS materials causes magnetic reluctance to become extreme. Because of this feature HTS-Disk in the proposed HTS-AFSPM machine does not allow the flux to enter or exit which causes leakage flux reduces. In order to better investigate and fair comparison, all analyses have done at the same condition using the finite element method (FEM) by Ansys Maxwell. The comparison results show that the proposed HTS-Disk AFSPM machine achieves higher back-EMF, permanent magnet (PM) flux, flux distribution, lower inductance and losses and fewer total harmonics distribution compared to conventional AFSPM machine.

Back EMF Waveform Comparison and Analysis of Two Kinds of Electrical Machines

In this study, the back electromotive force (EMF) waveforms of a flux switching permanent magnet (FSPM) machine and variable flux memory permanent magnet (VFMPM) machine with same main dimension were researched. Firstly, the simulation result showed that the maximum amplitude of phase back EMF waveform of FSPM machine was 245% larger than that of the VFMPM machine, and this was verified by the experimental result (243%). Secondly, the phase back EMF harmonics of the FSPM machine and VFMPM machine were compared, including the enhance flux condition and weaken flux condition of VFMPM machine. At last, the mutual demagnetization effect, which led to the difference amplitudes of maximum back EMF waveform between FSPM machine and VFMPM machine was analyzed. The comparison and analysis of the back EMF waveform will provide some qualitative advice for the future application research of the FSPM machine and VFMPM machine, such as application selection, optimization control method and so on.

Investigation of the Torque Production Mechanism of Dual-Stator Axial-Field Flux-Switching Permanent Magnet Motors

This paper studies the torque production mechanism of the dual-stator axial-field flux-switching permanent magnet (DSAFFSPM) machine. Due to the double-sided slotting design of such topology, more resultant air-gap working harmonics in the air-gap flux density are responsible for the torque production and the stator air-gap permeance is especially considered in the investigation. Based on the magnetic force (MMF)-permeance model, the composition and difference of the air-gap working harmonics are demonstrated. The DSAFFSPM machine torque contributions of the main working harmonics are analyzed theoretically and quantified by finite element analysis (FEA). The influence laws of the parameters on the working harmonics are shown and this effectively improves the motor operation performance. Finally, some experiments on the DSAFFSPM machine are carried out to validate the analytical and FEA results.

Modeling and analysis of a mesh-based equivalent magnetic circuit for a flux switching PM machine

<p indent=0mm>To precisely and efficiently predict the performance of a flux-switching PM machine, this study proposes a novel equivalent magnetic circuit model based on a meshing approach. This method includes developing the cross-shape magnetic meshes and combining the magnetic circuit model with mesh branches. The cross-shape meshes are generated in disordered magnetic fields to self-adaptively represent the flux distributions without magnetic field predelineation. The flux leakage and local saturation can be simultaneously considered. Furthermore, the lumped parameter magnetic circuit model is utilized in the uniform magnetic path region to shorten the computing consumption. The modeling accuracy and efficiency are both guaranteed. Moreover, the original rotor and the rotor with a magnetic barrier are modeled based on the advantage of fixed meshes, which avoids the rearrangement of the structure and efficiently analyzes the electromagnetic performance. The effect of rotor magnetic barrier structure on reducing the eddy current loss of permanent magnet is evaluated quickly and accurately. Finally, the effectiveness of the proposed EMN model is verified via comparison with finite element analysis and experimental tests.

Development of a Thermal Analysis Tool for Linear Machines

The thermal design is one of the most important stages in the design process of electrical machines. Thanks to software packages, like Motor-CAD, rotating machine designers can predict the thermal operation of the machines with high precision. However, a Motor-CAD equivalent for linear machines does not exist. Thus, linear machine designers must develop specific thermal analysis tools when designing the machines. In this article, a generic thermal analysis tool for different kinds of linear machines is presented. The model has been designed in MATLAB Simulink. Hence, it should be easy to implement for most engineers. The article describes the configuration of the different elements of the tool. The calibration parameters and procedure, and typical values of the calibration variables, are also given in the document. Finally, in order to demonstrate the generic nature of the tool, the model is experimentally validated via DC thermal tests to a linear induction machine and a linear switched-flux permanent magnet machine. The results show that, despite being simple and easy to implement, the model can predict the thermal operation of different machines with high precision.

Double Armature Partitioned Stator Switched Flux PM Machine for Electric Vehicle Applications

This paper investigates the performance of a partitioned stator switched flux PM machine that has double armature windings. The machine design is dedicated for electric vehicle applications. The modular structure, and the operation principles have been explained. Also, the design and optimization procedure for the machine including the rotor and stator number of poles and optimum parameters of the design have been clarified. The performance of the machine is compared with the conventional partitioned stator machine with a cylindrical inner stator and the salient inner stator machines, and the Prius IPM machine. The partitioned stator machines have the same main parameters which are globally optimized for optimum average torque. The comparison is based on the electromagnetic performance in the open-circuit and on-load analysis. The 2D finite element results show the superior performance of the double armature portioned stator machine based on the highest average torque, the minimum cogging torque, and best torque-current density and torque per PM volume characteristics.

A New High-Speed Dual-Stator Flux Switching Permanent Magnet Machine With Distributed Winding

This article proposes a new axial dual-stator flux-switching permanent magnet (FSPM) machine for high-speed applications. The machine adopts a fractional slot distributed winding, which has a higher winding factor, efficiency, and torque density. First, the high-speed FSPM machine topology and operating principle are introduced. By employing the winding complementarity principle, the unfavorable even harmonics of a single stator in the FSPM machine can be counteracted, resulting in an essentially sinusoidal permanent magnet (PM) flux-linkage as well as effectively reduced cogging torque and torque ripple. Second, based on the 3-D finite element method (FEM), both the no-load and on-load electromagnetic performances are obtained. Compared with the other three FSPM machines, the advantages of the proposed machine are highlighted. Finally, a high-speed FSPM prototype is manufactured and a test platform is built to measure the no-load and on-load performances, which verifies the theoretical analysis and simulated results.

Evaluation of the Self-Cooling Performance of a Flux-Switching Permanent Magnet Machine With Airfoil-Shaped Rotor

The objective of this article is to evaluate the self-cooling performance of a novel integrated flux-switching permanent magnet (FSPM) machine with an airfoil-shaped rotor. The rotor of the proposed integrated machine is functioning as both a rotor of the motor as well as an axial fan. It rotates to draw air from the ambient into the rotor and accelerate the flow through the rotor stage. The high-speed flow provides forced convection to the rotor, stator, windings, and magnets. Therefore, self-cooling is achieved. Accounting for manufacturing challenges of the airfoil blades, three-dimensional (3-D) printed blade caps are designed and assembled over the laminated rotor poles for the airfoil-shaped rotor. The electromagnetic performance of the continuous-skewed stator slot is compared with the step-skewed stator slot. Three housing configurations are proposed in terms of housing with radial inlets, housing with axial inlets, and no housing. The electromagnetic performance is verified by 3-D finite element analysis (FEA). The convective heat transfer coefficients of the three housing configurations are calculated by analytical methods and numerical simulations by 3-D computational fluid dynamics. The effect of encapsulations on the windings is also evaluated by FEA. A prototype machine is built and tested. Experimental results of measured temperature distributions on the stator and windings are included to validate the numerical simulation results.

2-D analytical modelling of novel consequent pole linear permanent magnet flux switching machine

2-D analytical modelling of novel consequent pole linear permanent magnet flux switching machine

High-Frequency Core Loss Analysis of High-Speed Flux-Switching Permanent Magnet Machines

Accurate prediction of core losses plays an important role in the design and analysis of flux-switching permanent magnet (FSPM) machines, especially during high-speed and high-frequency operation. Firstly, based on the numerical method, a high-frequency core loss prediction method considering a DC-bias magnetization component and local hysteresis loops as well as the harmonic effect is proposed. Secondly, the magnetizing characteristics of the silicon steel sheet and, consequently, the core loss of the electrical steel used as the core lamination are measured. Then, the loss coefficient of each core loss component is obtained by the data fitting tool. Based on the proposed method, the stator and rotor core losses of a three-phase, 12-stator-slot, and 10-rotor-pole (12/10) FSPM machine with different soft iron materials and driving modes are calculated. Finally, the results of the numerical method are verified by conventional finite element analysis.

Comparison Between Dual-Armature Linear Switched Flux Permanent Magnet Machine and Linear Surface-Mounted Permanent Magnet Machine Considering Thermal Conditions

It has been proved that dual-armature permanent magnet (PM) machines have higher power density than conventional PM machines under the same copper loss. However, the thermal conditions of these machines are different. This paper makes a fair comparison between a dual-armature linear switched flux PM machine (DALSFPMM) and a linear surface-mounted PM machine (LSPMM) by considering both electromagnetic performances and thermal conditions. First, the topologies of two machines and platform are introduced. Then, the 2D and 3D finite element (FE) models are employed for the electromagnetic and thermal analyses, respectively. During the machine optimization, the thermal analysis is used to determine the copper loss under the fixed machine dimensions, while the electromagnetic analysis is used to optimize the machine dimensions under the fixed copper loss. After iterations, two machines are optimized and their performances are compared. Under the limitations of 80 °C maximum PM temperature and 120 °C maximum winding temperature, the DALSFPMM can exhibit 38% higher thrust force density for the continuous duty and up to 43% higher thrust force density for the short-time duty. Finally, a prototype machine of DALSFPMM is tested to validate the analyses.

A Novel Mechanical Flux Weakening Method for Flux Switching Permanent Magnet Machine

— This article presents a novel mechanical field weakening method for flux switching permanent magnet (FSPM) machines to extend the torque-speed characteristic and improve the efficiency at high speeds. The proposed method consists of segmenting the permanent magnets (PMs) part along the back-iron radius into a circular shape embedded into the rectangular magnet. The circular-shaped magnet segments (CMSs) can then be rotated to enhance or short circuit the PMs flux. When the magnetization orientation of the PMs and the CMSs are in the same direction, the flux will flow as of that of the conventional FSPM machine, i.e. field strengthen. Conversely, when the high speed is required, the CMSs will be rotated 180°, and therefore, the PMs and the CMSs magnetization orientation will be in opposite direction, and therefore, a short circuit of the PMs flux will be created. This will lead to lower PMs flux linkage, and therefore, higher field weakening factor. A FSPM machine with 12/10 stator/rotor pole combination has been selected to investigate the proposed method. First, to study the proposed method, a comparison of the electromagnetic performance of the FSPM machine in flux strengthening and weakening states has been conducted and presented. Then, mechanical analysis of the proposed method has been made with focus on the mechanical rotating system and the consequent structural stress on the rotating magnet. In conclusion, the proposed method shown a good field weakening capability and improved torque-speed characteristics.

Comparative Study of Winding Configuration on a Multitooth Flux-Switching Permanent Magnet Machine

In this paper, based on a 6-stator-coil/17-rotor-tooth (6/17) conventional concentrated-winding multi-tooth flux-switching permanent magnet (C-MFSPM) machine, a novel full-pitch multi-tooth FSPM (FP-MFSPM) machine is proposed by changing winding configurations. Then, the electromagnetic performance of six FP-MFSPM topologies sharing the same 6-stator-coil but with different rotor teeth combinations, namely 6/13, 6/15, 6/17, 6/19, 6/21, and 6/23, is compared by using finite element analysis (FEA). The results show that 6/17 and 6/19 are the optimal stator-coil/rotor-tooth combinations for FP-MFSPM machines, which exhibit better electromagnetic performance, such as more enormous torque and smaller torque ripple. Thereafter, the existing C-MFSPM and the proposed FP-MFSPM machines with 6/17 and 6/19 structures are quantitatively compared in terms of no-load back electro-motive force (back-EMF), air-gap flux density, cogging torque, electromagnetic torque, torque ripple, etc. The FEA-predicted results validate that the proposed FP-MFSPM machines have more sinusoidal back EMF, larger torque output, and smaller torque ripple, which are superior to the C-MFSPM topologies.