Flux-switching Permanent Magnet Research Articles

A Comparative Study of Dual Stator With Novel Dual Rotor Permanent Magnet Flux Switching Generator for Counter Rotating Wind Turbine Applications

Compared with the single rotor wind turbine, a counter-rotating (CR) wind turbine with two rotor sets leads to twice power density. In this regard, dual stator CR (DSCR) permanent magnet flux switching generator (DSCR-PMFSG) is employed. However, in DSCR-PMFSG both rotor and armature parts are rotating and require slip rings for power transmission. These slip rings associate demerits of constant maintenance, poor speed regulation, increased cost, and additional slip ring losses, whereas DSCR-PMFSG offer lower flux and lesser power density. To overcome the demerits of DSCR-PMFSG as mentioned earlier, this paper proposed a novel dual rotor counter-rotating permanent magnet flux switching generator (DRCR-PMFSG) for wind turbine applications that eliminate the requirements of slip rings and retain brushless operation. The proposed DRCR-PMFSG share one stator connected back-to-back through a flux bridge that provides an alternate flux path between two mechanical ports associated with the inner rotor and outer rotor, contributing to the cumulative output. A detailed comparative analysis of DSCR-PMFSG and DRCR-PMFSG is performed under static characteristics, overload, and wide speed range to generate output power, voltage, current, power density, and efficiency. Quantitative comparative analysis under static analysis evident that proposed DRCR-PMFSG exhibits 33.29% higher flux, suppressed cogging torque and torque ripples up to 53.48% and 67.45%, respectively. Furthermore, a comprehensive quantitative analysis is performed under coupled overload and over-speed capability. Analysis exposes that in comparison with DSCRP-PMFSG, the proposed DRCR-PMFSG improves voltage regulation factor by 55.88%, output current enhanced by 67.9%, raise output voltage to 2.01 times, and power density to 1.72 times while maintaining the efficiency of 90.195% and achieving stable voltage profile with load variation. Finally, a detailed comparative analysis with conventional designs is performed and comprehensive mathematical modelling based on sub-domain model is developed accounting stator slot and rotor pole combinations, magnetic saturation, and winding configuration to validates finite element analysis (FEA) of JMAG Designer v.20.1.

A Novel Dual Rotor Permanent Magnet Flux Switching Generator for Counter Rotating Wind Turbine Applications

In this paper counter rotating (CR) dual rotor permanent magnet flux switching generator (CR-DRPMFSG) is designed and relatively studied with co- rotating DRPMFSG (CoR-DRPMFSG) for wind turbine applications. The developed CR- DRPMFSG and CoR-DRPMFSG share same stator linked with flux bridge which provide flux route. A comprehensive relative assessment of both CR- DRPMFSG and CoR-DRPMFSG are presented with static attributes, over-load, and over-speed capability for generating output voltage, output current, output power, power density, losses, and efficiency. Comparative study with static characteristics illustrates that developed CR- DRPMFSG shows 34.34% elevated phase flux which improve output power, cumulative output torque is improved by 23.86%, and suppressed cogging torque by 66.87% at CoR-DRPMFSG that results lower pulsation in instantaneous torque. Furthermore, a detailed performance analysis is investigated with different number of armature winding turns per phase and combined over-load and over-speed capability. Study discloses that in contrast with CoR-DRPMFSG, counterpart CR- DRPMFSG offer 27.17% higher output power that results 1.25 times power density with a good voltage regulation factor of 18.67%. In additional, despite of 2.27% improvement of efficiency in case of phase winding turns analysis and 4.81% increase in over-load and over-speed capability, contour efficiency map unveils that CR- DRPMFSG offer wide range of higher efficiency operating region during over-load and over-speed condition accompany with stable voltage profile with load variation.

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.

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.

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.

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 flywheel energy storage system: Based on the barrel type with dual hubs combined flywheel driven by switched flux permanent magnet motor

With the challenges of global carbon emissions and climate warming, energy recovery and reuse are becoming very important. Flywheel energy storage system (FESS), as a kind of energy storage systems (ESSs), can effectively convert electrical energy and mechanical energy to accomplish energy recovery and reuse. Additionally, the FESS has the characteristics of pollution-free, high energy, high efficiency, and durability. Thus, a novel FESS is proposed for the configuration, metal material and structure, and driving motor (M/G) to contribute to the development of FESS. First, the novel FESS is made of the metal materials rather than the carbon fiber, reducing manufacturing difficulty and cost. Second, the structure of dual hubs combined flywheel is designed to reduce the mass and obtain a larger moment of inertia, achieving higher energy storage. Third, a 12/10 switched flux permanent magnet motor (SFPM) with an outer rotor structure is designed to replace the conventional permanent magnet synchronous motor (PMSM) and is used as the M/G to achieve excellent operation performance. Finally, the barrel type of the configuration makes the novel FESS more compact and facilitates the realization of a vacuum chamber to remove the windage. Undoubtedly, the novel FESS is designed through the theoretical calculation of energy storage, structure strength and modal analysis, and M/G performance simulation. Accordingly, the novel FESS has a maximum speed of 13,500 rpm, storage energy of 20 kWh (discharge depth 99%), and the longest power consumption time of 2 h. Equally, a prototype is manufactured and tested. Consequently, the results testify the mechanical properties are excellent, the charging and discharging action is stable and rapid.

A dynamic model for the investigation of twisting effect in long flux‐ switching PM motors in ESPs

Shaft twisting occurs along the length of electric motors rotors. The twisting depends on the shaft properties and the transmitted torque. In Electrical Submersible Pumps, due to the high ratio of length to the diameter of the motor and the high load torque, the twisting effect occurs significantly. Thus, when such a condition emerges for an electric motor, the electromagnetic torque is not uniformly produced along the motor length, since shaft twisting results in rotor position variation with respect to the stator. Therefore, the twisting and the produced electromagnetic torque of the motor are interdependent. It means that these two issues cannot be studied separately and a model must be proposed to consider them together so that the electromagnetic performance of the motor can be studied under such conditions. Despite the importance of modeling the twisting effect for the electric motor, this issue has never been investigated before. In this article, a novel dynamic model for the flux-switching permanent magnet motor is proposed by which the shaft twisting effect is simulated to study the motor performance. Eventually, the twisting effect during startup and steady-state are studied as well as the effect of shaft diameter and motor length on shaft twisting. To evaluate the model, it is compared with the verified steady-state model for the flux-switching permanent magnet motor with the twisted shaft obtained from another article, and also results obtained by finite element analysis.

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.

Performance optimisation of a segmented outer rotor flux switching permanent magnet motor for direct drive washing machine application

Electrical machines are widely used in home appliances, the performance of which is mostly related to the quality function of the electrical machines. What has been used so far in home appliances brought with themselves a wide assortment of advantages and disadvantages. With the aim to overcome the drawbacks of the previously implemented electrical motors in washing machines, a new configuration of flux switching permanent magnet motor (FSPM) with the segmented outer rotor (SOR-FSPM) is proposed benefitting from a direct driven drum. To reduce the cogging torque as well as torque ripple and to improve the total harmonic distortion, cutting the stator in a way to lower overlapping between the rotor and stator pole, inserting notches into the poles of the rotor to modify the air gap between the stator teeth and the rotor segments are proposed. The Taguchi method and sensitivity analysis are further applied to find the best combination set of changes in such a way to smoothen the chart showing reluctance between stator and rotor and fix the zero-point crossing of the flux linkages in different rotor positions. Finally, the proposed SOR-FSPM is prototyped, and experimental results along with the finite element method results are discussed and compared in order to verify the design process.

Comparative Study of Stepwise Optimization and Global Optimization on a Nine-Phase Flux-Switching PM Generator

In this paper, the design procedure and optimization process of a multi-phase flux-switching permanent magnet (FSPM) generator for wind power generation system is investigated. Two different optimization methods—stepwise optimization and global optimization—are implemented and applied to the optimization of the proposed nine-phase FSPM generator-based wind power system. Both the advantages and disadvantages of two optimization methods are compared and analyzed. The results indicate that the stepwise optimization can achieve good effects on individual optimization objectives, whereas the global optimization can not only achieve a good optimization effect on a single objective, but also can find design point on the Pareto front, which can effectively optimize different multi-objects. The electromagnetic performance of the nine-phase FSPM generator is verified by experiments on a prototyped machine and the measured results show that the proposed generator exhibits the favorable characteristics of high torque, low torque ripple, and high efficiency.

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.