Flux Reversal Permanent Magnet Research Articles

A pole-changing flux reversal permanent magnet motor

In this paper, a pole-changing (PC) flux reversal permanent magnet (FRPM) motor is proposed for obtaining a wide speed range. According to the general air-gap field modulation theory, the permanent magnet (PM) magnetic field is modulated into a series of harmonics with different pole numbers by rotor teeth. By introducing an especial PM arrangement, two groups of working harmonics with different pole-pair numbers are generated in the proposed 12-7 PC-FRPM motor due to the modulation of rotor teeth. Based on the calculated slot pitch angles of these harmonics, two winding connections can be obtained for PC operation to achieve two operating modes. The electromagnetic performance of PC-FRPM motor before and after PC are analyzed using finite element analysis and verified by the experimental test results.

Design and Quantitative Analysis of Asymmetric Flux Reversal Permanent Magnet Linear Machine with Reduced Leakage Flux

Design and Quantitative Analysis of Asymmetric Flux Reversal Permanent Magnet Linear Machine with Reduced Leakage Flux

Comparative Analysis of Novel Asymmetric Consequent-Pole and Conventional Flux Reversal Permanent Magnet Machines

Torque density is a critical performance index for flux reversal permanent magnet (FRPM) machines. In this paper, a novel asymmetric consequent-pole (ACP) FRPM machine with alternate teeth wound is proposed. Different from the conventional consequent-pole FRPM machine with uniform “Fe/N-Fe/N-Fe/N” structure, the proposed ACP FRPM machine adopts “Fe/N/Fe-N-Fe/N/Fe” topology. With the novel topology, torque capability of the proposed machine is significantly improved due to the newly produced lower working harmonics of air-gap flux density. The operating principle of the proposed ACP FRPM machine is analyzed based on the magnetomotive force (MMF)-permeance model with variable winding factors and validated by finite element analysis (FEA). The effects of geometric parameters such as magnet, main tooth-tip and rotor tooth width on average torque and torque ripple are also investigated. Finally, a prototype has been manufactured to validate the theoretical results. With experimental test results, it is demonstrated that the proposed topology can achieve 109.1% higher back EMF and 55.7% higher torque density despite the stator current is reduced by 25.4% compared with the conventional consequent-pole FRPM machines.

Flux Reversal Permanent Magnet Machines With Single-Layer Non-Overlapping Windings

Single-layer (SL) non-overlapping windings are applied to flux reversal permanent magnet (FPRM) machines, to extend the family of stator-PM machines. The machine topology and operating principle are introduced, and the general rules of symmetrical phase flux-linkages in machines with various slot/pole number combinations are found. The even order coil flux-linkage harmonics can be cancelled in the resultant phase waveforms due to opposite polarities of either magnets or coils. Moreover, based on finite element (FE) analysis, the FRPM machines with different rotor pole numbers, equipped with SL or double-layer (DL) windings, are comprehensively compared. The results reveal that compared to their DL counterparts, the FRPM machines with SL windings (FRPM-SL) exhibit similar torques and iron losses, as well as enhanced flux-weakening and fault-tolerant capabilities due to higher self-inductances but lower mutual-inductances. A pair of FRPM-SL prototype machines are manufactured and tested to validate the predictions.

Accurate and Efficient Surrogate Model-Assisted Optimal Design of Flux Reversal Permanent Magnet Arc Motor

An accurate and efficient surrogate model plays a significant role in the optimal design of electrical motors. This paper presents an accurate and efficient surrogate modeling method for a flux reversal permanent magnet arc motor (FR-PMAM) based on machine learning algorithm. Specifically, the motor topology and the optimized design of the FR-PMAM are firstly illustrated. Then, the PM magnetic motive force-permeance model is developed to select structural parameters of FR-PMAM. After that, a finite-element analysis (FEA) model of FR-PMAM is calculated to obtain sample data. A machine learning algorithm random forest is introduced into the field of motor optimal design for the first time to evaluate the contribution of each parameter to the design objectives. Based on the sample data, an efficient machine learning algorithm CatBoost is innovatively employed to establish the accurate and efficient surrogate model of the FR-PMAM that can capture the complex function relationship between output objectives and input parameters. Subsequently, an improved genetic algorithm with the elitist reservation strategy is adopted to obtain the optimal combination of the structural parameters of FR-PMAM. Finally, a prototype of the FR-PMAM is manufactured. The FEA and experimental results validate the effectiveness of the investigated surrogate modeling method.

Investigation of a Novel Linear Partitioned Primary Hybrid-excited Consequent-pole Flux-reversal Permanent Magnet Machine

This paper proposes a novel linear partitioned hybrid-excited consequent-pole flux-reversal machine featuring a wide flux adjusting range with less PM consumption. Due to the space confliction between armature and field windings in conventional hybrid-excited machine, the consequent-pole partitioned primary structure is employed to improve the PM utilization ratio and further enhance the flux regulation capability. Firstly, the topology, operation principle and flux regulation mechanism are introduced. Then, using finite element method (FEM), the dimensional parameters of the proposed machine and a conventional machine for comparison are globally optimized for higher thrust force and wider flux adjusting range. The electrical performance of optimized structures including open-circuit airgap flux density, open-circuit phase back-electromotive force (back-EMF), flux-adjusting capability and force characteristics are investigated. Furthermore, demagnetization and normal force are analyzed. Finally, a prototype is manufactured to validate the effectiveness of the proposed topology and analysis. The proposed machine is observed to have better flux regulation capability than conventional machine with improved PM utilization ratio, which means it is suitable for wide speed range system applications.

Research on High-Torque-Density Design for Axial Modular Flux-Reversal Permanent Magnet Machine

The traditional flux reversal permanent magnet (FRPM) machine has high torque ripple due to the double salient-pole structure, and the effective air-gap length is increased by the permanent magnet structure of the stator tooth surface, which affects the size of the air-gap magnetomotive force (MMF). This paper proposes an axial modular flux-reversal permanent magnet (AM-FRPM) machine with attractive torque capabilities. Based on air-gap magnetic field modulation theory, a method to achieve optimal air-gap harmonic torque contributions was developed. Then, the principle for high-torque-density generation in the AM-FRPM machine under an alternating magnetization topology was investigated using the PM magnetic field modulation and armature reaction magnetic field modulation. In addition, the cogging torque suppression mechanism, which guides the selection of stator-slot and rotor-pole combinations, was investigated. In addition, a comprehensive comparison of the electromagnetic characteristics of two AM-FRPM machines and a traditional FRPM machine was conducted. Then, the advantages and disadvantages of the three machines were analyzed. Finally, prototypes were manufactured and tested to verify the correctness of the theoretical analysis.

Torque and magnetic suspension force generation in dual armature alternating pole bearingless flux reverse permanent magnet machine

Dual-armature alternating pole bearingless flux reversal permanent magnet (DAAPBFR) machines have the characteristics of high speed and non-contact operation; they are suitable for aerospace, flywheel battery, and other wide speed-range applications. Based on the analysis of the mechanism of torque and suspension force, the power dimension equation of the machine is given, which lays the foundation for the design of structural parameters. Finally, the influences of torque output capacity and radial suspension force of the machine are estimated, and the relationship between air gap magnetic density, copper loss, and torque is examined. The simulation shows that the DAAPBFR machine has good overload capacity.

Comparative Study of Biased Flux PM Machines Having Different Stator Core Segments and Armature Winding Configurations

This article proposes a comparative study of biased flux permanent magnet (BFPM) machines having different stator core segments and armature winding configurations. The topologies of the four investigated machines and their operating principles are introduced first. Then, in the case of same envelope size and copper loss, all four BFPM machines are designed based on the single variable optimization method to obtain higher average torque, along with their comparison of electromagnetic characteristics such as phase back-electromotive force (back EMF), cogging torque, and torque capability. It is shown that by exploiting both flux focusing (FC) and dual armature (DA) design, the average torque of the BFPM machine has a 132% sharp increase. Furthermore, to reveal the real performance of the DA-FC-BFPM machine, its comparison with machines such as DA doubly salient permanent magnet (DA-DSPM) machine, DA flux reversal permanent magnet (DA-FRPM) machine, DA flux switching permanent magnet (DA-FSPM) machine, wound rotor synchronous (WRS) machine, and surface-mounted permanent magnet (SPM) machine is performed. Finally, a prototype machine is built and tested to verify the finite-element predictions.

Analysis of the operating principle of a dual-armature consequent-pole bearingless flux reversal permanent magnet machine

This paper proposes a new type of dual-armature alternating pole bearingless magnetic flux reverse permanent magnet machine, which combines the advantages of the alternating pole structure and the dual-armature structure. This machine shows the advantages of high torque density and good fault tolerance, which can not only reduce the number of permanent magnets but also further improve the machine’s torque. It is suitable for use in wind power, aerospace, and other applications. The dual-armature alternating pole bearingless magnetic flux reverse permanent magnet machine is used to improve the torque performance and suspension force. Based on the dual-armature alternating pole magnetic flux reverse machine, by adding an additional set of stator teeth to suspended windings, a new type of dual-armature alternating pole bearingless magnetic flux reverse permanent magnet machine is obtained. The number of permanent magnets is halved, and each permanent magnet has the same polarity. The ferromagnetic pole piece next to the permanent magnet automatically acts as the other pole. Based on the introduction of its related structure, the stator flux, rotor flux, stator back electromotive force, cogging torque, electromagnetic torque, etc., are analyzed. This new machine can reduce the number of permanent magnets and has a higher torque conferring advantages of output capacity and low torque ripple.

Analytical prediction of the flux reversal permanent magnet machine with Halbach array magnets in rotor slot considering saturation

This study presents an improved sub-domain analytical model for the characteristic evaluation of the flux reversal permanent magnet machine with Halbach array magnets (FRPMM-HAM) in rotor slot. The influence of iron saturation is considered by equating iron reluctances into airgap. Based on the different material magnetic permeabilities, the FRPMM-HAM is divided into several regions, including slots, permanent magnets (PMs), airgap and so on. By solving the Maxwell equations in polar coordinate for each region according to the boundary conditions, the vector magnetic potential can be derived. According to the vector magnetic potential, the airgap flux density distributions are predicted and the electromagnetic characteristics are calculated. The average magnetic density of the tooth and yoke is combined with the Bertotti model to calculate the iron loss. Besides, the eddy current loss of PMs is also calculated. The accuracy of analytical results is validated via the finite element method (FEM).

Analysis and Cogging Torque Minimization of a Novel Flux Reversal Claw Pole Machine with Soft Magnetic Composite Cores

The performances of a novel flux reversal claw pole machine (FRCPM) using soft magnetic composite (SMC) cores is analyzed in detail. The developed FRCPM uses both a flux reversal permanent magnet machine (FRPMM) and claw pole machine (CPM). In this paper, the main dimensions are optimized to ensure that the FRCPM can achieve maximum torque. In addition, the rotor skewing technology applied in the paper leads to a reduction in cogging torque and torque ripple of the machine. The main electromagnetic parameters and performance are obtained using the 3D finite element method.

Investigation on Symmetrical Characteristics of Consequent-Pole Flux Reversal Permanent Magnet Machines with Concentrated Windings

Consequent-pole (CP) permanent magnet (PM) configuration suffers asymmetric electromagnetic characteristics although it saves PM usage. The CP-based stator-PM synchronous machines are investigated in this paper, with particular reference to symmetrical issues. The electromagnetic performances of the CP-based stator-PM synchronous machines are firstly evaluated. Afterwards, the rule of even order harmonics cancellation is presented for different slot/pole number combinations and winding layouts, based on which symmetrical phase flux-linkages can be obtained although the unbalanced magnetic flux naturally occurs. Moreover, based on the three-dimensional finite element analysis, the unipolar end leakage-flux caused by the asymmetric magnetic field is identified, and the risk of the shaft magnetization is revealed. Finally, a pair of prototype machines are fabricated and measured to validate the analyses.

Analysis of Open-Circuit Performances in Flux-Reversal Permanent Magnet Machines by Superposition Methods

In this paper, superposition methods including the superposition of a single stator tooth and the superposition of a single rotor tooth, are proposed to predict the open-circuit performances of flux-reversal permanent magnet (FRPM) machines. By the proposed superposition methods, the electromagnetic performances, such as air-gap flux density, electromotive force, cogging torque, and unbalanced magnetic pull (UMP) are investigated and verified by 2D finite element analysis (FEA). Further, according to the superposition methods, cogging torque reduction techniques can be acquired from both stator side and rotor side. In addition, the influence of stator-slot/rotor-pole-pairs (slot/pole) combination on UMP is also studied, and consequently, a reasonable slot/pole combination rule is suggested to avoid UMP. Then, an improved configuration for UMP reduction is also investigated and verified by FEA. Finally, the prototype machines are manufactured and tested to further verify the theoretical analysis and FEA predictions.

Analysis of a New Linear Dual Stator Consequent Pole Halbach Array Flux Reversal Machine

The permanent magnet machine has attracted much attention due to its high torque density at low speed and simple configuration. This feature is due to many magnetic pole pairs that flux in the air gap can be significantly changed with the smallest motion of the moving. In this paper, a linear dual stator flux reversal permanent magnet machine (LDSFRPMM) with toroidal winding is presented, which magnets embedded with Halbach and simple array on the translator and stator, respectively. The innovation of this structure over a conventional machine is the addition of a magnet between the stator teeth with the appropriate magnetic orientation, and finding the best width of permanent magnet on the stator and a change of the type of winding from the concentrated to the toroidal. By implementing these changes on a conventional machine, the main parameters of the machine such as back electromotive force (EMF), thrust force, power factor and permanent magnetic (PM) flux are increased which improves the performance of the proposed machine.

Robust Design and Analysis of Asymmetric-Excited Flux Reversal PM Linear Machine for Long-Stroke Direct Drive Propulsion

This article proposes a novel asymmetric-excited flux reversal permanent magnet linear machine (AE-FRPMLM). Different from the conventional FRPMLM with uniform “NS-NS” permanent magnet (PM) sequence, the proposed AE-FRPMLM adopts an asymmetric “NSN-S” PM sequence, which can greatly reduce half of the flux leakage and generate more effective harmonics for thrust force production. Utilizing multiobjective genetic algorithm coupled with 2-D finite-element analysis (FEA), the proposed machine is globally optimized to obtain the optimal deterministic values. Furthermore, the sensitivity and robust analysis is employed to check its robustness. The electromagnetic performances are investigated and compared with conventional FRPMLM, which shows that the thrust force capability can be significantly improved more than 20% at full range of electrical loadings. The proposed AE-FRPMLM is suitable for low-cost and long-stroke direct drive propulsion.

Analysis of Dual-Armature Flux Reversal Permanent Magnet Machines With Halbach Array Magnets

In this paper, a novel dual-armature (DA) flux reversal permanent magnet (PM) machine with halbach array magnets in the stator slot opening is proposed, which is abbreviated as DA-Halbach machine. Besides the stator armature windings, another set of windings is added in the rotor slots to further enhance torque performance via fully utilizing the rotor space. The influences of major geometric parameters on torque performance are investigated. Both DA-Halbach machine and conventional Halbach machine are optimized with the goal of maximum torque under the same copper loss using finite element (FE) method. The electromagnetic performance of two optimized machines are compared, the results show that the proposed DA-Halbach has larger torque and smaller torque ripple than conventional Halbach machine. When compared with surface-mounted PM machines, the proposed DA-Halbach machine still show better torque performance.

Hybrid Analytical Modeling of Air-Gap Magnetic Field in Asymmetric-Stator-Pole Flux Reversal Permanent Magnet Machine Considering Slotting Effect

This article proposes an accurate and computationally efficient hybrid analytical (HA) model for the air-gap magnetic field computation of asymmetric-stator-pole flux reversal permanent magnet machine, which can provide a thorough insight into the working mechanism by taking the slotting effects into account. The proposed HA model combines the subdomain method and Schwarz–Christoffel (SC) transformation, which can account for the stator and rotor slotting effects, respectively. The subdomain method is first employed to predict the air-gap magnetic field considering the rotor slotting effect by converting the machine geometry to a slotless stator model. Afterward, a complex relative permeance function is obtained by the SC transformation, in which the stator slotting effect is taken into account. Finally, the complete air-gap magnetic field distribution of the machine can be efficiently predicted by the proposed HA analytical model. The effectiveness of the proposed HA model is verified by both finite-element analyses and experimental results.

Optimization of Rotor Salient Pole Reluctance for Typical Field Modulated Electric Machines

The objective of this article is to investigate the possibility to improve the torque characters of electric machines featuring rotor salient pole reluctance from the perspective of the general airgap field modulation theory. The torque production mechanisms of two typical field modulated machines, namely, the magnetically geared machine (MGM) and the flux-reversal permanent magnet (FRPM) machine, are discussed based on the Maxwell stress tensor (MST) method, where the mono-harmonic mechanism of rotor PM machine like the MGM is revealed. Several common theoretical salient rotor pole configurations, like the upright/inverted trapezoidal configuration, are introduced in detail, based on which general and modified rotor configuration advices for the two electric machines are proposed to provide initial design and future optimization guidance. It is proven that there is a possible opportunity to make the torque characters better via reasonable selection of rotor configuration and topological parameters. Electromagnetic performances validation based on 2-D finite-element analysis, such as improved airgap magnetic field harmonic distributions, load flux linkage/electromotive force (EMF), and general torque performances of two field modulated machines is provided to demonstrate the effectiveness of theoretical analysis. It is also verified by experimental measurements on the FRPM machines with different pole pair combination.

Analysis of Novel Consequent Pole Flux Reversal Permanent Magnet Machines

In this article, a new type of consequent pole flux reversal permanent magnet (CFRPM) machine, which features more iron poles than PM poles under one stator tooth, is proposed to improve the torque density. The proposed CFRPM machine with 6 slots and 16 poles (6S16P) is compared with a 12S16P FRPM machine and its consequent pole type, as well as a conventional 6S4P surface-mounted PM (SPM) machine. The proposed 6S16P CFRPM shows the highest torque among the four machines, together with the highest torque per PM volume. For a fair comparison with the 12S16P FRPM machine and its consequent pole type, the torque ripple of the proposed 6S16P CFRPM is suppressed by using two-step skewed rotor. After employing 4° two-step skewed rotor, while exhibits comparable torque ripple, the proposed 6S16P CFRPM still has 43% and 22% higher torque compared with the 12S16P FRPM machine and its consequent pole type.