Flux Reversal Permanent Magnet Machine Research Articles

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.

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.

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 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.

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.

Consequent-Pole Flux Reversal Permanent Magnet Machine With Halbach Array Magnets in Rotor Slot

In the conventional flux reversal permanent magnet (FRPM) machine, half of the permanent magnets (PMs) produce the leakage flux at each operation moment, which results in poor utilization of magnets. In order to improve the magnetic flux utilization in the FRPM machine, this article proposes a novel consequent-pole FRPM machine topology with Halbach array magnets in the top of rotor slot, where Halbach array magnets in the rotor slot are employed to guide the flux into the rotor teeth to reduce the leakage flux. Therefore, compared with the conventional FRPM machine, the proposed counterpart exhibits larger back-electromotive force (back EMF) and torque density. In this article, the structure and operation principle of the proposed FRPM machine are investigated based on a classical 12-slot/17-pole FRPM machine topology. Furthermore, the electromagnetic performances of the proposed machine, including back EMF, electromagnetic torque, losses, flux-weakening, and overload capabilities are obtained and compared with the conventional machine by the finite-element method (FEM).

The effect of static and dynamic eccentricities on the performance of flux reversal permanent magnet machine

This study investigates the effect of static and dynamic eccentricities on the performances of flux reversal permanent magnet (FRPM) machine with even rotor pole number, i.e. FRPM machine with 12/10 stator/rotor combination. No-load and load performances of the machine are investigated under three rotor operating conditions including centricity, static eccentricity and dynamic eccentricity. The investigation has been carried out using 2D-FEA. It has been revealed that the 12/10 FRPM machine under normal operating condition has no unbalanced magnetic force, due to the even pole number of the rotor. On the other hand, such undesirable feature would be presented in the 12/10 FRPM machine as a result of the existing of static and dynamic eccentricities. Both static and dynamic eccentric machines exhibit unbalanced three-phase flux linkage as well as back-EMF. Moreover, three operating conditions of the investigated machine have the same fundamental cogging torque harmonic. However, low order harmonics are existed in the static and dynamic centric machines and are not found in the centric machine. Furthermore, about 16% less torque ripple delivered by the centric machine compared with both static and dynamic counterparts.

Optimal design of a flux reversal permanent magnet machine as a wind turbinegenerator

Flux reversal permanent magnet generators are well suited for use as wind turbine generators owing to their high torque generation ability and magnetic gear. However, they suffer from poor voltage regulation due to their high winding inductance. In this paper, a design optimization method is proposed for flux reversal generators in wind turbine applications. The proposed method includes a new multiobjective function. Cost, volume of the generator, and mass of the permanent magnet are considered in it independently and simultaneously. Besides the new objective function, the main superiority of this paper compared with published papers is considering winding inductance in optimization procedures as a constraint and analyzing the optimization results for different values of it. Also, for the first time, the equations for permanent magnet sizing are considered based on a demagnetization curve for designing a flux reversal generator. For this purpose, a step-by-step design procedure is proposed and sensitivity analysis is performed to determine the sensitivity of output parameters to specific electrical loading, the height of the permanent magnets, and the machine length-to-diameter ratio. Then a multiobjective optimization based on a genetic algorithm is carried out and the best combination of pole number and number of slots/pole/phase is obtained. Then, for this combination, the optimum value of the constraint is obtained, too. Then specifications and dimensions of the optimum flux reversal machine as a wind turbine generator is presented. Finally, a time-stepping finite element method is used to validate the design and optimization results.

A Novel Flux Reversal Claw Pole Machine With Soft Magnetic Composite Cores

This paper proposes a novel flux reversal claw pole machine (FRCPM) with soft magnetic composite (SMC) cores, the proposed FRCPM has both the advantages of flux reversal permanent magnet machine (FRPMM) and claw pole machine (CPM). Specifically, with the permanent magnets (PMs) are surface mounted on the surface of stator claw pole teeth with a determined pattern, the FRCPM can operate based on flux reversal principle. As the adopted winding is global ring winding and 3D magnetic flux stator core structure is similar to the CPM's, the FRCPM is operated based on magnetic flux characteristic of the CPM as well. Therefore, the FRCPM can be operated under relatively high rotate speed since there is no winding or PMs on rotor, and the weak PMs, ring winding and SMC stator cores are encapsulated together as a whole part. Moreover the adopted 3D magnetic flux path can bring FRCPM with relatively high torque ability, and the adopted SMC cores can bring FRCPM with low core loss at the high speed operation. The operation principle of FRCPM is explained, the power equation is deduced for obtaining the initial design, and the main dimensions are optimized to ensure the developed FRCPM can have good performance. The main electromagnetic parameters and performance of FRCPM are obtained based on using the 3D finite element method (FEM).

Stator-Slot/Rotor-Pole Pair Combinations of Flux-Reversal Permanent Magnet Machine

In this paper, the stator-slot/rotor-pole pair combination principle of flux-reversal permanent magnet machines is proposed considering both magnetization modes and magnetic flux leakage effects. First, arbitrary slot/pole combinations with different magnetization modes exhibit compensation effect or are not investigated and the reason why some special slot/pole combinations without compensation effect still exhibit a rather sinusoidal back electromotive force (EMF) is unveiled. Then, the winding factor of back EMF is given and the effect of slot/pole combination on electromagnetic performances is investigated. Finally, specific slot/pole combinations exhibiting fault-tolerant capability are also discussed. Correspondingly, the experiments are constructed to verify the theoretical analysis. Finally, a determination principle for reasonable slot/pole combining is summarized, where both the magnetization mode and coil pitch can be obtained aiming at maximum back EMF. Additionally, the proper slot/pole combinations suitable for different load conditions and fault-tolerant applications are also highlighted.

Comparative Analysis of Flux Reversal Permanent Magnet Machines With Toroidal and Concentrated Windings

In this article, the flux reversal permanent magnet (FRPM) machine with toroidal windings is presented and analyzed with reference to conventional concentrated windings. First, the influence of rotor pole numbers on FRPM machines with conventional concentrated windings is investigated. It is found that although the 12/13 stator slot/rotor pole FRPM machine has a high back electromotive force, the pitch factor, and magnet flux utilization ratio of concentrated windings are very low. By adopting toroidal windings instead of concentrated windings in the 12/13 FRPM machine, the pitch factor and resulted machine performance can be effectively improved. Finite-element analysis shows that the 12/13 FRPM machine with toroidal windings can produce 79% higher torque than its counterpart with concentrated windings. Then, the critical design parameters and detailed electromagnetic performance of FRPM machines with both winding types are analyzed and compared. It is shown that the machine with toroidal windings has higher torque, efficiency, power factor, and lower torque ripple, making it particularly suitable for low-speed, high-torque, and axial length limited applications. In addition, other feasible stator slot/rotor pole combinations to use toroidal winding are identified, with the aid of equivalent pole-pair number. Finally, two 12/13 FRPM prototypes with toroidal windings and concentrated windings are tested to validate the analyses.

Optimal Number of Magnet Pieces of Flux Reversal Permanent Magnet Machines

This paper aims to comprehensively analyze the influence of number of permanent magnet (PM) pieces on electromagnetic performance of flux reversal permanent magnet (FRPM) machines. First, the unified analytical model of FRPM machines having different numbers of PM pieces is established, from which the optimal number of PM pieces and the corresponding rotor pole number can be identified. It shows that by employing the optimal number of PM pieces instead of the conventional two on each stator tooth, additional back-EMF component can be generated which is beneficial to boost the machine performance. Then, the influence of critical design parameters including stator slot opening ratio, split ratio, and stator slot number is investigated, providing a guidance to the design of FRPM machines aiming at maximum output torque. In addition, both finite element analyses and experimental tests are conducted to verify the analytical analyses. For 6-slot-stator FRPM machines, experimental results show that more than 40% higher output torque can be achieved in the machine with optimal number of PM pieces when compared to the conventional one.

Analysis of Back-EMF in Flux-Reversal Permanent Magnet Machines by Air Gap Field Modulation Theory

In this paper, the back-electromotive force (back-EMF) characteristics of the flux-reversal permanent magnet (FRPM) machines with different magnetization methods and winding layouts are analyzed and synthesized based on the magneto motive force (MMF)-permeance model. The air gap field modulation theory is utilized to investigate the permanent magnet-MMF harmonics and open-circuit air gap flux density harmonics that make a contribution to back-EMF as well as its harmonics. Based on this analysis, the specific harmonic of back-EMF can be reduced by suppressing the corresponding PM-MMF harmonic. Besides, the influence of rotor pole number on back-EMF is also studied. It is found that with the aid of this modulation theory, the reasonable magnetization method, winding layout, and rotor pole number can be obtained to improve the back-EMF characteristics of an FRPM machine with an arbitrary slot/pole combination. Furthermore, prototype machines are manufactured and tested to verify the analytical predictions.

Investigation of stator slot/rotor pole combination of flux reversal permanent magnet machine with consequent‐pole PM structure

Here, the influence of stator slot and rotor pole combination on performance of flux reversal permanent magnet (FRPM) machine with consequent-pole permanent magnet (CPM) structure is analysed. First, for 12-slot FRPM machines, the torque capabilities of CPM and conventional surface-mounted PM (SPM) structure having different rotor poles are compared. It shows that the torques of CPM machines are largely affected by the rotor pole number while the torques of SPM machines are similar. This is further explained by the equivalent pole-pair number and corresponding saturation condition. The influence of stator slot number and PM width ratio on torque performance of the CPM-FRPM machine is then investigated. Finally, detailed electromagnetic performance of the 12/14 SPM- and CPMFRPM machine is analysed and compared.