Flux Reversal Permanent Magnet Research Articles

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.

Analytical Modeling of Flux-Reversal Permanent-Magnet Machines

An analytical model is proposed for the prediction of electromagnetic quantities of slotted flux-reversal permanent magnet (FRPM) machines. Equivalent current theory is used to model the effects of permanent magnets (PMs), stator slots and rotor grooves. First, the stator slots and rotor grooves are nullified and the Poisson equation is solved in a slotless stator and cylindrical rotor machine. The effects of the stator slots and rotor grooves are then considered by injecting equivalent magnetization currents (EMCs) respectively on the stator slots wall and on the rotor groove edges. The PMs are also replaced by EMCs. Finally, the results of the proposed analytical model are verified by means of the finite element analysis.

Comparative Analysis of Doubly Fed Flux-Reversal Permanent Magnet Machines With Different PM Arrangements and Consequent-Pole Topologies

In this article, two doubly fed (DF) flux-reversal permanent magnet (FRPM) machines with different PM arrangements are proposed, both of which have an additional set of armature winding in their rotor slots to further enhance the torque performance. Together with their one-set armature winding counterparts, comprehensive analyses and comparison among these four machines are conducted. The operation principles and winding configurations of these four machines are firstly introduced. Then, based on finite-element (FE) method, the electromagnetic performances of four machines after optimization with the purpose of maximum torque are compared in terms of no-load, on-load, and over-load capabilities. The results show that the DF-FRPM machine with consequent-pole structure offers the highest average torque and lowest torque ripple, which make it a promising candidate for low-speed and high-torque applications. A prototype machine has been manufactured and the FE results have been verified.

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).

Harmonic Analysis of Airgap Magnetic Fields in Doubly-Fed Flux Reversal Permanent Magnet Machines

Doubly-fed flux reversal permanent magnet (DF-FRPM) machine with two independent armature windings accommodating in stator and rotor slots separately exhibits larger torque density than conventional FRPM due to higher utilization rate of rotor space. In this paper, the investigation is focused on the airgap field modulation and torque contribution of dominating harmonics in DF-FRPM machine. Besides the open-circuit airgap flux density, both stator and rotor armature reaction are qualitatively analyzed by magneto-motive force (MMF)-permeance model considering stator and rotor saliency since the two independently supplied armature windings both make contributions to the torque production. The pole pairs and rotating speed of field harmonics are addressed. Dominating field harmonics that contribute to electromagnetic torque are identified and validated by finite element (FE) analysis.

Comparison of stator‐ and rotor‐surface‐mounted PM brushless machines

Flux-reversal permanent magnet (PM) machines can be considered as stator-surface-mounted PM (SSPM) machines, where normally a pair of magnets with reversal magnetization polarities is mounted on the surface of each stator tooth. Hence, the SSPM machines and the conventional rotor surface-mounted PM (RSPM) machines are rather similar since both machines house the PMs in the air-gap, and the only difference is the location of magnets in the stator side and rotor side, respectively. In this study, a comparative study between SSPM and RSPM machines is conducted to investigate the difference including topology, operation principle and performance. First of all, the topology of both machines is compared. Then, the operation principle in both machines is analysed based on the air-gap field modulation theory. Correspondingly, the characteristics of flux density harmonics either due to PMs or armature reaction are obtained. Therefore, the harmonics that make contribution to back-electromotive force and rated torque are quantified. Besides, other electromagnetic performances, e.g. overload capability, flux weakening ability and loss distribution are also evaluated. Finally, a 12/14 prototyped SSPM machine is manufactured and tested to verify analytical and finite element method-based prediction.

A Novel Tubular Partitioned Stator Flux-Reversal Permanent Magnet Linear Machine for Direct-Drive Wave Energy Generation

A novel tubular partitioned stator flux-reversal permanent magnet linear machine (PS-FRPMLM) is proposed for direct-drive wave energy generation. It consists of four flat PS-FRPMLMs and a moving aluminum tube, which not only combines the merits of permanent magnet machines and flux-reversal machines but also overcomes the space constraint between the permanent magnets and electric loadings. First, the topology and the operation principle are presented. Then, the proposed machines with different slot/pole combinations, i.e., 6/4, 6/5, 6/7, and 6/8, are optimized to obtain the maximum no-load electromotive force (EMF). Furthermore, the performances of these proposed machines are compared with those of conventional tubular FRPMLMs in both no-load and on-load states. The results show that this novel structure possesses lower cogging force, better PM utilization, and higher efficiency in the on-load state, which proves it to be suitable for application in direct-drive wave energy generation. Finally, a prototype of a single flat PS-FRPMLM is tested to verify the predicted finite element (FE) results.

Comparison of different magnet arrangement on performance of flux reversal permanent magnet (FRPM) machine

<span lang="EN-MY">This paper offers the analysis of performance of Flux Reversal Permanent Magnet (FRPM) machines with different type of magnet arrangements. There are two designs that have been proposed in this report, which one of them has a pair of permanent magnets (PM) with alternate polarities place on surface of stator tooth and the polarities of two adjacent PM at these two stators are identical. This PM arrangement is called as NS-SN configuration. Second design is NS-NS configuration that has different PM polarities on different stator tooth. By comparing this PM arrangement, generally the NS-NS configuration offers high speed and power. However, the NS-SN configuration shows higher maximum torque compared to the previous design. The design process for both configurations is completely using finite element analysis (FEA) which is JMAG-Designer. To make sure the coil phase is in correct position, the design configuration with coil arrangement tests are evaluated. Finally, each flux of both designs been observed by analyse their torque with various armature current density.</span>

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.

Comparison of different synchronous machines with stator‐side permanent magnets for industrial drive application

Three different synchronous machines with the permanent magnets in the stator (doubly salient permanent magnet, flux reversal permanent magnet, and flux switching permanent magnet machine) are compared for use as an industrial drive for 45 kW, 400 V Y, and 1000 …. 3000 min −1 . For comparison, finite element method simulations are carried out to investigate the torque density of the machines, and the results are explained based on the magnetic co-energy. The simulations show that the flux switching machine generates the highest torque density of the three machines. Therefore, a prototype flux switching machine is built, tested, and compared with a conventional permanent magnet synchronous machine (PMSM) with magnets on the rotor surface, the same size (stator outer diameter d so = 314 mm, axial length l Fe = 180 mm) and rating. The measurements indicate that the conventional PMSM and the flux switching machine have roughly equivalent electrical behaviour.

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.

Analysis of a Flux Reversal Machine With Quasi-Halbach Magnets in Stator Slot Opening

Flux reversal permanent magnet (FRPM) machine, with magnets mounted on or inserted into the stator, is favorable for the direct drive applications. In this paper, an FRPM machine with Quasi-Halbach array magnets in stator slot opening is introduced. The operation principle of the proposed machine is presented, and the combination of stator and rotor slot number is given. Several key parameters, that are split ratio, stator and rotor slot opening ratio, magnet ratio, and magnet thickness are carefully investigated, while four proposed FRPM machines with 12 stator slots and 10, 11, 13, 14 rotor slots are optimized for better performance. Moreover, the proposed FRPM machine is compared with a conventional FRPM machine, the analysis results indicate that the torque density of proposed machine is 2.2 times that of the conventional FRPM machine under the same copper loss with almost the same magnet usage. Finally, a 12 stator slot/10 rotor slot FRPM prototype is built to verify the theoretical analysis.

Modeling and Optimization of a Tubular Permanent Magnet Linear Motor Using Transverse-Flux Flux-Reversal Topology

In this paper, a novel tubular transverse-flux flux-reversal linear motor for long stroke applications is proposed. The proposed motor not only has the low-cost advantage of the existing flux-reversal permanent magnet (PM) linear motor (PMLM) by combining both PMs and armature winding in short primary, but also address the problem of complicated structure in conventional tubular PMLM by using the manufacturing process of the rotary motor. First, in order to reduce circumferential magnetic flux leakage and improve the utilization ratio of PM, the motor structure with the alternating distribution of double N poles and double S poles in the circumferential direction is designed, and the operating principle of the motor is presented. Then, the equivalent magnetic circuit model of the unit motor is established to derive the expressions of the back electromotive force (EMF) and the electromagnetic thrust. Third, the equivalent two-dimensional (2-D) finite-element method (FEM) is used to optimize the structural dimensions and analyze the static characteristics including the back EMF, the detent force, and the thrust. Meanwhile, the three-dimensional FEM verify the validity of the equivalent 2-D FEM. Finally, the experimental results verify the validity and the correctness of the topology structure and the design method of the motor.