Flux-switching Permanent Magnet Machine Research Articles

Principle of Flux-Switching PM Machine by Magnetic Field Modulation Theory Part II: Electromagnetic Torque Generation

Based on the back electromotive force generation principle in part I of the series papers, the electromagnetic torque generation mechanism of flux-switching permanent magnet (FSPM) machines is rethought in this article as part II from the perspective of air-gap modulation magnetic field. By magnetic field modulation theory, the air-gap armature magnetic field due to winding currents is modeled. Considering the unipolarity of the stator core, a novel concept of ‘fictitious modulation reluctance (FMR) rotor’ for FSPM machines is proposed. Then, by combining with the air-gap permanent magnet (PM) field and the FMR rotor, generation mechanisms of harmonic PM torque and reluctance torque are investigated. The requirements for FSPM machines to produce a stable electromagnetic torque are determined, i.e., <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">|mP_w</i> ± <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">vP_r</i> | = <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pm</sub> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m_rvM_fm</i> ≠0, and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ω_e</i> = <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P_rω_r</i> . Besides, the harmonics operation states and harmonic torque characteristics of FSPM machines are analyzed and calculated based on the Maxwell stress tensor method. Further, the average torque versus current density predicted by finite element is validated by testing on an exampled 12s/10p FSPM one.

Winding Configurations and Pole/Tooth Combinations of Doubly-Fed Flux-Switching Permanent Magnet Machines

The design rules of winding configurations and stator-pole/rotor-tooth (SP/RT) number combinations of doubly-fed flux-switching permanent magnet (DF-FSPM) machines are investigated in this paper based on coil electromotive force (EMF) vectors. The relationships between the components of stator and rotor coil-EMF vector diagrams are unveiled at first, including the numbers of stator and rotor phases, and the numbers of stator and rotor spokes. Then, the SP/RT number combinations are derived considering feasible stator/rotor phase number combinations and different winding configurations. The SP/RT number combinations are optimized considering the winding factors, magnetic field harmonics, unbalanced magnetic forces and machine diameter. It is shown that both of the stator and rotor pitch factors increase when the SP and RT numbers get closer. Furthermore, the influence of winding configurations and SP/RT number combinations on electromagnetic performances of DF-FSPM machines are analyzed by finite-element method. Finally, the analysis results are validated by experiment.

Comparison of Flux-Switching and Interior Permanent Magnet Synchronous Generators for Direct-Driven Wind Applications Based on Nelder–Mead Optimal Designing

The permanent magnet flux-switching machine (PMFSM) is one of the most promising machines with magnets inserted into the stator. To determine in which applications the use of PMFSM is promising, it is essential to compare the PMFSM with machines of other types. This study provides a theoretical comparison of the PMFSM with a conventional interior permanent magnet synchronous machine (IPMSM) in the gearless generator of a low-power wind turbine (332 rpm, 51.4 Nm). To provide a fair comparison, both machines are optimized using the Nelder–Mead algorithm. The minimized optimization objectives are the required power of frequency converter, cost of active materials, torque ripple and losses of a generator averaged over the working profile of the wind turbine. In order to reduce the computational time, the substituting profile method is applied. Based on the results of the calculations, the advantages and disadvantages of the considered machines were revealed: the IPMSM has significantly lower losses and higher efficiency than the PMFSM, and the PMFSM requires much less rare-earth magnets and copper and is, therefore, cheaper in mass production.

Multi-objective optimization of high torque density segmented PM consequent pole flux switching machine with flux bridge

Due to double salient structure, Flux Switching Machines (FSMs) are preferred for brushless AC high speed applications. Permanent Magnet (PM) FSMs (PM-FSMs) are suited applicants where high torque density (T den ) and power density (P den ) are the utmost requisite. However conventional PM-FSMs utilizes excessive rare earth PM volume V PM , higher cogging torque T cog , high torque ripples (T rip ) and comparatively lower (T den ) and P den due to flux leakage. To overcome the aforesaid demerits, a new high (T den ) Segmented PM Consequent Pole (CP) FSM (SPMCPFSM) with flux bridge and barrier is proposed which successfully reduces V PM by 46.52% and PM cost by 46.48%. Moreover, Multi-Objective Optimization (MOO) examines electromagnetic performance due to variation in geometric parameters for global optimum parameters with key metric such as flux linkage (Φ pp ), flux harmonics (Φ THD ) average torque (T avg ), T cog , T rip , T den , average power (P avg ) and P den . Analysis reveals that MOO improve Φ pp by 22.68%, boost T avg by 11.41%, enhanced P avg by 4.55% and increased T den and P den by 11.41%. Detailed electromagnetic performance comparison with existing state of the art shows that proposed SPMCPFSM offer T avg maximum up to 88.8%, truncate T rip up to 24.8%, suppress T cog up to 22.74%, and results 2.45 times T den and P den .

Electromagnetic torque capabilities of permanent magnet flux-switching machine using modular rotor

The use of a segmented rotor electric motor for lightweight electric vehicle applications has gained a lot of attention since the motor must have a high output torque and output power. Segmented rotor motors have performance indices that should be taken into consideration because not every machine is effective. Recently, permanent magnet flux switching machine (PMFSM) in salient rotor has become attractive for provide high torque and power. Undesirably, salient rotor inherited high iron loss and winding loss, Furthermore, PMFSM uses high PM volume and more flux leakage resulting in poor performance. This paper deals with a novel structure of modular rotor PMFSM with non-overlapping winding with minimal iron loss, high torque and high power. 2D finite element analysis (FEA) is used to investigate the performance of proposed motor in JMAG Designer 14.1. Three-phase operation of 12S/10P modular rotor PMFSM was designed and analysed based on the cogging torque, induced back emf, output torque and output power performances. The proposed motor securing the initial torque of 33.30 Nm and power of 12Kw at maximum current density of 30Arms/mm2. From the result it is concluded that modular rotor based PMFSM motor is suitable for light weight electric vehicles.

Optimal rotor poles and structure for design of consequent pole permanent magnet flux switching machine

Permanent magnet flux switching machines (PMFSM) have attracted significant research interest and are considered as competent candidates when higher torque density is primary requirement. However, conventional PMFSMs uses excessive rare earth PM volumes which ultimately increases machine the machine weight and PM cost. Moreover, the PMs extended at the stator yoke results in stator leakage flux which degrades the performance. To suppress the leakage flux and diminish the PM volume, the consequent pole PMFSM (CPPMFSM) with flux bridges and barriers encompassing partitioned circumferential and radial magnetized PMs is proposed, thereby ensuring an alternate magnetic path for the working harmonics which improves the modulation effect and flux distribution. Moreover, the influence of the rotor pole number on seven different rotor structures namely, curved rotor, trapezoidal rotor, wide rotor tooth tip, wide rotor base width, rectangular segmented and eccentric rotors are investigated based on the electromagnetic performance and stress distribution. Finite element analysis (FEA) reveals that the 12S-13P CPPMFSM with a wider rotor base offers comparatively better electromagnetic performance. Compare to the conventional PMFSM, the proposed CPPMFSM reduces the PM volume which minimizes the overall machine cost and weight, suppresses the torque ripples by 16.49%, diminishes total harmonic distortion (THD) by 35.24% and decreases cogging torque by 32.88%. Furthermore, the torque and power density are enhanced by 7.028% and 7.025% respectively.

Influence of Various Tooth Shape Topology for Single-Phase Permanent Magnet Flux Switching Machine

Permanent magnet flux switching machine (PMFSM) has the advantages of solid design structure, high torque performances, and high efficiency. The method to increase performance and decrease the cost of the motor through a selection of numbers of slot and pole is a major issue that needs to be solved. Therefore, to further improve the electromagnetic torque, a novel 4-4S-8P multi-tooth, 4S-8P segmental-tooth and single-tooth PMFSM machine respectively is proposed based on the slot pole analysis performance. Hence, the performance is including the flux linkage, cogging torque, back-electromotive force (back-emf), output torque, and power performance. The results display that the various tooth shape topology have a large impact on the performance design. JMAG Designer version 14.3 under 2D finite element analysis (2D-FEA) are used to complete the analysis. The results show that the right combination of a single-tooth 4S-8P PMFSM structure is the best choice according to the high performance of torque analysis.

Comparative Study of Consequent-Pole Switched-Flux Machines with Different U-Shaped PM Structures

This paper presents a comparative study of two consequent-pole switched-flux permanent magnet (CP-SFPM) machines with different U-shaped PM arrangements. In order to address the flux barrier effect in a sandwiched SFPM machine, two different alternate U-shaped PM designs are introduced to improve the torque capability, forming two CP-SFPM machine topologies. In order to reveal the influence of different magnet designs on the torque production, a simplified PM magneto-motive force (MMF)-permeance model is employed to identify the effective working harmonics in the two CP-SFPM machines. The torque contributions of the main working harmonics are subsequently quantified by a hybrid finite-element (FE)/analytical method. Multi-objective genetic algorithm (GA) optimization is then employed to optimize the design parameters of the proposed CP-SFPM machines. In addition, the electromagnetic characteristics of the CP-SFPM machines with two U-shaped PM arrangements are investigated and compared by the FE method. Finally, a 6/13-pole CP-SFPM machine with an optimally selected U-shaped PM structure is manufactured and tested to validate the FE analyses.

Magneto-Electric Coupling Network Model for Reduction of PM Eddy Current Loss in Flux-Switching Permanent Magnet Machine

This article proposes a mesh-based magneto-electric coupling network model for prediction and reduction of permanent magnet (PM) eddy current loss in a flux-switching permanent magnet machine. The key is to couple the electromagnetic inductions between the eddy current network and the equivalent magnetic network (EMN) in stator PMs dynamically. First, the eddy current networks of PMs are established with electric meshes. The electromotive forces of electric mesh are induced by considering double-side effects based on Maxwell's equations. Second, the stator meshing method is propose with PM segments, and combined in the EMN matching to the eddy current mesh. High efficiency and accuracy with detailed magnetic field distributions can be obtained. Then, the magnetic fields generated from EMN PM nodes are coupled in eddy current network to accurately predict the flow directions and density distributions. Finally, the original design and two other structures with rotor magnetic barriers are analyzed for reduction of eddy current losses. The effectiveness of the proposed model is verified by finite-element analyses and experimental results.

Performance analysis of a novel outer rotor flux‐switching permanent magnet machine as motor/generator for vehicular and aircraft applications

Herein, a novel study on outer rotor flux-switching permanent magnet (OR-FSPM) machines for motor/generator applications is presented. An improved magnetic equivalent circuit (MEC) is used for saturable machine model, and the performance analysis is presented in both dynamic and steady-state cases. A flexible MEC-based method is used, where the machines with arbitrary properties can be analysed. Moreover, the model accuracy can be tuned by selective parameters in the proposed method. It is shown that the machine can be used as a high efficiency 400 Hz Ground Power Unit (GPU) for aircraft application. Furthermore, the machine usage for in-wheel application in the hybrid and electric vehicles (HVs and EVs) is analysed. Comparison with 2D and 3D finite-element-method (FEM) shows the effectiveness and accuracy of the proposed MEC method, where shorter processing time is obtained compared with FEM.

Effect of permanent magnet material on the electromagnetic performance of switched-flux permanent magnet machine

The influence of permanent magnet materials on the electromagnetic performance of switched-flux permanent magnet (PM) machine having C-core stator assembly is investigated and compared. Both two-dimensional (2D) finite element analysis (FEA) and 3D-FEA are used in predicting the results. Presently, there has not been any study on the performance effect of using a wide range of different types of magnet on C-core switched-flux PM machine. Hence, there is a need for this latest investigation. The considered magnetic materials are: Alnico grade A500, Ferrite grade F5, Neodymium–Iron–Boron (NdFeB) grade N52, and Samarium–cobalt grade S24. The analysis shows that the best electromagnetic performance, including machine efficiency, would be obtained from a given electrical machine when it is equipped with NdFeB magnetic material due to its possession of the highest amount of magnetic remanence, coercive force, and energy product (BH)max. Consequently, the machine having ferrite magnetic material would produce the worst electromagnetic performance, although it is of the lowest cost.

Improved Vector Control Method based on Torque Current Integral Balance for Flux-switching Permanent Magnet Machines

Flux-switching permanent magnet (FSPM) machines can provide high torque density, strong flux-weakening capability, and high reliability, which makes these machines attractive in electrical drive systems. FSPM machines always employ different control methods, such as the vector control (VC) and direct torque control (DTC) methods. These methods exhibit different electromagnetic torque dynamic performances; hence, the dynamic performances of their rotor speeds are different. However,the proportional integral (PI) controllers of the speed loop in these methods are linear regulators, which hardly guarantee the optimal dynamic performance of the rotor speed. This causes the rotor speed to have several adjustments, overshoots, and a relatively long recovery time during the response to a sudden load change. Therefore, to achieve the optimal dynamic trajectory of rotor speed and maintain the excellent performance of the steady-state simultaneously, a torque-current ( Iq ) integral balance (IQIB) method, which can eliminate the restriction of the PI controllers on the dynamic performance of the rotor speed, is investigated for the VC system of FSPM machines. In the dynamic process, a group of optimal switch vectors is obtained to achieve the shortest recovery time and the minimum number of adjustments for the rotor speed without overshoot, thereby achieving an optimal dynamic performance for the system. Comparative experiments between the IQIB-based VC, VC, DTC, and improved DTC are conducted, and the accuracy and effectiveness of the proposed method are validated.

Comparative Analysis of Different Permanent Magnet Arrangements in a Novel Flux Modulated Electric Machine

A novel dual permanent magnet (PM) machine with Halbach segmentation flux modulation is proposed in this paper, which is evolved from a flux switching PM machine (FSPM). In order to improve the performance of the FSPM, several PM arrangement methods have been adopted and three new different structures have been investigated. To achieve a fair comparison, all the structures are under the same size and rotate at the same speed. The performances of output torque and back EMF are compared. The analysis results show that the dual PM with Halbach segmentation has the highest torque density and power efficiency. The torque is improved by 100.3% from the FSPM while the PM volume does not increase too much. The unique of this best structure is that it not only combines the vernier machine and FSPM machine together, but also reduces the torque ripple. The performance of the motor is verified by the simulation using finite-element analysis (FEA).

Design and Performance Analysis of a Novel Outer-Rotor Consequent Pole Permanent Magnet Machine With H-Type Modular Stator

In this paper a novel outer-rotor consequent pole permanent magnet machine (OR-CPPMM) with H-type modular stator core is proposed for higher average torque ( $T_{avg}$ ), flux linkage ( $\Phi$ ) and efficiency ( $\eta$ ) whereas low cogging torque ( $T_{cog}$ ), torque ripple ( $T_{rip}$ ) and harmonics content in flux linkage ( $\Phi _{THD}$ ) and back-EMF ( ${\mathrm {EMF}}_{THD}$ ). The proposed OR-CPPMM is investigated with different stator flux gaps width for static and dynamics electromagnetic performances. Analysis reveals that flux gaps in H-type stator core not only improve electromagnetic performance i.e., $\Phi $ is enhanced by 10.23%, $\Phi _{THD}$ is suppressed by 80.65%, diminished ${\mathrm {EMF}}_{THD}$ by 59.37%, truncate $T_{rip}$ by 44.37% and improve $T_{avg}$ by 15.99% but also exhibits better flux focusing effect to enhance flux linkage and diminish harmonic contents. In addition, H-type modular stator structure provide physical isolation of adjacent phase that de-couple the adjacent phase coupling flux which enhance self-inductance and weaken mutual-inductance and hence improve fault tolerant capability. In addition, to elaborate effectiveness of the proposed design and justification of OR-CPPMM novelty with H-type modular stator, electromagnetic performance is extensively compared with existing state of the art including E-core and C-core structure. Analysis and comparison with state-of-the-art reveals that proposed OR-CPPMM enhanced $\Phi $ by 65.35%, diminish $\Phi _{THD}$ by 67.24%, truncate $T_{cog}$ by 96.72%, suppresses ${EMF}_{THD}$ by 44.40%, diminish $T_{rip}$ by 77.23% whereas $T_{avg}$ is enhanced by 91.69%. Furthermore, the proposed design novelty is justified with comparison of OR-CPPMM with inner rotor and dual rotor permanent magnet flux switching machines. Comparison and analysis unveil that OR-CPPMM exhibits $T_{avg}$ higher up to 35.16%, truncate $T_{rip}$ up to 32.88%, enhanced $\Phi $ up to 22.13% and boost $T_{den}$ to 3.41 times at the cost of 2.58% increase in $T_{rip}$ .

Wind generator drivetrain performance and comparison of PM flux switching machines

This study is undertaken to highlight the competitive optimal performance of permanent magnet flux switching machines (PM–FSMs) in different wind generator drivetrains––low–speed (LS), medium–speed (MS) and high–speed (HS). The three–phase 12–stator slots/10–rotor teeth PM–FSM is selected for the study, for small–scale power applications. The design and optimisation is performed using a 2–D finite element analyses (FEA) tool. Thereafter, important features of the different wind generator drivetrains are evaluated and compared, especially in terms of cost of energy (CoE) versus performance. In the end, the study barely stops short of representing the MS as the best among the three drivetrains; however, it is clearly a preferred solution due to trade– offs in torque density and cost of generator.

Improved Current Dynamics of Proportional-Integral-Resonant Controller for a Dual Three-Phase FSPM Machine

Resonant controllers are commonly used in parallel with proportional-integral controllers in the current control of multiphase machines and other three-phase drives where current harmonics need elimination. However, additional oscillatory and slow poles arise with the resonant controllers, resulting in a degradation in both reference tracking and disturbance rejection. In this article, an improved current control scheme with a discrete-time PI-resonant controller is proposed for a dual three-phase flux switching permanent magnet (FSPM) machine to eliminate the current unbalance and harmonics. First, a partial prefilter is used in the resonant controller path, yielding a pole-zero cancelation for the resonant poles in the closed-loop system; thus, the oscillation in command response becomes negligible. Then, the active resistance method is employed to improve the low-frequency disturbance rejection, and the resonant poles are damped with a pole-placement strategy. Finally, the experimental results on a dual three-phase FSPM machine validate the effectiveness of the proposed method, which can be extended to other ac drives for harmonic suppression.

Analysis and optimization of a 12/14 double‐stator flux‐switching machine using low cost magnet

Flux-switching permanent magnet (FSPM) machine attracted a great deal of attention for industrial applications owing to its high efficiency and high torque/power densities. However, on the downside, it suffers from high cost of rare-earth permanent magnets (REPMs). Although employing ferrite magnets remarkably reduces the cost of material, ferrite magnet lower energy product will negatively affect the electromagnetic performance of this machine. As a solution, the double-stator flux-switching permanent magnet (DSFSPM) machine has been presented in this paper to improve the electromagnetic performance of a conventional ferrite based FSPM counterpart. In this regard, a new analytical approach followed by a brief discussion of the influence of rotor pole number on the electromagnetic performance of two DSFSPM machines with 10- and 14-pole rotors are studied. It is shown that 12/14 DSFSPM machine with ferrite magnets generates almost 30% more developed torque than the other with 10-pole rotor. Then, a comprehensive comparison on the electromagnetic performances of a 12/14 DSFSPM machine with ferrite magnets, and two 12/14 FSPM machines with REPMs and ferrite magnets are investigated by finite element method. Besides, a cost study highlights the monetary beneficial of the proposed 12/14 DSFSPM machine for the competitive EVs market. Furthermore, a laboratory scale 12/14 DSFSPM machine is designed based on analytical approach, optimized by Taguchi optimization method, and experimentally tested to validate both analytical and FEM results.

Characteristic analysis of flux switching PM machine with various pole and slot combinations

This paper examines the influence of pole and slot combinations on the electromagnetic performance of the flux-switching permanent magnet (FSPMs) machine. For this purpose, first the production of air gap flux density in machine analytically discussed. Next, five different pole and slot combination are selected by using the knowledge of air-gap flux density expression. The performances of the different combinations are analyzed and compared using the finite element analysis (FEA), and optimal pole and slot combination is suggested. It is found that the pole and slot combination has a dominant effect on machine performance and needs to be considered during the design stage.

Investigation of Torque Improvement Mechanism in Emerging Switched Flux PM Machines

This article aims to investigate and reveal the torque enhancement mechanism in several emerging switched flux permanent magnet (SFPM) machines using a unified torque equation with an improved winding factor function. Based on a hybrid finite-element (FE)–analytical method, the torque contributions of the major air-gap field harmonics in the conventional, C-core and E-core, and consequent-pole (CP) SFPM machines are identified and quantified by taking a conventional 12-stator-slot/13-rotor-tooth (12s13r) SFPM machine as a benchmark, which shows that the dominant torque proportions are contributed by the low-order field harmonics due to the amplification effect of the gear ratio. Besides, a low-order field harmonic impeding effect is observed in the conventional and C-core SFPM structures, resulting in a compromised torque capability. Whereas since the auxiliary teeth and stator iron bridge designs provide relatively lower magnetic reluctances for low-order harmonics, the E-core and CP structures can produce improved low-order harmonics and higher torques than the conventional one. Finally, some experiments on a CP-SFPM machine are conducted to validate the theoretical and FE analyses.

Magnetic Circuit Modeling of Dual-Armature Flux-Switching Permanent Magnet Machine

Three lumped-parameter magnetic circuit (LMC) models of dual-armature flux-switching permanent magnet (DA-FSPM) machines are proposed and compared in this article. First, the characteristics of the magnetic flux fields produced by the PM, stator armature reaction, and rotor armature reaction flux sources are analyzed, with particular attention paid to the air-gap and slot leakage flux paths. Based on the former analyses, three LMC models are developed, which consider the air-gap and slot leakage permeances in different ways. The electromagnetic performances of the DA-FSPM machines are predicted by the three LMC models and validated by the finite-element method, including the flux linkage, average torque, inductance, and power factor. The model accuracy sensitivity to the geometric parameters, copper loss allocation, electric loading, stator pole/rotor tooth number combinations, power level, and conductor distributions are analyzed. It shows that appropriate consideration of slot leakage permeance is important to improve the model accuracy.