Flux-switching Permanent Magnet Machine Research Articles

An Innovative Dual-Rotor Axial-Gap Flux-Switching Permanent-Magnet Machine Topology With Hybrid Excitation

In this paper, a novel dual-rotor axial-gap flux-switching permanent-magnet machine with dc excitation winding is proposed. First, the topology and operation principles of the proposed topology are clarified. Basic design equations and parameters are provided, and the electromagnetic analyses of the proposed flux-switching machine with 3-D FEA are performed. Parametric optimizations using 3-D FEA are completed for different dc excitations. A prototype machine is manufactured, tested, and validated. It is shown that the air-gap flux of the proposed axial-gap machine can be controlled in a wide range compared to conventional surface magnet machines.

Enhancing Capabilities of Double Sided Linear Flux Switching Permanent Magnet Machines

Double sided linear flux switching permanent magnet machines (DSLFSPMMs) exhibit high thrust force density, high efficiency, low cost and robust double salient secondary (stator) structures. The aforementioned unique features make DSLFSPMM suitable for long stroke applications. However, distorted flux linkage waveforms and high detent forces can exaggerate thrust force ripples and reduce their applicability in many areas. In order to enhance thrust force performance, reduce thrust force ripple ratio and total harmonic distortion (THD) of no-load flux linkages, two structure-based advancements are introduced in this work, i.e., asynchronous mover slot and stator tooth displacement technique (AMSSTDT) and the addition of an active permanent magnet end slot (APMES). Furthermore, single variable geometric optimization (SVGO) is carried out by the finite element method (FEM).

Analysis of coupling between two sub‐machines in co‐axis dual‐mechanical‐port flux‐switching PM machine for fuel‐based extended range electric vehicles

The permanent magnet (PM) field coupling between inner and outer machines of co-axis dual-mechanical-port flux-switching PM (CADMP-FSPM) machines is investigated. Firstly, the relationships between the inner and outer stator teeth are analytically evaluated, with three key stator teeth types defined, i.e. series, parallel, and independent teeth. Secondly, the negative effects of PM field coupling, including high even-order electromotive force (EMF) harmonics, three-phase EMFs asymmetry and DC bias component in flux-linkages, are investigated and verified by two CADMP-FSPM machines, namely, 5/6-12/22, and 5/6-18/42 structures. It is found that for avoiding the negative effects of PM field coupling, all inner and outer stator teeth types should be the same, thus, a 10/12-12/22 structure CADMP-FSPM machine is introduced for analysis. Thirdly, the performance of the 10/12-12/22, 5/6-12/22, and 5/6-18/42 structures, featured by PM field distributions, d-axis flux-linkage ripples, cogging torques, electromagnetic torques, losses and efficiencies, are comparatively analysed by finite element (FE) analysis. The results indicate that the 10/12-12/22 structure exhibits the lowest PM field coupling level and the best performance. Moreover, the 10/12-12/22 structure can avoid all the negative effects of PM field couplings. A prototyped 10/12-12/22 CADMP-FSPM machine is built and tested to verify the FE predicted results.

Flux-Switching Permanent Magnet Machine with Phase-Group Concentrated-Coil Windings and Cogging Torque Reduction Technique

We herein propose a novel high-torque-density flux-switching permanent magnet machine (FSPMM) which adopted phase-group concentrated-coil (PGCC) winding and a cogging torque reduction technique. The PGCC winding was applied to increase the torque density. In order to maximize the torque of the FSPMM that utilizes the PGCC windings, the performance according to stator slots/rotor poles combinations were compared. A machine which had 12 stator slots and 13 rotor poles (12S13P) was selected for its top average torque value. However, the 12S13P PGCC FSPMM contains high cogging torque that must be reduced. The cogging torque reduction technique is applied, and the parameters used in the technique are further optimized to achieve the target average torque, while suppressing the cogging torque as much as possible. The optimization process was performed with a collaboration of the genetic algorithm and Kriging method. The analysis results of the optimized design exhibited huge reductions in the cogging torque and eventually in the torque ripple from the initial machine, with reasonable average torque reduction. The entire work was evaluated experimentally using a manufactured prototype.

Vibration Suppression for Flux-Switching PM Machines

The flux switching permanent magnet (FSPM) machines are widely studied in recent years due to their robust rotor structure, good flux-weakening capability, good heat dissipation, etc. Nevertheless, they always suffer from serious vibration and noise as a result of the doubly-salient structure. In this paper, the analytical expression of the air-gap electromagnetic force in regular FSPM machines is derived in terms of spatial order and frequency, and it shows that the FSPM machines with a close stator–rotor tooth combination would produce serious stator vibration owing to the low-order spatial harmonics in the air-gap electromagnetic force. In this paper, a dual-stator dual-rotor (DSDR) FSPM machine topology is presented to suppress the stator vibration. First, the operating principle and the mechanism of vibration suppression of the DSDR machine topology are investigated in detail. Meanwhile, its influences on the electromagnetic performances, such as the output torque and end effect, are also investigated. Finally, two prototypes, the regular topology and the DSDR topology, are designed, manufactured, and tested. The experiment results verify the analysis, and it is found that the maximum and averaged vibration velocity amplitudes of the dominated harmonic can be reduced to 54% and 41%, respectively, by using the DSDR topology.

Elementary Analysis of Segmental Stator Flux Switching Permanent Magnet Machine

<span lang="EN-US">Segmental structure is common especially for a rotor in electrical motor. It is to reduce the cost of production, conveniently replace, and as a module where the sum of electromagnetic torque produced comes from each segmental stator add up together. Thus, in this paper will be focusing on the elementary analysis of a segmental stator for single phase 6Slot-12Pole and 3 phase 6Slot-15Pole Switched-Flux Permanent Magnet Machine (SFPMM) as the chosen design for analysis validation from coventional permanent magnet flux switching machine to a new segmental stator structure of SFPMM. It will be focusing on the initial design and to prove that it can be operate as a flux switching machine by implement a 2D Finite Element Analysis simulations such as a No-load analysis (flux linkage, cogging torque, back emf) and Load-analysis (average electromagnetic torque. Elementary result shows that the electromagnetic torque produce for both design are 10.6 Nm and 99.95 Nm and proved that it can produce high torque although it does not surpass the conventional SFPMM. A further research and optimization will be needed to obtain a higher torque compared to conventional SFPMM.</span>

Analysis of a Novel Transverse Laminated Rotor Flux Switching Machine

Flux-switching permanent magnet machines with a segmented rotor are attractive alternatives for high torque and power density and high-speed applications. However, the motor doubly salient structure generates high torque ripples. In order to mitigate this problem and enhance motor torque density, a new flux-switching machine topology with transverse laminated rotor segments is proposed in this paper. An analytical model of the proposed machine for calculation of d - and q -axis inductances and developed torque for various number of rotor segments laminations are presented, as well. A finite element model of the proposed motor with various number of segments laminations is simulated in order to evaluate the analytical results. The results are compared with analytical outcomes that show acceptable accuracy of the analytical model. It is also shown that torque ripple is seriously suppressed, whereas average developed torque and efficiency are considerably increased in this new proposed topology. Eventually, the proposed rotor structure mechanical robustness is evaluated by structural finite element analysis. It is shown that the proposed design is mechanically reliable for low- and high-speed applications.

Analysis of double‐sided sandwiched linear flux‐switching permanent‐magnet machines with staggered stator teeth for urban rail transit

Linear flux-switching permanent-magnet (LFSPM) machines exhibit significant potential in many applications. A double-sided sandwiched LFSPM (DSSLFSPM) machine with high thrust force capability is investigated in this study. After being optimised for optimal thrust force using Maxwell 2D, this machine is found to deliver higher thrust force when compared with an optimised conventional 12/14 LFSPM machine. However, low thrust force ripple is also required in many applications. Thus, in order to reduce the thrust force ripple, the DSSLFSPM machine is improved by a staggered stator teeth structure and an end permanent-magnets method, then, two improved machines are obtained. The improved machines can reduce the thrust ripple to a very low level without thrust force density decrease. Further, the stator yoke thickness of the improved machines is optimised to reach optimal thrust force density. Finally, the performance of the DSSLFSPM-ST machines is analysed including the normal force, the efficiency and the power factor. It shows that the improved DSSLFSPM machines exhibit relatively low normal force and high thrust force density as well as low thrust ripples, indicating that they are suitable for long-stroke applications.

Design of Rotor Excited Axial Flux-Switching Permanent Magnet Machine

In this paper, a new structure of permanent magnet axial flux-switching machine with segmented rotor has been introduced. The 12-pole stator has been installed between two 8-pole segmented rotors, and the excitation system has been connected to the rotor. This topology enhances the design of flux-switching permanent magnet machines. With this new topology, an increase in the torque density, the reduction the total harmonic distortion, simple construction, and the reduction of cogging torque have been achieved. The harmonic spectrum of the back electromagnetic force has also been improved. This topology provides an optimum power for the electric vehicles because of the short axial length and the high power density along with the low vibration and noise due to lower torque ripple and cogging torque. The three-dimensional time-stepping finite-element analysis is used to determine the flux linkage, back electromagnetic force, the output torque, and the cogging torque. A comparative analysis is made of the proposed topology and related topology in the literature.

Comparison of the Stator Step Skewed Structures for Cogging Force Reduction of Linear Flux Switching Permanent Magnet Machines

Linear flux switching permanent magnetic (LFSPM) machines, with the armature windings and magnets both on the mover in addition to a robust stator, are a good choice for long stoke applications, however, a large cogging force is also inevitable due to the double salient structure, and will worsen the system performance. Skewing methods are always employed for the rotary machines to reduce the cogging torque, and the rotor step-skewed method is a low-cost approximation of regular skewing. The step skewed method can also be applied to the linear machines, namely, the stator step skewed. In this paper, three stator step skewed structures, which are a three-step skewed stator, a two-step skewed stator and an improved two-step skewed stator, are employed for the cogging force reduction of two types of LFSPM machines. The three structures are analyzed and compared with emphasize on the influence of the skewed displacement on the cogging force and the average thrust force. Based on finite element analysis (FEA), proper skewed displacements are selected according to maximum difference between the reduction ratio of the cogging force and the decrease ratio of the average thrust force, then, the corresponding results are compared, and finally, valuable conclusions are drawn according to the comparison. The comparison presented in this paper will be useful to the cogging force reduction of LFSPM machines in general.

Optimisation and design comparison of 10-kW and 3-MW PM flux-switching machines for geared medium-speed wind power generators

The paper details the design optimisation and comparison of two different rare-earth permanent magnet flux-switching machines (PM-FSMs)—12/10 and 12/14—for geared medium-speed wind power generators. The focus is mainly on trade-offs in the performance of these two machines at 10 kW and 3 MW power levels, with highlights on the multi-objective evolutionary optimal performance of small-scale to utility-scale wind turbines. Based on finite element analyses (FEA) and multi-objective design optimisation (MDO), different streams of optimal solutions are obtained and studied. As an indication of the potentials of the proposed PM-FSM wind generators, even for rare-earth-free concepts, the 3 MW designs portray significantly improved torque density thanks to the fixed rotor speed considered at both power levels, and also, smaller torque ripple profiles are conceived due to differences in the calculated saliency ratios, compared to their 10 kW designs. Another finding is based on the nonlinearity of the MDO process on the objective performance of the different machine topologies at the different power levels, which was necessitated by the optimal behaviour of certain design variables such as the split ratio, slot opening width, current density and PM width. Uncharacteristically, the results also reveal possibilities for higher efficiency in 12/14 machines compared to the 12/10 machines, due to positive relationships approximated from general evaluations conceived in the MDO search space in the former, for the split ratio and current density when plotted against the active mass. Lastly, a comparison between 2-D static and 3-D transient FEA processes on some selected benchmarks displayed good agreement.

Analytical Modeling of Magnetic Field Distribution in Multiphase H-Type Stator Core Permanent Magnet Flux Switching Machines

An exact analytical method for magnetic field and electromagnetic torque calculation in H-type stator core permanent magnet flux switching machines (HC PM FSM) considering slotting effects, magnetization orientation and winding layout has been proposed in this paper. The analytical method uses a sub-domain approach and is based on the resolution of Laplace and Poisson equations and Maxwell equation in polar coordinate. The proposed method is applied on the performance computation of two prototypes HC PM FSMs, i.e., a one-phase 12S-15P and a three-phase 24S-10P motor. The results of these models in open-circuit and full-load conditions are validated by FEM method.

Double-stator switched flux permanent magnet machines having low rotor pole numbers

In this paper, double-stator switched flux permanent magnet (DS-SFPM) machines having low rotor numbers and whose stator teeth and rotor pole numbers are relatively same is investigated. Quantitative comparison of their electromagnetic performance is also given. Two-dimensional finite element (2D-FEA) analysis is employed in the prediction of the developed machines’ performance. It is observed that the open circuit flux-linkage waveforms of the analysed machines having odd rotor poles are both symmetrical and sinusoidal in contrast to its even number rotor pole counterparts whose waveforms are asymmetrical, non-sinusoidal and unbalanced. More importantly, the developed machines with odd rotor pole numbers exhibit higher torque density than its even rotor pole equivalents. Keywords : Harmonics, low rotor pole, PM usage, and unbalanced back-EMF.

Optimal Design and Analysis of the Novel Low Cogging Torque Axial Flux-Switching Permanent-Magnet Motor

The axial field flux-switching permanent-magnet machine (AFFSPM) is one of the most efficient machines which is appropriate for high torque and low-speed direct-drive applications. In this paper, the novel axial field flux switching machine with sandwiched permanent magnet (AFFSSPM) is proposed in order to increase torque density and decrease cogging torque. The proposed model equipped with an advanced phase-group concentrated-coil winding to obtain a unity displacement winding factor. Two three-phase 6-stator-slot (S)/10-rotor-pole (P) and 12(S)/19(P) configurations of the proposed model are investigated. Some specific design issues, including the sandwiching pole angle, the stator tooth angle, and the rotor pole angle have been optimized to obtain the maximum torque density and minimum cogging torque by artificial neural network and non-sorting genetic algorithm II. Moreover, the static electromagnetic characteristics are investigated. Compared with the conventional AFFSPM and 6(S)/10(P) AFFSSPM, the 12(S)/19(P) proposed machine shows higher torque density, lower cogging torque, and higher level of fault-tolerant capability. In order to improve the dynamic performance of the AFFSSPM motor, a space vector modulation-direct torque and flux control (SVM-DTFC) scheme is proposed. The AFFSSPM motor exhibits excellent dynamic performance with proposed scheme.

Design, Analysis and Model Predictive Control of an Axial Field Switched-Flux Permanent Magnet Machine for Electric Vehicle/Hybrid Electric Vehicle Applications

In this paper, an axial field switched-flux permanent magnet (AFSFPM) machine with stator-PM, which has a high power/torque density and efficiency feature as well as shorter axial length, is designed, analyzed and controlled. The topology, operating principle and design procedure of the AFSFPM machine are labored and discussed. The electromagnetic performance, including the flux linkage, back-EMF, cogging torque, winding inductance and field-control capability, are studied based on 3-D finite-element analysis (FEA). In order to investigate the operating performance of the machine in the whole speed range, a continuous-control-set model predictive control (MPC) method for the AFSFPM machine is proposed. Based on the stage control targets, the maximum torque per ampere (MTPA) and maximum output power flux-weakening strategies are presented in constant torque and constant power regions, respectively. Finally, a prototype of AFSFPM machine has been manufactured and experimentally evaluated and the results show that the MTPA strategy increases the load capability and the flux-weakening strategy broadens the constant power operation range. Moreover, the anti-load-disturbance capacity and dynamic response performance are improved under the MPC method. As a result, the proposed AFSFPM machine drive system is excellent alternative for electrical vehicles (EVs) or hybrid EVs (HEVs).

Closed-Form Solutions Using Offset Angle for Winding Configurations of Flux-Switching Permanent Magnet Machines

This paper presents a novel perspective to understand different winding configurations of flux-switching permanent magnet (FSPM) machines. A simple analytical method is used for the calculation of total offset angle of flux linkages by taking into account an offset angle of stator slot and rotor poles. The closed-form solution is presented to find the sequence of phase windings. The 12-slot/10-pole and 12-slot/13-pole FSPM machines are conceptually segregated into two sets of 6-slot/10-pole and 6-slot/13-pole machines, respectively. This is used to address even harmonic elimination and winding configuration properties in even and odd number of rotor pole configurations. Finite element analysis and experimental results verify the concept.

Analytical Modelling of Open-Circuit Flux Linkage, Cogging Torque and Electromagnetic Torque for Design of Switched Flux Permanent Magnet Machine

Magnetic saturation and complex stator structure of Switched Flux Permanent Magnet Machine (SFPMM) compels designers to adopt universally accepted numerical method of analysis i.e. Finite Element Analysis (FEA). FEA is not preferred for initial design due to its computational complexity and is time consuming process because of repeated iterations. This paper presents an accurate analytical approach for initial design of proposed twelve-stator-slot and ten-rotor-tooth (12/10) with trapezoidal slot structure SFPMM. Air-gap Magnetic Equivalent Circuit (MEC) models with Global Reluctance Network (GRN) methodology is utilized for calculation of open-circuit flux linkage. Fourier Analysis (FA) for cogging torque, and Maxwell Stress Tensor (MST) method for electromagnetic torque where radial and tangential components of the air-gap flux density are produced by the currents flowing in three phase armature winding. Analytical predictions are validated by FEA utilizing JMAG software and shows errors less than ~2% for open-circuit flux linkage, ~4.2% for cogging torque, and ~2% for average electromagnetic torque.

Cogging force reduction in linear tubular flux switching permanent-magnet machines

Abstract The aim of this paper is to explore the possibility of using linear tubular flux switching permanent magnet machines in a free piston energy conversion (FPEC) system. In FPEC systems, acceleration and therefore speed are often relatively high, which impose to have a reduced number of poles, meanwhile the cogging force will be relatively high. In order to reduce the cogging force two techniques are combined. The analysis is done using finite element method.

Partitioned Topologies of Switched Flux Permanent Magnet Machines for Electric Vehicles

Partitioned Topologies of Switched Flux Permanent Magnet Machines for Electric Vehicles

Preliminary Design Investigation of Dual Stator HE FSM using Segmental Rotor

To drop the effect of air transportation on the atmosphere as well as to advance fuel productivity more-electric aircraft (MEA) architectures is a well-known approach. As the electrical machines are competent to deliver higher torque densities and are foremost for the viability of electrical driving force for aircraft applications. For these reasons a new category of machine has been familiar and published in last decade known as flux switching machine (FSM). FSMs comprises all excitation sources on stator side without winding robust rotor structure. Additionally, FSMs are classified into three types such as permanent magnet (PM) FSMs, field excitation (FE) FSMs and hybrid excitation (HE) FSMs. PM FSM and FE FSM use PM and FE coil for their excitation sources respectively, whereas both PM and FE coil are used in HE-FSM for excitation. Afterwards, HE FSMs have shown higher torque to weight ratios with higher efficiency during research in the last decade. Yet, in existing structures of HE FSMs, there is flux cancellation between the fluxes of PMs and FE coil which causes to reduce the performance of machines. Hence, in this paper, a novel structure of dual stator (DS) HE FSM with segmented rotor has been proposed and analyzed. The main reason of dual stator is to make the separate flow fluxes in HE machines to avoid cancellations. The proposed novel DS HE FSM has a simple structure using dual stators to endorse separate dual excitations to be used in fault conditions. The proposed structure has been analyzed using commercial 2D FEA package, JMAG-designer. Initially, this paper presents the coil test analysis of proposed DS HE FSM to confirm the working principle. Besides, performance analysis has been carried out at no load and load conditions.