Flux-switching Linear Machine Research Articles

Review of linear flux-switching machines for variable speed applications

Purpose This paper aims to present an overview of permanent magnet linear flux-switching machines (PMLFSM), field excited LFSM and hybrid excited LFSM (HELFSM) topologies as presented in literature for transportation systems such as high-speed trains and maglev systems. Design/methodology/approach The structural designs of different configurations are thoroughly investigated, and their respective advantages and disadvantages are examined. Based on the geometry and excitation sources, a detailed survey is carried out. Specific design and space issues, such as solid and modular structures, structure strength, excitation sources placement, utilization of PM materials, and flux leakage are investigated. Findings PMLFSM provide higher power density and efficiency than induction and DC machines because of the superior excitation capability of PMs. The cost of rare-earth PMs has risen sharply in the past few decades because of their frequent use, so the manufacturing cost of PMLFSM is increasing. Owing to the influence of high-energy PMs and magnetic flux concentration, the efficiency and power density are higher in such machines. PM is the only excitation source in PMLFSM and has constant remanence, limiting its applications in a wide speed operation range. Therefore, the field winding is added in the PMLFSM to flexibly regulate the magnetic field, making it a hybrid excited one. The HELFSM possess better flux linkage, high thrust force density and better flux controlling ability, leading to a wide speed range. However, the HELFSM have problems with the crowded mover, as PM, field excited and armature excitation are housed on a short mover. So, for better performance, the area of each excitation component has to compete with each other. Originality/value Transportation of goods and people by vehicles is becoming increasingly prevalent. As railways play a significant role in the transportation system and are an integral part of intercity transportation. So, this paper presents an overview of various linear machines that are presented in literature for rail transit systems to promote sustainable urban planning practices.

Performance analysis of modular mover hybrid excited flux switching linear machine

Performance analysis of modular mover hybrid excited flux switching linear machine

Analysis of a Discrete Stator Hybrid Excited Flux Switching Linear Machine

A discrete stator hybrid excited flux switching linear machine (DSHEFSLM) is proposed in this paper. The proposed DSHEFSLM uses a discrete stator to reduce the iron loss and overall cost of the machine. Assistant teeth are used at both ends of the mover to overcome the unbalance in the three phases, which is a global issue in linear machines. Field excitation (FE) is used, which adds field regulation capability to the proposed machine and makes it suitable for a wide speed operation range. A magnetic equivalent circuit model is used to find the suitable coil combination and no-load flux linkage. The multiobjective genetic global optimization is used to optimize the design parameters of the whole machine while keeping the slot area, electric and magnetic loadings constant. A correlation table is drawn to show the impact of different design parameters on average thrust force. The optimization has increased the peak-to-peak flux linkage by 11%, average thrust force by 34.60%, thrust force density by 34.60%, decreased thrust force ripples, and detent force by 21.05% and 8.58% respectively. The proposed machine has reduced the volume of the permanent magnet by 39.18% and offers 28.09% higher average thrust force and thrust force density compared to the flux switching permanent magnet machine proposed in the literature.

Experimental Validations of Hybrid Excited Linear Flux Switching Machine

Linear Flux Switching Machines (LFSMs) possess the capability to generate adhesive thrust force, thus problems associated with conventional rotatory electric machines and mechanical conversion assemblies can be eliminated. Additionally, the unique features of high force/power density, efficiency, and a robust secondary structure make LFSMs a suitable candidate for linear motion applications. However, deficiency of controllable air-gap flux, risk of PM demagnetization, and increasing cost of rare earth PM materials in case of PMLFSMs, and inherent low thrust force capability of Field Excited LFSMs compels researchers to investigate new hybrid topologies. In this paper, a novel Double-Sided Hybrid Excited LFSM (DSHELFSM) with all three excitation sources, i.e., PMs, DC, and AC windings confined to short moving primary and segmented secondary providing short flux paths is designed, investigated, and optimized. Secondly, unequal primary tooth width optimization and additional end-teeth at all four corners of the primary equip proposed design with balanced magnetic circuit and reduced end-effect and thrust force ripples. Thirdly, the measured experimental results of the manufactured proposed machine prototype are compared with corresponding simulated model results and shows good agreements, thus validating the theoretical study.

Design and analysis of dual‐stator hybrid excited linear flux switching machine for long‐stroke applications

In this work, a novel dual-stator hybrid excited linear flux switching machine (DSHELFSM) is proposed. The proposed machine is suitable for long-stroke applications as all the excitation sources are mounted on a short mover and the stator is completely passive. Second, the proposed machine uses ferrite magnets rather than the expensive rare earth permanent magnets (PMs) with the addition of field excitation to achieve flux-regulation capability at various field currents. An iron bridge that provides an additional path for flux linkage to complete its circuit is used. Various design parameters such as split ratio, stator pole width, width and height of PM, the width of the iron bridge, width of mover's tooth, and stator slot depth are optimised using multivariable geometric optimisation (MGO) while keeping the slot area, electric and magnetic loading constant. The optimised design has improved the performance as compared to the initial design. Furthermore, the results obtained by 2D analysis are verified by 3D analysis. Thermal analysis is carried out to set the operating limit of the proposed machine.

Analytical Airgap Field Model and Experimental Validation of Double Sided Hybrid Excited Linear Flux Switching Machine

Linear Flux Switching Machines (LFSMs) are suitable candidates for long stroke applications as they confines all excitation sources to primary thus leaving completely passive, robust, and low cost secondary. Permanent Magnet LFSMs (PMLFSMs) enables high thrust force density and efficiency. However, deficiency of controllable air-gap flux, risk of PM demagnetization, and increasing cost of rare earth PM materials diverted researchers towards Field Excited LFSMs (FELFSMs). FELFSMs wiped out aforementioned PMLFSM’s shortcomings at the cost of low thrust force density. In this paper, merits of PMLFSM and FELFSM are combined by proposing a novel Hybrid Excited LFSM (HELFSM). Proposed machine is excited by PMs, Field Excitation Coils (FECs), and Armature Windings (AWs). However, complex magnetic circuit of poly-excited HELFSM compels designers to adopt FE Analysis (FEA) for design, analysis, and optimization. To decrease dependency on computationally complex and time consuming FEA, an analytical model combining lumped parameter magnetic equivalent circuit, Fourier analysis, Laplace equation, and Maxwell Stress Tensor method is proposed to predict open-circuit flux linkage, B-EMF, normal and tangential components of no-load and on-load magnetic flux density, detent, and thrust force performance. Finally, predictions of the developed analytical model are validated with corresponding FEA and experimental results.

Performance comparison of partitioned primary hybrid excited linear flux switching machine

To avoid the problem of crowded primary and rising temperature of permanent magnet (PM), the design of partitioned primary hybrid excited linear flux switching machine (PP-HLFSM) positions the armature, and field excitation coil winding on separate part of the mover. This article examines the performance analysis of different structures of unaligned structure of PP-HLFSM and compared the proposed designs by reducing the usage of PM to half in terms of volume from 25,920 mm3 to 12,960 mm3, for both concentrated and toroidal winding structure leading toward cost effectiveness. This article scales down the cost of proposed designs for elevator long stroke application. Based on finite element analysis (FEA) and boundary element analysis, the electromagnetic performance of the machine is studied in detail. Single variable optimization is implemented to optimize both the proposed structures. Analysis includes flux linkages, flux strengthening, average force characteristics, force–velocity and power–velocity curves, copper losses, iron losses, efficiency, thrust force density and power density, and demagnetization analysis. Comparison of conventional structure with proposed designs are made in terms of flux, thrust force, losses, efficiency, power density, demagnetization of PMs, and thermal analysis, along with 3D FEA analysis. Finally, the proposed structures are analytically validated.

A Novel Hybrid-Excitation Switched-Flux Linear Machine With Partitioned-Excitations

This article proposes a novel hybrid-excitation switched-flux linear machine with partitioned-excitations (PE-HESFLM), which places the armature windings and field winding into different primaries. It can be geometrically taken as the combination of a conventional flux-switching linear machine and an additional primary for accommodating the field winding. Therefore, the proposed machine can exhibit increased armature and field slot areas so that the competition for space between these two winding types is effectively mitigated, which in return translates to improved thrust density and flux-adjusting capability. First, the configurations of the proposed PE-HESFLM are introduced, following which different slot/pole combinations are globally optimized based on genetic algorithm (GA). Finally, the electromagnetic performances are comparatively investigated. It is shown that the proposed machine can effectively improve the thrust density and flux-adjusting capability, so that the proposed machine configuration is a particularly good candidate for applications which require wide-speed capability.

Investigation of a Partitioned-Primary Hybrid-Excited Flux-Switching Linear Machine With Dual-PM

A novel partitioned-primary hybrid-excited flux-switching linear machine with dual-PM excitation (DP-PPHEFSLM) is proposed and investigated in this paper. Unlike conventional single-primary hybrid-excited topologies, this proposed topology separates armature windings and field windings into two different parts of the partitioned-primary, with each part also having sandwiched or buried PMs. Due to greatly increased armature and field slot areas, it thus solves the problem of a crowded primary, which is typically encountered with conventional structures. Besides, the thrust density is further increased by skillfully positioning PMs on both primary parts. In this paper, first, the topology, operation principles, and viable primary/secondary pole-number combinations of the proposed machine are elaborately addressed. Based on 2D finite-element method (FEM), the proposed machines are globally optimized using genetic algorithms and their electromagnetic performances further investigated. Moreover, the proposed machine is compared with conventional topologies in terms of electromagnetic performances, which shows that the proposed machine exhibits multiple merits such as higher thrust density, improved space utilization, and more flexible flux control capability. Finally, a 6/7 DP-PPHEFSLM prototype machine is manufactured and tested to validate the 2D FEM-predicted results.

Development and Analysis of Novel Flux-Switching Transverse-Flux Permanent Magnet Linear Machine

The flux-switching transverse-flux permanent magnet linear machine (FSTFPMLM) is proposed in this paper, combining the advantages of the transverse-flux linear machine and the flux-switching linear machine. First, the structure and operating principle of the FSTFPMLM is presented. Second, the magnetic field of a simplified FSTFPMLM is numerically computed by the three-dimensional (3-D) finite-element method (FEM). Third, the thrust characteristics of the machine, including the thrust force, cogging force, and force ripple, are numerically analyzed. The influence of structure parameters on the thrust characteristics has been analyzed by the 3-D FEM. The law of thrust, cogging force, and force ripple as the pole pitch ratio between primary and secondary, and the ratio between the tooth width and pole pitch of the secondary variable provides the guidance to design FSTFPMLM, which aims to achieve a larger thrust, smaller cogging and force ripple using less permanent magnet materials. The thrust force capabilities of FSTFPMLM are compared with other topologies of linear machines. Finally, the prototype and experimental setup have been developed, and the calculated results and the measured results are in good agreement.

Design and Optimization of Complementary Field Excited Linear Flux Switching Machine With Unequal Primary Tooth Width and Segmented Secondary

Linear flux switching machines (LFSMs) are one of the recently emerging and competitive candidates for long stroke applications due to high thrust force density, low cost and robust secondary, and high reliability. In the past decade, permanent magnet linear flux switching machines (PMLFSMs) with continuous secondary is researched by numerous researchers. However, cost of rare earth permanent magnet and iron material for continuous secondary in case of long stroke application makes PMLFSMs not an economical choice. In order to incorporate advantages of segmented secondary, such as: less use of stator iron, high power factor, and less critical saturation, a novel complementary dual mover field excited linear flux switching machine (FELFSMs) with segmented secondary and parallel magnetic structure is proposed and investigated in this paper. Furthermore, geometry-based deterministic optimization approach based on finite element analysis (FEA) is adopted to uplift overall thrust force profile, reduce secondary iron volume, and balance magnetic circuit of the machine. During optimization process, magnitude difference of flux flow between ac winding tooth and dc winding tooth is observed, that compel designers to go for unequal primary teeth design. Finally, optimal ac and dc current densities of geometrically optimized model and without any cooling arrangements are investigated for maximum average thrust force and minimum thrust force ripple ratio.

A HTS-Excitation Modular Flux-Switching Linear Machine With Static Seals

This paper proposes and analyzes a novel high-temperature superconducting (HTS) modular flux-switching linear machine for long-stator applications, which adopts the stator with a low-cost salient-pole iron core and accommodates both the armature windings and HTS-excitation windings on the short mover, thus facilitating static seals of cooling Dewar for the HTS windings. The key of the proposed machine is to employ a modular mover structure composed of separate phase modules to achieve a complementary pattern, such that the cogging force can be significantly offset to effectively reduce the force ripple while offering the advantages of very symmetrical back electromotive force (EMF) and high fault tolerance. The operation principle and optimization analysis of the proposed machine with concern on the HTS-excitation characteristics are carried out. Also, by using the two-dimensional finite element method, the electromagnetic performances of the proposed machine are investigated to verify its validity. The results show that it can offer symmetrical and sinusoidal back-EMF, high fault tolerance, and low force ripple.

Investigation of a tubular dual-stator flux-switching permanent-magnet linear generator for free-piston energy converter

This paper describes a tubular dual-stator flux-switching permanent-magnet (PM) linear generator for free-piston energy converter. The operating principle, topology, and design considerations of the machine are investigated. Combining the motion characteristic of free-piston Stirling engine, a tubular dual-stator PM linear generator is designed by finite element method. Some major structural parameters, such as the outer and inner radii of the mover, PM thickness, mover tooth width, tooth width of the outer and inner stators, etc., are optimized to improve the machine performances like thrust capability and power density. In comparison with conventional single-stator PM machines like moving-magnet linear machine and flux-switching linear machine, the proposed dual-stator flux-switching PM machine shows advantages in higher mass power density, higher volume power density, and lighter mover.