Permanent Magnet Linear Machine Research Articles

A Tubular Staggered-Teeth Transverse-Flux PMLM With Circumferentially Distributed Three-Phase Windings

This paper investigates a special tubular staggered-teeth transverse-flux permanent-magnet linear machine (TST-TFPMLM) for a free-piston Stirling power generating system. With the complicated flux leakage characteristic of the TST-TFPMLM considered, the general forms and evaluation method of the flux leakage are investigated by finite-element analysis, and the distribution law and reduction method of the flux leakage are obtained. To help the initial design of the TST-TFPMLM, both back electromotive force (EMF) and thrust are taken as the main concerned aims, and the influence of some primary structural parameters on both back EMF and thrust is studied. To improve the key performances of the TST-TFPMLM, the power factor is investigated with respect to the dimensions of permanent magnets (PMs), winding turns, armature current, internal power factor angle, and tooth tip dimensions. Furthermore, the methods of improving both efficiency and thrust density are explored. A prototype machine is manufactured and tested, and satisfactory experimental results are obtained, showing the feasibility of the TST-TFPMLM for the free-piston Stirling power generating system. This investigation provides a new idea to solve the drawbacks of conventional transverse-flux PM linear machines, which include complicated structure, poor manufacturability, high flux leakage, and low power factor.

Flux concentrated doubly salient linear permanent magnet machine

Different topologies of Vernier permanent magnet (PM) machines have been proposed for direct drive low-speed applications due to their high thrust and power density. However, this type of machine can suffer from low power factor (PF). In this study, a flux concentrated doubly salient linear permanent magnet machine with V-shape PM arrays is proposed and compared to a consequent pole (CP) type machine. Using the configuration of V-shaped PMs allows the flux to be concentrated in iron spacers located between two pieces of PMs. This feature is shown to result in an improvement of the airgap flux density, which allows a reduction in electrical loading and hence an improvement in power factor. In order to achieve a fair comparison, two doubly salient linear permanent magnet machines with different PMs’ configurations have been analysed and compared using transient FEA. The investigated machines have the same overall machine and, crucially, magnet volume. The results confirm that the proposed V-shape machine is capable of higher thrust force, higher no-load back EMF and can achieve a higher PF of 42% compared to the consequent pole machine, while it consumes the same amount of the PM material.

Linear consequent pole Halbach array flux reversal machine

This paper presents a linear variable reluctance permanent magnet (LVRPM) machine where the armature winding and inset Halbach array permanent magnets (PMs) are mounted on E-core stators. The Halbach array consists of a vertically magnetised PM pole and a salient ferromagnetic iron pole (split tooth) sandwiched between two horizontal PMs. The translator consists solely of laminations with salient iron poles. As a variable reluctance machine, it exhibits inherent magnetic gearing and a higher force and power density than the conventional synchronous PM machines. Finite element analysis (FEA) has been used to investigate the effect of machine parameters. The logical development of the LVRPM from the more conventional Vernier Hybrid machine is presented, including a near 50% reduction in magnetic flux leakage and a higher flux per unit magnet mass.

Development of a consequent pole transverse flux permanent magnet linear machine with passive secondary structure

Transverse-flux machines have the advantage of high force density owing to the peculiarity of decoupling of electric loading and magnetic loading. In this paper, a novel consequent-pole transverse-flux permanent magnet linear machine (CP-TFPMLM) is proposed and investigated. The origination of the proposed machine is from an existing transverse-flux flux-reversal linear machine (TF-FRLM), by partially replacing permanent magnet poles with soft magnetic iron for further reducing the cost of magnets. The fundamental structure and operating principle are introduced at first. The electromagnetic performance, including back EMF, detent force, and thrust force, are investigated with the finite element method. The proposed machine can achieve similar performance as compared to the TF-FRLM but with half of the magnets are used.

Comparative Study of Linear Superconductivity Machine With Different Stator and Winding Configurations

Compared with rotary electrical machines in linear drive applications, linear machines without rotary-linear motion conversion equipment can have higher force density and efficiency. Linear superconductivity machines (LSMs), consisting of high-performance superconducting magnets instead of permanent magnets, can offer very high force density and efficiency compared with other linear machines, such as linear induction machine, linear permanent magnet machine, and so on. In this paper, LSMs with different stators and winding configurations are investigated, specifically LSMs with concentrated or distributed windings, and unilateral or bilateral side stators. The electromagnetic parameters and performance of these LSMs are calculated and compared by using the finite element method, and then, the main difference between various design methods in LSM has been presented.

Electromagnetic Characteristic of a Novel Linear Flux Switching Machine With Three-Dimensional Magnetic Circuit

The novel linear flux switching permanent magnet machine with a three-dimensional magnetic circuit is proposed in this paper, which is suitable for aerospace, missile launch, and other fields, benefiting from high thrust force and low cost. First, the basic structure and working principle of the machine are introduced. Second, the equivalent magnetic circuit model considering the variable reluctance is established and the equations are put forward for magnetic analysis. Third, the simplified finite element model is performed to calculate the field distribution, the air-gap flux density, the flux linkage of winding, and the back electromotive force. Finally, a prototype is constructed and experiments show a good agreement with analysis.

Tubular unified magnetic‐field flux‐switching PMLM for free‐piston energy converter

A tubular flux-switching permanent-magnet linear machine (PMLM), which features unified magnetic field between the mover and two stators, is investigated for free-piston energy converter. The topology evolution, topology, operating principle and design considerations of the machine are thoroughly analysed. With the sinusoidal speed characteristic of free-piston Stirling engine considered, a tubular unified magnetic-field flux-switching PMLM is designed by finite-element analysis. Several main structural parameters, which include the outer and inner radius of the mover, the mover tooth width, the magnet thickness, the tooth widths of both the outer and inner stators and the widths of both the outer and inner stator yokes are studied to achieve high-force and mass-power density. Finally, the proposed machine is compared with two typical flux-switching PMLMs. The comparison results show that the unified magnetic-field flux-switching PMLM is suitable for applications which require high-power density, light mover structure and fast dynamic.

Improving the Thermal Performance of Rotary and Linear Air-Cored Permanent Magnet Machines for Direct Drive Wind and Wave Energy Applications

Air-cored machines offer benefits in terms the elimination of magnetic attraction forces between stator and rotor. With no iron in the stator there is not a good thermal conduction path for heat generated by Joule losses in the stator winding. Results from both models and experimental tests are provided in this paper to investigate different methods of cooling air-cored windings, including natural air-cooling, direct liquid cooling, and the use of heat pipes.

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.

Design and Analysis of a New Bipolar-Flux DSPM Linear Machine

In this paper, a new permanent magnet (PM) linear machine, termed the bipolar-flux (BF) doubly salient PM (DSPM) linear machine, is proposed and implemented. This BF-DSPM machine incorporates the stator-PM structure and the mover-PM structure into the DSPM machine topology. It consists of a mover with fault-tolerant teeth (FTT) and a stator with consequent poles. The FTT structure can provide the feature of phase-to-phase independence, thus offering the fault-tolerant capability. By using finite element analysis, the electromagnetic performances of the proposed machine are analyzed and then quantitatively compared with that of the flux-reversal PM machine, PM brushless DC (BLDC) machine and dual-PM machine. It confirms that the proposed machine can offer the advantages of high power density, high force density, and fault-tolerant capability. Experimental results are also given to verify the feasibility of the proposed machine.

Global Quantities Computation Using Mesh-Based Generated Reluctance Networks

Global Quantities Computation Using Mesh-Based Generated Reluctance Networks

Design and Analysis of an Interior Permanent Magnet Linear Vernier Machine

A novel interior permanent magnet linear vernier machine (IPM-LVM) is proposed and analyzed in this paper. Compared to the existing surface-mounted permanent magnet linear vernier machine (SPM-LVM) and the SPM-LVM with Halbach arrays, the proposed machine can offer higher flux density in both the air-gap and armature iron core, which lead to a higher back electric motive force (back EMF) and higher thrust density under the same mover volume and heat capacity. Besides, it is proven that the proposed IPM-LVM also has a lower demagnetization risk compared to the SPM-LVM. Furthermore, in order to reduce the thrust ripple of the proposed machine, the three-sectional structure is adopted in this paper, which makes the proposed IPM-LVM exhibit high thrust density and low thrust ripple at the same time.

Design and Analysis of Linear Hybrid-Excited Slot Permanent Magnet Machines

Novel linear hybrid-excited slot permanent magnet machines (LHESPMMs) are proposed in this paper. First, the topology and geometric parameters of the LHESPMMs with 12 slots are introduced, and the corresponding basic operating principle is investigated. To the 12-slots and 10/11/13/14-poles LHESPMMs, global optimization using genetic algorithm is implemented. Then, the electromagnetic performances including the flux linkage, back-electromotive force, detent force, and static force–current characteristics are comparatively studied using the 2-D finite-element (FE) analysis. It is shown that 12-slots/13-poles (12s/13p) are the optimal slot/pole combinations. Furthermore, the thrust force performances of 12s/13p linear variable flux reluctance machine (LVFRM), linear vernier permanent magnet machine, and LHESPMM are compared. It shows that LHESPMM can provide much higher thrust force than does LVFRM. With the increase of current, LHESPMM exhibits better thrust force capability than that of the other two machines. Finally, a prototype of 12s/13p LHESPMM is manufactured and tested to validate the 2-D FE predicted results.

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).

Investigation and Analysis of Force Production Mechanism for Partitioned Stator Flux Reversal Permanent Magnet Linear Machine

Investigation and Analysis of Force Production Mechanism for Partitioned Stator Flux Reversal Permanent Magnet Linear Machine

Modular airgap windings for linear permanent magnet machines

This study proposes an offset concentrated wound air-core linear synchronous machine for launch applications where reduced supply volt-amp per newton (VA/N) and attraction force is essential. A winding factor model based on the conductor distribution is derived and used to analyse the winding factor of possible topologies. Two configurations, 3-coil/4-pole and 12-coil/14-pole, have high fundamental winding factors and are selected for the design comparisons. Machines using single- and double-sided offset windings are compared. The results obtained for these selected designs show that the 3-coil/4-pole design with offset winding provides the highest thrust due to its higher winding factor, but the 12-coil/14-pole design has lower supply VA/N. The implementation of the offset windings reduces VA/N. A significant reduction can be seen when the long stator short rotor arrangement is considered. A half-segment prototype is built and tested. The experimental results obtained validate both the algebraic and three-dimensional finite element analysis.

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.

Analysis of Overhang Effects Using Conductor Separation Method in Coreless-Type PM Linear Machines

The axial overhang of the permanent magnet (PM) has widely been used to enhance the thrust per loss, particularly in air-core structure where the radial flux density is low. This communication investigates PM overhang effects in coreless-type PM linear machines. To analyze the structure where the magnet length exceeds the active length of the mover coil, a new approach using the conductor separation method is introduced and developed to calculate the electromagnetic thrust of the linear machine designed with the overhang magnet. The proposed method is based on an extended 3-D winding factor and a lumped parameter magnetic circuit model to take end effects into account. It is noted that presented overhang analysis can be applicable to any configurations of wound copper coil. The validity of analytical results derived by the proposed method is confirmed by 3-D finite element and experimental results.

A Novel HTS Flux-Reversal Linear Permanent Magnet Machine With a Lower Number of Mover Teeth and Higher Thrust Density

Compared to the conventional flux-reversal linear permanent magnet machine (FRLPM), a novel high-temperature superconducting (HTS) FRLPM with a lower number of mover teeth and higher thrust density is proposed in this paper. In order to explain the superiority of the proposed machine, the back electromotive force of the regular FRLPM, the lower mover teeth number FRLPM (LMT-FRLPM), and the LMT-FRLPM with HTS bulks (HTS LMT-FRLPM) are derived in this paper. The analytical results are validated by the finite-element method (FEM). Furthermore, the thrust performances of the regular FRLPM, LMT-FRLPM, and HTS LMT-FRLPM at rated load are also calculated by the FEM, which verifies the outstanding thrust performances of the proposed HTS LMT-FRLPM.

Thrust force enhancement and ripple reduction of a sandwiched linear flux switching permanent magnet machine with segment stator for urban rail transit

Linear flux‐switching permanent magnet (LFSPM) machines have significant potential in many applications like urban rail transit, automobile and naval. In order to reach high thrust force capability, a sandwiched LFSPM machine (SLFSPM) is investigated in this paper to enhance the usage of both PMs and steel. This machine is found to have higher thrust force after being optimized for maximum thrust force and compared with a optimized conventional 12/14 LFSPM machine based on FEA. However, big thrust ripples will limit its application in many areas. Thus, the SLFSPM machine is improved with two end PMs to suppress the thrust ripple that caused by the unbalanced back‐EMFs, and then, to reduce the thrust ripples that caused by cogging force, the SLFSPM machine with segment stator struture (SLFPM‐SS) is proposed, and the cogging force can be minimized without thrust force capability decrease. Based on FEA results, the SLFPM‐SS machine can maintain high thrust force capability and at the same time, achieve small thrust force ripples and high sinusoidal back‐EMFs. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.