Tubular Linear Machine Research Articles

Design of a Novel Hybrid-Excited Transverse Flux Tubular Linear Machine With Complementary Structure

The transverse flux tubular linear machine (TF-TLM) has merits of high power density and efficiency. However, excited by constant permanent magnet (PM), it is hard for TF-TLM to regulate its flux effectively, which restricts its further application in wave energy conversion (WEC). In contrast, the inherent higher order harmonics existing in the induced voltage may cause the additional loss and produce overvoltage, which should be eliminated to prompt power quality. Therefore, to strengthen the flux regulation capability of TF-TLM and improve the generated power quality, a novel hybrid-excited TF-TLM (HE-TFTLM) with complementary structure is proposed in this article. The key is that a parallel and complementary structure is constructed for hybrid excitations of both dc windings and PMs installed on the stator to enhance the flux regulation capability and eliminate the even-order harmonics in the induced voltage. In addition, the stator consequent-pole design boosts the output thrust density. According to the 3-D finite element analysis (FEA) results, output thrust force reaches 279.14 N, and the power density of the proposed machine can be effectively improved to 154 kW/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> at rated excitation.

Cogging Force Optimization of Double-Sided Tubular Linear Machine With Tooth-Cutting

The double-sided tubular linear machine (DSTLM) has a more compact structure than general single-sided motors, resulting in a higher power density, typically at the cost of a higher cogging force. To reduce this aspect and make it more suitable for applications in wave energy conversion systems or elevator driver systems, a new tooth-cutting topology is proposed in this article. The Schwarz–Christoffel mapping method is used to model and analyze the magnetic field and cogging force of the DSTLM. Based on the analytical model and the relationships between the cutting dimensions and the force performances, optimization is carried out by using a differential evolution algorithm. The optimization and the experiment results show that the proposed tooth-cutting topology can effectively reduce the cogging force at the small cost of weakening average thrust.

Multi‐physics analysis of double‐sided tubular linear machine with misalignment faults

Multi air-gap tubular linear machines usually take the form of a double-sided tubular linear machine (DSTLM). Such machines have a higher space utilisation and higher power density than their single air-gap counterparts, but at the same time the structure is more complex. It is traditionally very difficult to mechanically implement a movement between two slotted stators, whilst maintaining an even air gap distribution. Thermally, the inner stator is another complex aspect of a DSTLM. However, very little understanding of these two aspects and how they influence the performances of tubular machines exists today. Therefore in this paper, the aim is to accurately analyse the influence of temperature rise and eccentricity fault on the performances of DSTLM. A two-way electromagnetic-fluid-thermal multi-physics coupling model of the DSTLM is established. The variations of electromagnetic, fluid and thermal characteristics with the eccentricity are systematically analysed. A physical prototype is manufactured and the analysed results are verified by the experiments.

Performance Analysis of Tubular Partitioned Stator Flux-Reversal Linear Machine With Different Slot/Pole Combinations and Winding Structures

Due to the low speed of the waves, the high-power-density direct-driven wave energy generation system (DD-WEGS) is important. For the DD-WEGS, a tubular partitioned stator, single-layer winding flux-reversal linear machine (TPS-SL-FRLM) is developed in this article. First, the topology structure is introduced and compared with that of the double-layer winding one (TPS-DL-FRLM). Then, the TPS-SL-FRLM with different slot/pole combinations, i.e., 6s/5p, 6s/7p, 12s/11p, and 12s/13p, is analyzed and optimized by a single-variable method to obtain maximum no-load electromotive force (EMF). The 12s/11p TPS-SL-FRLM is selected and further optimized by global optimization methods. When compared with the TPS-DL-FRLM at both no-load and load states, the TPS-SL-FRLM has about 13% higher output voltage and 8.6% higher output power. A prototype is adopted to validate the predicted results. It means that the 12s/11p slot/pole combination and single-layer winding configuration have unique advantages to tubular linear machines in DD-WEGS.

Translator Eccentricity Analysis in Tubular Linear Machines Using Quasi-3-D Finite Element Method Modeling

This paper attempts to present a quasi-3D finite element method technique for modeling and analyzing tubular linear permanent magnet machines (TLPM) with translator eccentricity. Normal tubular linear machines can be modeled effectively using 2D axisymmetric models, but with the introduction of the eccentricity factor into the geometry the axis symmetry is no longer valid, and hence 3D modeling techniques become the only way for studying the machine. However, sometimes 3D modeling can become time-consuming and requires a huge amount of resources especially for non-linear problems, so the interest in modeling techniques that can represent the problem at hand with less computation time and relatively accurate results is high. A quasi-3D technique was specifically developed to be able to represent the eccentricity in TLPMs. The finite element method (FEM) was used for modeling. Eccentricity analysis has been carried on two different TLPM structures using the proposed quasi-3D, and the results from the quasi-3D model were compared to those obtained using the 3D FEM model. Both the open circuit and the on-load operating conditions were studied with the magnetic saturation taken into account. The behavior and the accuracy of the proposed model varied between the two studied structures and for the different operating conditions, and with very low computation time and cost the results obtained from the quasi-3D model were satisfactory in general except for certain cases.

Power flow in the air gap of linear electrical machines by utilization of the Poynting vector: Part 1 ‐ Analytical expressions

Analytical solutions and estimations for the power flow in the air gap of linear electrical machines of different geometries are derived from Poynting's theorem. The different geometries considered are flat one-sided, multi-sided, and tubular linear electrical machines. The radial power flow for all considered geometries is dependent on the area of the air gap, the electric field, the magnetic field, and the load angle. The tangential power flow for both flat one-sided and tubular linear electrical machines is dependent of the area of the air gap, number of poles, the electric field, the magnetic field, and the load angle. The number of poles could be increased to decrease the tangential power flow in flat linear electrical machines. The expression for the tangential flow in tubular linear electrical machines is so complicated that it is difficult to draw conclusions from it.

Analytical Modeling of Variable-Reluctance Tubular Resolver Based on Magnetic Equivalent Circuit and Conformal Mapping

Compared with flat linear structures, tubular linear machines do not face edge effects, making their performance better than their flat counterparts. In this article, a novel linear variable-reluctance resolver with tubular configuration is proposed. To optimize the design of an electromagnetic structure, modeling methods are used. Thus, in this article, an analytical model for the proposed resolver is presented. This model is based on the magnetic equivalent circuit (MEC) method and is considerably less time-consuming than finite element analysis (FEA), yet provides accurate results. A conformal mapping is employed to compute the permeance of the air-gap. The proposed model is then utilized to compensate the resolver’s performance for the longitudinal end-effects. The results of the MEC model are compared with those of FEA, and good agreement is seen. Finally, the compensated sensor is experimentally built and tested, and the simulation results are verified.

A Novel Tubular Switched Reluctance Linear Machine Shielding From Longitudinal End Magnetic Effect

Traditional linear machines are under great influence of longitudinal end effect because of their finite stacking lengths in transverse and longitudinal directions. Longitudinal end effect causes imbalance of phase performance so that linear machine's force fluctuation is aggravated. The negative impact of longitudinal end effect on a flat type switched reluctance linear machine (SRLM) is verified in this paper. In order to avoid this problem, a novel tubular switched reluctance linear machine (TSRLM) is proposed, which can shield from unexpected impact of end effect. In structure, there is no transverse cut in tubular linear machines, so tubular linear machines can evade the influence of the transverse end effect. The equivalent magnetic circuit of this TSRLM is analyzed in this paper, which proves that the TSRLM is also not influenced by longitudinal end effect. A prototype is manufactured, and its corresponding hardware platform is established. A series of simulations and experiments verify that there is no deviation performance among phases in the proposed TSRLM. Accordingly, the traditional longitudinal end effect in linear machines caused by longitudinal cuts can be thoroughly evaded in proposed TSRLM.

Development of a Novel Transverse Flux Tubular Linear Machine With Parallel and Complementary PM Magnetic Circuit for Precision Industrial Processing

The transverse flux permanent-magnet (PM) linear machine has attracted much attention in high-performance direct-drive applications because of its high torque density and efficiency. However, due to its inherent large open-circuit flux leakage, the prominent cogging force makes it difficult to obtain a high accuracy in position and speed control, which restricts its potential for precision industrial processing applications. To overcome this problem, a novel transverse flux linear machine is proposed in this paper. The key is by creatively combining a consequent-pole mover design and a stator-segment-interlacing configuration in such a way that a parallel and complementary transverse magnetic circuit is realized for the moving PMs, which can effectively minimize the open-circuit leakage flux and cogging effect. In this paper, the machine structure, operation principle, and theoretical modeling are introduced, with its electromagnetic performance evaluated by using the finite-element method. A prototype is also built for the experimental verification, and relevant test results agree well with the finite-element predications.

A Novel Tubular Switched Reluctance Linear Launcher With a Module Stator

Electrical machines with transverse-flux (TF) paths have flexible structures, which may help to improve the performance of machines. Comparing to the flat-type structure in linear machines, the tubular-type structure is good for improving the electromagnetic thrust density. In this paper, a novel single-phase tubular-type switched reluctance linear launcher with TF path is proposed. Its stator is composed of several U-shaped modules, and windings are coiling on the yokes of these modules of the stator. This structure differs from the traditional tubular linear machine, and it avoids two windings squeezing in one stator slot so that the winding assembling process is easy. Gear-shaped poles on mover form more effective magnetic circuits than conventional machines. In the design process, the sensitivity analyses on five important parameters are conducted with the finite-element method (FEM) to achieve better performance on thrust density. The prototype has been manufactured and tested. The static and dynamic performances measured through experiments coincide well with the simulation results. These prove the correctness of the calculated FEM results and the well-manufactured machine, and its superiority in thrust density is verified.

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.

Improvement of Tubular Permanent Magnet Machine Performance Using Dual-Segment Halbach Array

In this paper, a modification of the dual-segment permanent magnet (PM) Halbach array is investigated to improve the performance of the tubular linear machine, in terms of flux density and output power. Instead of a classical Halbach array with only radial and axial PMs, the proposed model involves the insertion of mig-magnets, which have a magnetized angle shifted from the reference magnetized angles of axial and radial PMs. This structure leads to the elimination of flux leakage and the concentration of flux linkage in middle of the coil; therefore, the output power is increased by 13.2%.

Analytical Modeling and Experimental Verification for Electromagnetic Analysis of Tubular Linear Synchronous Machines With Axially Magnetized Permanent Magnets and Flux-Passing Iron Poles

This paper presents the analytical modeling and experimental study for electromagnetic analysis of tubular linear synchronous machines with axially magnetized permanent magnets, accounting for the flux-passing iron pole. The field domains are divided into five regions: air gap (I, III), coreless winding (II), outer magnet mover (i), and nonmagnetic material (IV). The governing equation in all subdomains can be solved, and the field distribution can be obtained by applying the boundary conditions to the interfaces between the subdomains. The analytical solutions allow for the prediction of the back electromotive force, inductance, and generating characteristics in closed forms. The magnetic field and electromagnetic performance obtained by the analytical method were compared with those obtained by the finite element method and experimental test. In turn, these facilitate the characterization of the machines and provide a basis for comparative studies, design optimization, system dynamic modeling and simulations, and control development.

Tubular linear permanent magnet synchronous machine applied to semi-active suspension systems

PurposeSemi-active suspension systems with electromagnetic dampers allow energy regeneration and the required control strategies are easier to implement than the active suspensions are. This paper aims to address the application of a tubular linear permanent magnet synchronous machine for a semi-active suspension system.Design/methodology/approachClassical rules of mechanics and electromagnetics were applied to describe a dynamic model combining vibration and electrical machines theories. A multifaceted MATLAB®/Simulink model was implemented to incorporate equations and simulate global performance. Experimental tests on an actual prototype were carried out to investigate displacement transmissibility of the passive case. In addition, simulation results were shown for the dissipative semi-active case.FindingsThe application of the developed model suggests convergent results. For the passive case, numerical and experimental outcomes validate the parameters and confirm system function and proposed methodology. MATLAB®/Simulink results for the semi-active case are consistent, showing an improvement on the displacement transmissibility. These agree with the initial conceptual thoughts.Originality/valueThe use of linear electromagnetic devices in suspension systems is not a novel idea. However, most published papers on this subject outline active solutions, neglect semi-active ones and focus on experimental studies. However, here a dynamic mechanical-electromagnetic coupled model for a semi-active suspension system is reported. This is in conjunction with a linear electromagnetic damper.

Pole Shape-Based Reduction of the Harmonic Content of the IPM T-LSM Air Gap Flux Density

This paper presents a sizing approach dedicated to the reduction of the harmonic content of the air gap flux density of interior permanent magnet tubular-linear synchronous machines (IPM T-LSMs) based on pole shaping. The study is initiated by a formulation of the air gap flux density of conventional IPM T-LSMs equipped with flat-shaped poles. In the second step, the established model is reformulated with emphasis on the pole shape variation characterized by two parameters: the pole air gap radial width and the pole head opening. Following its experimental validation, the resulting model is applied to the sizing of the pole shape in an attempt to reduce the harmonic content of the air gap flux density. The developed sizing procedure considers the effect of the above-defined parameters on the harmonic content of both the radial and axial components of the air gap flux density. The study is achieved by the selection of a set of parameters for which both radial and axial components of the air gap flux density exhibit their lowest spatial harmonic distortion.

Magnetic Flux Distribution of Linear Machines with Novel Three-Dimensional Hybrid Magnet Arrays.

The objective of this paper is to propose a novel tubular linear machine with hybrid permanent magnet arrays and multiple movers, which could be employed for either actuation or sensing technology. The hybrid magnet array produces flux distribution on both sides of windings, and thus helps to increase the signal strength in the windings. The multiple movers are important for airspace technology, because they can improve the system’s redundancy and reliability. The proposed design concept is presented, and the governing equations are obtained based on source free property and Maxwell equations. The magnetic field distribution in the linear machine is thus analytically formulated by using Bessel functions and harmonic expansion of magnetization vector. Numerical simulation is then conducted to validate the analytical solutions of the magnetic flux field. It is proved that the analytical model agrees with the numerical results well. Therefore, it can be utilized for the formulation of signal or force output subsequently, depending on its particular implementation.

Magnetic field and force output analysis of tubular linear machines with two structure topologies

Magnetic field and force output analysis of tubular linear machines with two structure topologies

A New Method for Determining the Magnetic Properties of Solid Materials Employed in Unconventional Magnetic Circuits

To evaluate the quality of magnetic materials used in electrical machines, accurate material characterization is required. For common, solid (nonlaminated) ferromagnetic materials, characterization procedures such as the toroidal ring sample test method are capable of mapping electromagnetic properties with reasonable accuracy. This is true when the investigation is for solid materials to be used in conventional magnetic circuits, i.e., where the flux paths and induced eddy currents follow the more common “radial” characteristics, as in a standard rotating machine. When solid ferromagnetic materials are employed in unconventional machine structures, such as for transverse flux machines or tubular linear machines, classical methods are not capable of achieving an accurate representation of the flux conditions in the machine, thus resulting in inaccurate characterization data that usually underestimate the total loss prediction. In this paper, a new testing method is proposed to impose the correct flux conditions for solid materials (used in tubular linear machines) and accurately map the eddy current losses in the solid parts. The proposed method uses a simple experimental test setup to characterize the power loss of solid, ferromagnetic material. The basic experimental results from the new setup are compared to results from three-dimensional finite element analysis.

Optimal design of slotless tubular linear brushless PM machines using metaheuristic optimization techniques

Optimal design of slotless tubular linear brushless PM machines using metaheuristic optimization techniques

No-load Features of T-LSMs With Quasi-Halbach Magnets: Application to Free Piston Engines

The paper is devoted to the prediction followed by the enhancement of the no-load features of tubular linear synchronous machines (T-LSMs) with quasi- Halbach magnetized PMs in the mover. The study is initiated by the prediction of the spatial repartition of the no-load air gap flux density. Then, a formulation of the back-EMF and the cogging force, based on the predicted spatial repartition of the no-load air gap flux density, is developed, considering 1) the case of an infinite length machine and 2) the case of a finite length one. A case study, corresponding to an initial concept, is treated with the prediction of its no-load features. The study is extended to the enhancement of these features with emphasis on the effects of two influent sizing parameters, assuming an infinite length machine. This enables the identification of a preoptimized concept. The back-EMF and the cogging force of this latter are then predicted in the case of a finite length machine. A further enhancement of these features is gained, thanks to a quasicancellation of the end effect. The prediction of the back-EMF and the cogging force of the optimized T-LSM with quasi- Halbach magnetized PMs has clearly demonstrated the effectiveness of the proposed approach.