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This study is aimed at investigating the growth rate of azimuthal perturbation modes in an ideal annular linear induction pump model. The positive growth rate of azimuthal perturbation modes is associated with the unstable behaviour of the annular linear induction pump and is known in the literature as MHD instability characterized by strong low-frequency oscillations of magnetic field, flowrate, and pressure. A linear stability analysis of a height-averaged quasistationary main flow in the ideal annular linear induction pump has been conducted, where only temporally evolving azimuthal modes of the axial velocity and magnetic field perturbations were considered. The obtained results predict damped or damped oscillating perturbations in a stable regime as a function of Rm, Rms, N and κm. In the studied parameter range, an amplification of perturbations without oscillations was observed above the instability threshold. It can be concluded that the analysed model of the ideal annular linear induction pump cannot predict experimentally and numerically the observed low frequency oscillations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Operation of Vernier machines is based on flux modulation. They have some advantages including maintaining the rated torque in motor applications and the rated output power in generator applications at low speeds, high torque density and relatively low torque ripple due to their magnetic gear property and fault‐tolerance. In recent years, the motor with various topologies has been developed for different applications. Therefore, analysing and monitoring different faults is essential in the design and implementation stages. This study has two main purposes. First, to introduce an accurate frequency index independent of load variations for detecting the turn‐to‐turn short circuit (TTSC) faults in the stator windings of a permanent magnet Vernier machine. Second, modelling the machine in a healthy condition and in the presence of TTSC faults to investigate its effect on machine performance and output characteristics. An analytical model is presented using the modified winding function theory under the TTSC fault by taking into account the effect of stator slots which enhances the accuracy of the air‐gap permeance function estimation. In the process of calculating the fault index, frequency components of the output characteristics of the machine are obtained from the mathematical equations of the magnetic field. It is shown that the proposed indicators are robust against load variations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This study proposes a new high-temperature superconductor (HTS) modular flux-switching linear machine for rail transit, in which the armature windings and HTS field windings are placed on the short mover, while the long stator is only made of segmented low-cost iron. The key is to adopt a modular mover consisting of three separate phase modules whose positions are mutually 120° electrical degrees apart to greatly offset the cogging force for suppressing the thrust force ripple, accompanied with the features of high-fault tolerance. Also, the HTS excitation can produce stronger magnetic field than permanent magnet excitation to obtain a high force density; meanwhile, it easily regulates the air-gap flux density for achieving flexible high-speed constant-power operation. The operation principle and general design method of the proposed machine with concerning the HTS-excitation pattern are described in details. By using the finite element analysis, the machine performances are comparatively analysed with its counterpart without using modular mover to verify its validity. The results show that the proposed machine can offer more sinusoidal back electromotive force, better fault tolerance, higher thrust force and smaller force ripple. [ABSTRACT FROM AUTHOR]

Linear permanent magnet Vernier machines (LPMVM) have received more and more attention in recent years due to the advantages of high thrust density and low thrust ripple, which are both required in many direct-drive applications. In this paper, a double-sided toroidal-winding LPMVM (DSTWLPMVM) is proposed, and the thrust ripple sources for this type of machine are analyzed. To emphasize the specificity of LPMVM in aspect of thrust ripple optimization, a traditional fractional-slot linear permanent magnet synchronous machine is selected as a reference. Two indexes [amplitude difference (AD) and phase shifting (PS)] are defined to quantify the thrust ripple caused by the AD and the PS among three-phase electromotive force (EMF), respectively. Additionally, detent force is also considered when optimizing the three-phase EMF. Finally, a prototype of DSTWLPMVM is manufactured and tested. The measured EMF is basically symmetrical sinusoidal waveforms and the peak-to-peak value of the detent force is lower than 10 N. [ABSTRACT FROM AUTHOR]

The finite-element method is widely used in predicting performance parameters and, furthermore, finding the optimal design of linear machines by parameter sweeping analysis. Since there are usually thousands of sample points to be evaluated, where, for each sample point, a transient finite-element analysis having linearly moving parts is needed, it is a time-consuming process when finding the optimal design parameters. For traditional finite-element methods considering linear motion, either remeshing or overlapping composite mesh technique is needed at each time step, which, however, increases the computation burden. To accelerate the optimal design of linear motors using transient finite-element computation, a novel method based on a combination of mesh deformation and nonconforming mesh connection techniques is proposed in this paper. First, when the geometric design parameters are updated, a fast remesh-free mesh deformation method is used to deform the mesh. Then, in the transient finite-element solution process, a simple and robust mesh deformation method is used to update the mesh for each time step, and a mesh connection technique is adopted to make the solution continuous across the interface of stator and mover meshes. Numerical results are demonstrated to show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper analyzes the flux characteristics and normal force of the double-sided switched reluctance linear machine (SRLM) under the asymmetric air gap. The magnetic equivalent circuit (MEC) of the machine and the details of the flux paths configuration at six distinct mover positions under the asymmetric air gap are included. Then, six special mover position magnetization curves are calculated by solving the MEC with the method of Gauss–Seidel. The magnetic flux-linkage model and thrust model based on six distinct mover positions are established by analytical polynomial. Three-dimensional (3-D) finite-element method (FEM) simulation and the experimental study with the prototype hardware are carried out to validate the accuracy of the MEC model calculated for the flux linkage and normal force. The six distinct mover positions flux linkage and normal force calculated by the MEC are consistent with the 3-D FEM calculated data and experimental data. It indicates that the proposed method to calculate the flux linkage and the normal force is feasible and effective. The dynamic analysis is also conducted. The simulated phase current waveforms are also consistent with the experimental results. It indicates that the presented method can be used to simulate the phase current under the asymmetry air gap effectively. The normal force under different asymmetry rates is analyzed, which provides the theoretical basis for reducing the unbalanced force of the double-sided SRLM. [ABSTRACT FROM AUTHOR]

In order to limit the armature current within a safe region, this paper proposes a finite control set model predictive control (FCS-MPC) method for linear induction machines (LIMs) by adding a penalty overcurrent term in the cost function. The modulation strategies based on two and three voltage vectors are combined with FCS-MPC so as to reduce the current ripples and steady-state tracking errors. Three different search methods have been developed to help reduce the computational burden by excluding many unsuitable participating voltage vectors and combinations in advance. These search methods are also effective for FCS-MPC with current limit. Finally, some key performance indexes are fully compared for LIMs controlled by different FCS-MPC-based modulation strategies through comprehensive numerical simulation and experiments on a test bench with two 3-kW arc induction motors. It is shown that the proposed low-complexity control strategies can effectively avoid overcurrent under any circumstances. [ABSTRACT FROM AUTHOR]

The novel partitioned-primary hybrid-excited flux-switching linear machines (PP-HEFSLMs) with unaligned and aligned structures are proposed, which exhibit advantages of direct-driven, wide speed operation, robust secondary, etc. Unlike conventional hybrid-excited topologies, the proposed PP-HEFSLMs accommodate armature and excitation windings on two separated parts of the partitioned primary, which solves the problem of crowded primary; hence, both flux-adjusting ratio and thrust force density are effectively improved. The topology and operation principle of the two PP-HEFSLMs are introduced in detail first. Based on finite-element method (FEM) analysis, major geometric parameters are investigated and optimized then. For the optimized structures, the electromagnetic performances, i.e., thrust force characteristics, demagnetization, flux-regulation capability, and inductances are calculated and further compared. The results manifest both structures show a satisfactory flux-adjusting ratio particularly for an aligned structure and good fault-tolerant capability due to tiny mutual inductances between phases. Although the thrust density of the aligned structure is relatively low compared with its unaligned counterpart, it can be taken as a mechanical flux-weakening method by aligning permanent magnets with armature teeth. Finally, three-dimensional FEM analysis is performed to validate the two-dimensional FEM predicted results. [ABSTRACT FROM AUTHOR]

The paper presents a novel technique for modeling ladder-secondary single-sided linear induction machines. Saturation effect is considered by core non-linearity characteristic for both primary and secondary. The proposed modeling method is based on magnetic equivalent circuit with adjustable accuracy. The machine parameters such as its dimensions, pole numbers, bar numbers, and also model accuracy can be chosen arbitrary in the proposed model. The end effect is considered by virtual teeth at the entry and exit ends of the machine primary. The results of the proposed method are compared with finite element method (FEM) in terms of accuracy and processing time. The results show the effectiveness of the proposed method. In addition, due to having long processing time of the FEM, the proposed method is a very suitable manner for modeling of this particular machine. Also, the accuracy of the proposed method has been confirmed by experimental results, in starting. [ABSTRACT FROM AUTHOR]

This paper discusses the development of a new topology of cylindrical transverse flux linear machine for use with a free piston engine. Despite its three-dimensional flux path, the stator of this topology can be made from regular laminated components and only the translator includes soft magnetic composites. The design development is discussed, including alternative winding and fabrication techniques. Finite element analysis, results of a laboratory prototype, and numerical-reluctance analysis are all used to give insight into the machine characteristics. By using flux and flux linkage factors, the tradeoff between force requirement and power factor is explored. It is shown that the power factor of this topology will generally vary from 0.89 to 0.6, which compares well with other transverse flux machines. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this paper, the end forces caused by the longitude end effects in linear permanent magnet synchronous machines (LPMSMs) are analyzed and minimized. First, the left/right-end forces are calculated based on an analytical model and the Maxwell stress tensor, in which the optimal integration surfaces are investigated. Then, based on the spectrum analysis of the left/right-end forces, two different methods are adopted to minimize the fundamental and high-order harmonics, respectively. The optimal length of the primary iron is obtained from the phase difference of the fundamental and a two-step iteration instead of the trial-and-error with the finite element method. Furthermore, step-skewed auxiliary irons are added to the primary end to eliminate the high-order harmonics. Third, to reduce the secondary end effect when the primary moves to the secondary end, a compensation method of adding mirror permanent magnet is proposed and good results are obtained. Finally, an LPMSM prototype is manufactured and experiments are conducted. The experimental results verify the theoretical study. [ABSTRACT FROM PUBLISHER]

As compared to other renewable energy technologies, the ocean waves are huge, largely untapped energy resource, and the potential in extracting energy is considerable. There is a lack of convergence on the best method of extracting energy from the waves, despite previous innovations, which has generally focused on the concept and design of the wave energy converter (WEC) technology, making the strategies for enhancing the efficiency of WECs important. This paper presents the performance analysis and design optimization of a single-slotted permanent-magnet linear generator. The magnetic field distribution in a cylindrical coordinate has been established. The magnetic field provides a prediction for the thrust force, flux-linkage and back-electromotive force (B-EMF), and also facilitates the characterization of the proposed machine as well as provides a basis for design optimization and dynamic modeling of the system. Finite Element Analysis (FEA) has been used for the design optimization of the proposed generator. The proposed generator has been optimized with respect to the leading design parameters Rm/Re and Tmr/TP. Thus, from the results, it can be observed that the generator has a very good efficiency to serve as WEC. [ABSTRACT FROM AUTHOR]

This paper presents a parallel-hybrid-excited linear vernier machine (PHE-LVM) for direct-drive oceanic wave power generation. By equipping a set of field winding in the mover yoke, hybrid excitation for the proposed PHE-LVM is realized: the air-gap flux can be flexibly controlled via adjusting the magnitude and polarity of the DC current in the field winding. With this merit, the operating performances in the wave power generation, such as the output voltage, load capacity and power factor can be improved. Firstly, the proposed PHE-LVM topology based on homopolar machine configuration is presented, with the consequent-pole PM poles mounted on the surface of the stator, while the DC field winding is wound around the mover yoke. Secondly, the operating principle of the proposed PHE-LVM is described with corresponding theoretical analysis. Thirdly, by using the 3-D finite element method, the power generation performances of the proposed PHE-LVM are evaluated. Finally, a prototype machine is also implemented and tested. Experimental results well agree with the analytical data. [ABSTRACT FROM AUTHOR]

This paper discusses the tracking coordination of a linear switched reluctance machine (LSRM) network based on a global feedback control strategy with a full-state observation framework. The observer is allocated on the follower instead of the leader to form a leader--follower--observer network, by utilizing the leader as the global feedback tracking controller and the observer as the observation of the full states. The internal model compensator (IMC) is applied to the leader for the improvement of the network performance. The full-state information of the LSRM network is reconfigured by the output of the LSRM where the observer is located to provide necessary feedback information to the leader. Then, the controllability and observability of the leader--follower--observer network with the IMC are inspected, serving as a basis for the design of the global controller with the IMC and full-state observer. Experimentation verifies the effectiveness of the proposed network control scheme and the results demonstrate that both the absolute and the relative accuracy can be simultaneously improved, compared to the LSRM network with only the consensus algorithm and no global feedback mechanism. [ABSTRACT FROM AUTHOR]

Four modular permanent magnet linear machines (PMLMs) with E-core and C-core primary segments and 12-slot/13-pole (12s/13p) and 12-slot/14-pole (12s/14p) slot/pole combinations are compared in this paper. The influences of flux gap width on the electromagnetic performances and power losses have been investigated based on 2-D finite-element modeling. It has been found that, by choosing proper flux gap width, not only the average thrust force can be improved but also the force ripple and iron losses can be reduced for all the machines. Also, the E-core modular PMLM has higher thrust force and lower detent force compared with the C-core modular PMLM with respect to the same slot/pole combination. Moreover, the 12s/13p modular PMLMs can achieve better electromagnetic performances than the 12s/14p ones regardless of E-core or C-core primary structures. Finally, by shaping the end teeth, the detent force and force ripple of the four modular PMLMs are further mitigated. The 12s/13p E-core modular PMLM is proven to be the best type among these four modular machines. [ABSTRACT FROM AUTHOR]

In this paper, an approach combining current pulses injection and fuzzy logic observer to measure the air gap length of linear machines is proposed. A polymer enclosed by a coil is produced and selected as the test object. The characteristics and production process for the polymer is introduced and its magnetic feature has been studied. Injecting current pulses is used to calculate the self-inductance of the coil fixed on the cores that is directly influenced by the air gap length from the polymer. By using a fuzzy logic observer, the air gap length can be estimated precisely according to the variations of the self-inductance. Experimental results show the effectiveness of the proposed measurement method and the results prove that the proposed method is suitable for the air gap measurement for linear machines. [ABSTRACT FROM AUTHOR]

This paper proposes a novel dc-excited flux-modulated linear machine with a new primary structure for utilizing amorphous core. Although amorphous core is regarded as a good candidate in highly efficient electric machines, and is being investigated for decades, it has not been widely used in electric machines yet. The key challenge is the difficulty in slotting. For the new structure, the difficulty in slotting is avoided. Furthermore, the proposed machine is economical and has a robust double salient structure without any permanent magnets, and both single-toothed field and armature windings are located together in the primary core. By regulating the field excitation, the machine can operate at a wide speed range. Due to the low loss of amorphous core, this machine shows high efficiency at high speed. [ABSTRACT FROM AUTHOR]

In this paper, a high-temperature superconductor dual-stator spoke-type linear vernier machine (HTS-DSSLVM) is proposed for wave energy extraction, which offers high-thrust force density and better power factor due to leakage flux reduction. HTS bulks are introduced in between the split flux modulation teeth to shield the leakage flux and hence improve the force density and power factor. The electromagnetic characteristics of the machine are comprehensively investigated and compared with that of a recently presented dual-stator spoke-type linear vernier machine (DSSLVM). The results show that the proposed machine yields higher thrust force and better power factor than the DSSLVM due to reduced leakage flux in the proposed machine. [ABSTRACT FROM AUTHOR]

In order to fully utilize the high-energy nature of permanent magnet (PM) material, the stator-PM structure and the mover-PM structure of linear machines are integrated into one doubly salient PM machine topology, leading to a new class of doubly salient dual-PM linear machines. In essence, PMs are mounted on both the stator and mover iron cores while avoiding magnetic saturation, hence offering the high force density and high power density. Meanwhile, it consists of a fault-tolerant tooth stator and a consequent-pole mover, which can provide the fault-tolerant capability and exert the salient effect, respectively. By using finite-element analysis, the proposed machine is optimized for application to regenerative shock absorbers which can provide on-board renewable energy harvesting in vehicles. The machine performances are analyzed and quantitatively compared with that of its counterparts including the stator-PM linear machine and the mover-PM linear machine. Moreover, both the flat and tubular morphologies of the proposed machine are quantitatively compared and discussed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The finite element method (FEM) is widely used for accurate design and analysis of electric machines; however, it suffers from long execution time. In this paper, for the first time hardware acceleration of two-dimensional FEM for a single-sided linear induction motor on the field programmable gate array (FPGA) is proposed. The nonlinearity of the iron core as well as the movement are taken into consideration. A new sparse solver is proposed based on left-looking Gilbert–Peierls algorithm for the system of linear equations of FEM that need to be solved in different iterations and time steps. Implementation of the model is performed in a massively paralleled and deeply pipelined hardware architecture using VHDL coding with single precision floating-point number representation. The proposed emulation was performed at various time steps resulting in significant average speedup of 9.73 times in comparison with JMAG-Designer as a commercial finite element software, and the overall hardware latency of each time step for the emulation was 49.2 ms in average with minimum achievable FPGA clock of 5.59 ns. [ABSTRACT FROM PUBLISHER]

Linear flux-switching permanent magnetic (LFSPM) machines are good choices for long stroke applications. These machines deliver high thrust force density in addition to the machine structure where permanent magnetics (PMs) and windings are all on the short mover. For LFSPM machines, their performance is always affected by big thrust force ripple. In this paper, for two C-core LFSPM machines of high thrust force capability, including a 6/13 C-core LFSPM (6/13LFSPM-C) machine and a sandwiched C-core LFSPM (SLFSPM-C) machine, and a thrust force ripple reduction method is proposed. The proposed method is developed by reducing the slot effect component of the cogging force based on staggered stator tooth, and suppressing the thrust force ripple caused by unbalanced three phase back-electromagnetic forces (EMFs) based on two end PMs. Based on finite element analysis (FEA) results, both C-core LFSPM machines can achieve small thrust force ripples as well as high sinusoidal back-EMFs, and at the same time, maintain high thrust force capability with the proposed method. It was also found that, the improved SLFSPM-C machine exhibited the same thrust force capability as the improved 6/13LFSPM-C machine, but with a much smaller thrust force ripple. [ABSTRACT FROM AUTHOR]

Arrangement of permanent magnet (PM) poles and windings influences the magnetic field and force output of linear machines significantly. Various designs of PM linear machines have been proposed by researchers, either putting PM poles inside and coils outside, or vice versa. However, there is no systematic comparison of these two types of designs in literatures. The purpose of this study is to compare the magnetic field and force output of linear machines with different PM and winding structure topologies. Halbach array can not only produce high flux density, but also has self-shielding effect. So it is employed for the analysis. Tubular structure is used because it helps to reduce flux leakage and enhance the system output performance. The magnetic field distribution of tubular linear motors with internal and external PM poles are formulated with Bessel functions, and the force output is thus obtained from Lorenz force law. The analytical models of magnetic field and force output are then validated with numerical computations. By utilizing the verified analytical models, design optimization is conducted with penalty functions for the two machine structures. The magnetic field and force output performance are then compared. It shows that the machine structure with internal PM poles helps to generate high force output. The study in this paper can also be implemented for the design of rotary machines. [ABSTRACT FROM AUTHOR]

The E-core hybrid-excitation linear switched-flux permanent magnet machine (LSFPMM) is low cost, which not only accommodates armature and permanent magnets (PMs) in short primary, but also cuts half of PM volumes compared with its C-core counterpart. It also can easily adjust the air gap magnetic field flexibly through the injection of different DC currents. This paper introduces E-HELSFM with different end shapes firstly, while a shape with the best symmetry of flux and minimal detent force is developed and further investigated. Based on finite element model, the flux-adjusting principle of the proposed hybrid-excitation motor is presented, and certain geometric parameters are optimized for better flux-regulating capability and larger thrust force density. Then, the field ratio, which means the ratio of field area to a single slot area, is optimized to reach a tradeoff between force density and flux-adjusting capability. For the optimized model, the flux-adjusting as well as thrust force performances under different excitation conditions are investigated. Then, the flux-weakening control under different excitation levels is discussed. The simulated results show that the optimized machine exhibits good constant power operation capability through flux-weakening control and enhanced overload ability by flux-enhancing control. [ABSTRACT FROM AUTHOR]

Linear induction machines (LIMs) are widely used in the electromagnetic launch systems. Based on the MgB2 type superconducting wires, a superconductive LIM with an electrodynamic type structure (EDS) is proposed in this paper. The moving primary magnetic field induces eddy current in the conductor plate and the inductive eddy magnetic field acts back on the primary field. The lift force and thrust force will be produced between the primary and the secondary. Referred to the analysis of some famous researchers’ theory and achievements, an improved method is proposed and applied to MgB2 type superconducting LIM. The calculation results are obtained and compared with finite-element analysis. The results indicate the method is practical and valid, which can lead the design and save design time. [ABSTRACT FROM PUBLISHER]

This paper investigated the rule table optimization of fuzzy power system stabilizer (FPSS) benefiting from rule basis of related previous studies. In the previous studies, fuzzy rules for Power System Stabilizer (PSS) were obtained by trial and error according to the experience of experts. There were a few rule tables occurred in that way in the literature. In this subject field, five rule tables with a few differences among them were taken. Genetic algorithm (GA) was employed as an optimization method, and single machine infinite bus (SMIB) model was used for simulation system. This work proposed to contribute optimization performance of FPSS adding these rule tables to the initial population of GA. Thus GAs reached an optimum solution more quickly. Simulation studies and the integral of absolute error (IAE) performance results for four loading conditions were shown. The effectiveness of the proposed approach was discussed by comparing it with the five rule tables. [ABSTRACT FROM AUTHOR]

This paper presents an experimental characterization and comparison of the performances achieved by a Tubular Linear Induction Motor (TLIM) prototype with different typologies of primary winding connections. More in detail, three different configurations have been considered, analyzed and discussed: full-pitch star, 5/6 shortened pitch star and 5/6 shortened pitch double star. For this purpose, an experimental test bench at the Sustainable Development and Energy Saving Laboratory (SDESLab), University of Palermo, Italy, has been set-up. The obtained results have allowed the identification of the best winding configuration for different applications intended for the motor. Moreover, in comparison with classic approaches that involve mathematical equations for winding design, the proposed experimental work is suitable for TLIM winding designs: indeed, more accurate results are obtained and approximation coefficients avoided. [ABSTRACT FROM AUTHOR]

A single-phase tubular permanent-magnet linear machine (PMLM) with hybrid Halbach/axially-magnetizedPMarrays is proposed for free-piston Stirling power generation system. Machine topology and operating principle are elaborately illustrated. With the sinusoidal speed characteristic of the free-piston Stirling engine considered, the proposed machine is designed and calculated by finite-element analysis (FEA). The main structural parameters, such as outer radius of the mover, radial length of both the axially-magnetized PMs and ferromagnetic poles, axial length of both the middle and end radially-magnetized PMs, etc., are optimized to improve both the force capability and power density. Compared with the conventional PMLMs, the proposed machine features high mass and volume power density, and has the advantages of simple control and low converter cost. The proposed machine topology is applicable to tubular PMLMs with any phases. [ABSTRACT FROM AUTHOR]

An introduction to articles in the issue is presented on topics including the design of a novel transverse-flux tubular linear machine, electromagnetic analysis of a double-side permanent-magnet linear synchronous motor adopting the structure of staggering two primaries, and a reliability of a double-sided linear switched reluctance generator system.

The fourteen papers in this special section focus on the design and control of linear machines (LEMs). The subjects of these papers embrace the main subjects of interest of the scientific community related to LEMs, ranging from innovative procedures for the optimal design of such machines, to their analysis with finite elements, to advanced control techniques, suitably devised for specific applications. [ABSTRACT FROM AUTHOR]

Two linear induction accelerators (LIAs) have been in operation for a number of years at the Los Alamos Dual Axis Radiographic Hydrodynamic Test (DARHT) facility. A new multipulse LIA is being developed. We have computationally investigated the beam breakup (BBU) instability in this advanced LIA. In particular, we have explored the consequences of the choice of beam injector energy and the grouping of LIA cells. We find that within the limited range of options presently under consideration for the LIA architecture, there is little adverse effect on the BBU growth. The computational tool that we used for this investigation was the beam dynamics code linear accelerator model for DARHT (LAMDA). To confirm that LAMDA was appropriate for this task, we first validated it through comparisons with the experimental BBU data acquired on the DARHT accelerators. [ABSTRACT FROM PUBLISHER]

Permanent-magnet (PM) magnetization state estimation is important both for torque control and monitoring in conventional permanent-magnet synchronous machines (PMSMs). Furthermore, this can be critical for variable flux machines (VFMs). Use of high-frequency signal injection methods for PM magnetization state estimation in NdFeB magnets has already been proposed. These methods make use of the variation of the PM high-frequency resistance with the PM magnetization state due to the magnetoresistive effect. This paper addresses the generalization of magnetization state estimation using high-frequency signal injection to other types of magnets like SmCo and ferrite, as well as to other magnet structures, e.g., isolated and nonisolated segmented magnets. Use of the magnetoresitive effect for the detection of irreversible/reversible PM demagnetization will also be shown to be viable. [ABSTRACT FROM PUBLISHER]

This paper describes the development of a real time error measuring device for the simultaneous measurement of movement errors in straightness, yaw and roll in a linear machine stage. It was designed specifically for measuring errors in the spatial positioning of meso-scale machine tool stages. The arrangement of the optical path and design of the optical elements make it easy install the device on a linear stage. Roll, yaw and horizontal straightness error motions are sensed using the reflection of a laser beam from a plane mirror. A nonlinear measurement model was derived and simulation analysis showed this could be linearized when the measurement angle error was smaller than 0.05°. The measurement ranges of the proposed system are ±30″ for θ x , ±20″ for θ y and ±30 μm for the z-axis. The measurement precision was verified using a laser interferometer and an electronic level and the accuracy of the angular error and straightness error measurements were found to be in the range of ±0.25″ and ±0.5 μm respectively. The extended measurement uncertainties (95% confidence level) were: 0.46″ for θ x error motion; 0.46″ for θ y error motion; and 0.616 μm for straightness. [ABSTRACT FROM AUTHOR]

The purpose of this work was to study laser-assisted machining (LAM) according to the tool path inclination angle of a titanium alloy workpiece. Previous studies have investigated using LAM for the linear machining of difficult-to-cut materials. However, during the linear machining of an inclined planar workpiece, the laser spot is deformed into an elliptical shape, and then, the tool follows the long major axis of the elliptical laser spot. For tool path inclination angle machining, the tool follows the arbitrarily oriented direction of the elliptical laser spot. Thus, determining the preheating temperature of the workpiece by tool path inclination angle processing is different from that of linear processing. In this work, a study was carried out to optimize the preheating and machining based on the tool path inclination angle. The optimal laser power according to tool path inclination angle was determined through thermal analysis, and the thermal analysis results were compared with the results from preheating experiments. Also, machining experiments were conducted using the as-determined laser power. [ABSTRACT FROM AUTHOR]

Free-piston engines (FPEs) are known to have a greater thermal efficiency (40–50%) than an equivalent and more conventional four-stroke reciprocating engines (30–40%). Modern FPEs are proposed for the generation of electric and hydraulic power, with a potential application in hybrid electric vehicles. The numerous FPE configurations considered to date have almost exclusively operated using a two-stroke thermodynamic cycle to improve the thermal efficiency, however it is well known that the application of two-stoke cycles can be limited by noise and exhaust gas emissions constraints. In this article, a numerical model is used to investigate the techno-feasibility of operating Newcastle University’s FPE prototype using a two- or four-stroke thermodynamic cycle. If operated as a four-stroke cycle, the linear generator must be used as both a motor and a generator resulting in a more irregular piston motion compared to corresponding operating in a two-stroke cycle. In four-stroke cycles, almost half the indicated power is consumed in overcoming the pumping losses of the motoring process. Whilst the heat release process is appears to be closer to a constant volume process when operated on two-stroke engine cycle, the peak cylinder pressure and compression ratio proved lower. In addition, a narrower power range is reported for a four-stroke cycle despite a corresponding higher thermal efficiency. [ABSTRACT FROM AUTHOR]

The aim of this paper is to propose an efficient and unique reluctance network (RN) model for all translator displacements of a linear hybrid motor. This model has to consider several translator positions to analyze the linear motor performances. The proposed RN model takes into account the magnetic characteristic and the flux leakage. Consequently, the proposed model gives precise results of the electromagnetic characteristic. The RN model considers an interesting solution to deal quickly with an optimization task of a large number of constraints and parameters. The developed model is coupled with sequential quadrating programming method for an optimization process of the linear machine. The obtained results confirm the efficiency of this method for modeling and optimization of the linear machine. [ABSTRACT FROM AUTHOR]

In this paper, a vernier motor with a spoke permanent-magnet (PM) structure instead of a surface PM is proposed in order to obtain higher power factor (PF) and flux density. However, upon investigating this structure with a single gap, unique effects that virtually eliminate the vernier effect are analytically identified. To avoid these effects and improve the PF, a spoke PM vernier motor with a double gap is then proposed. Analytic equations for back electromotive force and the PF are then derived for this motor in terms of various geometric factors such as the numbers of magnets and winding poles, the magnet thickness, etc. For a case study, the practical achievable maximum power and PF are calculated and verified with accurate simulations. [ABSTRACT FROM AUTHOR]

A new flux reversal permanent magnet (FRPM) linear machine known as the partitioned stator FRPM (PS-FRPM) linear machine is proposed. The structure and the operation principle of the machine are described, and the major design parameters are optimized for maximum thrust force. A periodic model is also used in the analysis in order to highlight the significant effect of the longitudinal end effect on the machine performance, particularly in terms of unbalanced magnetic circuit and cogging force. Furthermore, the proposed machine is compared with the conventional FRPM linear machine. It is concluded that higher thrust force, less cogging force, and consequently less thrust force ripple can be obtained by the proposed machine. [ABSTRACT FROM PUBLISHER]

Permanent magnet (PM) tubular machines have been applied to many applications, since they offer high force density with no end winding and no net attractive force between the mover and the stator. In this paper, two novel PM tubular machines named partitioned stator interior PM (PS-IPM) and partitioned stator surface-mounted PM (PS-SPM) tubular machines are proposed. Both the proposed machines are optimized for maximum thrust force, and their electromagnetic performance has been compared. It is found that the PS-IPM tubular machine has higher thrust force capability and better magnet utilization compared with the PS-SPM tubular machine. However, due to lower cogging force, the PS-SPM tubular machine has fewer thrust force ripples. Furthermore, the effect of the cross-coupling magnetic saturation on PM flux linkage, and the $d$ -axis and $q$ -axis inductances for both the proposed machines is investigated. It is demonstrated that the PM flux linkage and the $d$ -axis and $q$ -axis inductances are affected by the cross-coupling magnetic saturation. Moreover, the force–velocity characteristics of the proposed machines are calculated and compared. It is observed that both the machines have good constant power operation capability. [ABSTRACT FROM PUBLISHER]

In this study we apply the Support Vector Machine (SVM) combined together with Distance Correlation (DC) to the forecasting of Dst index by using 80 intense geomagnetic storms ( Dst ≤ − 100 nT ) from 1995 to 2014. We also train the Neural Network (NN) and the Linear Machine (LM) to verify the effectiveness of SVM. The purpose for us to introduce DC is to make feature screening in input datasets that can effectively improve the forecasting performance of the SVM. For comparison, we estimate the correlation coefficients (CC), the RMS errors, the absolute value of difference in minimum Dst ( Δ Dst min ) and the absolute value of difference in minimum time ( Δ t Dst ) between observed Dst and predicted one. K -fold Cross Validation is used to improve the reliability of the results. It is shown that DC-SVM model exhibits the best forecasting performance for all parameters when all 80 events are considered. The CC, the RMS error, the Δ Dst min , and the Δ t Dst of DC-SVM are 0.95, 16.8 nT, 9.7 nT and 1.7 h, respectively. For further comparison, we divide the 80 storm events into two groups depending on minimum value of Dst . It is also found that the DC-SVM is better than other models in the two groups. [ABSTRACT FROM AUTHOR]