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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]

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]

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]

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]

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]

Analysis of armature reaction field and inductance is extremely important for design and control implementation of electromagnetic machines. So far, most studies have focused on magnetic field generated by permanent-magnet (PM) poles, whereas less work has been done on armature reaction field. This paper proposes a novel analytical modeling method to predict the armature reaction field of a coreless PM tubular linear machine with dual Halbach array. Unlike conventional modeling approach, the proposed method formulates the armature reaction field for electromagnetic machines with finite length, so that the analytical modeling precision can be improved. In addition, winding inductance is also analytically formulated to facilitate dynamic motion control based on the reaction field solutions. Numerical result is subsequently obtained with finite-element method and employed to validate the derived analytical models. A research prototype with dual Halbach array and single phase input is developed. Experiments are conducted on the reaction field and inductance to further verify the obtained mathematical models. [ABSTRACT FROM PUBLISHER]

The air gap of tubular linear motors moves linearly, causing heat transfer states of the motor to alternate repeatedly. Thus, the heat transfer coefficients of the mover inner surface and the stator outer surface vary constantly. In this paper, the combination model of the thermal circuit and temperature field is established to calculate the transient temperature rise of a tubular linear motor with short and movable primary. The equivalent thermal circuit model of the moving air gap and the temperature field models of the primary (also named as mover) and secondary (also named as stator) are established. The thermal boundary conditions and the correlations among them are analyzed. By this method, the complicated variation and distribution of the heat transfer coefficients are gained. Moreover, the transient temperature rise of the motor is calculated. This method takes advantage of the flexibility of the thermal circuit method and the accuracy of the temperature field method. The calculated and tested results of the prototype are compared and analyzed. [ABSTRACT FROM PUBLISHER]