Thrust Force Capability Research Articles

Optimal gear ratio selection of linear primary permanent magnet vernier machines for wave energy applications

AbstractLinear permanent magnet vernier generators offer a high capability of force density, making them appealing configurations for wave energy harvesting systems. In absolute terms, the performance of these machines is significantly influenced by the selection of slot/pole combinations based on the magnetic gearing effect. For the first time, this paper aims to investigate the impact of different gear ratios on a wide array of linear primary permanent magnet vernier machines (LPPMVMs) with different slot/pole combinations based on fair criteria to offer a more comprehensive understanding of gear ratio selection. To find the optimal number of slots and poles, the response surface methodology is adopted to obtain a robust design and make a fair comparison among LPPMVMs with optimum design characteristics using a cost‐effective approach for the fast and reliable optimisation process. The higher gear ratios result in higher thrust force capability. This will help establishing a new route toward faster develpment of advanced LPPMVMs. The power loss models of LPPMVMs are studied to predict their steady‐state and transient thermal behaviours, verifying their stability and safety, while a simple external forced convection method can be utilised. To verify the model, finite element analysis is exploited to confirm the electromagnetic and thermal analysis results and provide a more exhaustive investigation.

Unbalanced magnetic pull in angular eccentricity magnetic screw

AbstractThis paper investigates the unbalanced magnetic force (UMF) produced by angular eccentricity in a magnetic screw. The principle of eccentricity is briefly outlined and an analytical expression that can be used to predict UMF of a magnetic screw is established. A 3D magnetic screw model with helically magnetized permanent magnets (PM) has been built and simulated in ANSYS Maxwell with different angular eccentricities. Comparing the finite elements (FE) simulation and analytical calculation results, there is a certain difference in the UMF of the magnetic screw, which is also caused by the asymmetry of the magnetic screw structure. It has been shown that compared to the linear tubular PM motor with the same thrust force capability, the magnetic screw has a much small UMF, which greatly simplifies the mechanical design of the magnetic screw.

Optimization and Experimentation of Fault-Tolerant Field Excited Linear Flux Switching Machine With Concentrated and Toroidal Windings for Rail Transportation System

In this article two double-sided Field Excited Linear Flux Switching Machines (FELFSM) are analyzed. Both machines share the same robust and compact stator structure with a modular mover design having different winding configurations namely concentrated and toroidal. The proposed machines have a low-cost owing to the lack of rare earth materials, a high fault-tolerant capability due to the modular construction of the mover, and flux controllability due to field current variation. The initial designs are optimized through a genetic algorithm using JMAG software ver. 20.1. to maximize the thrust force and minimize thrust force ripples ratio. After optimization, the average thrust force in Machine I and Machine II is increased by 31.96% and 32.31%, respectively. Additionally, a mathematical model is developed to compute electromagnetic thrust force and fault-tolerant capability. The electromagnetic performance of both machines are compared through 2D FEA. Both analytical and FEA-based designs are verified through experimental validation on the developed prototype. Finally, a coupled electromagnetic-thermal study is carried out, with the temperature of the prototype being visualized experimentally using a Fluke VT04 IR thermometer.

Experimental Validations of Hybrid Excited Linear Flux Switching Machine

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

Analysis and Evaluation of Hybrid-Excited Doubly Salient Permanent Magnet Linear Machine With DC-Biased Armature Current

This article investigates a hybrid-excited doubly salient permanent magnet linear machine (HDSPMLM) with dc-biased armature current. With the adoption of integrated open winding, dc bias can be achieved by zero-sequence current, which helps to enhance the dc excitation and further highly improves the thrust force density. First, the machine topology and drive circuit are described. By injecting the dc currents into the armature windings with special arrangement, the dc field windings in conventional HDSPMLM can be eliminated, where the phase currents are dc-biased sinusoidal currents. Then, magnetomotive force-permeance model is built to analytically calculate the air gap hybrid-excited field harmonics, and further verified by finite element analysis. Moreover, the flux linkage, back-electromotive force, and static force-current characteristics between the proposed and conventional HDSPMLMs are comparatively studied. Thanks to the improved exciting field and armature magneto-motive force with integrated open winding, the thrust force capability can be significantly enhanced by 85.5% on the premise of rated power dissipation. The proposed machine is suitable for the operation of short-time large-thrust condition. Finally, the experiments on a prototype of the HDSPMLM are carried out for validation.

Design and Analysis of Hybrid-Excited Flux Modulated Linear Machines With Zero-Sequence Current Excitation

This article investigates a hybrid-excited flux modulated linear machine (HEFMLM) with zero-sequence current excitation. With the adoption of integrated open winding, zero-sequence current can be utilized to provide the dc excitation and further improve the thrust force density. First, the machine topology, drive circuit, and operation principle are described. Then, the magnetomotive force (MMF)-permeance model is built to analytically calculate the air-gap hybrid-excited field harmonics and further verified by finite element (FE) analysis. Moreover, the electromagnetic performances including open circuit characteristics, flux regulation capability, thrust force characteristics, and demagnetization risk are comparatively studied. Due to the improved exciting field and armature MMFs with integrated winding, the thrust force capability can be significantly enhanced by 22.6% on the premise of rated copper loss. Besides, the proposed HEFMLM exhibits high thrust force density compared with the other three types of HEFMLM, benefitting from a high pole-pair number of permanent magnets (PMs) along with a more obvious magnetic gearing effect. Finally, a prototype of the HEFMLM is carried out for experimental validation.

Robust Design and Analysis of Asymmetric-Excited Flux Reversal PM Linear Machine for Long-Stroke Direct Drive Propulsion

This article proposes a novel asymmetric-excited flux reversal permanent magnet linear machine (AE-FRPMLM). Different from the conventional FRPMLM with uniform “NS-NS” permanent magnet (PM) sequence, the proposed AE-FRPMLM adopts an asymmetric “NSN-S” PM sequence, which can greatly reduce half of the flux leakage and generate more effective harmonics for thrust force production. Utilizing multiobjective genetic algorithm coupled with 2-D finite-element analysis (FEA), the proposed machine is globally optimized to obtain the optimal deterministic values. Furthermore, the sensitivity and robust analysis is employed to check its robustness. The electromagnetic performances are investigated and compared with conventional FRPMLM, which shows that the thrust force capability can be significantly improved more than 20% at full range of electrical loadings. The proposed AE-FRPMLM is suitable for low-cost and long-stroke direct drive propulsion.

Comparative Study of Partitioned Stator Permanent Magnet Tubular Machines with Different Winding Configurations

In this study, partitioned stator permanent magnet (PS-PM) tubular machines having single- and double-layer windings layouts have been investigated. Two configurations of PS-PM tubular machines were considered, i.e. partitioned stator surface mounted permanent magnet (PS-SPM) and interior permanent magnet (PS-IPM) tubular machines. A comprehensive comparison has been carried out in order to investigate the impact of the winding layouts on such machines. It should be mentioned that the FE package that is used in this paper is (ANSYS Maxwell). It has been noted that irrespective of machines configurations, i.e. either PS-SPM or PS-IPM tubular machines, similar thrust force capability, higher average thrust force per magnet volume, lower thrust force ripple as well as cogging force and higher fault tolerance capability can be delivered by PS-PM tubular machines with single-layer winding compared to that with double-layer winding.

Design Optimization and Performance Investigation of Linear Doubly Salient Slot Permanent Magnet Machines

Novel linear doubly salient slot permanent magnet machines (LDSSPMMs) are investigated in this paper. First, the machine topology and operation principle are introduced, and the choices of feasible slot/pole combinations and winding configurations for three armature phases are discussed. Then, the 12 slots and 10/11/13/14 poles LDSSPMMs with double-layer (DL)/single-layer windings are globally optimized using genetic algorithm. The electromagnetic performances including flux linkage, back electromotive force (back EMF), detent force, and static force-current characteristics are comparatively studied using two-dimensional (2-D) finite-element analysis (FEA). It shows that 12 slots/13 poles (12s/13p) and DL winding are the optimal choices to provide higher thrust force as well as lower force ripple. Moreover, the risk of local irreversible demagnetization of PMs is analyzed, which only occurs at very limited corners of the PMs and can be eliminated by PM shaping. Furthermore, the electromagnetic performances between linear variable flux reluctance machines (LVFRMs), linear hybrid-excited slot PM machines, linear primary yoke PM machines, and LDSSPMMs are comparatively studied. It shows that LDSSPMM can provide much higher thrust force than LVFRM at the same copper loss. With the increase of copper loss, LDSSPMM exhibits better thrust force capability than other machines. Finally, a prototype of 12s/13p DL-LDSSPMM is manufactured and tested to validate the 2-D FEA predicted results.

Multiobjective Optimization of a Double-Side Linear Vernier PM Motor Using Response Surface Method and Differential Evolution

This paper designs a double-side linear vernier permanent-magnet motor, which incorporates the merits of high thrust force capability, high power factor, and high efficiency. Since the parameters of the motor are very sensitive and the high thrust force capability comes along with the high force ripple, a framework of multiobjective optimization is proposed to improve the overall motor performances. The sensitivity analysis is used to select significant variables and the multiobjective differential evolution with ranking-based mutation operator is conducted with the response surface models to generate the Pareto solution set. The electromagnetic performances of the optimal motor are compared with the initial motor by simulating step by step based on finite-element analysis. Finally, a prototype motor is manufactured and the experimental results validate the improved motor performances.

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.

Analysis of double‐sided sandwiched linear flux‐switching permanent‐magnet machines with staggered stator teeth for urban rail transit

Linear flux-switching permanent-magnet (LFSPM) machines exhibit significant potential in many applications. A double-sided sandwiched LFSPM (DSSLFSPM) machine with high thrust force capability is investigated in this study. After being optimised for optimal thrust force using Maxwell 2D, this machine is found to deliver higher thrust force when compared with an optimised conventional 12/14 LFSPM machine. However, low thrust force ripple is also required in many applications. Thus, in order to reduce the thrust force ripple, the DSSLFSPM machine is improved by a staggered stator teeth structure and an end permanent-magnets method, then, two improved machines are obtained. The improved machines can reduce the thrust ripple to a very low level without thrust force density decrease. Further, the stator yoke thickness of the improved machines is optimised to reach optimal thrust force density. Finally, the performance of the DSSLFSPM-ST machines is analysed including the normal force, the efficiency and the power factor. It shows that the improved DSSLFSPM machines exhibit relatively low normal force and high thrust force density as well as low thrust ripples, indicating that they are suitable for long-stroke applications.

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.

Thrust Force Ripple Reduction of Two C-Core Linear Flux-Switching Permanent Magnet Machines of High Thrust Force Capability

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.

Design and Analysis of Low-Cost Tubular Fault-Tolerant Interior Permanent-Magnet Motor

Tubular motors are suitable for active vehicle suspension due to their zero net radial force and volumetrically efficient. This paper proposes a new low-cost tubular fault-tolerant (TFT) interior permanent-magnet (IPM) motor for the high reliability operation of the active vehicle suspension system. The key is that the proposed motor incorporates the concept of fault-tolerant teeth to provide the desired decoupling among phases and adopts the ferrite magnet material to reduce the usage of rare-earth PMs. Its electromagnetic performances are investigated, such as flux linkage, back electromotive force, mutual- and self-inductances, and detent and thrust forces. A finite-element method is employed to verify the theoretical analysis, showing that the proposed TFT PM motor not only has the merits of low-cost, strong mechanical integrity, but also offers good fault-tolerant ability and high thrust force capability.

Comparative Study of Novel Tubular Partitioned Stator Permanent Magnet Machines

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.

Calculate the air-gap magnetic field of tubular permanent magnet linear motor base on equivalent surface current model

The air-gap magnetic field is an important design parameter for tubular permanent magnet linear motor including surface-mounted PMs (TPMSLM), as it significantly influences the thrust force capability and efficiency. Based on the results indicate that the existing analytical research methods of the air-gap magnetic field is not accurate. This tool has calculated the air-gap magnetic field of the current-carrying coil. Next, the analytic formula of air-gap magnetic field of the motor is derived from the equivalent surface current model. In order to verify the validity and accuracy of the proposed method, we took approximately a TPMSLM to analyse it. The results show that: the analytical method and finite element method to calculate the air-gap magnetic field were both in good agreement. The proposed motor air-gap magnetic field method is quick, effective, and had a high accuracy rate.

Analytical Determination of Optimal Split Ratio of E-Core Permanent Magnet Linear Oscillating Actuators

The split ratio, i.e., the ratio of stator bore radius to stator outer radius, is an important design parameter for permanent-magnet (PM) linear machines, as it significantly influences the thrust force capability and efficiency. The optimal split ratio for maximum thrust force is investigated analytically for both surface-mounted PM (SPM) and interior PM (IPM) E-core linear oscillating actuators. It utilizes simple lumped magnetic circuit models and accounts for the magnetic saturation, the curvature effect, the fringing effect, and the armature reaction effect which may greatly affect the accuracy of the analytical model for the optimal split ratio. The optimal split ratio for both SPM and IPM prototype actuators is found to be around 0.55. The developed analytical models are validated by both finite-element analyses and measurements.

Design Considerations for Tubular Flux-Switching Permanent Magnet Machines

This paper describes a tubular, three-phase, flux-switching permanent magnet (PM) brushless machine that combines salient features from switched reluctance (SR) and conventional PM brushless machines. Feasible slot-pole number combinations, which are also applicable to rotary flux-switching machines, are derived. This paper also examines an alternative stator winding configuration, which is unique to the tubular machine topology. It is shown that this yields ~10%-15% higher thrust force capability as compared to a flux-switching machine equipped with a conventional winding.

Three-dimensional analysis of tubular permanent magnet machines

This paper presents results from a three-dimensional finite element analysis of a tubular permanent magnet machine, and quantifies the influence of the laminated modules from which the stator core is assembled on the flux linkage and thrust force capability as well as on the self- and mutual inductances. The three-dimensional finite element (FE) model accounts for the nonlinear, anisotropic magnetization characteristic of the laminated stator structure, and for the voids which exist between the laminated modules. Predicted results are compared with those deduced from an axisymmetric FE model. It is shown that the emf and thrust force deduced from the three-dimensional model are significantly lower than those which are predicted from an axisymmetric field analysis, primarily as a consequence of the teeth and yoke being more highly saturated due to the presence of the voids in the laminated stator core.