Thrust Force Ripple Research Articles

A Novel Negative-Sequence Current Injection Method for Reducing LVPMM Electromagnetic Thrust Ripple Considering Static Longitudinal End Effect

The thrust force ripple of a linear motor includes positioning force and electromagnetic thrust ripple. Compared to the conventional rotary motor, linear vernier permanent magnet machines (LVPMM) break at both ends, leading to three-phase asymmetry. This article focuses on the elimination of the electromagnetic thrust ripple caused by the special structure of the LVPMM, and an asymmetrical current control strategy using in power grids is introduced to the drive system. However, unlike power grids working at a fixed frequency, the drive system of the LVPMM needs variable speed operations, and some improvements are made to the original method. High bandwidth of current loop is guaranteed, and the stability of the control system is achieved with the proposed method. Experimental results obtained are presented. It verifies that the asymmetrical current control strategy reduces electromagnetic thrust ripple by more than 67%.

Thrust force ripple reduction of H‐LVPMM based on dynamic harmonic current compensation

Through the structural optimisation, the Halbach array-linear vernier permanent magnet machine (H-LVPMM) offers a higher force with extremely low ripple. However, thrust force ripple is minimised rather than eliminated and it reduces the precision of the control system. The thrust force ripple includes cogging force, end force and electromagnetic thrust ripple. Since the structural optimisation makes three phases balanced, the electromagnetic thrust ripple can be ignored. Here, a disturbance observer is proposed to observe and compensate the thrust force ripple by injecting the correspondent harmonic current into the closed-loop controller in a feedforward method. It leads to second, fourth and sixth harmonic components in the q-axis current. The closed-loop current control with vector proportional and integral (VPI) regulator is applied to guarantee the current tracking accuracy of the harmonic components. Parameters are optimised according to the thrust force ripple harmonics and the open-loop Bode diagram. The impact of thrust ripple is eliminated by the proposed control method. Experimental results show the validity of the disturbance observer and the VPI current controller.

Analysis and Reduction of Detent Effect in Magnetic Lead Screws With Parallel Magnetized Permanent Magnet Segments

This paper deals with the analysis and suppression of detent effect in the magnetic lead screw (MLS), which is equipped with parallel magnetized permanent magnet (PM) segments to approximate the helical PM for manufacturing simplicity. The detent effect is caused by the non-uniform magnetization along the helical PM, and behaves as both thrust force ripple and torque ripple during the transmission process. In this paper, a three-dimensional (3-D) analytical model of the MLS is established to analyze and predict the air-gap magnetic field, and the thrust force and torque are then derived, as well as their ripple components. It demonstrates that the harmonic order of the ripples is solely dependent on PM segments' quantities per helix turn on both the nut and screw. The analytical analysis is verified by extensive 3-D numerical computations. The impact of load angel and quantities of PM segments on the detent effect are investigated. It's shown that the torque ripple suffers more seriously than thrust force ripple, and both ripple percentages drop with the increase of load angle. And it is highlighted that larger least common multiple of PM segments' quantities on screw and nut is conducive to improving the average values of thrust force and torque, and reducing the detent effect.

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.

Development and Analysis of Novel Flux-Switching Transverse-Flux Permanent Magnet Linear Machine

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.

Model Predictive Thrust Force Control of a Linear Flux-Switching Permanent Magnet Machine With Voltage Vectors Selection and Synthesis

To reduce the thrust force ripple of a complementary and modular linear flux-switching permanent magnet machine, a model predictive thrust force control (MPTFC) is developed and implemented in this paper based on the active voltage vectors selection (AVVS) and two-voltage-vector synthesis (TVVS). First, the active voltage vectors are screened and assigned to the specific sector, instead of traversing all the possible vectors, and consequently, significantly decrease prediction workload. Second, for the elimination of the weighting factor in the conventional MPTFC, the control object is transformed from the thrust force and stator flux to the stator flux only by using the load angle. Third, to achieve the steady-state performance improvement, the TVVS approach is applied in each control period, where the optimal TVVS and its dwell time are simultaneously obtained by only one cost function. Both simulated and experimental results verify that the steady-state performance improvement can be realized by the developed MPTFC through comparing with normal hysteresis current control and conventional MPTFC strategies.

Influence of Armature Windings Pole Numbers on Performances of Linear Permanent-Magnet Vernier Machines

Linear permanent-magnet vernier (LPMV) machine has attracted more and more attention for several advantages including high power density and low cost. Both magnets and windings are located on the short mover, while the long stator is only consisting of iron, which is very suitable for long stroke applications. This paper investigates the influence of armature windings pole-pair numbers on the electromagnetic performances of LPMV machine by using an analytical method based on the finite element. The aim of this paper is to make a comprehensive comparative study of the machine with different armature windings pole-pair numbers while keeping slot number as a constant, select the topology of high performances and recommend suitable application areas. The performances of machines with the armature windings pole-pair numbers $P_{\mathrm {w}}= 1$ , 3, 6 are analyzed in detail. Finally, a new modular LPMV machine with $P_{\mathrm {w}} = 6$ , which possess higher thrust force, lower thrust force ripple, and high fault-tolerant capability, is prototyped and experiments are conducted for validation.

Performance comparison and optimisation of dual mover linear permanent magnet flux switching machine

Short moving primary and rigid low-cost secondary are important requirements of linear machines designed for long stroke applications. In the race, linear permanent magnet flux switching machine (LPMFSM) is a competitive candidate by confining excitation sources to short mover, thus making stator robust and low cost (made of only iron). However, single-sided LPMFSM exhibit a demerit of high normal (attraction) force due to its topology. In order to rectify the problem and enhance thrust force profile, two novel double-sided LPMFSMs are proposed with dual stator and dual mover topologies. After stator pole study, both topologies with same design dimensions are analysed and compared by 2-D finite element method here. Detailed analysis revealed that 12/14 DMLPMFSM exhibit low numerical values of thrust force ripples and detent force while maintaining average thrust force value. Hence, 12/14 DMLPMFSM is selected and optimised by structure-based deterministic optimisation (SBDO) approach to further enhance thrust force profile. Finally, comparison of initial and optimised design of 12/14 DMLPMFSM is presented to validate optimisation procedure.

Design and Optimization of Complementary Field Excited Linear Flux Switching Machine With Unequal Primary Tooth Width and Segmented Secondary

Linear flux switching machines (LFSMs) are one of the recently emerging and competitive candidates for long stroke applications due to high thrust force density, low cost and robust secondary, and high reliability. In the past decade, permanent magnet linear flux switching machines (PMLFSMs) with continuous secondary is researched by numerous researchers. However, cost of rare earth permanent magnet and iron material for continuous secondary in case of long stroke application makes PMLFSMs not an economical choice. In order to incorporate advantages of segmented secondary, such as: less use of stator iron, high power factor, and less critical saturation, a novel complementary dual mover field excited linear flux switching machine (FELFSMs) with segmented secondary and parallel magnetic structure is proposed and investigated in this paper. Furthermore, geometry-based deterministic optimization approach based on finite element analysis (FEA) is adopted to uplift overall thrust force profile, reduce secondary iron volume, and balance magnetic circuit of the machine. During optimization process, magnitude difference of flux flow between ac winding tooth and dc winding tooth is observed, that compel designers to go for unequal primary teeth design. Finally, optimal ac and dc current densities of geometrically optimized model and without any cooling arrangements are investigated for maximum average thrust force and minimum thrust force ripple ratio.

Investigation of Novel Multi-Tooth Linear Variable Flux Reluctance Machines

Novel multi-tooth linear variable flux reluctance machines (LVFRMs) are proposed in this paper. First, the topologies and feasible primary-/secondary-pole combinations of singleand multi-tooth LVFRMs with six primary poles are introduced. Based on the analytical analysis of permeance model, the maximum average force can be obtained when the dc field and ac armature copper losses are equal. Moreover, four small teeth per primary pole (n = 4) LVFRM exhibits the largest average force. Furthermore, the electromagnetic performances of singleand four-tooth LVFRMs with N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> = nN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> + 1 are comparatively studied using the 2-D finite-element analysis (FEA). It is shown that 6/25 primary-/secondary-pole four-tooth LVFRM can provide higher force capability and lower force ripple than that of 6/7 primary-/secondary-pole single-tooth LVFRM at relatively low copper loss. Similar to singletooth LVFRMs, four-tooth LVFRMs with N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> = nN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> ± 1 exhibit more sinusoidal back electromotive force, larger thrust force and lower force ripple than those with N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> = nN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> ± 2. Finally, the 3-D model of 6/25 primary-/secondary-pole four-tooth LVFRM is investigated to validate the 2-D FEA predicted results.

Enhancing Capabilities of Double Sided Linear Flux Switching Permanent Magnet Machines

Double sided linear flux switching permanent magnet machines (DSLFSPMMs) exhibit high thrust force density, high efficiency, low cost and robust double salient secondary (stator) structures. The aforementioned unique features make DSLFSPMM suitable for long stroke applications. However, distorted flux linkage waveforms and high detent forces can exaggerate thrust force ripples and reduce their applicability in many areas. In order to enhance thrust force performance, reduce thrust force ripple ratio and total harmonic distortion (THD) of no-load flux linkages, two structure-based advancements are introduced in this work, i.e., asynchronous mover slot and stator tooth displacement technique (AMSSTDT) and the addition of an active permanent magnet end slot (APMES). Furthermore, single variable geometric optimization (SVGO) is carried out by the finite element method (FEM).

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 &amp; 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.

Modeling and Static Analysis of Primary Consequent-Pole Tubular Transverse-Flux Flux-Reversal Linear Machine

A novel primary consequent-pole tubular transverse-flux flux-reversal linear machine (TTFFRLM) is proposed in this paper. The permanent magnets (PMs) of the machine are located on the inner surface of the short teeth of the primary iron cores for reducing the amount of PM in long stroke drive systems, and the primary is easily manufactured. The structure and principle of this machine are analyzed in detail. Based on the unit machine, a no-load equivalent magnetic circuit model is established by using the magnetic circuit method. Then, the equations of the no-load back electromotive force (back-EMF) and the electromagnetic thrust force are deduced. The simulation models of the unit machine are established by equivalent 2D finite element method (FEM) for saving computation time, and the static characteristics, including the flux field, the no-load back-EMF, and the electromagnetic thrust force, are analyzed. Detailed simulation and experimental results of a three-phase 4-poles 12-slots machine are given. The results verify the correctness and effectiveness of topology, model, and analysis method of the proposed TTFFRLM. Compared with the conventional TTFFRLM, the proposed prototype has the advantages of a lower cost and smaller electromagnetic thrust force ripple.

Design and Performance Investigation of Novel Linear Switched Flux PM Machines

A novel partitioned primary linear switched flux permanent magnet (PLSFPM) machine is presented, which adopts an odd number of primary poles. For the design objective of minimum thrust ripple, the optimized novel PLSFPM machine with 9 primary/10 secondary (9/10) pole combination is obtained. To this optimized PLSFPM machine, the electromagnetic performance is analyzed in detail and compared with that of the original one. The merits of this 9/10 pole combination are also proved by comparative study with other three available pole combinations. Moreover, comparison between the proposed PLSFPM machine and a conventional linear switched flux permanent magnet machine has been performed, which shows that the proposed machine can achieve better performances under both open-circuit and load conditions. The corresponding prototype is manufactured and the influences of possible machining errors during manufacture on thrust force performance are discussed. Finally, the experiment is carried out, which verifies the predicted results. The research shows that the proposed PLSFPM machine with 9/10 pole combination has high thrust force and low thrust ripple.

Comparative Study of Stator Configurations of a Permanent Magnet Linear Oscillating Actuator for Orbital Friction Vibration Actuator

A PM orbital friction vibration actuator (OFVA) which composes four linear oscillating actuators (LOA) is proposed in this paper. This paper presents the design, analysis, and experimental validation of stator configuration of a permanent magnet LOA to improve its thrust force characteristics. First, the magnetized topology and the coil configuration are interpreted. The optimization design goal of the LOA was established and the end effects of the actuator are illustrated. The influences of stator design parameters on the performance of LOA were investigated and the optimal parameters have been identified with reference to the thrust force density and thrust force ripple. Results showed that a quasi‐Halbach magnetized E‐cored LOA with obtrapezoid teeth has the best electromagnetic performances of all the LOAs examined here. Finally, the predicted thrust force characteristics were validated by measurements on a prototype actuator.

Optimum design of end edge in discontinuous armature permanent magnet linear motors for automation transportation systems

Discontinuous armature permanent magnet linear motors (DAPMLMs) have recently been proposed to address problems such as the increase of material costs and maintenance fees. However, because of their discontinuous arrangement, the end edge of the armature produces considerable detent forces, which act as a thrust force ripple during operations, resulting in diminished control performance and causing vibration and noise in the machine. Therefore, in this paper, we propose a novel structure of stair-shaped auxiliary teeth applied on the armature end edge of DAPMLMs with concentrated winding, to reduce the end edge detent force generated by the armature discontinuous arrangement. Taguchi’s design of experiment (DOE) method is used for the optimum design of the stair-shaped auxiliary teeth. The experiment deign models are drawn from the orthogonal array of design parameters. Moreover, we analyze the influence of the design parameters on the objective function via 2-D finite element analysis, and verify the validity of the proposed stair-shaped auxiliary teeth by applying the optimum design values obtained via signal-to-noise ratio (S/N ratio) analysis.

리니어 펄스모터의 고정자 상권선 적층에 따른 추력 리플 저감 기법 연구

The stator phase winding of a linear pulse motor, which is a new type of linear motor, is comprised of two phases and is structurally characterized by a stacking method in which the winding of one phase is laid on top of the winding of another phase. Such a structural characteristic induces a difference in the flux linkage resulting from the flux of each stator phase winding in the same condition. The difference in the induced flux linkage acts as a kind of thrust ripple component in terms of the generated thrust. Thus, in order to maintain consistent thrust force, a method is required to solve the problem caused by the structural singularity. Hence, in this study, we present a technique for reducing the thrust force ripple generated by the stacking of the stator phase windings of a linear pulse motor through the generation of a compensating current reference value of the current controller in order to keep the torque constant. The proposed compensating algorithm is validated by simulations and experimental results.

Effect of the number of blades and solidity on the performance of a vertical axis wind turbine

Two, three and four bladed ϕ-shape Vertical Axis Wind Turbines are simulated using a free-wake vortex model. Two versions of the three and four bladed turbines are considered, one having the same chord length as the two-bladed turbine and the other having the same solidity as the two-bladed turbine. Results of the two-bladed turbine are validated against published experimental data of power coefficient and instantaneous torque. The effect of solidity on the power coefficient is presented and the instantaneous torque, thrust and lateral force of the two-, three- and four-bladed turbines are compared for the same solidity. It is found that increasing the number of blades from two to three significantly reduces the torque, thrust and lateral force ripples. Adding a fourth blade further reduces the ripples except for the torque at low tip speed ratio. This work aims to help choosing the number of blades during the design phase of a vertical axis wind turbine.