Force Ripple Research Articles

Calculation of Electromagnetic Thrust for Long Primary Double Sided Linear Induction Motors with Secondary of Arbitrary Length

The expressions of the air gap flux density and secondary current density of long primary double-sided linear induction motor (LPDLIM) with arbitrary secondary length are derived by the numerical method, which with the secondary as the moving reference frame. The effects of the forward and backward components of end effects on the normal travelling wave and the secondary current density are analyzed respectively, and their temporal and spatial distributions are presented. And then the electromagnetic thrust and its ripple expression considering the longitudinal end effect of the air gap magnetic field and the components of the secondary current density are solved. The slip characteristics distribution of each electromagnetic thrust and thrust ripple components, and the contribution of end effect to resultant thrust and force ripple of the motor with arbitrary secondary length are investigated. Finally, the thrust characteristics of the LPDLIM with arbitrary length secondary are verified by the results of the FEM model. The calculation shows that the appropriate secondary length can reduce the thrust ripple of the LPDLIM.

Comparison of rare‐earth and hybrid‐magnet mover configurations for a permanent magnet synchronous linear motor

Force ripple and cost reduction are two of the main challenges in optimising the design and increasing the market uptake of permanent magnet synchronous linear motors (PMSLM). Two mover configurations are compared in depth; one made entirely from rare-earth materials while another consisting of a hybrid (rare-earth/ferrite) magnet layout. First, the rare-earth PMSLM is optimised and designed. Based on the same design and simulation methods, a hybrid PM materials with structure PMSLM is then proposed, optimised and designed using NdFeB at the centre pole-section and ferrite at the edges. The two configurations of the PMSLM and their relative merits/demerits are compared using the simulation results of the flux density distribution in the air gap, back electromotive force (EMF), and cogging force. The hybrid-magnet structure PMLSM has a better magnetic performance, and the force ripple is reduced by around 1%. Furthermore, the magnet material cost of the hybrid-magnet PMLSM is reduced by nearly 25% compared with the original PMLSM. Finally, a prototype of the rare-earth and hybrid-magnet PMSLM is manufactured and tested to validate the modelling techniques and the results.

Optimal Design of High-Speed Double-Sided Linear Permanent Magnet Motors With Segmented Trapezoidal Magnetic Poles

For the kilometer-level electromagnetic launch system, a high-speed double-sided linear permanent magnet (PM) linear motor is presented in this paper. To enhance the average thrust force, reduce the thrust ripple and normal force of linear motor, a segmented trapezoidal PM shaping method is proposed. Compared with conventional PM shaping method, the segmented trapezoidal PMs achieves less force ripple, greater average force and lower manufacturing difficulty. The risk of PM demagnetization fault has been taken into account. To reduce the losses in the mover of the linear motor, a non-metallic light-weight mover structure is proposed. The effectiveness of segmented trapezoidal PMs and non-metallic light-weight mover are verified by the finite element method and experiment.

A Rotary-Linear SPM Voice Coil Motor With PM Flux Bridges for Output Performance Improvement

This paper proposes a rotary-linear surface-mounted permanent magnet (PM) voice coil motor (RL-SVCM) with PM flux bridges in place of the iron flux bridges in a traditional RL-SVCM for enhancing average torque and force ripple but slight damage of torque ripple and average linear force. The iron flux bridges in a basic RL-SVCM cannot participate in the generation of rotary torque. In contrast, the PM flux bridges in the proposed RL-SVCM can participate in the generation of rotary torque. The magnetic equivalent circuit (MEC) is used to analyze the magnetic circuits of the basic and proposed models. The results explain the reasons for the performance improvements achieved by the proposed motor. The finite element method (FEM) is used to derive the precise output performance of the basic and proposed motors. Additionally, a prototype of the proposed RL-SVCM with PM flux bridges was manufactured for experimental verification. Close agreement between the experimental results and FEM results validates the feasibility of the proposed RL-SVCM.

Force and Velocity Ripple Reduction of the New Linear Motor

Force and Velocity Ripple Reduction of the New Linear Motor

Reduction of Thrust Force Ripple of High Temperature Superconducting Linear Flux-Switching Motors using Asymmetry Mover Structure

Compared with traditional linear motors, such as Linear Permanent Magnet Motors (LPMs) and Linear Induction Motors (LIMs), Linear Flux-Switching Permanent Magnet (LFSPM) motors have the merits of high efficiency, power density, with simple and robotic secondary structure. Despite these advantages, the flux-weakening ability of LFSPM motor is limited and thus the speed range of it is not ideal. As a promising choice, it is feasible to replace the PMs of LFSPM motors with coils made with High Temperature Superconducting (HTS) tapes. By using HTS material, High Temperature Superconducting Linear Flux-Switching Motors (HTS-LFSMs) have good flux-weakening ability while inheriting the edges of LFSM motors. Since the existence of HTS coils, the cooling system has a minimum size and has to take up certain room of the motor. When it comes to applications where the volume of motor is strictly restrained, there may not be enough room for a basic pattern of typical pole pitch combinations for HTS-LFSM, such as 12-7 or 12-9, leading to large thrust ripple. To solve this problem, a method of reducing thrust force using asymmetry mover structure is proposed based on a 9-5 pole pitch ratio. The mechanism and working principle are analyzed and the validation is verified with the help of Finite Element Method (FEM).

Analysis of Electromagnetic Force Ripple in a Bearingless Synchronous Reluctance Motor

A bearingless machine should be designed to maximize the average and to minimize the ripple in the electromagnetic torque and levitating force. In a bearingless synchronous reluctance machine (BSynRM), the complex rotor design and the levitation winding create a rich spatial and temporal spectrum of the magnetic flux density in the airgap, which affects both the torque and force ripple. In this article, a novel method is introduced to compute the electromagnetic forces from the spatial harmonics of the airgap flux density. A new indexing method is introduced to classify the spatial harmonic wavenumbers and temporal harmonic frequencies of the flux density in the electromagnetic force. The proposed model enables the understanding of the spatial harmonic footprint on the temporal frequencies of the electromagnetic force ripple. The study is carried out through finite element simulations, which are verified by prototype measurements.

Vibration Optimization of FSCW-IPM Motor Based on Iron-Core Modification for Electric Vehicles

In this paper, to optimize vibration of the fractional slot concentrated winding interior permanent magnet (FSCW-IPM) motor for electric vehicles (EVs) without sacrificing any torque performance, modifications of iron-core structures are proposed. First, the effects of basic stator/rotor auxiliary slots on torque, cogging torque, torque ripple, and 2nd order spatial harmonic of radial force are investigated by finite element analysis (FEA). The combinations of stator/rotor auxiliary slots, which can optimize vibration with maintained torque, are analyzed. To improve torque and optimize vibration, uneven airgap rotor is proposed. With variation of the uneven air-gap rotor, torque improvement and vibration reduction do not contradict each other. The vibration levels of FSCW-IPM motors are calculated by magnetic-mechanical coupling models, while the peak vibrations are optimized with the proposed methods. Inductance, torque, and vibration experiments of the FSCW-IPM motor with the uneven airgap rotor are performed. The theoretical and experimental results both validate effectiveness of the proposed methods for torque improvement and vibration optimization.

Analysis of a New Partitioned-Primary Flux-Reversal Hybrid-Excited Linear Motor

A new partitioned-primary flux-reversal hybrid-excited linear motor is proposed and investigated in this article, which features an asymmetrical double-sided primary structure. The novelty of this motor lies in the adoption of a partitioned-primary structure by moving the field excitation winding to an additional primary, thus it benefits from improved space utilization ratio since both armature and field windings can be separately mounted. First, the topology, feasible slot/pole combinations, and operating principles of the proposed machine are introduced. The magnetic flux density distributions in two air-gap regions are comparatively studied from the perspective of magnetic gearing effect. Then, global optimization of the proposed motor with different slot/pole combinations is performed to maximize both the output thrust force and flux-adjusting range based on 2-D finite-element analysis (FEA). In addition, the electromagnetic performance of the motors including flux-adjusting capability, thrust force, detent force, and force ripple with different slot/pole combinations are comparatively investigated. Finally, a 6-slot/7-pole prototype is manufactured and tested to verify the FEA and calculations. It is shown that the proposed motor, benefiting from a partitioned-primary topology, exhibits very good flux-adjusting capability and overloading capacity. Thus, it has good prospect in applications that require flexible speed control.

Design and Analysis of a Novel Transverse-Flux Tubular Linear Switched Reluctance Machine for Minimizing Force Ripple

This article proposes a novel transverse-flux tubular linear switched reluctance (TF-TLSR) machine for long-stroke applications, in which the armature windings are placed on the short primary, while the long secondary is made of only low-cost iron ring. The key for the proposed machine is to innovatively introduce the complementary tooth structure into the primary salient-pole design and equip the complementary machine unit configuration in the primary construction for the purpose of minimizing the force ripple. The principle of force ripple reduction by using these complementary structure configurations is illustrated in depth. The analytical calculations of the winding inductance and thrust force of the proposed machine are developed with the air-gap magnetic path modeling. By using the 3-D finite element analysis (3-D-FEA), the sensitivity study of two key structural parameters on the force characteristics is also carried out, based on which a satisfactory TF-TLSR machine is finally determined. Consequently, a prototype is fabricated for experimentation testing, and the FEA and experimental results are comparatively demonstrated, which verifies the validity of the design ideas of using a complementary concept for minimizing force ripple in the proposed machine.

Thrust Force Analysis of Slotless Permanent Magnet Linear Generator for Wave Energy Converter

The WEC (Wave Energy Converter) that uses a permanent magnet linear generator continues to develop. The most important thing to know in designing WEC with a linear electric generator is the thrust required by the linear generator itself. Therefore, this paper discusses and analyses the thrust that occurs in linear electric generators used in WEC systems. Linear electric generators are simulated using FEMM (Finite Element Magnetic Method) software. FEMM simulation is used to analyse the magnitude of the induced magnetic field received by the conductor at a certain position of the stator. The conductor is given a constant current so that it produces thrust force between the stator and translator; the magnitude of thrust force depends on the magnitude of the magnetic field at the position. In the design and analysis, conductors ware given 3A. The maximum thrust force in the linear electric generator design is 79N, and the average force is 75N, force ripple is 1,2%. The design of the permanent magnet linear generator was done, and the WEC system should produce thrust force at least equal to the force that the generator requires.

Axial Magnetic Force Analysis and Optimized Design for Single-Phase BLDC Slim Fan Motors

The typical manner to generate the axial magnetic force is to utilize the magnetic path design by upward magnet offset (UMO) that is the permanent magnet (PM) shifted upward relative to the stator in the single-phase BLDC slim fan motors. The other special method is to increase a permeable material, with an air-gap (AG <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i-m</sub> ), under the PM to generate the axial magnetic force. The axial magnetic force and its ripples are the important factors in the slim fan design and will further affect the performances of the acoustic noise and axial vibration. In this article, a magnetic circuit model is constructed to execute the mathematical theoretical analysis of the magnetic field. The trait of the phase opposition between the magnetic force ripples generated in the stator core and lower iron plate is used to optimize the ripple of the total axial magnetic force by the offset effect, and in the meantime, to remain the desirous average value. A 3-D model is created to execute the finite-element analysis and simulation. The cross-matching simulation among the different degrees of UMO and AGi-m is executed and an optimized model is defined. A solid model of a slim fan motor is verified in the practical experiment, and the results present the effectiveness in the reduction of acoustic noise and vibration.

New elevator system constructed by multi‐translator linear switched reluctance motor with enhanced motion quality

In this work, a new elevator system created by a linear switched reluctance motor is presented. Unlike conventional linear motors, the proposed linear motor has more than one translator. Each phase in a translator generates a pulsing force; hence, the total generated force has noticeable ripple making it difficult to soft motion. In order to solve this problem, similar phases in different translators have been located in positions with specified distances together. As a result, similar force pulses would be shifted so that they can compensate together. An appropriate control strategy has been designed for the system, which can control the current, force, speed, and position simultaneously. A conventional proportional–integral controller and an adaptive fuzzy controller have been used to control the speed. In order to have a precise study, a prototype elevator system along with its control unit has been made and the obtained results have been compared with the simulation results. These results confirm that the proposed structure can significantly produce force and speed ripples.

A Study on Design of Tubular Linear Reluctance Generator Taking Account of Leakage Elements

The focus of the work demonstrates the validation of the new shape translator taking account of leakage elements in linear oscillating generator for a series hybrid electric vehicle. By comparison and analysis using the various shapes of translator teeth, it is studied to minimization of the force ripple and increasing useful magnetic flux by equivalent magnetic circuit (EMC) and finite element method (FEM). It will be analyzed considering the leakage reluctances for a more practical and effective analysis, and design process of tubular linear reluctance generator. At last, the trapezoidal shape of translator is selected as optimal model among the proposed translator teeth in tubular linear reluctance generator. The results of this study will give elaborate information about the design rules and the performance data of linear gensets.

Investigation of New IPM Linear Machine Configuration with Low Permanent Magnet Used

Permanent magnet (PM) machines have received numerous attentions, since they are distinguished by many desirable features including simple construction and high efficiency. However, high price of the permanent magnet material may be considered as the main problems of such machines. Hence, the demand of PM machine with high efficient PM materials used is increased. In this study a new configuration of PM linear machine with high efficient PM material utilization, named as V-shape interior PM linear machine is investigated. The mentioned machine has been compared to the conventional I-shape counterpart. In order to perform sensible comparison, I-shape and V-shape machines have been designed with identical main design specifications. It has been observed that the V-shape topology shows better PM material utilization. It should be noted that about 43% higher efficient PM used is obtained by the V-shape machine compared to the conventional I-shape corresponding. It should be noted that the V-shape machine has been designed with about 51.6% less total permanent magnet volume compared to I-shape machine. Moreover, the introduced machine offers less cogging force as well as thrust force ripple than that of the conventional machine.&#x0D;

An Improved Direct Torque Control for a Single-Winding Bearingless Switched Reluctance Motor

The direct torque control (DTC) and direct force control (DFC) method were introduced to reduce the torque and levitation force ripple in single-winding bearingless switched reluctance motors (SWBSRMs). However, it still has some disadvantages. Firstly, the flux-linkage control is not suitable for the DTC method in SWBSRMs. On the one hand, it can increase the torque ripple. On the other hand, the RMS current can be increased and then the torque-ampere ratio is decreased. Secondly, the vectors selection is also unreasonable, which can increase the torque ripple further. In order to solve these problems, an improved control method based on DTC and DFC method for SWBSRMs is proposed in this paper, which can obtain high torque-ampere ratio and low torque ripple simultaneously. In the proposed method, the flux-linkage loop control is not needed and the space voltage vector table is improved. The experimental results show that the torque ripple is reduced by 66.7%, the torque-ampere ratio is increased by 200% and the switching times in one electrical period are reduced by 47.3%.

Source Independence of Force Ripple in Linear Induction Machines

In this article, it is shown that in a linear induction machine (LIM), the force ripple that arises due to the magnetic asymmetry does not depend on whether the LIM is being fed from a voltage source or a current source. When the LIM is fed from a three-phase balanced voltage source, the primary voltage is balanced but the LIM draws an unbalanced current from the supply. When the LIM is fed from a three-phase balanced current source, the primary current is balanced but an unbalanced voltage appears across the LIM terminals. In both these cases, the unbalance creates a ripple in the propulsive force of the LIM. This force ripple increases with the increase in the speed of the LIM. This article shows that at any given speed, the percentage of the ripple component in the propulsive force remains constant irrespective of all operating conditions. The variation of the force ripple with the speed can be represented by a curve, which is unique for one LIM. This curve neither depends on the value of the primary voltage or primary current, nor does it depend on the nature of the energy source from which the LIM is being supplied. The force ripple arises from the flux distortion due to end effects and can, therefore, be instrumental in estimating the amount of end effects existing in an LIM.

Comparative analysis of new improved force split-teeth Linear Switched Reluctance Motor for high speed transit systems

Linear Motors forms an integral part of propulsion systems used in linear motor propelled high-speed transport systems. Generally, motors such as linear induction and linear synchronous are preferred worldwide for these applications. In spite of showing the immense capabilities, linear switched reluctance motor (LSRM) is still under research for applications in high-speed systems. This paper focuses on a LSRM with enhanced propulsion force for the application in high-speed transportation systems. It has a linear structure with moving translator for direct force transmission and two-teeth in each stator pole to attain better force performance. In the proposed motor, translator teeth count is more as compared to the stator teeth count. A 6/16 LSRM with three- phase split-teeth stator has been proposed. The performance of the proposed 6/16 LSRM has been compared with 6/4 and 6/8 three-phase conventional motors to highlight the improvements in the proposed motor. The paper also modifies the proposed 6/16 LSRM into 12/32 configuration to analyse its force ripple reduction capability. The performance of the 6/16 is compared with the 12/32 LSRM. All the motors are modelled and analysed in 3D with the help of finite-element analysis (FEA). The paper optimizes the 6/16 LSRM using parameter based cumulative deterministic optimization algorithm (PBCDOA) to maximize its propulsion force. The FEA based analysis shows better force performance for the proposed motor.

Analysis of the Fractional Pole-Pair Linear PM Vernier Machine for Force Ripple Reduction

Linear permanent magnet Vernier machine (LPMVM) is attracting more and more attentions recently due to its simple structure, high efficiency, and high thrust density at low speed. In this article, a novel fractional pole-pair linear permanent magnet Vernier machine (FP-LPMVM) is proposed, which gives more freedom in the design of the LPMVM to reduce the force ripple of the machine. The operation and force ripple reduction principles of the FP-LPMVM are also given in this article with the help of analytical equations. It is found that some of the proposed FP-LPMVM exhibit inherent good performances such as high EMF symmetry and low thrust ripple due to the combining of the flux modulation effect and the FP-LPMVM. In order to verify the theoretical analysis in this article, two LPMVM prototypes (i.e., 12 slots 20 poles integer pole-pair LPMVM and 18 slots 29 poles fractional pole-pair LPMVM) are manufactured, tested, and compared with each other. The experimental results are consistent with the FEA results, and the validity of the analysis and the superiorities of the proposed FP-LPMVM are verified.

The effect of a single‐sided pole shoe and slot on reducing torque ripple in a switched reluctance motor

SummaryThe switched reluctance motor (SRM) has the high level of vibration and noise, whose application is greatly limited in many fields. In this article, a novel stator for a SRM is designed to reduce torque ripple and is suitable for one‐directional or low‐speed reverse rotation. On the one hand, a shoe is added to the stator pole side in the rotating forward direction from the completely unaligned to the aligned position. On the other hand, a slot is set on the top of stator tooth. First, causes of vibration and torque ripple are analyzed. Second, it is indicated by the equivalent magnetic circuit (EMC) method that the air gap permeability of the model with the single‐sided pole shoe is larger than that of the conventional model in the nonoverlapping region between the stator and rotor. The influences of the angle and height of shoe on the air gap magnetic density, radial force, and torque ripple are analyzed. Third, the results from EMC method show that the radial force can be reduced by opening a slot at the top of stator pole arc. The width and depth of slot which has effect on the radial force and torque ripple are analyzed. Finally, finite element analysis results show that the decreases of 34.52% for the radial force wave peak and 43.39% for the torque ripple are achieved at the cost of a decrease of 8.54% for the average torque of the single‐sided pole and the slot model of the stator pole compared with the conventional model. Some experiments for the two prototypes verify that the torque ripple and radial force can be reduced by adopting the new model.