Tubular Linear Permanent Magnet Research Articles

Initial Sizing of Tubular Linear Actuators Using Simplified Maxwell Stress Tensor Method

This paper presents an innovative method for performing the initial sizing of tubular linear actuators (TLAs). Based on the Maxwell Stress Tensor (MST), an analytical expression is developed that allows the calculation of the force produced by a TLA in a quick and simple way. This expression can be employed for determining dimensional parameters considering the electric and magnetic loadings usually found in such electromagnetic devices. This technique can be applied to design slotless or slotted tubular linear permanent magnet synchronous motors (TLPMSM). In order to validate the developed method, four topologies of TLPMSM are considered. The calculated results of the developed analytical expression are presented and compared with results obtained by means of a magnetostatic finite element analysis (FEA). Additionally, the test results of a TLA prototype were used to validate experimentally the expression of force calculation by means of the MST method.

Modeling and Research on a Laminated Tubular Linear Oscillating Generator for Free-Piston Stirling Energy Conversion

The tubular linear oscillating machine can achieve reciprocating movement directly without auxiliary transmission mechanisms, which is widely used in the free-piston energy conversion system. To achieve a lower thrust ripple and eliminate the eddy current effect, a circumferential silicon steel stack is usually utilized in the stator, however, it results in assembling difficulties. In this article, a radially split lamination tubular linear permanent magnet oscillating machine with auxiliary configuration (RSL-TLPMOMA) is proposed to solve the problem. First, the laminated coefficient expression of split-laminated is deduced, the influence of laminated number and radius ratio on laminated coefficient is discussed, and the optimal combination of the laminated number under different radius ratios is given. Second, the subdomain (SD) method is used to analyze RSL-TLPMOMA, the auxiliary teeth, slot, and end effect are considered. Finally, a prototype is manufactured and tested.

Translator Eccentricity Analysis in Tubular Linear Machines Using Quasi-3-D Finite Element Method Modeling

This paper attempts to present a quasi-3D finite element method technique for modeling and analyzing tubular linear permanent magnet machines (TLPM) with translator eccentricity. Normal tubular linear machines can be modeled effectively using 2D axisymmetric models, but with the introduction of the eccentricity factor into the geometry the axis symmetry is no longer valid, and hence 3D modeling techniques become the only way for studying the machine. However, sometimes 3D modeling can become time-consuming and requires a huge amount of resources especially for non-linear problems, so the interest in modeling techniques that can represent the problem at hand with less computation time and relatively accurate results is high. A quasi-3D technique was specifically developed to be able to represent the eccentricity in TLPMs. The finite element method (FEM) was used for modeling. Eccentricity analysis has been carried on two different TLPM structures using the proposed quasi-3D, and the results from the quasi-3D model were compared to those obtained using the 3D FEM model. Both the open circuit and the on-load operating conditions were studied with the magnetic saturation taken into account. The behavior and the accuracy of the proposed model varied between the two studied structures and for the different operating conditions, and with very low computation time and cost the results obtained from the quasi-3D model were satisfactory in general except for certain cases.

Linear tubular permanent magnet motor for an electromagnetic active suspension system

This work presents the comparative study of the linear tubular permanent magnet motor (LTPMM) for the active suspension system in vehicles. To analyse and design the LTPMM, a finite element-based optimisation process is proposed. Since the proposed method reconstructs the entire field by storing the information of the air-gap magnetic flux distribution in the form of a snapshot, it provides high accuracy and a reduced computation time. The magnetic fields are analysed in LTPMMs with external and internal permanent magnets that are classified according to the position of the permanent magnet. In the comparative analysis, an optimal model for the LTPMM is presented, taking into account characteristics such as thrust, detent force and THD. Especially, various magnetisation patterns are considered to accomplish high force density. The analytical model is verified by performing finite element analysis and experiments.

Analysis of a Tubular Linear Permanent Magnet Oscillator With Auxiliary Teeth Configuration for Energy Conversion System

The tubular linear permanent magnet oscillator (TLPMO) has been widely used in the industrial field as an energy conversion machine. Detent force is an obvious drawback of TLPMO, and one of the efficient ways to minimize this phenomenon is by adding auxiliary teeth. In this article, a magnetic field reconstruction (MFRC) method is proposed to analyze the TLPMO comprehensively, in which the auxiliary-teeth, slot, and end effects are included. First, the subdomain conversion model is used to consider the end effects of the slotless magnetic field under no-load condition. Thereafter, the two-step Schwarz–Christoffel transformation method is launched to account for auxiliary-teeth and slot effects. Subsequently, the MFRC technology is performed to integrate the above-mentioned results, and the forces are obtained. Finally, the accuracy of the presented method is validated by comparing the results from the FEA model and experiment of the TLPMO prototype. The main contribution of this article is presenting a hybrid method that has a good tradeoff between the computation time and accuracy. The analytical results using the MFRC method closely agree with that of the FEA model, and it has less than 7% deviation compared with the experimental measurement. Hence, it can be regarded as an efficient tool in the initial design procedures of TLPMO.

Modeling and optimization of tubular linear permanent magnet eddy current brake with Halbach array

This paper provides an analytical method for calculating the electromagnetic field of the tubular linear permanent magnet eddy current brake. The method of separating variables based on Fourier series is used to solve the boundary value problem, and the analytical solution of electromagnetic field is obtained. The braking force is obtained by calculating the Lorentz force. Then the accuracy of the analytical method is verified by comparing the analytical solutions with the solutions obtained by finite element method (FEM). In order to improve braking performance in a limited space, the parameter analysis is carried out to investigate the influence of various structural parameters on the braking characteristics. According to the results of parameter analysis, the range of design parameters is determined. Finally, a multi-objective optimization is applied to find the optimal design parameters of the eddy current brake. The braking force increases by 27% and the volume of permanent magnet decreases by 7.7% after optimization.

Field Reconstruction Method for Linear Tubular Permanent Magnet Motor

This paper considers a linear tubular permanent magnet motor (LTPMM) for an active suspension system. The LTPMM has an end effect due to its structure. This can be an important factor for analysis and design of the LTPMM because it distorts the air-gap magnetic flux distribution. The field reconstruction method (FRM) was developed for an effective evaluation of the magnetic field in the electric machine. It can reduce the computation time using the basis-function which reconstructs the air-gap magnetic flux distribution with a static finite element analysis. In this paper, we adopted the FRM to evaluate the LTPMM. However, the FRM has been applied only to the rotating machines and does not take into account the distortion of the magnetic flux distribution in the LTPMM. To deal with this problem, we proposed an enhanced FRM with new basis-function. The proposed method is verified by comparing between experiment result, conventional and enhanced FRM.

Modeling of electromechanical processes of the linear permanent magnet motor drive of the one-mass vibro-impact system

The paper presents the tubular linear permanent magnet vibratory motor at a vibro-impact operating mode. The model for research of electromechanical processes in the one-mass vibro-impact system with the linear permanent magnet motor drive, which is founded on an equivalent circuit with the lumped parameters, is offered. Electric parameters of the model are dependent on operating frequency and consider magnetic losses in the motor core. Determination of calculation scheme parameters was made on the basis of field calculation by means of a finite element method. Owing to an axial motor symmetry the problem was considered in axisymmetric approach, by means of the equations of a quasi-stationary magnetic field in a time domain that has allowed considering the eddy currents in massive poles of the motor anchor. Determination of magnetic losses was made experimentally, by means of a prototype of the linear permanent magnet vibratory motor. Mechanical equivalent circuit parameters were determined experimentally, by means of the damped oscillation method and with the help of direct weighing of construction elements. We applied the Hertz’s formula for modeling of an impact force. The solution of the system dynamic equations was made by means of structural modeling in the Simulink/Matlab software package. Furthermore, we calculated characteristics of the one-mass electromechanical system in dependence of the impact parameters and operating frequency. For the validation of the calculation model, experimental studies of electromechanical characteristics of system with use of a prototype of the linear permanent magnet motor, which works in vibro-impact mode, are executed. Comparative calculation by means of the developed model is executed.

A Linear Permanent Magnet Synchronous Motor for Large Volume Needle-Free Jet Injection

Needle-free jet injection allows delivery of liquid drugs through the skin in the form of a narrow fluid jet traveling at high speed, minimizing the risk of accidents. The use of a controllable actuator to drive this process has many advantages, but the voice coil actuators previously used are too large and heavy for practical use with common injection volumes (1 mL). We instead propose a compact slotless tubular linear permanent magnet synchronous motor design for jet injection. The design was determined by utilizing a semi-analytical electromagnetic modeling technique to predict the performance of any given motor design, an optimization scheme for the motor mass at a given power dissipation, and an automated routine for estimating cogging force using finite-element analysis. A prototype motor was constructed, with a nominal mass of 322 g, a stroke of 80 mm, and a target operating power of 1.2 kW; experimental data show that the motor constant is within 10% of the target, and that the cogging force is in close agreement with the model. Test ejection of water into a force sensor verified that the motor is fit for needle-free injection. The design methodology explained here shows the benefits to integrated design optimization of both the actuator and the load, particularly in systems that drive fluid pressure loads, and also opens the door to controllable injector designs for larger volumes.

Design and Optimization of Tubular Linear Permanent Magnet Generator with Performance Improvement Using Response Surface Methodology and Multi-Objective Genetic Algorithm

Linear generators are electric machines which generate electrical energy from linear movement. Since these machines can lift gear wheel or power train, they have begun to be used widely nowadays. Since their working areas differ according to speed and power characteristic, this study contains design and optimization of tubular linear generator for free piston practices. The design performed response surface optimization through design variables acquired as a result of sizing via interface. The association between the determined design variables and the sizes of generator output was examined. In addition, these sizes were used for objective functions of increasing efficiency, decreasing overall volume and increasing general performance and their optimum values were found by using Multi-Objective Genetic Algorithm. Initial and optimum design data were compared with Ansys Maxwell 2D. With overall performance increase, 22,78% decrease was seen in total mass, while 11,7% decrease was seen in cost. In addition, prototype linear generator was made in line with initial geometry data and it was applied with crank slider mechanism.

Tubular linear permanent magnet synchronous machine applied to semi-active suspension systems

PurposeSemi-active suspension systems with electromagnetic dampers allow energy regeneration and the required control strategies are easier to implement than the active suspensions are. This paper aims to address the application of a tubular linear permanent magnet synchronous machine for a semi-active suspension system.Design/methodology/approachClassical rules of mechanics and electromagnetics were applied to describe a dynamic model combining vibration and electrical machines theories. A multifaceted MATLAB®/Simulink model was implemented to incorporate equations and simulate global performance. Experimental tests on an actual prototype were carried out to investigate displacement transmissibility of the passive case. In addition, simulation results were shown for the dissipative semi-active case.FindingsThe application of the developed model suggests convergent results. For the passive case, numerical and experimental outcomes validate the parameters and confirm system function and proposed methodology. MATLAB®/Simulink results for the semi-active case are consistent, showing an improvement on the displacement transmissibility. These agree with the initial conceptual thoughts.Originality/valueThe use of linear electromagnetic devices in suspension systems is not a novel idea. However, most published papers on this subject outline active solutions, neglect semi-active ones and focus on experimental studies. However, here a dynamic mechanical-electromagnetic coupled model for a semi-active suspension system is reported. This is in conjunction with a linear electromagnetic damper.

Comparative Analysis and Experimental Verification of a Linear Tubular Generator for Wave Energy Conversion

To improve the power density and reliability of radial (RS-TLPMG) and quasi-Halbach (QH-TLPMG) magnetization tubular linear surface-mounted permanent magnet generators under realistic sea-state conditions, a novel tubular linear generator with multilayer interior permanent magnets (MI-TLPMG) for wave energy conversion is proposed and analyzed in this paper. Using finite element analysis (FEA), a comprehensive comparison of air gap flux density, flux linkage, back electromotive force (back-EMF), load, and no-load performance is investigated to verify the advantages of the proposed machine. The FEA results indicate that MI-LTPMG with a flux-concentrating effect has higher back-EMF, air gap magnetic flux density, flux linkage, and output power than do the other two machines. Finally, a prototype is manufactured and measured on the test platform and wave tank. The experiment and simulation results show a great agreement with each other.

Research on the Field-Modulated Tubular Linear Generator With Quasi-Halbach Magnetization for Ocean Wave Energy Conversion

A field-modulated tubular linear generator (FMTLG) with quasi-Halbach magnetization is proposed for ocean wave energy conversion. The FMTLG, which is equipped with field-modulated technology and quasi-Halbach arrays, can overcome the disadvantages of heavy weight and inefficiency caused by low-speed ocean waves to some extent. To design and optimize the FMTLG in a short time, the open-circuit magnetic field distribution is established with an analytical method. Results of a finite-element method show that the back EMF of the FMTLG is 43% higher than that of a tubular linear permanent magnet generator (TLPMG) with quasi-Halbach magnetization. A novel assistant tooth of the FMTLG makes the cogging force eight times smaller than that generated by the TLPMG. Finally, a prototype is manufactured to verify the simulation results by experiments.

A Simplified Subdomain Analytical Model for the Design and Analysis of a Tubular Linear Permanent Magnet Oscillation Generator

We present a simplified 2-D analytical subdomain model to predict the open-circuit magnetic field of a tubular linear permanent magnet oscillation generator (T-LPMOG) to account for its primary and secondary end effects. At present, the magnetic field calculations of the T-LPMOG are typically analyzed in cylindrical coordinates, and the end effect is neglected accordingly to apply the periodic boundary. In this paper, a simplified 2-D analytical subdomain model in polar coordinates is proposed to consider the end effect. First, a coordinate transformation method is adopted to establish the 2-D subdomain analytical model, the cylindrical coordinates are converted into polar coordinates, and the T-LPMOG is analyzed under this new coordinate system. Next, the subdomain method is used to analyze the analytical model by solving Laplace’s equation and the Poisson equation. Based on the simplified analytical model, the flux density and back-electromotive force are obtained. The analytical results are verified using the finite element analysis (FEA) method, and the computational times compared with the FEA method are provided. Finally, a T-LPMOG prototype is manufactured and tested, and the results show that the proposed analytical model can be useful in the initial design and optimization of the T-LPMOG.

Minimization of Eddy-Current Loss in a Permanent-Magnet Tubular Linear Motor

This paper presents a minimization of eddy-current loss (ECL) in permanent-magnet (PM) of three tubular linear PM motors (TLPMMs). Three-dimensional Finite-Element Analysis has been used for the simulations. The ECL component is usually not taken into consideration in conventional PM motors. In present technologies, ECL is generated inside magnets of PM motors, due to both the high conductivity of the rare-earth magnets and the harmonics of the slot. This loss can increase the temperature inside the magnets and that may deteriorate their magnetic properties and potential risk of thermal demagnetization. Therefore, in the translator, segmented magnets has been used, because the cancelation of the ECL with this technique is possible as illustrated by the FEA results. Meanwhile, for the stator core of the three proposed motors, soft magnetic composite (SMC) material, Somaloy 700 has been used for its low cost and approximately zero ECL.

Design and Analysis of a Field-Modulated Tubular Linear Permanent Magnet Generator for Direct-Drive Wave Energy Conversion

A two-body buoys power generation system using the field-modulated tubular linear permanent magnet generator (FM-TLPMG) is proposed for direct-drive wave energy conversion in this paper. The traditional linear generator has disadvantages of large weight and low-power density caused by the slow speed of ocean wave. The FM-TLPMG can overcome these disadvantages in some extent through accelerating the speed of the traveling magnetic field. In order to design a suitable FM-TLPMG for the direct-drive wave energy conversion in a short time, ocean wave theory is applied to analyze hydrodynamic problems of the two-body buoys and calculate the operating velocity of FM-TLPMG in the sea. A 2-D analytical model for FM-TLPMG design is presented to obtain the electromagnetic field distribution by solving the Laplace and Poisson equations for each region. The analytical result has been compared with the finite-element analysis and shows its validation for the design.

Feature Investigation of a T-LPMSM Following the Selection of Its Slot-Pole Combination

This paper investigates the no-load and the on-load behavior of a fractional-slot tubular-linear permanent magnet synchronous machine (T-LPMSM). The study is initiated by the selection of the machine slot-pole combination. To do so, a formulation of the air gap flux density, based on the solution of the magnetic potential vector equation in the air gap and in the PM regions, is derived. The electromagnetic model allows the prediction of the phase back electromotive forces (EMFs) and of the cogging force. The effect of the slot-pole combination on these features is then considered to the aim of the optimal selection of the slot per pole and per phase. A case study considering the optimized slot per pole and per phase number is treated where the analytically predicted no-load features are validated by finite element analysis (FEA). The investigation is extended to the on-load characteristic which is predicted by FEA and is validated by experiments.

Modeling and State Feedback Controller Design of Tubular Linear Permanent Magnet Synchronous Motor

In this paper a state feedback controller for tubular linear permanent magnet synchronous motor (TLPMSM) containing two gas springs, is presented. The proposed TLPMSM controller is used to control reciprocating motions of TLPMSM. The analytical plant model of TLPMSM is a multi-input multi-output (MIMO) system which is decoupled to some sub single-input single-output (SISO) systems, then, the sub SISO systems are converted to sub-state space models. Indeed, the TLPMSM state space model is decoupled to some sub-state spaces, and then, the gains of state feedback are calculated by linear quadratic regulation (LQR) method for each sub-state space separately. The controller decreases the distortions of the waveforms. The simulation results indicate the validity of the controller.

FORCE CHARACTERIZATION OF A TUBULAR LINEAR ELECTROMAGNETIC ACTUATOR USING FINITE ELEMENT ANALYSIS METHOD (FEM)

This paper presents an extensive characterising study of two novel electromagnetic actuators, each with different constructions and characteristics aiming to analyse the behaviour and output characteristics of the two designs. The two actuators are Tubular Linear Reluctance Actuator (TLRA) and Tubular Linear Permanent magnet (TLPM) with Halbach array actuator. The study covered the variation of three parameters, which are the actuator air gap, number of turns and actuator size. A comparative section was also presented for the purpose of comparison. The study concentrated extensively on the two characteristics of both actuators known as output thrust force and working range as they are considered as two main concerns of any actuator design. The simulation was used to show the differences between the two designs in many design aspects such as force, displacement and effects of parameters variations. The applied simulation was performed using 3D Finite-element Ansys software, which is capable of showing the magnetic field distribution in the whole actuator and predicting the strength and length of the output stroke.

Analytical Prediction of the No-Load Operation Features of Tubular-Linear Permanent Magnet Synchronous Machines

This paper is aimed at an analytical approach to predict the no-load operation features of tubular-linear permanent magnet synchronous machines (T-LPMSMs). These are currently considered as viable candidates for wave energy conversion. The developed approach is based on the derivation of the air-gap flux density, considering both the first- and second-type modified Bessel functions of appropriate orders. Following its formulation, the air-gap flux density is applied for the prediction of the no-load operation features, with a focus on the cogging force, the phase flux linkages, and the back electromotive forces. A case study is treated considering three axial arrangements of a T-LPMSM, such as the case of an infinite length machine, the case of a finite length machine, and the case of a finite length machine enabling a quasi-cancellation of the end effect. A comparison between the analytically predicted features and those numerically computed by a 2-D finite-element analysis has led to good agreement.