Tubular Linear Machine Research Articles

Cryogenic Characterization of Copper-Wound Linear Tubular Actuators

Electrical machine power density can be increased by liquid nitrogen (LN) cooling, since these machines operate at low resistivity and have a high heat transfer coefficient. This paper describes the experiments carried out on a short stroke tubular linear permanent magnet machine with copper windings and LN cooling. A cryogenic test rig for linear actuators was designed and built, and tests were carried out aimed at highlighting inherent current limiting capability, electric parameter variation in the fall from room to cryogenic temperatures, and actuator high thrust density. Shear stress reaches 17.8 kN/m2, and thrust-to-copper-loss ratio is 4 N W-1/2, which are significantly better compared to conventional actuators.

TUBULAR LINEAR INDUCTION MACHINE AS A FAST ACTUATOR: ANALYSIS AND DESIGN CRITERIA

In this paper, some design criteria for a Tubular Linear Induction Motor (TLIM) as a fast actuator are considered. The in∞uence of geometrical and physical parameters on the operating conditions of a TLIM are investigated by means a quasi-analytic model. The model is based on the application of the Fourier Transform both in space and in time. The Fourier transform in space is introduced to take into account the flnite length of the stator windings in the axial direction. The transient electrical response of the motor at standstill following the insertion of a three-phase system of voltage generators is performed by the Fourier transform in the time. Linear movements are very usual in mechanical engineering, especially in industrial robots, where linear speeds up to several meters per second are often required. These movements are usually obtained by using rotating motors in combination with rotation to translation mechanism. The resulting systems may have poor performance; in particular, an excessive time delay may prevent their use as fast actuators (1). The complexity of these systems can be overcome by using linear actuators. It is well known that tubular linear induction machines have the highest force to moving mass ratio when compared with other linear motors; this property makes these devices very attractive to be used as servo motors since they may have better performance in terms of reduction of delay times with respect to those of traditional systems. The simplest approach to model these linear motors is based on

Analytical Modeling of Flat and Tubular Linear PM Machines with Surface-Mounted Magnets and Semi-Closed Slots

Analytical Modeling of Flat and Tubular Linear PM Machines with Surface-Mounted Magnets and Semi-Closed Slots

Performance Analysis of a Novel Magnetic-Geared Tubular Linear Permanent Magnet Machine

This paper presents a novel tubular linear permanent magnet machine for direct-drive applications, in which a magnetic gear is integrated with a tubular linear machine, aiming to improve the thrust force density and enhance the machine efficiency. The operating principle of the proposed machine is introduced and the machine design with improved thrust force density is presented and discussed. By using circuit-field-motion coupled time-stepping axisymmetric finite element method (FEM), the steady-state as well as transient performances of the machine are simulated. The FEM computation results are consistent with those obtained theoretically, hence verifying the validity of the machine design.

Optimisation of a tubular linear machine with permanent magnets for wave energy extraction

PurposeThe purpose of this paper is to optimise the cost‐based performance of a tubular linear generator and to minimise cogging forces.Design/methodology/approachOptimisation of a tubular linear generator with longitudinal flux topology has been undertaken using a finite element method. The computational models used have been verified experimentally.FindingsThe use of an oversized stator linear generator design as opposed to an oversized translator design has the potential to increase the output electromotive force per unit material cost by 25 per cent for slotless iron core topologies and approximately 14 per cent for air core topologies. For cogging force minimisation, optimisation of the length of the stator core is an effective technique for both oversized stator and oversized translator constructions. Comparisons of magnet materials also indicate that the higher cost of rare earth magnets to ferrites is compensated by their superior specific performances.Originality/valueIn this paper, a broader range of design parameters than in previous investigations has been optimised for the slotless iron core and air core topologies. The result relating to cogging force reduction and cost savings (in particular) has the potential to make direct drive wave energy extraction a more competitive technology in terms of reliability and cost.

Armature Reaction Magnetic Field of Tubular Linear Surface-Inset Permanent-Magnet Machines

This paper presents an exact 2-D analytical model for predicting the armature reaction magnetic field in idealized structures of permanent-magnet tubular linear machines with surface-inset mounted magnets. The armature reaction magnetic field distributions is analytically derived and compared to finite-element analyses. The analytical solution allows the prediction of the machine inductance and reluctance force in closed forms, and facilitates the evaluation of any possible partial irreversible demagnetization of the magnets. It can also be used to estimate resistance limited eddy-current losses in armature windings and permanent magnets. The developed analytical model can be advantageously used for the analysis and design of a class of linear tubular machines.

The Thrust Characteristic Investigation of Transverse Flux Tubular Linear Machine for Electromagnetic Launcher

This paper investigates the thrust characteristics of the transverse flux tubular linear machine, including theoretical analysis and numerical calculation. The influence of structure parameters on the thrust force and cogging force characteristics is analyzed in detail. Special attention is paid to the length of stator segment, air-gap length, and pole-arc coefficient. The analysis results provide a foundation for the optimum design of electromagnetic launcher.

Influence of the Permanent Magnet Magnetization Length on the Performance of a Tubular Transverse Flux Permanent Magnet Linear Machine Used for Electromagnetic Launch

This paper investigates the underlying influence of permanent magnet (PM) magnetization length on the performance of a tubular transverse flux PM linear machine working as the propeller of an electromagnetic launcher, including its main flux linkage, cogging force, and thrust force. The theoretical analysis is brought forward and verified with 3-D numerical computations. It is shown that the cogging force increases with the increase of the PM magnetization length, whereas the main flux linkage and thrust force do not follow this rule, which is quite different from that in conventional PM machines.

Analysis and Computer-Aided Simulation of Cogging Force Characteristic of a Linear Electromagnetic Launcher With Tubular Transverse Flux Machine

This paper investigates a linear electromagnetic launcher with tubular transverse flux permanent-magnet linear machine (TFPMLM). Special focus is given on its cogging force characteristic, including the theoretical analysis and computer-aided simulation. Both 3-D and equivalent 2-D finite-element analyses are performed to calculate the cogging force, and the results are compared. It is shown that the proposed 3-D to 2-D equivalence can predict the cogging force of the tubular TFPMLM in an accurate and fast way.

Analytical Modeling of Magnetic Field in Surface Mounted Permanent-Magnet Tubular Linear Machines

We present an exact 2-D analytical model for predicting the magnetic field in idealized structures of surface mounted permanent-magnet tubular linear machines that account for the stator slotting effect. The open-circuit and armature reaction magnetic field distributions are analytically derived and compared to finite-element analyses. The on-load magnetic field calculation is based on the superposition of the component fields due to permanent magnets and armature field reaction. Our model can be advantageously used for the analysis and design of a class of linear tubular machines.

Design, Prototyping, and Analysis of a Novel Tubular Permanent-Magnet Linear Machine

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper, we present a new tubular permanent-magnet linear machine with square-shaped cross section and derive its corresponding analytical model by solving Maxwell equations and applying the superposition theorem. The analytical field solution is necessary for obtaining an analytic form of the machine parameters and variables such as the self- and mutual inductances of the windings, the thrust force, and the windings electromotive force (EMF). These provide a valuable tool for tubular machine analysis, design, and optimization. In order to achieve maximum force density, we optimized the design parameters of the proposed machine using the analytical model. We used finite-element analysis and experimental results to demonstrate the validity of the developed analytical model. Again using the Fourier series of the cogging force and its harmonic analysis, in this paper, we introduce two techniques for cogging force reduction in the new tubular linear permanent-magnet machine. The first technique reduces the cogging force due to interaction between the permanent magnets and the stator teeth, and the other reduces the cogging force due to finite length of the armature. These techniques are straightforward, and their implementations in the tubular linear permanent magnet machine with square cross section are easy. We investigated the effectiveness of the proposed techniques in cogging force reduction by 3-D finite-element analysis and experimental measurements. </para>

Design of a double‐sided tubular permanent‐magnet linear synchronous generator for wave‐energy conversion

PurposeThe purpose of this paper is to present a double‐sided tubular linear machine layout direct‐drive applications, with particular focus on wave‐energy conversion. The paper documents both the computational and mathematical analysis of this novel machine layout.Design/methodology/approachThe selection and finite‐element optimisation of the permanent‐magnet array is presented. The machine is then modelled using magnetic circuit theory. By simultaneously solving the system of equations, a demonstrative design is developed and simulated so as to validate the mathematical model and compare the performance of the new layout with a traditional layout.FindingsA surface‐mounted magnetic array, with unshaped‐poles, is most suitable for the proposed layout. The mathematical model exhibits a suitable level of accuracy for design and analysis purposes. The calculated resultant force differs from the FEA calculation by 1.85 per cent. A higher force‐density is exhibited by the proposed layout, when compared with flat layouts, with a reduction of 36.5 per cent in the spatial footprint and magnetic material of the machine.Research limitations/implicationsAlthough the research is focused on the application of wave‐energy conversion, the techniques are application‐independent. However, certain design decisions should be reviewed for other applications.Practical implicationsThe practical implementation of such a machine poses many mechanical obstacles. These have been solved in theory, and are being implemented at the time of writing.Originality/valueThe combination of a double‐sided and a tubular layout has not previously been researched. This research fills that void and provides designers with the technical background and a mathematical model for development of such devices.

Calculation of Magnetic Field of Tubular Permanent-Magnet Assemblies in Cylindrical Bipolar Coordinates

The paper solves a 3D magnetostatic problem in a cylindrical bipolar system of coordinates by separation of variables. The analytical solution applies to the field area between two nonconcentric cylindrical surfaces located in a close proximity to each other. The paper applies the method to the calculation of the magnetic field of a tubular linear permanent-magnet machine with an off-centered rotor and to the analysis of the field of a two-roller magnetizing fixture.

A Tubular-Generator Drive For Wave Energy Conversion

This paper illustrates the operation of a tubular-machine drive as a linear generator for a heave-buoy wave energy conversion. Linear generators, which are adopted in marine power plants, offer the advantage of generating without introducing any conversion crank gear or hydraulic system. The use of a tubular-machine topology allows the electromagnetic thrust density to be improved. This paper briefly summarizes the principles of marine wave buoy interaction and reports the design analysis and control of a permanent-magnet (PM) synchronous tubular linear machine based on a scaled generator prototype and on a rotating simulation test bench

Finite element analysis of saturation effects in a tubular linear permanent magnet machine

PurposeThe aim of the paper is to find the simple and accurate model for the analysis of a drive with a tubular linear permanent magnet machine (TLPMM). Attention is paid to the models that take into account the saturation effects and is useful in the calculations of electromagnetic forces.Design/methodology/approachA circuit model and a field‐circuit model (FCM) are considered. The FCM includes finite element (FE) formulation for the axisymmetric electromagnetic field, equations which define the connections of windings and converter elements, and expressions that describe the control system. The FE method is used to determine the parameters of the circuit model. In order to simplify the circuit model, saturation effects caused by armature reaction are ignored. The electromagnetic force calculation is based on the virtual work principle and uses an approximate expression for the derivative of system co‐energy. The results obtained for the proposed models have been compared.FindingsThe proposed FE method of force calculation conforms with the applied method of movement simulation. For the rotor position when the cogging force is equal to zero the calculated cogging force is “almost” zero within seven‐decimal‐place accuracy. The effects of armature reaction on the performance of a TLPMM machine are similar to those which occur in a classical DC machine; in particular the demagnetising effect caused by saturation is observed.Originality/valueThe paper shows the influence of the saturation effects on the electromagnetic force of a TLPMM. In the case of “strong saturation”, the classical circuit model may be inappropriate for engineering calculations.

Design optimisation and comparison of tubular permanent magnet machine topologies

The influence of the leading design parameters on the performance of slotless tubular permanent magnet machines, and the relative merits of different tubular linear machine topologies, are deduced from analytical field solutions. The force capability and force ripple are established as functions of a set of dimensional ratios, with due account of magnetic saturation and subject to a specific thermal constraint. The results provide an effective means of making comparative studies and optimising machine designs, and will aid the design process when addressing a given performance specification.

A general framework for the analysis and design of tubular linear permanent magnet machines

A general framework for the analysis and design of a class of tubular linear permanent magnet machines is described. The open-circuit and armature reaction magnetic field distributions are established analytically in terms of a magnetic vector potential and cylindrical coordinate formulation, and the results are validated extensively by comparison with finite element analyses. The analytical field solutions allow the prediction of the thrust force, the winding emf, and the self- and mutual-winding inductances in closed forms. These facilitate the characterization of tubular machine topologies and provide a basis for comparative studies, design optimization, and machine dynamic modeling. Some practical issues, such as the effects of slotting and fringing, have also been accounted for and validated by measurements.

Dynamic performance of a brushless DC tubular drive system

The authors describe the computer-aided analysis of the dynamic performance of a tubular linear machine system with permanent magnetic cogging forces. These forces include not only the conventional tooth cogging force apparent in both linear and rotary machines but also a force unique to permanent magnet linear machines that is due to the finite length of the stator. System equations which describe both the machine and the inverter supply are solved by a step-to-step numerical method to find the dynamic performance of the machine in an oscillator mode. The work is verified by experimental results obtained for a practical model. >