Permanent Magnet Linear Synchronous Machine Research Articles

A Feasibility Study on a New Doubly Salient Permanent Magnet Linear Synchronous Machine

Permanent magnet linear synchronous motors (PMLSMs) have been successfully adopted in a wide variety of industry applications due to improved servo-capability and outstanding dynamic characteristics. However, the conventional PMLSMs need a large amount of permanent magnet (PM) material in the stator resulting in significant cost rise. This paper proposes and analyzes a new doubly salient PM linear synchronous machine (DSPMLSM). The proposed configuration consists of consequent pole stator to reduce PM material and modular mover structure to reduce force ripples. Four different models are chosen and compared by two-dimensional finite element analysis (FEA). The analysis reveals that the proposed DSPMLSM uses only a half amount of PMs, while retaining almost the same characteristics as the conventional PMLSMs.

Synthetic loading applied to linear permanent magnet synchronous machines

Linear permanent magnet (PM) machines are applicable to a number of prototype renewable energy devices and therefore are candidates for deployment. Synthetic loading for efficiency evaluation of linear PM synchronous machines is described and evaluated. Synthetic loading is a technique that eliminates the need for an external mechanical load to absorb generated shaft power during rated load efficiency tests. As such it is a technique ideally suited to the large linear PM generators proposed for renewable applications. Mathematical expressions for synthetic loading are derived for the linear PM synchronous machine using the dq machine model that includes core loss. Synthetic loading and standard efficiency tests, as methods of efficiency evaluation, are simulated using MATLAB and SIMULINK. Simulation data are verified by experiment for both the synthetic loading test and the standard efficiency test. Simulation and experimental results show that the synthetic loading method is capable of evaluating the efficiency of linear PM synchronous machine under test. The results show good agreement with standard efficiency tests. The key contribution of this work includes the mathematical expressions of synthetic loading applied to linear PM synchronous machines, the hardware and software implementation of the technique and the validation of the synthetic loading as a technique for efficiency evaluation of linear PM synchronous machines.

A Linear Magnetic-geared Free-piston Generator for Range-extended Electric Vehicles

This paper proposes a novel linear magnetic-geared machine for the free-piston generator in range-extended electric vehicles. The key is to integrate a linear magnetic gear into a linear permanent magnet synchronous machine to form a single machine, which can offer high efficiency and high power density for electricity generation. The low-speed mover of the proposed machine is directly coupled with the pistons of the internal combustion engine and reciprocates with the pistons. Due to the magnetic gear effect, the high-speed mover which is also the translator of the synchronous machine can travel at high speeds, hence offering high power density design and generating electricity with a high voltage. By using finite element analysis, the machine performance is analyzed and verified.

Performance improvement of permanent magnet machines by modular poles

Modular permanent magnet poles have recently been proposed to enhance the performance of permanent magnet machines and improve the exploitation of used magnet materials. An optimisation method for these poles is proposed for use in linear permanent magnet synchronous machines. The main objective of the optimisation is to select proper dimensions and material properties of modular permanent magnet poles to enhance the machine developed thrust. The optimisation is carried out based on a mathematical model of the machine obtained analytically. In particular, the developed thrust of linear permanent synchronous machines with modular poles is given by the model. Genetic algorithm is then employed to optimise pole parameters where the ratio of thrust ripples to average thrust is chosen as an objective function. Extensive investigations carried out by analytical and finite element methods confirm that substantial lower thrust ripples are produced with almost the same average thrust.

Dynamic range evaluation of linear permanent magnet machine through design parameters estimation and continuous motion

In the case of the manufactured linear permanent magnet synchronous machines (PMLSMs), dynamic range evaluation for system efficiency and performance limits is difficult to accomplish because of the moving length restriction with mover and the absence of interface between the design field and control field. To solve this problem, this paper presents a dynamic analysis based on design parameters by magnetic field analysis of the linear PM machine. And then, maximum operating range of the system is estimated considering the control method of a fixed dc-link voltage of the inverter. This analysis is verified from the dynamic experiments through continuous progressive motion of the manufactured disk-type PMLSM by current control.

Flux Distribution in Linear Permanent-Magnet Synchronous Machines Including Longitudinal End Effects

We investigated the longitudinal ends' influence on the flux distribution in a permanent-magnet linear synchronous machine with an analytic model and with numeric finite-element methods. We derived a general analytic expression, on closed form, from a linear reluctance model. The model reveals that the flux in a linear machine differs from that in a rotating machine in several aspects. The longitudinal ends introduce a pairwise coupled flux pattern, which will behave differently in circuits with odd or even numbers of magnets. In linear machines with an even number of magnets the pairwise coupled flux will spread throughout the whole machine, whereas in linear machines with an odd number of magnets it will be transformed into an equally distributed flux in the middle. The latter case will give rise to a nonsymmetric air gap flux distribution, where every second pole has larger flux. We confirmed the pairwise coupled flux and the nonsymmetric air gap distribution predicted by the analytic model by finite-element simulations. We noted additional effects when nonlinear behavior of the steel is taken into account. We conclude that saturation counteracts the pairwise coupled flux pattern at the longitudinal ends. Again, a nonsymmetric air gap flux distribution occurs as the pairwise coupled flux is transformed into an equally coupled flux. The pairwise coupling of the flux and the nonsymmetric air gap flux distribution give rise to a number of secondary effects, which we discuss.

Design and dynamic analysis of permanent magnet linear synchronous machine for servoapplication

In servosystem demanding precision dynamic characteristics, application of the permanent magnet linear synchronous machines (PMLSMs) has an advantage of analysis convenience by simple geometry and thrust ripple reduction from the sinusoidal back electromotive force and excited stator. Therefore, this paper presents the design of surface-mounted PMLSM with a slotless iron-cored stator according to coil turns to satisfy the rate thrust. Also, from the dynamic analysis for servoapplication of manufactured motor with heavy mass, we offer an accurate range of the dc link voltage and acceleration in rate speed. This is applied to speed reference profile considering the system characteristics in total length of moving position.

Electrical generators for direct drive wave energy converters

Wave power devices traditionally use conventional rotary electrical machines for power conversion. However hydraulic systems or air turbines are required to convert the low reciprocating motion of the wave device to rotation at 1500 rpm. The concept of a direct drive system is introduced, in which a reciprocating electrical machine is driven at the same speed as the device. A linear permanent magnet synchronous machine is compared to the transverse flux machine in a basic design study for this application. The latter machine is identified as offering the best potential. Electromagnetic and electric circuit models are developed to investigate the performance of the transverse flux machine in a wave energy converter. Measures are suggested to optimise the performance of the machine.

Characteristics of a disc permanent magnet linear synchronous machine with back iron

A disc permanent magnet linear synchronous machine (DPMLSM) with back iron is presented in this paper. The proposed machine is to fulfil the requirements of high efficiency and large torque for electric vehicle (EV) applications. The back iron plays an important role in enhancing flux linkage and reducing flux leakage so that the designed machine has characteristics of high flux and power density to reduce the physical volume of EV. The steady-state, dynamic operating characteristics, and three-dimensional (3-D) finite element analyses are obtained to demonstrate the performance of the machine. Experimental results show that the proposed machine has a very low line current distortion with just a six-step inverter and a very wide range of operating speed without gear-ratio devices.

Analytical modeling of a new disc permanent magnet linear synchronous machine for electric vehicles

This paper develops an analytical approach based on a qd0 reference frame model to analyze dynamic and steady state characteristics of disc permanent magnet linear synchronous machines (DPMLSMs). The established compact mathematical model can be more easily employed to analyze the system behavior and to design the controller. Superiority in operational electromagnetic characteristics of the proposed DPMLSM for electric vehicle (EV) applications is verified by both numerical simulations and experimental investigations.

Analysis of fields and forces in a permanent magnet linear synchronous machine based on the concept of magnetic charge

Two-dimensional and three-dimensional field distributions produced by permanent magnets (PMs) of a permanent-magnet linear synchronous motor (PMLSM) are obtained in analytical forms, based on the concept of magnetic charge and the method of images. The determination of electromagnetic forces and parameters of this type of a motor is examined. The proposed method and the resulting simplified formulas are useful for the design and analysis of PMLSMs as well as for other types of PM motors. Calculated results compare favorably with the experimental results, and thus validate the assumptions and the analysis. >

Fields in permanent magnet linear synchronous machines

The determination of electromagnetic fields in permanent magnet linear synchronous machines (PMLSM's) to form the basis for the evaluation of forces and parameters of PMLSM'S (to be presented in a subsequent paper) is discussed. Analytical techniques applied to permanent magnet rotary synchronous machines are modified and adapted to PMLSM's. Fields are determined analytically in a single-sided PMLSM, and computed results by the finite-element method are compared with those obtained experimentally. A good correlation between the results obtained by the three procedures-analytical, finite-element computational, and experimental-validates the approximations used in the analysis.