Due to the difference of movement and boundary conditions between long-primary double-sided linear induction motors (DSLIMs) and short-primary DSLIMs, the longitudinal end effect is different. This paper analyzes the dynamic longitudinal end effect of long-primary LIMs according to the basic principle and electromagnetic field theory and explains the difference of magnetic field traveling wave and its influence between these two kinds of DSLIM. The equivalent circuit model and correction factors considering the end effect are described through theory analysis. To verify the validity of the model, 3-D field analysis by Ansoft 3-D is implemented, and the field distribution is presented. The analysis results have a good agreement with the results where the end effect is considered than that where the end effect is not considered. A useful conclusion is that, with proper selection of the secondary poles and proper attention to the slip that the machine is operating at, the end effect will have a much smaller influence than that in the short-primary DSLIM. It provides a good way for this kind of machine design and industrial application in the future.

Research on End Effect of Linear Induction Machine for High-Speed Industrial Transportation

Linear induction motors (LIMs) are the best solution to the problem of producing linear motion directly, but the low efficiency, low power factor, and longitudinal end effect (LEE) are their major problems. These problems become more baneful in high-power and high-speed applications. For example, in the transport industry, they lead to high energy consumption, high input current that occupies transmission line capacity, and phase unbalance. Thus, it is necessary to overcome these problems; furthermore, the decrease in motor weight results in lower cost and better performance of linear induction motors. In this paper, first we present an accurate equivalent circuit model (ECM). Then, we introduce a new factor, Klee, which can illustrate the end effect intensity in the LIM. At the next stage, we investigate the influence of motor design parameters on the efficiency, power factor, and end effect intensity. Then we develop several different muliobjective functions, which will be used to improve efficiency, power factor, end effect intensity, and motor weight. This procedure will be done by analytic method and by using the particle swarm optimization technique. Results will show the accuracy of the equivalent circuit model and the improvement of objective functions at the end of the optimization procedure. Two-dimensional finite-element analysis evaluates the results from the ECM.

Optimum Design of Single-Sided Linear Induction Motors for Improved Motor Performance

The linear induction motor (LIM) applied in low-speed Maglev train produces not only the thrust force to drive the train, but also the normal force that affects the levitation system. Three finite element models are employed to investigate the influence of transverse edge effect, longitudinal end effect, transverse edge shape of secondary aluminum plate and its temperature, etc., on the force performance under different slip frequency. For the transverse edge effect, a precise correction factor is proved to be more suitable than the common Russell and Norsworthy's factor. An analytical method using an equivalent circuit model is improved based on an existing model for nonferromagnetic secondary LIM. The amendments account for the primary iron loss, the eddy current of secondary back iron, and the calculation of normal force. Based on this equivalent circuit model, the performance curves of thrust force, normal force, efficiency, and power factor against the train velocity are obtained for given slip frequency and thrust force. The influences of transverse edge, longitudinal end, and air gap length are also investigated. Analytically predicted results are validated by finite element models and measurements.

Investigation of Forces in Linear Induction Motor Under Different Slip Frequency for Low-Speed Maglev Application

A novel steady-state equivalent circuit model for linear induction motors is presented in this paper. The novelty resides in classification and inclusion of end effects that are considered static and dynamic, namely as speed-independent and speed-dependent end effects. The Duncan model is used to address the dynamic end effect and appropriately modified to account for the saturation of back iron. The static end effect, which manifests itself by the alternating field component, is represented by an additional circuit branch similar to the branches of the motor with an alternating magnetic field. Each type of end effect is modeled and included separately. The results regarding determination of basic performance characteristics are compared with those obtained from finite element (FE) simulation. The procedure to identify the parameters of this circuit using a FE model is also presented.

A Novel Equivalent Circuit Model of Linear Induction Motors Considering Static and Dynamic End Effects

In rotating machines, no end effects occur because of their cylindrical geometry, which has no ends in the direction of movement. In linear motors, however, either the rotor or the stator has a finite length, and end effects occur because of the part having finite length entering or exiting the magnetic field. End effects occur as magnetic waves having attenuation, and play a major role in the performance of linear induction motors (LIMs), especially at high speeds. As the speed increases, efficiency decreases because of longitudinal end effects. This decrease in efficiency has a braking effect. In high-speed maglev devices, such as trains, the efficiency and performance of the LIMs become very important. We report on our investigation of end effects by the finite-element method.

Investigation of End Effects in Linear Induction Motors by Using the Finite-Element Method

This paper presents a fast and accurate d-q axis equivalent circuit model of linear induction motor (LIM) for drive system simulations. The developed model was built based on nonlinear transient finite element analysis to obtain the asymmetric d-q equivalent constants for static end effect and the distorted air gap distribution by velocity for dynamic end effect. The model was implemented in a vector control environment through the creation of a d-axis magnetizing inductance to account for the reduction of the magnetizing inductance due to eddy current. Since the d-q axis equivalent circuit model of LIM considering both end effects has not been exactly completed, the significance of the work is that it provides an accurate d-q axis equivalent circuit model of LIM for utilization in simulation environments

Dae-Kyong Kim

Papers

A Novel Equivalent Circuit Model of Linear Induction Motor Based on Finite Element Analysis and Its Coupling With External Circuits