Abstract
Since the linear induction motor commonly work with a laterally asymmetric secondary as it is applied to pull rail vehicles, this paper presents a complete equivalent circuit model considering the asymmetry to predict thrust, vertical and transversal forces. First, six correction factors are presented to quantify the variations in the air-gap magnetic flux and secondary induced current as the linear induction motor operating with a laterally asymmetric secondary. Second, it develops a circuit model based on the existing T-model for the rotary induction motor and two correction factors for the magnetizing branch, which is used to indicate the electromagnetic variations in the air-gap flux and secondary plate due to the asymmetry. Third, the mathematical expressions for the thrust, vertical and transversal forces are derived by applying the equivalent circuit model. Then, the six correction factors are calculated with a prototype motor, and the results of them are comprehensively analyzed. Finally, the characteristics in the prototype motor are calculated with the mathematical expressions in a range of rated speed, and validated by the experimental measurements carried out on a test rig and line for linear motors.
Highlights
LINEAR induction motors (LIMs) are widely applied in urban transportation system, e.g. linear metro, low- and medium speed maglev train, due to their own advantages: propelling vehicle without any transmission gear, low vibration noise, etc. [1]
Since I21 is not relative to the x-component of I21, this paper introduces a factor κ4 to correct I21 when it calculates the thrust in the LIMs with an asymmetric secondary, and the factor κ4, which may be called the distortion factor to the y-component of I21, is defined by
When a laterally asymmetric secondary is applied in the LIM, the transversal forces respectively produced by left and right side are not equal, and they are in the opposite directions
Summary
LINEAR induction motors (LIMs) are widely applied in urban transportation system, e.g. linear metro, low- and medium speed maglev train, due to their own advantages: propelling vehicle without any transmission gear, low vibration noise, etc. [1]. In [21], for simplifying complicate calculation, it proposes an intelligible circuit model for LIMs, which is so-called Duncan model in this paper, by inheriting T-type circuit In the model, it assumes the longitudinal air-gap magnetic flux distribution is described by an exponential function, and the further improvements based on Duncan model are presented in [22,23]. Based on [23], this paper firstly comprehensively analyses the variations in the air-gap magnetic flux and secondary induced current due to the asymmetric secondary, and proposes six correction factors (κ1-6), which is based on the electromagnetic field quantity expressions and derived from 3D analytical method, to describe the variations in circuit model instead of the electromagnetic field analytical method.
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