Three-dimension Analysis Of Characteristics For Linear Induction Motor With Primary Lateral Offset

The single-sided linear induction motor applied to the rail transit system usually works with a laterally asymmetric secondary due to the special operation condition of crossing the bend or the rail switch.When the laterally asymmetric secondary is applied in the linear induction motor,the lateral distributions of magnetic flux density and secondary eddy current are distorted,and the lateral force is emerged,which seriously affects the efficiency of the linear motor and the vehicle stability.In order to solve the issues above,this thesis calculates and analyzes two kinds of linear induction motors with flat and cap-secondary,and obtains the variation trends of the thrust,lateral force and normal force with the varied displacement of the asymmetric secondary,and provides references for improving efficiency and reliability of the linear induction motor with an asymmetric secondary as well as the performance optimization of motor control.The main research contents of this thesis are as follows:(1)Analysis of the traction characteristics in the linear induction motors with the laterally asymmetric secondary.Using ANSYS to perform the 3-D finite element simulation for two kinds of linear induction motors,i.e.with the flat secondary,with the cap-secondary.The distortion rates in air-gap magnetic flux density and secondary eddy current of the linear induction motor are defined when the motor works with an asymmetric secondary,and the variation curve of the distortion rate with the secondary displacement is obtained,the contour map of the 3-D electromagnetic force on the surface of the secondary plate is given.And the influences of the change of the 3-D electromagnetic force on the stability of the vehicle running under different secondary displacement are comprehensively analyzed,which show that the vehicle can get more stable when motor crosses a curve below the rated slip rate.(2)Analysis of braking characteristics of the linear induction motor with the laterally asymmetric secondary.Considering the special working conditions of vehicle braking in bend rail,the transient field simulations for the linear induction motors with two different secondary structures are carried out by applying 3-D finite element method.The relations between the air-gap magnetic flux density and secondary eddy current with secondary displacement and slip are given,and the 3-D force density contour map of 3-D electromagnetic force is obtained.The curves of the braking force,lateral force and normal force with slip under different secondary displacements and influences of the displacements on vehicle stability are analyzed.When the vehicle is braked,it should cross the curve at a lower speed.(3)Comparison of the characteristics in the linear induction motors with two different secondary structures.Based on the simulation results of the two kinds of linear induction motors,the electromagnetic characteristics is compared under the driving and braking conditions.Based on the simulation results,the 3-D electromagnetic force,the air-gap magnetic flux density,the eddy current,the secondary eddy current loss,efficiency,the distortion rate of the air-gap magnetic flux density in the linear induction motors with flat and cap-secondary are compared when they both work with the laterally asymmetric secondary.The results show that the performance of cap-secondary is better,but the 3-D electromagnetic force changes more drastically compared with the flat type when the lateral offset.(4)Experiment of the linear induction motor with the laterally asymmetric secondary for rail car platform.For evaluating the negative effects caused by the asymmetric secondary to rail trains,a rail car testbench for the linear induction motors is designed and built.The experimental data proves that the error of the calculated value obtained by the finite element analysis is within 10%,which verifies the accuracy of the finite element calculation.Moreover,the test platform is a complete replica of the actual rail transit system,so its results have certain guiding significance for the vehicle to pass the curve smoothly.Through the measurement of the 3-D electromagnetic force under different offsets,different frequencies and different slip rates,the construction process of the optimized system is promoted.