Comparative Study On Low-cost Reluctance Linear Motors For Rail Transit

Based on the technical and parameter requirements of the linear motors in rail transit,several types of new linear motors are investigated in this paper,including linear flux-switching permanent magnet(LFSPM)motor with segmented secondary,linear synchronous reluctance motor(LSyn RM)and permanent magnet-assisted linear switched reluctance motor(LSRM).These motors are very suitable for long-distancce applications such as rail transit system because their simple and robust secondary which only consists of iron core.The winding is located on the short primary,which is easy to maintain and low in cost.Therefore,they are of great high value to investigate.This paper summarizes the advantages and disadvantages of LIM for rail transit and its development status.In order to solve the problem of low efficiency and power factor of LIM and improve the electromagnetic performance,based on the primary size and operation index of LIM,a LFSPM motor with segmented secondary,a LSyn RM and a permanent magnet-assisted LSRM are designed respectively.For the LFSPM motor with segmented secondary,the working principle and thrust generation mechanism of the motor are studied firstly.The results show that more than 93%of the electromagnetic thrust of the motor is generated by the joint action of several main harmonic magnetic fields.Then,according to the complementary magnet circuit theory,a topological structure is proposed,in which its secondary and primary pole pitch ratio(τ_s/τ_p)is 12/7.The key parameters such as thrust,thrust ripple,power factor and efficiency are studied by finite element analysis.For LSyn RM,an 8-pole and 72-slot topology is determined by analyzing the pole slot ratio,winding structure and air magnetic barrier in the secondary.The primary structure is identical to the LIM in this paper.And the secondary structure is a kind of magnetic barrier which can increase the inductance difference of d-axis and q-axis and reduce the thrust ripple.For LSRM,based on the traditional LSRM,a permanent magnet auxiliary excitation is introduced to improve the motor thrust.The results show that LFSPM motor and LSyn RM have better output characteristics,in which the power factor of the LSyn RM is increased by adding low-cost ferrite material to the secondary air magnetic barrier,while the thrust of permanent magnet assisted LSRM is lower than LIM,which can not meet the requirements of rail transit.Because the two-dimensional finite element analysis ignores the end of the winding,in order to reduce the error between the simulation model and the actual model,more detailed mesh generation and accurate calculation are carried out through the three-dimensional finite element analysis,and the two-dimensional model is corrected.Finally,the system cost and energy consumption of the motors based on Guangzhou Metro Line 4 were estimated and compared in detail.The time required to recover the material cost by using the new motor compared with LIM is expected,and thus the application prospect of the studied motor is concluded.A low-power prototype of the LFSPM motor with segmented secondary is made.The no-load characteristics and loading performance of the prototype are verified by experiment,which proves the feasibility of the motor design scheme and the correctness of the finite element simulation results.