Thermal Field Analysis And Loss Optimization Of Linear Induction Motor With Discontinuous Secondary Induction Plate

Rail transit vehicles with short primary single-sided linear traction motors have been widely developed in the field of urban rail transit at home and abroad because of their simple structure,small turning radius,strong climbing ability,no adhesion limitation,low noise,easy maintenance and low tunnel construction cost.Normally,the primary and secondary of linear induction motors are fully overlapped and coupled.However,in the actual construction project of rail transit,the secondary plate cannot be laid continuously due to the influence of topography and other factors,and the secondary induction plate appears to be discontinuous.This makes the linear induction motor overcurrent in the primary winding when passing through the discontinuous area of the secondary inductor plate,resulting in increased copper consumption and higher temperature rise in the primary motor.In this thesis,the electromagnetic field and thermal field of the motor are studied under the special conditions of discontinuous secondary induction plate of linear induction motor.Firstly,the domestic and international applications of linear motors and their advantages are introduced,and the current situation of domestic rail lines using linear induction motors is focused.The current status of the research on the special working condition of the secondary plate intermittent and the thermal field of the motor is also described.Secondly,based on the completed analysis of the force characteristics and static/dynamic side end effects in the operation of linear induction motor,this paper introduces the theoretical basis for calculating the electromagnetic field of the motor and completes the calculation of the electromagnetic field of the linear induction motor operating under normal operating conditions.It is found that the induced voltage,three-phase current,magnetic chain,thrust force,normal force and copper consumption fluctuate greatly during the start-up phase when the linear induction motor is running under normal operating conditions.However,these parameters are stabilized in a certain range after stable operation of the motor.The fluctuation of three-phase self-inductance is smaller during the start-up phase,and there is basically no fluctuation during the operation of three-phase mutual inductance.Thirdly,a linear induction motor model with interrupted secondary plates is developed and the motor electromagnetic field is calculated for this particular operating condition.The results show that the induced voltage decreases by 14.85%,the three-phase current increases by 28%,the copper loss increases by 42.3%,and the motor thrust fluctuates significantly when the motor primary passes through the intermittent region.Also in this paper,the heat dissipation coefficient and heat conduction coefficient of the motor were calculated,and the thermal field of the linear induction motor with intermittent secondary plate was analyzed by using the calculated loss of electromagnetic field as the heat source.The motor thermal field distribution shows that the maximum temperature of the motor primary becomes higher when passing through the intermittent region,and can reach up to 74.5℃.Finally,this paper presents the equivalent circuit model of linear induction motor considering the edge-end effect,and based on this,the equivalent circuit model of linear induction motor with intermittent secondary induction plate is established.The simulation results show that the equivalent circuit model is consistent with the overall trend of the finite element calculation results,and copper loss error within 10%.However,the equivalent circuit model provides another fast analysis method for linear motors considering the case of intermittent secondary plates.