Research On Electromagnetic Thrust Optimization Of Double Sided Long Primary Linear Induction Motor

In order to simulate the space microgravity experiment,the electromagnetic ejection system requires that its electromagnetic propulsion device must produce enough large and stable electromagnetic thrust in a short ejection stroke.The Double-sided Long Primary Linear Induction Motor(DSLPLIM)has the characteristics of light secondary mass(When the load and thrust are fixed,the acceleration can be as large as possible),small thrust ripple,zero secondary normal force,and high reliability,which can meet the large thrust requirements of the simulated space microgravity experimental system.Therefore,the research on the electromagnetic thrust characteristics of the DSLPLIM has important application significance.In this paper,taking a DSLPLIM as an example,the influence of one-dimensional field analysis,electromagnetic design method and structural parameters on the performance of the linear induction motor is studied,and the multi-objective optimization of the motor is carried out.It mainly includes the following contents:Firstly,the analytical expression of air-gap magnetic density of DSLPLIM considering end-effect is deduced based on electromagnetic field theory and integral calculation of primary traveling wave current layer and secondary current,and the factors affecting the thrust ripple are analyzed theoretically.In order to weaken the influence of end effect on thrust ripple,the hairpin type full-filled winding is used to improve the sinusoidal distribution of air gap flux density,and the analytical expression is obtained after winding improvement.At the same time,taking an existing motor as an example,the sinusoidal property of air gap flux density before and after winding modification is verified.Finally,based on the analytical calculation of one-dimensional field,according to the principle of complex power balance of field and circuit calculation,the equivalent circuit considering the backward component of magnetic field is derived.Secondly,according to the design principle of linear induction motor and the performance requirements of the motor,based on the magnetic circuit calculation method,the structural parameters of a DSLPLIM are designed.The electromagnetic characteristics of no-load,rated load and reduced frequency starting operation of the designed motor are calculated and analyzed.Then,the effects of different types of primary windings on the electromagnetic thrust and thrust ripple of the motor were studied.At the same time,considering the convenience of the manufacturing process and the installation and transportation of the motor,the single-layer concentric winding,which is suitable for the modular design and manufacture,is selected.The influence of the secondary slot and its structural parameters(such as slot width,slot height and primary and secondary slot fit)on the thrust ripple is also studied.The optimization of the secondary structure is realized by using the method of finite element parameter scanning.Lastly,in order to optimize the electromagnetic performance(electromagnetic thrust and thrust fluctuation,etc.)of the designed DSLPLIM,the sensitivity analysis is carried out by Latin hypercube sampling(LHS)using the parametric simulation model of the motor.According to the sensitivity of the electromagnetic thrust and thrust ripple to each optimization variable,the number of optimization variables participating in the multi-objective optimization is determined.Based on the modified PSO algorithm,the multi-objective optimization of the motor is carried out,and a set of optimal solutions with high electromagnetic thrust and low thrust ripple are obtained.