Research On Control Strategy Of Doubly Fed Linear Motor Based On Urban Rail Transit Train

With the development of the urban rail transit system,the urban rail transit train driven by linear motor has received increasing attention.Because it has the merits of small turning radius,direct drive, good climbing ability.The linear motor that are widely used in urban rail transit system are linear synchronous motor and linear induction motor,doubly-fed linear machine possesses the characteristics of linear synchronous motor and linear induction motor,it can achieve asynchronous, synchronous and doubly-fed operation mode,so it has important significance in studying doubly-fed linear machine.This article is focused on doubly-fed linear machine and the control strategy of doubly-fed linear machine is studied.Firstly.according to the basic principle of electrical machine,the doubly-fed linear machine’s mathematical model under d-q synchronous coordinate system is established,the d-axis stator flux oriented frame is selected and the double closed-loop control system of doubly-fed linear machine with stator flux oriented is designed.Due to the problem of current decoupling in the mover side,two kinds of voltage feed-forward methods are studied,the control system that adopting the improved voltage feed-forward method has fast dynamic response,strong decoupling ability.The reason of stator flux oscillations is analyzed,and two kinds of methods of damping the stator flux oscillations are introduced,compared,one is feedback of the derivative of the flux,the other is ADRC technology.The results of simulation show that the method adopting ADRC technology not only damp out the flux oscillations,but hardly affect current decoupling.Secondly, stator current oriented vector control strategy of doubly-fed linear machine is investigated,as well as the doubly-fed linear machine’s mathematical model.By analysing the control principle of stator current oriented,the control strategy both the stator side and the mover side are designed,and verified by simulation.Adopting stator current oriented vector control strategy have the advantage of that slip power can be transferred to the mover side and the capacity of converter on the mover side should be dropped when the motor is starting up or working at lower speed.Finally,speed-sensorless technology is introduced and analyzed,the algorithm of model reference adaptive system(MRAS) is mainly studied,and the MRAS speed observer that based on mover current is designed. It concludes that the MRAS speed observer that based on mover current have better performance on speed estimation.