Three-dimensional Electromagnetic Forces Analysis And Decoupling Control Of Linear Induction Traction Motors

Linear metro and mid-/low-speed Maglev trains equipped with linear induction motors(LIMs),which have many merits,e.g.higher climbing ability,good traction performance,enhanced rail adaptability,low vibration and noise pollution,low cost,etc.,quite satisfy the requirement of the rail transit development for metropolis.However,the vertical and lateral forces in LIMs commonly have some negative impacts on the operation of the trains equipped with LIMs.Therefore,investigating the formation mechanism and analysis method of the thrust,vertical and lateral forces in LIMs and exploring the decoupling control of the three forces may reduce the negative influences of the vertical and lateral forces on the operation of the trains and broaden the application range of LIMs in the linear transit system.This dissertation introduces the application and classification of linear motors and reviews electromagnetic analysis and vector control method for LIMs,especially in the field of vector control with the forces decoupling strategy.Plus,it focuses on the analysis of the key and difficult points of the forces decoupling control.For achieving the force decoupling control for LIMs,a series of work around the modeling LIMs with space harmonic techniques,establishing equivalent circuit(EC)and devising forces decoupling strategy are made and summarized as follows:In Chapter Ⅱ,first,the author briefly analyzes the longitudinal and transversal end effects in LIMs,and the special secondary constructions of LIMs.Second,it proposes a 3D analysis of the electromagnetic field in LIMs based on the space harmonic techniques to take all the phenomena above,and presents a longitudinal MMF model based on the winding current function,which considers the unbalanced 3φ current,the half-filled slot and the compensated winding,as well as the transversal MMF model taking the winding end-regions and the laterally asymmetric secondary sheet into consideration.Third,for the composite secondary construction,it gives electromagnetic equation and boundary condition of different material layers in the analysis model,and derives the mathematical expressions of thrust,vertical and lateral forces with the electric and magnetic field quantity in each layer.Finally,it concludes that the analysis method presented by this chapter are flexible and compatible to handle the issues above,and provides the theoretical basis of the equivalent circuit and force decoupling control for LIMs.In Chapter Ⅲ,the author firstly presents some correction factors for the longitudinal and transversal end effects with the electric and magnetic field mathematical expression derived by the Poynting theorem and quasi-2D electromagnetic analysis model.Second,the parameters of the equivalent circuit can alternatively be calculated by the 3D analysis method.Third,apart from the electromagnetic field theorem,it proposes an equivalent circuit for LIMs considering the thrust,vertical and lateral forces based on the longitudinal flux distribution model,which is related to the 3D electromagnetic field model rather than the 1D electromagnetic model.The method with regard to the flux distribution model has some merits,e.g.the clear physical meaning,the simple calculation procedure,and lays an essential foundation for the vector control with a spatial 3D force decoupling strategy.In Chapter Ⅳ,the author firstly presents the decoupling curves between the thrust and the vertical force,the thrust and the lateral force based on the mathematical expressions with the electromagnetic theorem and the EC presented by this dissertation,respectively.Second,a spatial 3D force decoupling strategy is designed for the operating characteristics of the rail transit system.Third,some sub-models of the vector control system are reconstructed based on the EC considering the spatial 3D force.Finally,the vector control simulation regarding the force decoupling strategy shows that the value of the normal force and the lateral force converge to the command value satisfying requirement of the thrust command.This dissertation systematically studies a 3D electromagnetic characteristics analysis method based on the space harmonic techniques and a spatial 3D force decoupling control of LIMs for urban transit.In Chapter V,a linear rail test platform is designed for a prototype LIM,and the traction characteristics of the prototype LIM at typical power frequencies worked with different secondary displacement are experimentally measured.In addition,some experimental validation and simulation results are arranged in each end of Chapters II,III,IV.The experimental results verified the analysis results derived from the proposed model and method.