Multidomain Design And Optimization Of High-Current Density Permanent Magnet Linear Electrical Machines

In recent years,permanent magnet synchronous linear motors(PMSLMs)are increasingly used in high-end CNC machine tools because of the characteristics of high location accuracy,high acceleration,fast response,and high reliability,etc.In the paper,a high-current density PMSLM is taken as the research project after knowing the development background of high-end CNC machine tools and the PMSLM application status on high-end CNC machine tools.The purpose of this thesis is to research the thermal characteristics of the PMSLM,which will affect the position accuracy of the PMSLM.Some relative problems are researched in this thesis.For the magnetic design of high-current density PMSLM,firstly,a high-current density PMSLM is designed based on the topology,including the number of permanent magnet and slot,winding connection,etc.A finite element analysis model is built,and the cogging force of this PMSLM are reduced by optimizing the slot-tooth effect and end effect.What's more,the combined use of two types of permanent magnets is proposed to reduce the cogging force and product cost.The back EMF are calculated when the current density of the PMSLM is different,and the highest current density of the PMSLM is selected.For the thermal field analysis of PMSLM,the heat source and thermal conductivity coefficients of each component are researched.Especially the thermal conductivity coefficient of slot section,which is vulnerable due to the insulation deterioration because of ohmic loss of copper conductors in the slot are the main heat source of the PMSLM,and the thermal conductivity coefficient is relatively small.What's more,slot section contains different materials,for example,copper conductor,epoxy resin,wire enamel,insulation paper,etc.,which makes the thermal conductivity coefficient is hard to be obtained.In this paper,a calculation model and method for the thermal conductivity coefficient of slot section are proposed based on the thermal conductivity coefficient calculation method of Gasar porous metal material,and the calculation results are compared with the results obtained by the existing method,including the two flat layer method,parallel method and classic estimate method.Besides,the proposed method is applied in calculating the thermal conductivity coefficient of Litz wire,and the results are verified by the ASTM D5470 meter bar approach directly,which makes the proposed method being further verified.In order to reduce the computing time of this multidomain on the premise of guaranteeing the accuracy of calculation thus improving the practicability.Through interpolation and fitting of a polynomial,the average wind velocities and heat transfer convection coefficients of different external surfaces of PMLM are obtained,which makes the fluid field separated from the coupled calculation.Based on the basic theory of electromagnetic calculation,hydromechanics,heat and mass transfer,a simple 3-Dimentional(3-D)flow model without considering the inner structure of mover is built.Besides,the flow condition of the water in the pipe are researched.Through researching the mathematic models of electromagnetic field,thermal field,and fluid field,the strong coupling between electromagnetic field and thermal field,and weak coupling between fluid field and thermal field are proposed to research the thermal characteristics of the PMSLM.Based on the results obtained by the multidomain,the thermal characteristics of the slot section of the PMLM is researched,as well as the temperature rise characteristics of each section of the PMLM.In the end,the relationship between current density,peak temperature,load duration time,and cooling time are summarized.A PMSLM prototype is produced based on the electromagnetic design and water-cooling structure design.Combined with the power analyzer,multi-channel temperature tester,Ball screw platform,etc.,the experiment platform for testing the the electromagnetic performance,such as the cogging force,back EMF,force with load,etc.and the temperature characteristics are established.The temperature rise experiment is divided into two sections,one is measured when the PMLSM is working on the normal status,in the other case the three phrase currents of the PMSLM are different.The PMSLM with natural cooling structure and water-cooling structure are tested and compared in that two cases.