Design And Optimization Of A Less-Rare-Earth Stator Permanent Magnet Machine With Tooth-Yoke-PM-Combined Structure

The permanent magnet(PM)machines have been widely applied in aerospace,industry,electric vehicles,agriculture fields and many other applications due to their inherent advantages of high power density,high efficiency and compact size.However,the PM materials are now facing some problems.Firstly,rare earth,the raw materials of PM,is a kind of non-renewable resources.And with the excessive exploitation and inefficient processing,the residual amount of rare earth resources has decreased rapidly,which lead to a sharp rise in the price of rare earth materials.Secondly,since the rare earth is the indispensable strategic resources for some sophisticated equipment and sophisticated weapons,hence it is now facing the risk of unstable supply.Permanent magnet machine is one of the most important applications of rare earth permanent magnet,so how to reduce the rare earth permanent magnet used in PM machines has become the research direction to relieve rare earth crisis.In this paper,the current researches of less rare earth machines are introduced first and a new kind of stator-PM less rare earth machine is proposed to solve the difficulties in stator-PM machine design.The machine uses the rare earth permanent magnet(REPM)and ferrite as its excitation source,where the REPM is located in the surface of the stator tooth and the ferrite are placed in the stator yoke.In addition,the magnetization directions of the two kinds of PM are also unique.By using the reasonable position of PMs and the unique magnetization direction,the REPM used in the machine can be reduced while maintaining the relatively high electromagnetic performance of the machine.Then,based on the structural characteristics,the operating principle of the machine is introduced.And according to the principle,a series of formulas and several design rules are derived to relate structure size and electromagnetic performances.Next the general design method of the machine is described and the initial design is conducted.In order to further improve the electromagnetic performance of the machine,a new parameters stratified multi-objective optimization method based on the sensitivity and correlation is proposed.The optimization method not only analyzes the influence of parameters on the objective,but also considers the cross effects between parameters.The parameters are stratified based on the sensitivity analysis and correlation evaluation result.Therefore,optimization dimension can be reduced and the optimization efficiency can be improved.Moreover,two different compensation optimization strategies are proposed to solve the problem of torque ripple due to the difference of equivalent air gap length.The optimization results of the two optimization strategies are analyzed and compared.And the final optimization model is obtained by optimizing the rotor-skewed angel of one of the previous optimization model.In order to obtain more accurate electromagnetic performances of the machine,the magnetic field distribution,air gap flux density,flux linkage,back EMF,cogging torque and output torque are analyzed.In addition,the utilization ratio of REPM is analyzed by comparing the traditional doubly salient permanent magnet machine.Then,the anti-demagnetization ability of the machine is evaluated by theoretical analysis and finite element simulation.Finally,a prototype is built based on the final optimization model,and the test platform is built.The simulation and experimental results verify the correctness and effectiveness of the design and optimization of the machine.