Design Of An Outer-rotor Variable Fux Permanent Magnet Synchronous Motor For In-wheel Direct-drive Applications

Traditional permanent magnet synchronous motor is difficult to take into account the large torque under the low speed and wide constant power speed range.The hybrid permanent magnet(PM)variable flux memory motor(VFMM)is a new type of motor proposed in recent years.It utilizes the irreversible demagnetization principle of low coercivity permanent magnet to realize the field weakening from the motor body,meanwhile,it has the characteristics of high torque density and wide magnetic field speed,and its copper consumption and iron consumption are lower than that of the conventional permanent magnet motor.Moreover,the hybrid VFMM has wide application prospect in the field of electric vehicle.However,due to the difficulty of magnetization of permanent magnets in the hybrid VFMM,the mutual influence of different permanent magnets and the complex magnetization mechanism have many technical problems in the design of electromagnetic scheme,it needs to have a urgent breakthrough.Under the National Natural Science Foundation of China,"the research for a new type of Outer-rotor Permanent Magnet Machines for electric vehicle's In-wheel Drives",this paper carries out research on the calculation for Magnetic Circuit electromagnetic of the hybrid permanent magnet(PM)variable flux memory motor(VFMM)driving electric vehicle wheel.the performance analysis of magnetizing and Demagnetization with finite element method,parameter optimization for motor structure,analysis of the motor control strategy and performance.The key technical problems such as the selection of the mixing ratio of permanent magnets,the reduction of saturation and magnetizing current are solved,and the field weakening control strategy and performance are improved.The paper provides theoretical basis and practical guidance for the design and popularization of VFMM.The main technical innovations in this paper are as follows:1?The hybrid VFMM combines NdFeB permanent magnet and the AlNiCo permanent magnet,the relationship between the two is complex,and the mixing ratio is difficult to determine.In this paper,the equivalent magnetic circuit model of the hybrid VFMM is established,and the ratio of the two kinds of permanent magnets of AlNiCo and NdFeB is calculated.The mathematical formula of the size range of AlNiCo is deduced,all of which provide a theoretical basis for the selection of permanent magnet size.2?Compared with the design of traditional permanent magnet motor which only considers the demagnetization curve of the second quadrant of the permanent magnet,the working point of the AlNiCo permanent magnet in the hybrid VFMM has strong nonlinearity in the four quadrants.In this paper,the finite element model of the hybrid VFMM is established.By using Preisach hysteresis model and finite element method(FEM),the magnetization mechanism of permanent magnet and magnetization is analyzed.3?For the problem that the hybrid VFMM requires alarge saturation magnetizing current problem,the PM size and Stator and rotor size are optimized,which reduce the cost of the drive system.The change law of maximum magnetizing current required by the system is summarized with the variation of the motor parameters,which provides the basis for the design of the motor parameters.4?The mathematical model of the hybrid VFMM is proposed,and the paper pointes out the difference between the hybrid VFMM and the traditional model.Meanwhile,The method of voltage limit ellipse and current limit circle analysis is improved.The torque characteristics and efficiency characteristics of the motor under different magnetization are analyzed.It is proved that the hybrid VFMM proposed in this paper has the advantages of wide power range and high efficiency.The Simulation design method for the hybrid VFMM proposed in this paper has important reference value for the optimization design of motor with similar principle.The resultsshow that the motor has a large torque output capacity,can effectively adjust the permanent magnet flux,extends the speed range,and is suitable for electric vehicle hub direct-drive motor.