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

In-wheel motor direct-drive is a promising driving mode for electric vehicles,also an important development direction in the future.The proper type drive motor with excellent performance is the key to ensure good power and operational performance for electric vehicles.For the existing direct-drive motors,there are still some deficiencies or unsolved problems in the aspects of high effieiency,high power density,the balance of low speed high torque and wide speed range,etc.The hybrid permanent magnet(PM)variable flux memory motor(VFMM)is a new type of motor proposed in recent years.For the permanent magnet of low coercive force can be easily magnetized and has the characteristics of”memory" function.lt can realize the field weakening from the motor body,.Meanwhile,It has the advantages of high torque density,wide weak magnetic speed regulation and high efficiency.However,due to the difficulty of magnetization of permanent magnets in the hybrid VFMM,the mutual influence of different permanent magnets and the increasing difficulty of control.There are still many problems in magnetization analysis and motor control strategy to be solved.This paper attached to 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".To determine the speed and torque required in hub motor design,the dynamic analysis of electric vehicles to be carried out.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,magnetization and demagnetization analysis with the finite element method,optimization of motor structure parameters and performance analysis.The key problems such as the determination of size of AlNiCo are solved,and the theoretical basis and practical guidance are provided for the design and promotion of the adjustable flux permanent magnet motor.The main innovative work of this paper is as follows:The working point of AlNiCo in VFPMM can change within the four quadrant.that is different from traditional permanent magnet motor,permanent magnet in the traditional permanent magnet motor working point only in the second quadrant.Because of its low coercivity and "memory1' function,the residual flux density of AlNiCo can be adjusted,and the adjustment of air gap flux can be realized.However,the hybrid VFMM combines NdFeB permanent magnet and the AlNiCo permanent magnet in the meanwhile,the relationship between the two is complex,and the size of magnet is difficult to determine.For this problem,the equivalent magnetic circuit model of the hybrid VFMM is established in this paper.According to the operation principle of the VFPMM,the mathematical formula of the size range of alnico permanent magnet is derived,which provides theoretical basis for the determination of permanent magnet size.In order to simulate the performance of the motor under different magnetization conditions,by using Preisach hysteresis model and finite element method(FEM)in this paper,the magnetization mechanism of permanent magnet and magnetization is analyzed.The torque characteristics of the motor under different magnetization conditions are analyzed and the loss analysis of the motor is carried out,too.It is proved that the hybrid VFMM proposed in this paper has the advantages of wide power range and high efficiency.The results show 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.